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Miocene phreatomagmatic volcanism at Tihany (Pannonian Basin, Hungary)
Abstract
A late Miocene (7.56 Ma) maar volcanic complex (Tihany Maar Volcanic Complex Ð TMVC) is preserved in the Panno-nian Basin and is part of the Bakony±Balaton Highland Volcanic Field. Base surge and fallout deposits were formed around maars by phreatomagmatic explosions, caused by interactions between water-saturated sediments and alkali basalt magma carrying peridotite lherzolite xenoliths as well as pyroxene and olivine megacrysts. Subsequently, nested maars functioned as a sediment trap where deposition built up Gilbert-type delta sequences. At the onset of eruption, magma began to interact with a moderate amount of groundwater in the water-saturated sand. As eruption continued phreatomagmatic blasts excavated down-ward into limestones, providing access to abundant karst water and deeper to sandstones and schist both providing large amount of fracture-®lling water. At the surface, thiwet' eruption led to the emplacement of massive tuff breccias by fall, surge, mud¯ow and gravity ¯ow deposition. The nature of the TMVC maar eruptions and their deposits appears to depend on the hydrological condition of the karst and/or fracture-®lling aquifer, which varies seasonally with rainfall and spring runoff. The West and East Maar volcanoes of TMVC are interpreted to represent low water input from the karst and/or fracture-®lling aquifersummer vent'), whereas the East Maar is interpreted to have formed when abundant karst and/or fracture-®lling water was availablespring vent'). q 2001 Elsevier Science B.V. All rights reserved.
... Recent studies suggest that maar volcanoes (commonly referred to as maar-diatremes) are not necessarily 'simple' volcanic landforms: their evolution could be more complex regarding the geochemical composition of the melt (e.g., maar-dome complexes; Ureta et al., 2021;Uslular et al., 2022), or the rapid changes in external or internal conditions resulting, for example, in maar-scoria cone complexes Kereszturi and Németh, 2012;Németh andKereszturi, 2015, Tchamabé et al., 2016;Benamrane et al., 2023). External water, which is necessary to maintain the MFCI (i.e., the phreatomagmatic explosions) can be supplied from different sources even simultaneously as the eruption locus migrates downward in the upper crust (Tihany-type maar; Németh et al., 2001) excavating country rocks in progressively deeper level causing the formation of a funnel-shaped diatreme (Lorenz, 1986;Go et al., 2017). The excavated fragments are involved into the eruption column as accidental lithics (Lorenz, 1973(Lorenz, , 1986Fisher and Schmincke, 1984). ...
... Mesozoic limestone around the BBHVF is the main host of karstic aquifers commonly feeding wells and springs in the area (Tóth et al., 2023). Karst water reservoirs are very important for volcanism, as they provide groundwater (coolant) to interact with rising magma (fuel) to trigger phreatomagmatic explosions (Németh et al., 2001;Lorenz, 2003;Auer et al., 2007;Cardello et al., 2020;Mountaj et al., 2020;Benamrane et al., 2023). The Mesozoic carbonates are also known beneath Szent György Hill (starting at ca. 500 m depth; Márton, 2001;Móga et al., 2017;Kelemen et al., 2017). ...
... The rapid change in the fragmentation style back to phreatomagmatic (Sampling point 9) suggests that a new aquifer was able to step in refueling the MFCI. According to other publications of the BBHVF (Németh et al., 2001;Martin and Németh, 2004;Auer et al., 2007;Kereszturi et al., 2010) these water-bearing, fracture-controlled aquifers are the regionally widespread Mesozoic carbonates (below 500 m paleodepth according to the geological map of Budai et al. (1999) supplemented by the calculated erosion rates for Szent György Hill by Németh and Martin (1999)). The carbonates consist of dominantly karstic water-bearing limestones (Budai et al., 1993(Budai et al., , 1999Tóth et al., 2023). ...
... The occurrence and evolution of maar volcanoes are generally controlled by the location, abundance and the type of underground and/ or surface water (Heiken, 1972;Lorenz, 1986;Sohn andChough, 1989, 1992;Németh et al., 2001). In the MAVF groundwater in the prevolcanic rocks was stored in two main hydrogeological units (Amraoui, 2005): (1) a shallow sub-surface water table located in the Plio-Quaternary fluvio-lacustrine and volcanic deposits. ...
... Stratigraphic logging was conducted on the crater rim (e.g., proximal settings) and along suitable longitudinal valleys where exposures were suitable for stratigraphy logging of medial to distal section. Sedimentary facies were distinguished based on dominating grain size, nature and percentage of constituents, sedimentary structures, and bed geometry (Sohn and Chough, 1989;Chough and Sohn, 1990;Németh et al., 2001). ...
... This unit was deposited in 'dry' conditions indicated by the absence of accretionary lapilli, and the lack of soft-sediment deformation associated with bomb sags, compared to that produced by wetphreatomagmatic eruptions described in Tihany (Pannonian Basin), Hungary (Németh et al., 2001), Pahvant Butte, Utah (White, 2001), Sinker Butte Tuff Cone, Idaho (Brand and White, 2007), and the 1958 Capelinhos eruption, Faial, Azores (Cole et al., 2001). ...
The Lechmine N'kettane is a Quaternary volcano, located within the Middle Atlas Volcanic Field (MAVF) in central Morocco. It is built on the faulted contact between Liassic limestone and Plio-Quaternary fluvio-lacustrine deposits. In map-view it consists of an elliptical maar crater, surrounded by a tephra ring, within which a scoria cone is nested in its northern crater zone.
The Lechmine N'Kettane volcano is monogenetic in the sense of its small eruptive product volume and lack of evidence of significant time breakthrough it grows. The volcano formed from an eruptive locus that migrated laterally and vertically within the short duration of the eruption in a zigzagging pattern, along a complex set of generally NE-SW and NW-SE-trending faults. It represents a perfect example of how a volcano form and evolve
under the influence of a combination of specific factors such as the lithological characteristics of the substrate, its hydrogeological parameters, magma flux and the local structural framework of the country rocks.
The petrographic, granulometric and morphological (including terrain modelling) analyses of the Lechmine N'kettane pyroclastic deposits show that it was constructed in four eruptive phases with variable eruptive styles.
The first, relatively dry, phreatomagmatic phase, that took place on a NE-SW fault in the northeastern part of the crater, was generated by the interaction between the ascending basaltic magma with meteoric water in the karst aquifer hosted by the Liassic limestone. The second phase is represented by a magmatic scoria fallout deposit whose explosion locus moved westward, along the same NE-SW fault. During the third phase, the explosion center migrated southward, along a NNW-SSE fault, and produced the last phreatomagmatic event by interaction
of magma and water-saturated Plio-Quaternary sediment. The fourth eruptive phase is a purely scoria event, corresponding to the construction of the nephelinitic scoria cone in the northwestern part of the tephra ring.
Between eruptive products formed in respective eruptive phases no evidence was recognized to establish significant time gaps between their formation.
... Beaucoup de travaux de recherche ont été fait sur les volcans monogéniques, mettant l'accent sur leur nature depuis la source jusqu'à la surface (Brenna et al., 2010;Nemeth et al., 2003;Smith et al., 2008;Valentine et Hirano, 2010). L'ascension rapide du magma et la courte histoire éruptive des volcans permettent d'étudier différents aspects de ce volcanisme, par exemple ils peuvent renseigner sur l'évolution magmatique des systèmes qui ont alimenté plusieurs petits volcans pendant de longues durées (des millions d'années) (Brenna et al., 2012;Geyer et Martí, 2010;Kereszturi et al., 2011;Németh, 2011;Németh et al., 2001;Valentine et Perry, 2007). ...
... Le litage est bien souligné surtout pour les dépôts distants de l'évent, les lits étant plans, ondulés ou entrecroisés: chaque lit peut être massif ou granoclassé. Les termes descriptifs de téphras et de roches pyroclastiques sont ceux proposés par (Schmid, 1981 (Cas et Wright, 1987;Chough et Sohn, 1990;Dellino et La volpe, 2000;Németh et al., 2001;Sohn et Chough, 1989;Valentine et al., 2000;White et Schmincke, 1999). ...
... Several studies were conducted on tephra rings of maars in different regions of the world in order to retrace stages and mechanisms of phreatomagmatic volcanic eruptions (Brenna et al. 2010;Jordan et al. 2015;Sohn et al. 2012;Tchamabé et al. 2013). Research that are based on tephrostratigraphy methods have significantly improved knowledge about the evolution of tephra ring around maar craters, especially the sedimentation process of pyroclastic facies (Cas and Wright 1987;Chough and Sohn 1990;Dellino and La volpe 2000;Németh et al. 2001;Sohn and Chough 1989;Valentine and Giannetti 1995;Valentine 1987;White and Schmincke 1999). However, many shadows persist on the sequential organization of tephras and their causal relationship with the eruptive mechanism. ...
The application of structural petrology, tephrostratigraphy and chemical-mineralogical analysis methods to the basic lava of the Lachemine n'Aït el Haj volcano (LNH) in the Causse of the Middle Atlas made it possible to interpret the volcanic dynamics of this mixed phreatomagmatic-strombolian building, set up during the Quaternary.
Pyroclastic overlays, as well as fine ash and tephras, allow us to appreciate the importance,
frequency and chronology of NHL volcano eruptions. These are organized in: i/ two
phreatomagmatic sequences with a clear dominance of the debris of the liasic limestone
basement over fresh or juvenile magma emitted in the form of projections of lapillis, bombs and blocks, ii/ a strombolic phase will follow the first phreatomagmatic phase, initiated by the collapse of a thick basalt flow thanks to a slightly tilted collapse relayed by a pyroclastic plume, iii/ A discontinuous tuff ring, terminal will crown the NHL maar.
Tectonic analysis from healed fractures in pyroclastic deposits allows stress systems to be reconstructed with the identification of localized distensions supported by fracture geometry, the presence of tectoglyphs, the mixed nature (strombolian-phreatomagmatic) of the volcanism and the mechanisms of syn-eruptive tectonics. This subsidence, constrained by the NW-SE to WNW-ESE directions, tends towards a regime that decreases NE-SW, during the phreatomagmatic-strombolian transition.The origin of water in the hydromagmatic phase can be superficial (rivers, lakes, marshes, etc.) or underground, justified by the position of the NHL volcano on the path of cryptokarstic faults.
The lava produced by the NHL volcano is a poorly differentiated basalt (MgO: 11-14%; Zr/Y: 10; La/Yb: 41 and Sm/Yb: 5.5) with an olivine (85% Fo) and clinopyroxene (Diopside-augite) composition. The ratios La/Nb <1; LaN / YbN : 28 and 30 and Zr / Nb : 3, indicate a significant fractionation characteristic of alkaline intraplate basalts common to OIB or E-MORB. The formation of these basalts is controlled by the partial fusion of an enriched peridotite at a depth of about 65 km at the lithosphere-asthenosphere boundary.
The melting rate remains low around 2%, which explains the lack of a real magmatic reservoir installed on the Middle Atlas plateau. The LNH maar is one of numerous well preserved monogenic volcanoes of the Causse of the Middle Atlas. The appropriation of this geoheritage is very important for tourism and territorial development of the region
Key words :Volcanism, quaternary, Middle Atlas, Lachemine n'Aït el Haj, petrography, geochemistry, structurology, valorization, geotourism
... Maardiatreme volcanoes are surrounded by a low rim of bedded pyroclastic ejecta, of several metres to over 100 m high, with a radial width of 2-5 km (when measured from the centre of the maar) [4,6,7]. Recent studies following a tephrostratigraphic approach have significantly enhanced our knowledge on the evolution of the tephra ring around maar craters, with an emphasis on pyroclastic facies and depositional processes [8][9][10][11][12][13][14][15] [16][17][18][19][20][21][22]. Research by Houghton and Hackett [23] and Martin and Németh [24] offer insights on the identification of strombolian and phreatomagmatic eruption styles, whereas [25][26][27] discussed the explosion mechanism, and [1], [25], [28] the quantification and control of water during fragmentation. ...
... It was, therefore, not able to be accessed in its entirely, reducing the main descriptions to proximal sections, where some deposits features are displayed. Beds and layers were described, and lithofacies recorded, using a combination of grain size, bed thickness, fabric, structures, relative sorting, grading pattern, lithification, unconformities, and sedimentary features and the relative juvenile to lithic pyroclasts ratio according to [8][9][10][11][12][13][14][15][16][17][18][19], [29,38]. Determination of clasts sizes, shapes, types, and abundances were limited to qualitative appreciations. ...
... The three main stratigraphic units distinguished initially on the basis of their general stratifications each contain one or many of the volcanism related facies [15,16] described in this section and interpreted in terms of depo- [35,36], and [37]. c) 3D view of the BMM vicinity showing the scar of an ancient maar at its west side. ...
... Maardiatreme volcanoes are surrounded by a low rim of bedded pyroclastic ejecta, of several metres to over 100 m high, with a radial width of 2-5 km (when measured from the centre of the maar) [4,6,7]. Recent studies following a tephrostratigraphic approach have significantly enhanced our knowledge on the evolution of the tephra ring around maar craters, with an emphasis on pyroclastic facies and depositional processes [8][9][10][11][12][13][14][15] [16][17][18][19][20][21][22]. Research by Houghton and Hackett [23] and Martin and Németh [24] offer insights on the identification of strombolian and phreatomagmatic eruption styles, whereas [25][26][27] discussed the explosion mechanism, and [1], [25], [28] the quantification and control of water during fragmentation. ...
... It was, therefore, not able to be accessed in its entirely, reducing the main descriptions to proximal sections, where some deposits features are displayed. Beds and layers were described, and lithofacies recorded, using a combination of grain size, bed thickness, fabric, structures, relative sorting, grading pattern, lithification, unconformities, and sedimentary features and the relative juvenile to lithic pyroclasts ratio according to [8][9][10][11][12][13][14][15][16][17][18][19], [29,38]. Determination of clasts sizes, shapes, types, and abundances were limited to qualitative appreciations. ...
... The three main stratigraphic units distinguished initially on the basis of their general stratifications each contain one or many of the volcanism related facies [15,16] described in this section and interpreted in terms of depo- [35,36], and [37]. c) 3D view of the BMM vicinity showing the scar of an ancient maar at its west side. ...
... Several studies were conducted on tephra rings of maars in different regions of the world in order to retrace stages and mechanisms of phreatomagmatic volcanic eruptions (Brenna et al. 2010;Jordan et al. 2015;Sohn et al. 2012;Tchamabé et al. 2013). Research that are based on tephrostratigraphy methods have significantly improved knowledge about the evolution of tephra ring around maar craters, especially the sedimentation process of pyroclastic facies (Cas and Wright 1987;Chough and Sohn 1990;Dellino and La volpe 2000;Németh et al. 2001;Sohn and Chough 1989;Valentine and Giannetti 1995;Valentine 1987;White and Schmincke 1999). However, many shadows persist on the sequential organization of tephras and their causal relationship with the eruptive mechanism. ...
... Several sites around the crater during the fieldwork allowed the characterization and identification of the different pyroclastic facies (55 m thick of volcanic deposits). The description of the pyroclastic levels is based on a combination of several criteria such as the size, the bedding, the grading, arrangement, and shape of the clasts (Brand et al. 2009;Cas and Wright 1987;Chough and Sohn 1990;Dellino and La volpe 2000;Martin and Nemeth 2007;McPhie et al. 1990;McPhie et al. 1993;Németh and White 2003;Németh et al. 2001;Sohn and Chough 1989;Sulpizio et al. 2007, Sulpizio et al. 2014Valentine and Giannetti 1995;Valentine 1987;Valentine et al. 2000;White and Schmincke 1999). A correlation based on sedimentological analyses and lithofacies led to the determination of the tephrostratigraphic evolution of the maar. ...
... The contact between levels describes the wet character of the deposits (Fig. 8b). Thickness and stratification, poor grading, and the occasional inverse grading of lapilli tuffs suggest rapid deposition of suspended particles, high PDC with a little traction (Chough and Sohn 1990;Németh et al. 2001). The dominance of juvenile clasts reflects a more magmatic influence in the explosion (change in the ratio water/magma) (Fisher and Schmincke 1984). ...
Lechmine n’Aït El Haj (LNH) is a monogenetic plioquaternary maar, lying in the volcanic province of the MiddleAtlas. It is a 110-m-deep crater located in the Liassic limestones. The tephra deposits surrounding the crater are mainly made up of depositional units (surges and projectas) interpreted as deposits of phreatomagmatic origin. They are topped by a small unit of massive breccia tuff reflecting magmatic deposits. The maar is a result of the interaction between the ascending magma and karstic water, in an intraplate volcanism context.Water, causing this eruption, is drained by an open system of fractures in the limestone. The explosion started by phreatomagmatic dynamism, producing a big stack of pyroclastic deposits and pyroclastic falls. During the eruption, the crater grows progressively from the eruptive center to the Northwest. The upper part of the phreatomagmatic deposits is characterized by a typical mud crack structure. A transition to a strombolian dynamism occurred throughout the end of volcanic activity. Meanwhile, a lava flow, coming from the volcanic plateau, discharged in the crater’s center. With the eruption resumption, the lava is strongly fragmented; therefore, a small cone is created especially in the northern flank of the maar. Towards the end of the volcanic activity, a supply of karstic water causes another transition of the eruptive style from strombolian to phreatomagmatic dynamism. A significant karst collapse in the southern flank of the LNH maar has occurred, leading to its current morphology.
... These phases could be separated by short time intervals, but never with the necessary timeestablished in decades (Connor et al. 1997)-for the solidification of the feeding duct. Therefore, despite its structural and volcano-morphological complexity, this type of architecture can also be considered as a monogenetic construction (Németh et al. 2001). ...
... Although, Timanfaya is associated with the existence of a single feeding system, when the eruption is observed in its entirety, the high volume of material emitted throughout the eruption is outside the spectrum of typically monogenetic volcanoes established by Németh et al. (2001). Timanfaya could fit into the category of grouped monogenetic volcanism (Németh et al. 2001). ...
... Although, Timanfaya is associated with the existence of a single feeding system, when the eruption is observed in its entirety, the high volume of material emitted throughout the eruption is outside the spectrum of typically monogenetic volcanoes established by Németh et al. (2001). Timanfaya could fit into the category of grouped monogenetic volcanism (Németh et al. 2001). This high volume, anomalous in the historical volcanism, could also be related, to a certain extent, with the phases of activity that characterised the first subaerial stages of construction of the insular shields of the Canary Islands. ...
The inventory of the Lanzarote and Chinijo Islands UNESCO Global Geopark (UGG) includes 82 geosites, out of which 17 are linked to the deposits associated with the eruptions of Timanfaya, that took place between 1730 and 1736, and Chinero and Tinguatón eruption, which occurred in 1824. The volcanic field originated during these two historical events occupies a 210 km² area, which represents 25% of the island surface, and is formed by numerous lava flows and large-scale volcanic lineaments. This volcanic field contains more than 30 cones that show numerous and valuable tectonic, structural, volcanological and geomorphological features that are enhanced by their favorable state of conservation. All of them are included in protected sectors that contribute to its dissemination and conservation. In this chapter, the detailed geological study of the Geosites associated with the historical volcanism of Lanzarote is carried out, a general overview of the main geological landmarks of the evolution of both eruptions. The study of the cones that make up the volcanic field shows that the temporary-space variations of the eruptive styles, the architecture of the resulting volcanoes, as well as their geochemical and tectonic features, represent an excellent example of the complexity of monogenetic volcanism of intraplate oceanic islands.
... Taddeucci et al., 2010), however, Valentine et al. (2017) is highly skeptical of using crater size as a reliable proxy for explosion energy at maar-diatremes, proposing instead that multiple explosions with "epicenters within each other's reference footprints" will produce a progressively larger and deeper circular crater. We try to explain the Ocotenco maar eruption through two valuable examples from literature: the Tihany East Maar (Pannonian Basin, Hungary; Németh et al., 2001) and the Cerro Overo maar (Central Andes, Chile; Ureta et al., 2021). In both cases, mafic mantle-derived melts reached the surface in a closed-system rapidly experiencing degassing. ...
... In both cases, mafic mantle-derived melts reached the surface in a closed-system rapidly experiencing degassing. For both, it is proposed that in the initial eruptive phase the water-magma interaction could have been suppressed or (i) by the large confining pressure of the caprocks on the aquifer (Németh et al., 2001), or (ii) by high magma supply rate overwhelms the available groundwaters flow (Ureta et al., 2021). The ongoing eruption (hours to days? ...
... Maars are volcanic craters forming as a result of multiple explosions produced by the interaction of magma with groundwater during phreatomagmatic eruptions Németh et al., 2001;Valentine et al., 2011;Kereszturi and Németh, 2012). As the crater floor subsided below the syn-eruptive surface (Lorenz, 2007;Sohn, 1996;Valentine and White, 2012), the pre-maar country rocks are exposed in their crater walls (White and Ross, 2011) and, beneath the crater, a diatreme structure is formed, extending downward in a funnel-like shape that terminates in the irregular root zone (White and Ross, 2011). ...
... As the crater floor subsided below the syn-eruptive surface (Lorenz, 2007;Sohn, 1996;Valentine and White, 2012), the pre-maar country rocks are exposed in their crater walls (White and Ross, 2011) and, beneath the crater, a diatreme structure is formed, extending downward in a funnel-like shape that terminates in the irregular root zone (White and Ross, 2011). The low-profile pyroclastic ring formed around the crater commonly has successive layers of fallout and pyroclastic density current deposits (Lorenz, 1973;Németh et al., 2001;Wohletz and Sheridan, 1983), whose spatial and volumetric distribution of extra-crater ejecta depends on the explosions depth (Graettinger et al., 2015). Maar volcanoes commonly have a crater lake, however, they can also be dry. ...
Atexcac is a maar volcano, which forms part of the monogenetic volcanic field of the Serdán-Oriental Basin, in the eastern sector of the Mexican Volcanic Belt. This volcanic landform was originated by a combination of phreatic, magmatic and phreatomagmatic explosive eruptions. During the formation of the distinct depositional facies, fluctuations in the water availability of the local aquifer, as well as in the magma flux, were probably responsible for the different mechanisms of magmatic and phreatomagmatic fragmentation and the production of the two main populations of fragments (breccia and cross-bedded deposits particles), whose morphological features, allow us to infer the dominant regime (brittle or ductile), fragmentation mechanism (magmatic or phreatomagmatic) and conditions of bubble growth dynamics and fragmentation processes during the ascent of magma through the conduit. We conclude that the breccia particles were derived from dominant magmatic explosions while the cross-bedded deposits particles are thought to be generated from explosive phreatomagmatic events. 3D imaging based on high-precision X-ray microtomography was used to determine the vesicularity of juvenile fragments of the Atexcac maar. Calculated vesicularity index, vesicle number density (VND) and vesicle morphology indicate important processes of coalescence of gas bubbles, during the ascent of the magma. VND's Atexcac clasts suggests vesicle mechanisms similar to medium-intensity eruptions, reported in the literature. The elongated and polylobular vesicle morphology of the Atexcac clasts reveals early acceleration of magma and subsequent coalescence events at most stages of gas bubble growth.
... Thorarinsson et al., 1964) in many places in the world. Although their dynamics and ejecta deposit mechanisms are now well documented (e.g., Heiken, 1974;Fisher, 1979;Wohletz and McQueen, 1984;Fisher and Schmincke, 1984;Lorenz, 1986;Lorenz, 1987;Sohn and Chough, 1989;Németh et al., 2001;White, 2007, 2009;Nemeth et al., 2012;Agustin-Flores et al., 2014;Agustin-Flores et al., 2015, Németh andSzabolcs, 2020), they are still not fully understood. We know that, in continental areas such as the MA, hydrovolcanic eruptions result from explosive sub-aerial activity related to the interaction between a rising magma and water, either trapped at depth (aquifer) or stored at the surface (pool, marsh, river, etc.). ...
... If a volcanic activity happens in the same time as these climate variations, the hydrodynamic changes in the karst must have an impact on the volcanic dynamics. This has already been emphasized in the Miocene to Pliocene Bakony-Balaton Highland volcanic field in Hungary (Németh et al., 2001) and in a Plio-Pleistocene district of Central Mexico (Aranda Gomez and Luhr, 1996). ...
The small (≈500 km²) Azrou-Timahdite basaltic area (Middle Atlas Magmatic Province, Northern Morocco) lies on a Lias (200-180 Ma) karst plateau of medium altitude (between 1,750 and 1,950 m). This area includes 23 small-sized Early Pleistocene (2.5–0.8 Ma) scoria cones and 30 Middle Pleistocene (around 0.6–0.5 Ma) hydrovolcanic edifices. The Pleistocene was a period of strong climatic instability in North Africa: three peaks of aridity would have occurred near 2.8 Ma, 1.7 Ma and 1.0 Ma (DeMenocal, 2004), but the period between 500 and 650 ka would belong to a predominantly wet stage (Jimenez et al., 2010). The scoria cones of the Azrou-Timahdite area would therefore formed when the climate was dry and the hydrovolcanic edifices when it was wet. The hydrovolcanic edifices of the Azrou-Timahdite area are peculiarly interesting because they display an exceptional diversity in terms of morphologies and ejecta deposits which can be only explained by interaction of magma with variable amounts of water, sometimes even during a single eruptive event. The karst regions like the Middle Atlas Plateau are very sensitive to fluctuations in rainfall and during a wet climatic episode the deep karst is permanently saturated with water while the epikarst has degrees of saturation that vary with the topography. Our study suggests that the diversity of hydrovolcanic dynamics in the Azrou-Timahdite area could be linked not only to the degree of saturation of the epikarst but also to the thickness of the transmission zone separating the deep water-saturated karst and the epikarst which also depends on the topographic position of the eruptive sites.
... The presence of magmatic explosion products record additional variations during an eruption scenario. The HBVF deposits are similar to stratigraphic descriptions published on other tephra ring sequences (Fisher and Waters 1970;Sohn and Chough 1989;Aranda-Gomez et al. 1992;Nemeth et al. 2001;Haller and Nemeth 2006;Carrasco-Núñez et al. 2007;Vazquez and Ort 2006;Geshi et al. 2011;Valentine 2012;Valentine and Cortés 2013;van Otterloo et al. 2013;Valentine et al. 2015). The recognition of these depositional facies in published stratigraphic sections from multiple volcanic fields enables a comparison of a wide range of tephra rings. ...
... Near-optimal scaled depth discrete explosions early with a possible transition to shallower-than-optimal scaled depth explosions Tihany maars (Nemeth et al. 2001) Dune form beds dominate lower sequence with increasing occurrence of massive tuff breccias alternating with cross-bedded tuffs Minimum couplets-6 ...
Experimental work and field observations have inspired the revision of conceptual models of how maar-diatreme eruptions progress and the effects of variable energy, depth, and lateral position of explosions during an eruption sequence. This study reevaluates natural tephra ring deposits to test these new models against the depositional record. Two incised tephra rings in the Hopi Buttes Volcanic Field are revisited, and published tephra ring stratigraphic studies are compared to identify trends within tephra rings. Five major facies were recognized and interpreted as the result of different transportation and depositional processes and found to be common at these volcanoes. Tephra rings often contain evidence of repeated discrete phreatomagmatic explosions in the form of couplets of two facies: (1) massive lapilli tuffs and tuff breccias and (2) overlying thinly stratified to cross-stratified tuffs and lapilli tuffs. The occurrence of repeating layers of either facies and the occurrence of couplets are used to interpret major trends in the relative depth of phreatomagmatic explosions that contribute to these eruptions. For deposits related to near-optimal scaled depth explosions, estimates of the mass of ejected material and initial ejection velocity can be used to approximate the explosion energy. The 19 stratigraphic sections compared indicate that near-optimal scaled depth explosions are common and that the explosion locations can migrate both upward and downward during an eruption, suggesting a complex interplay between water availability and magma flux. Reverse to normal coarse-tail graded tuff breccias inferred to be the product of closely timed phreatomagmatic explosions, and deposits of magmatic gas-driven explosions, were observed interspersed with discrete explosion deposits. This study not only provides a framework for more detailed interpretations of eruption sequences from tephra rings but also highlights the gap in our understanding of syn-eruptive hydrology and variations in magma flux that enables phreatomagmatic explosions.
... Lorenz 2003). However, there are several alternative explanations, including (1) a lower flux of water into the central 'mixing zone' due to cementation or alteration effects, that decreased the matrix porosity and thus the accessibility of water (Aranda-Gómez and Luhr 1996;Németh et al. 2001); (2) a significant reduction of water entry into the vent by virtue of a rapid increase in magma discharge rate (e.g. Houghton and Schmincke 1989) or (3) exhaustion of water-saturated sediments during earlier eruptions (e.g. ...
... Ort and Carrasco-Núñez 2009) and/or a reduced availability of groundwater due to environmental or seasonal effects (e.g. Németh et al. 2001). The abundance of crystals in the rocks (Fig. 12d, e) suggest that they were relatively high viscosity, slow-moving lava flows, although the presence of sheared vesicles (Fig. 12d) and inferentially high strain rates may have led to reduced viscosity (e.g. ...
Lamproite volcanoes are uncommon in the geological record but are exceptionally well preserved in the Betic Cordilleras of SE Spain, where they erupted during the Late Miocene (Tortonian to Messinian stages). The parent melts are thought to have been channelled through major lithospheric faults to erupt at or near the faulted margins of Neogene sedimentary basins. Lamproite magmas are thought to be relatively CO2-poor (<1 wt %) and are typically characterised by an effusive eruption style and the development of lava lakes and scoria cones. Cabezo María is a relatively small (?550 m diameter) lamproite volcano that was emplaced within the shallow-water marine-influenced Vera Basin. The lamproites are compositionally similar to those of the Roman Province and generally less potassic (K2O<5 wt%) than other (ultra-) potassic rocks in SE Spain (e.g. Cancarix, Fortuna). The initial eruption stages were dominated by explosive magma-water interactions and the formation of peperites. These are characterised by angular fragments of glassy lamproite lavas (and isolated lobes) incorporated in sediments, locally showing the effects of thermal metamorphism. Further, elutriation pipes and ‘jigsaw-fit’ textures are observed in the peperites. The lavas and peperites are overlain by outward-dipping well-stratified scoria deposits defining part of a cinder cone, which is inferred to have emerged above sea level. Steep internal contacts with inward-dipping, structureless breccias likely represent the inner wall deposits of a central conduit. The deposits are cross-cut by late-stage dykes, which supplied fissure eruptions of geochemically similar lavas capping the scoria cone. The transition from explosive to effusive behaviour may reflect the decreased availability of water, possibly due to downward migration of the feeder conduit below the level of water-saturated sediments.
... The deeper part of the funnel-shaped crater is filled with breccias of shattered country-rocks, known as diatremes. Despite the diatreme is filled with disintegrated country-rocks and therefore should be more prone to erosion, it may in many cases form hills (e.g., Németh et al. 2001Németh et al. , 2007Fodor et al. 2005;Latutrie and Ross 2019;van Wyk de Vries et al. 2022;Hencz et al. 2024). How can an originally negative landform become positive, when the disintegrated rocks of the diatreme fill should weather and undergo erosion faster than the surrounding unaffected rocks? ...
The Bídnice hill near Litoměřice, Czech Republic, has been recognized as a volcanic structure during a survey for a new railway connection between Prague and Dresden, where after several campaigns of combined geophysical survey, it has been concluded, that Bídnice is actually a deeply eroded peanut-shaped maar-diatreme volcano forming a positive morphology. The reason for the higher resistance of the disintegrated rock in the diatreme fill against the erosion when compared to surrounding country rocks was the main question of our presented research. While other positive morphology diatremes in the region are mostly associated with high-viscosity differentiated alkaline rocks (namely phonolites), the Bídnice diatreme comprises intrusions of basic rock (SiO2 ca 38 wt.%), classified as olivine nephelinite. From thegeophysical survey of the internal structure, comprising magnetometry and electrical resistivity tomography, a spoon-like subsurface intrusions of the olivine nephelinite were found. A smaller outcrop of the intrusive system penetrating the diatreme provided a K–Ar age of 27.06 ± 0.57 Ma (Oligocene). The results of the geophysical survey were then used to create a 3D geological model to better understand and interpret the geological setting. A system of coherent sills, even with a rather low thickness in the case of low-viscosity (ultra)mafic rocks, may be responsible for the reinforcement of the diatreme leading in slower erosion, and therefore resulting in the significant positive topography of eroded maar-diatreme volcano. In addition, sub-horizontal intrusions provide more homogeneous reinforcement of the diatreme again sterosion compared to subvertical dykes, those would be exposed by the selective erosion in the form of small ridges.
... The magma plumbing systems of these volcanoes are generally simple and consist of small volumes (typically < 1 km 3 , commonly < 0.1 km 3 ) of individual magmatic batches (Walker, 1993;Smith and Nemeth, 2017). However, some volcanoes have recently been reported to have complex plumbing systems with magma flowing through an upper conduit connected to various geometrically intricate pathways and hydrological systems (Németh et al., 2001;Valentine and Krogh, 2006;Németh and Martin, 2007;Brenna et al., 2011;Valentine et al., 2011). Therefore, the interpretation of the magma plumbing systems of these volcanoes is not always straightforward and needs to be based on carefully analyzed geochemical data of pyroclastic deposits. ...
The Suwolbong tuff ring is a basaltic monogenetic volcano in the Quaternary intraplate volcanic field of Jeju Island, Korea. The tuff ring was formerly interpreted to have had a congested magma plumbing system consisting of multiply-sourced dike complexes, based on stepped and mixed chemical trends of alkaline to sub-alkaline glassy pyroclasts. Microscopic observations, petrological analysis, and componentry analysis of the glassy pyroclasts reveal, however, that some of the glassy pyroclasts in the tuff ring are accidental and inappropriate for interpreting magmatic processes. Juvenile particles are vesicular, alkaline in composition, mainly contain olivine, clinopyroxene, and plagioclase phenocrysts, and comprise about 35 vol% of the deposits. In contrast, accidental particles are non-vesicular, alkaline to subalkaline in composition, less abundant (avg. 8 vol%), and show alteration rims. The accidental particles are interpreted to have been derived from the volcaniclastic layers deposited before the eruption of the Suwolbong tuff ring. When removing the effects of the accidental particles and considering only the geochemical characteristics of the newly defined juvenile particles, the Suwolbong tuff ring is interpreted to have had a rather simple, not necessarily congested, plumbing system fed by independently ascending multiple magma batches. This study shows that the interpretation of the properties of the source magma and the magma plumbing system in monogenetic volcanoes must be performed after clearly distinguishing between juvenile and accidental particles based on rigorous microscopic analysis of pyroclastic materials.
... e. paleoclimatología, ambiente eruptivo; subaéreo vs subacuático, estructura de la cuenca sedimentaria y condiciones hidrológicas), así como la evolución tectónica de la región en la cual están localizadas. Las erupciones hidromagmáticas forman parte del volcanismo monogenético, y suelen registrar historias eruptivas complejas (Freda et al., 2006;Németh et al., 2001;White & Ross, 2011;Kereszturi & Németh, 2013;Kurszlaukis & Fulop, 2013), abarcando una serie de condiciones eruptivas resultantes de mezcla efectiva de magma, regularmente de baja viscosidad con agua subsuperficial, transferencia rápida de calor del magma al agua, y subsecuentemente la explosión disparada por la interacción agua-magma definida como interacciones de combustible fundido-refrigerante o MFCI (Molten Fuel Coolant Interaction, por sus siglas en inglés; Lorenz, 1973Lorenz, , 1987Zimanowski et al., 1986Zimanowski et al., , 1997Zimanowski, 1998;Büttnet et al., 1999;. Materiales resultantes de tales erupciones comprenden variedad de partículas incluyendo piroclastos juveniles que generalmente consiste en fragmentos del magma pobres en vesículas, que poseen morfologías de bloque (equant), con estructuras de enfriamiento rápido (fracturas dendríticas), escalonadas y partículas adheridas (Büttner et al., 1999), fragmentos del basamento preexistentes (líticos) en hasta 80% (Zimanowski et al., 1986), gas magmático, vapor, y con frecuencia agua (White & Houghton, 2000). ...
La Joya de Los Contreras es una de cuatro estructuras freatomagmáticas que forman parte del Campo Volcánico Santo Domingo, un campo volcánico monogenético asociado a magmatismo intraplaca del Pleistoceno al norte del estado de San Luis Potosí (México), relacionado a fallamiento extensional y adelgazamiento cortical. Estudios previos incluyen geoquímica de lavas y xenolitos, pero no abundan en la evolución volcánica de la secuencia piroclástica. La Joya de los Contreras es un cráter volcánico excavado en calizas (Formación El Abra, Cretácico superior), de forma elíptica y dimensiones de 1,160 m de diámetro por 210 m de profundidad. Expone lavas máficas en la base (basanitas), un anillo de tobas muy bien preservado y expuesto, y también lavas máficas en la cima de la secuencia. Con el objeto de conocer los procesos magmáticos y freatomagmáticos que le dieron origen, se desarrolló un levantamiento estratigráfico y análisis de facies, petrografía, granulometría, componentes y geoquímica. La secuencia se compone de 1) Unidades pre-maar, lavas máficas, basanitas y aglomerados; 2) Unidades formadoras del maar, tobas conformando el anillo; y 3) Unidades post-maar, lavas coronando la secuencia. Se fechó una de estas últimas en 447 ± 11 ka (edad 40Ar/39Ar en roca total). La historia volcano-estratigráfica resulto en la reconstrucción de 5 fases eruptivas que van de efusiva-estromboliana pre-maar a freatomagmática explosiva, con variaciones en proporciones de interacción agua-magma y cerrando estromboliana-efusiva post-maar. Aunque no hay evidencia directa de una diatrema a profundidad, se infiere su existencia en base a diversos criterios geomorfológicos, tales como el alto volumen de material calcáreo lítico en el anillo de tobas (excavación y relleno – reciclaje), la relación de aspecto del cráter y su relleno.
... The nature of the bedrock plays a very important role in the crater growth of maars, and field studies have shown that unconsolidated rocks can lead to larger diameters [111,112]; whereas, in the studied volcanic field, all the maars are located on limestone bedrock of the Liassic and Eocene age. The only parameter that influences the size of the craters and the variation in the shape of the maars in the Middle Atlas is the distribution and physical state of the water in these limestone beds [85,[112][113][114]. Thus, in our field observations, such as stratigraphy, presence or absence of lithic fragments, accretionary lapilli, and cauliflower bombs, we show several cases of phreatomagmatic to magmatic transition, and vice versa, resulting from variation and depletion of the water source, such as Timahdite (maar-cone) [30], Lachmine Lakbir (maar-cone), Lachmine N'kettane (Ln1) (maar-to-scoria cone), and west of Hebri (scoria cone-to-maar). ...
The Middle Atlas Volcanic Field (MAVF) covers an area of 1500 km2, with a total erupted volume of solid products (e.g., Dense Rock Equivalent or DRE) estimated to be more than 80 km3. The MAVF comprises 87 monogenetic basaltic volcanoes of Tertiary-Quaternary age as scoria cones (71%) and maars (29%). These monogenetic basaltic volcanoes have various morphologies (e.g., circular, semi-elliptic, elliptic in map views). They can be isolated or form clustered monogenetic complexes. They are largely grouped in the Middle Atlas, in an intraplate geotectonic context forming two distinct major alignments (N160–170° and N40–50°), each closely associated with regional structural elements. By the best estimates, the preserved bulk pyroclastic products do not exceed 0.7 km3, and they show large textural and componentry diversity (e.g., bedded/unbedded, coarse/fine, dense/scoriaceous fallout and pyroclastic density current deposit, etc.). Lava flows also demonstrate great variety of preserved surface textures, including pāhoehoe, ‘a’ā, and clastogenic types. Morphostructural features of lava flows linked to lava flow dynamics have also been recognized, and the presence of hornitos, columnar jointed basaltic flow units, lava tubes, tumuli, and clastogenic lava flows have been recognized and mapped. Some half-sectioned dykes expose interior parts of magmatic shallow feeding pipes. The current morphology of the volcanoes of the MAVF reflects various syn- and post-eruptive processes, including (1) erosional features due to weathering, (2) gravitational instability during and after volcanic activity, (3) vegetation impact, and (4) successive burial of lava flows. The documented volcanic features of this typical monogenetic volcanic field form the core of the region’s geoheritage elements and are considered to be unique in the new African geoheritage context. Hence, they will likely form the basis of future geotourism, geoeducation, and geoconservation ventures.
... Another reason could lie in the availability of water, which usually drives the eruption style (phreatomagmatic versus magmatic). This can depend either on local conditions at the scale of a single eruption (depletion of water in the aquifer as the eruption progresses) or regional water table fluctuations due to paleo-climatic changes over an entire eruptive cycle (Németh et al. 2001;Kereszturi et al. 2010;Kshirsagar et al. 2016;Agustín-Flores et al. 2021). Heaney (1991), for example, proved through fossil pollen records that the climatic conditions in the Late Pleistocene were much drier than today for this region. ...
Southeast Asia is home to a large number of active and well-studied volcanoes, the majority of which are located in Indonesia and the Philippines. Northern Southeast Asia (Myanmar, Cambodia, Laos, Thailand and Vietnam) also hosts volcanoes that for several reasons (post-World War II conflicts, poor accessibility due to dense vegetation, no known historical activity) have been poorly studied. Systematic assessments of the threat these volcanoes pose to resident populations do not exist, despite evidence of numerous eruptions through the late Pleistocene and likely even during the Holocene. A recent study inferred the location of the Australasian meteorite impact to be beneath the Bolaven Volcanic Field in southern Laos; this study provided a wealth of data for the field: in particular, mapping of vents and flows, and their relative or absolute ages. The Bolaven Volcanic Field (16 Ma—< 40 ka) has a surface area of about 5000 km², contains nearly 100 scoria cones and more than 100 individual lava flows. Some lava flow systems are as long as 50 km, with thickness ranging from a few meters at the flow edges, up to > 50 m in some locations. Building upon this foundation, we used the Bolaven Volcanic Field as a case study for assessing the potential exposure of populations and infrastructure to lava flows during future effusive eruptions. Our study uses remote sensing to map past flows and vents (i.e. scoria cones), lava-flow simulations from new simulated vents, and open-access exposure data, to assess hazards and exposure. Our results show that future vents are most likely to occur in a N-S band atop the Bolaven plateau, with some flows channelling into canyons and spilling down the plateau flanks onto lower plains that support more populated areas such as the provincial centre, Pakse. Our exposure assessment suggests that around 300,000 people could experience socio-economic impacts from future lava flow inundations. The largest impacts would be on two of the main economic sectors in the region, agriculture and hydropower. The potential also exists for life-threatening explosions from interactions between magma and surface waters, which are abundant in the region. We estimate an average recurrence interval of approximately 10,400 years, based on information from lava flows and scoria cones.
... III-1). La description des niveaux pyroclastiques repose sur une combinaison de plusieurs critères tels que la taille des éléments, la puissance des bancs, le litage, le granoclassement, l'agencement et la structure des clastes (Cas and Wright, 1988;Sohn and Chough, 1989;Chough and Sohn, 1990;White and Schmincke, 1999; Dellino and La Volpe, 2000; Valentine and Fisher, 2000;Németh et al., 2001). Le terme "lit" est utilisé par Sohn and Chough (1989) pour désigner des couches dont l'épaisseur varie entre 1 cm et 1 m, bien que ces couches peuvent être composées de nombreux lits minces. ...
The Middle-Atlas volcanic province represents an important magmatic activity center
arranged into monogenic volcanoes during the Quaternary. Due to the variability of eruption dynamic styles and their combination, different pyroclastic successions and initial geometries were generated. The changes in the dominant eruption style trigger a new phase of edifice growth and therefore increases the complexity of the eruption history. On the basis of criteria regarding morphostructural aspects, eruptive styles, position, and nature of associated volcanic products, four volcanogenic groups were highlighted: i / cones, ii / maars associated with tuff rings, iii / compound cone-maar volcanoes, and iv / lava flows. Each group can be subdivided into subgroups according to the variety of forms and styles of activity during a single eruptive event.The application of the methods of physical volcanology, tephrostratigraphic and chemical�mineralogical analysis on the mafic lavas of the Timahdite volcano, which is regarded as the
archetype of mixed Maar-cone volcanism. Our methodology made it possible to interpret the eruptive dynamics of this edifice raised on North Middle-Atlasic fault corridor, in two major phases: first phreatomagmatic conditioned by the water-magma interaction between magma Oued Guigou waters, then Strombolian. In the first case, the juvenile magma is composed of magnesian olivine (Fo80-85) and diopside-augite-type clinopyroxene. Amphibole is a monomineral residue clast of a mantle xenolith drained by rising magma. Lavas produced by the second Strombolian phase contain the same composition in addition to nepheline. Rare xenocrystals of albite feldspars indicate the sweeping of basicrustal material.Major and trace element analyzes carried out on mafic Strombolian lavas attest to an undersaturated alkaline signature for these basalts classified into two types: nephelinites and normative nepheline basanites. The nephelinites constitute the main part of the pyroclastic fallout relayed by a basanite massive flow which reflects the transition to a terminal effusive regime. These intraplate basalts are not cogenetic. Their formation would be controlled by the partial fusion of enriched peridotite presumably with spinel, attested by the presence of the same xenoliths in these lavas. The partial melting takes place at a depth of 65km at the
lithosphere-asthenosphere limit. The melting rate remains low around 1 to 2% for
nephelinites and 3 to 4% for basanites, which justifies the lack of a real magmatic reservoir under the Middle-Atlas plateau.
Key words: Volcanism, Quaternary, Middle-Atlas, Timahdite, Petrography, Geochemistry
... Gilbert-type deltas form in a variety of tectonically active settings, including extensional, compressional, and transtensional basins. They are also common in high-relief physiographic settings where accommodation is not primarily created by tectonics, such as incised valleys, fjords, or proglacial lakes; they can even form in lakes inside volcanic craters (Nemec et al., 1999;Németh et al., 2001;Gutsell et al., 2004;Kostic et al., 2005;Eilertsen et al., 2011;Gobo et al., 2014a;Leszczyński and Nemec, 2015;Winsemann et al., 2018). These deltas form important nodes in sediment-delivery pathways linking continental hinterlands to subaqueous lacustrine (Bowman, 1990;Bestland, 1991;Lee and Chough, 1999;Ilgar and Nemec, 2005;Sztanó et al., 2010) and marine depocentres (Colella, 1988;Mortimer, 2004, Mortimer et al., 2005García-García et al., 2006a;Breda et al., 2009;Ciampalini and Firpo, 2015;Rees et al., 2018). ...
Steep-fronted Gilbert-type deltas are common features of tectonically active settings, as well as of physiographic settings where accommodation is dictated by landforms with steeply inclined margins, such as incised valleys, fjords, and proglacial lakes. Existing facies models for Gilbert-type deltas are largely qualitative; this study presents a quantitative analysis of the variability in facies architectures of such deltas. A database approach is used to characterize the preserved sedimentary architecture of 62 Gilbert-type deltas of Cretaceous to Holocene ages developed in various basin settings worldwide. Data on 706 architectural elements and 12,872 facies units are used to develop quantitative facies models that describe the variability in architecture and facies of Gilbert-type deltas at multiple scales of observation, and to account for the possible controls exerted by allogenic and autogenic factors.
The analysed data reveal high variability in the geometry and facies of Gilbert-type deltas. The thickness of the examined deltas varies from 2 to 650 m, yet positive scaling between delta thickness and length is consistently recognized across the studied examples, which is interpreted in terms of relationships between accommodation, sediment supply and delta lifespan. Based on their facies character, the deltas are classified into gravel- and sand-dominated types, with contrasting facies organizations of topset, forest and bottomset elements, and by different relationships between facies and dimensions; yet, both types exhibit significant spatial variability in the distribution of sediments linked to debris flows or turbidity currents, and in vertical stratal trends. Changes in allogenic (e.g., changes in base-level or, rate of sediment influx) and autogenic mechanisms (e.g., channel avulsion) are inferred as causes for significant differences in facies organization, both across distinct deltas and within individual deltaic edifices.
The study highlights the marked variety of architectural and sedimentological (e.g., grain size, depositional processes) properties of Gilbert-type deltas. Findings allow the relation of outcrop observations to a general template and the quantitative determination of potential analogues with which to assist the prediction of the dimensions and facies of deltaic sedimentary bodies in the subsurface. Information on facies relationships and basinward variability of Gilbert-type deltas is valuable for the recognition and correlation of deltaic bodies in the subsurface.
... Phase 5 Eruption of Pahoehoe lava flows with characteristically ghost soriaceous clasts localized along spatter-lava flows forming clastogenic flows. Phase 6 In the final eruptive history of scoria cone, injection of squeezed lava/ tephra through fractures produce coherent and pyroclastic dikes that fed the pyroclastics and lava flows magma-water interaction forming phreatomagmatic mafic tephra (Wohletz and Sheridan 1983;Johnson 1989;Chough and Sohn 1990;Sohn and Chough 1990;Cioni et al 1992;Lorenz 2000;Németh et al. 2001;Sottili et al. 2010;Lefebvre 2013;Brand et al. 2014;Murcia et al., 2015;Németh and Kósik 2020;Ureta et al. 2020a, b). ...
An integrated stratigraphic, sedimentological, volcanological, and geochemical studies were conducted for the first time on the eruptive products of the Marssous volcano, Bahariya Depression, Western Desert, Egypt. The rarity of complex volcanological studies in the west Red Sea rift makes these investigated volcanoes important as they offer a clue to the style of volcanism, eruptive environment and magma genesis during magmatism complimentary to those areas extensively studied in the Arabian Peninsula toward Syria and Eastern Turkey. The Marssous volcano is small monogenetic scoria cone that shows a polyphase feeding system, consisting of unconformable superimposed characteristic effusive-to-explosive eruptive units, suggesting a wide spectrum of diverse eruptive styles through a complex feeder network. On the basis of the sedimentological characteristics, field relationships, lava flow textures and granulometric indicators, five volcanic units have been identified from the base to top as (1) coherent porphyritic massive basalts (Bpm), (2) stratified tuff beds (Unit 1), (3) crude-bedded lapilli tuff beds with bombs (Unit 2), (4) massive agglutinate beds (composed of spatter and fluidal bombs) formed by lava fountains (Unit 3), (5) porphyritic vesicular basalts (Bpv), and (6) subvolcanic feeder intrusions. The degree of vesicularity and the size of the clasts increase from thin Unit 1 (ash to lapilli) through more thick Unit 2 (lapilli-bomb) to Unit 3 (breadcrusted scoriaceous bomb) as an indicative of an increased magma flux and the high eruptive energy together with an enlarged of degassing fragmentation. There is consequently a progressive evolution from an initial Phreatomagmatic explosive stage followed an initial effusive event to dry magmatic explosive (Strombolian & Hawaiian) and effusive eruptive styles in the later. With eruption progression, the external water to fuel Phreatomagmatism was diminished relatively early in the eruptions giving way to accumulate a pyorclastic fall deposition of Strombolian to Hawaiian lava-fountain episodes together with effusive eruptions, all together forming the majority of the pyroclastic and effusive successions of Gabal Marssous. These eruptive phases have happened during a continuous deposition without any time pauses in a short period of time as a result of a single cone-forming eruptions. The Marssous volcano shares resemblances in terms of inferred eruption style and structures with other scoria cones elsewhere in the broad regional context such as North Africa, Mediterranean province, and Arabian Peninsula, and thus provides an outstanding field laboratory to explore scoria cones architecture and growth from a global perspective. This volcano event is a key tectono-stratigraphic marker for an early manifestation, coinciding with the initiation of Red Sea rifting opening.
... Additionally, pyroclastic DB stratification has been reported but without being the specific focus of study, lacking a detailed description or not being discussed in terms of formative flow regime (e.g. McDonough et al., 1984;Wilson, 1985;Boudon et al., 1993;Cole et al., , 2001Scott et al., 1996;Colella & Hiscott, 1997;Bestland & Krull, 1999;Allen, 2001;Cagnoli & Ulrych, 2001;N emeth et al., 2001;Dellino et al., 2004;Brown et al., 2007Brown et al., , 2008Sulpizio et al., 2007;Parejas et al., 2010;Mattsson & Tripoli, 2011;Cas et al., 2017). An in-depth consideration is often hampered by unclear nomenclatures mixing description and interpretation, as well as by confusions on flow-dynamics concepts. ...
Sedimentary structures deposited from dilute pyroclastic currents are largely dominated by the products of metre‐scale dune bedforms containing backset lamination. Since the first seminal works in the 1970s, the vast majority of the literature called these structures antidunes and chutes‐and‐pools. This consensus led to a loose terminology, either as descriptive terms for structures containing backset beds or as an interpretation of hydrodynamic conditions related to Froude‐supercritical flows. Here, the main characteristics of pyroclastic dune bedforms are summarized and classified under four categories. The literature is examined and a discussion is provided regarding a possible interpretation in terms of supercritical‐flow bedforms, including antidunes, chutes‐and‐pools and cyclic steps. The interpretation of pyroclastic dune bedforms as related to supercritical conditions is a possibility among others, yet open questions remain, and under the present state of knowledge alternative interpretations are equally valid. There is consensus that an interpretation of pyroclastic dune bedforms as related to supercritical flows implies deposition from a basal underflow supporting an internal free‐surface formed at a density interface within the overall current structure. Antidunes are likely to be limited to low‐angle, incipient bedforms. Chutes‐and‐pools may occur in the form of series of steep truncations formed by an erosive supercritical ‘chute’, with a depositional signature occurring exclusively in the subcritical ‘pool’ of a Froude jump. Rare examples of cyclic steps may be found as large‐scale undulations with superimposed metre‐scale bedforms, or for short‐scale, fully‐aggrading structures in periodic trains. Additionally, some pyroclastic bedforms may be formed by granular flows passing granular Froude jumps or as frozen granular stationary waves. The dominance of chutes‐and‐pool structures over bedforms characterized by relatively more stable morphodynamics (antidunes and cyclic steps) could be the likely result of pulsating flow conditions and abrupt high‐rate deposition, impeding stable flow conditions. In a majority of cases, the growth of pyroclastic bedforms appears triggered by the influence of an inherited bed topography and by bed‐flow feedback effects. Apart from a possible interpretation as supercritical bedforms, other specific dynamics of dilute pyroclastic currents may well explain the characteristics of pyroclastic dune bedform structures. In particular, the inherent turbulence fluctuations, internal organization and highly depositional dynamics may be key to the formation of pyroclastic dune bedforms. In this respect, rather than solely focusing on the Froude dimensionless number of the formative current, theoretical considerations accounting for the Reynolds, Richardson and Rouse dimensionless parameters may be also implemented for the understanding of pyroclastic bedforms.
... As the area was denuded during the Paleogene, only from the late Miocene can we find sediments next in connection with the development of the Pannonian Inland Sea (Korbély 2011). At this time, volcanic activity has also started forming phreatomagmatic explosions, basalt magmatism and postvolcanic geyser activities in the region (Németh et al. 2001). Only the latter is represented in the study area . ...
Assessment is the initial step for experts on geoheritage and geotourism when designating geosites in a certain area. During this process, geologically interesting outcrops, formations and places are examined with the use of different criteria to see if they are suitable for geoconservation and geotourism purposes. A quantitative assessment method-Modified Geosite Assessment Model (M-GAM)-was applied in the study area, which is part of the Bakony-Balaton UNESCO Global Geopark in Hungary. M-GAM uses a weight factor (importance) that expresses the opinion of geotourists about 27 infrastructural, tourism and scientific indicators. This factor was examined by questionnaires at nine geosites in the area. At each site, we determined a unique importance value, which shows significant difference from site-to-site and reflects the opinions of visitors about the geosite. The M-GAM method is originally aimed at applying a common weight on each of the 27 criteria during the assessment of selected sites. While this approach is valid, we demonstrated that the method can be extended because the weights spatially vary and can be used to draw conclusions on geosite management. Practically, the evaluation of the factors obtained in this way offers an individual development plan for every site. The current state of improvement direction, the level of communication and the interpretability of the geo-objects can also be determined. In this way, we can get a more realistic development strategy for the geosites.
... Analog experiments suggest that craters with one explosion epicentre tend to be circular and likely reach 560 m in diameter after tens of explosions and associated collapse, while large and complex craters require lateral vent migration Valentine et al. 2015). Furthermore, multiple coalesced maar craters are also present in Huguangyan and Qingtongyang maars in Leizhou Peninsula, indicating that lateral vent migration commonly occurred during the formation of large maars in the region, in accordance with observations of many large maars around the world (e.g., Németh et al. 2001;Auer et al. 2007;Jordan et al. 2013;Amin and Valentine 2017). ...
As the second common type of volcanic vent on Earth, maar-diatreme volcanoes and their post-eruptive lacustrine sediments are a main focus of volcanology, palaeolimnology, palaeoclimatology and palaeontology. A number of maar-type volcanoes have been found in Leizhou Peninsula, South China, but little is known about their eruption processes and detailed stratigraphy of the post-eruptive sediments. We present a combined geophysical and geological analysis to study the eruptive history and post-eruptive sediment stratigraphy of a large maar, the elliptical (1.8 × 3.0 km ² ) Jiudouyang (JDY) maar. The lacustrine stratigraphy revealed by drilling cores shows that the JDY maar lake has three major stages of evolution: (i) deep-lake sedimentary environment characterized by high autochthonous diatom productivity; (ii) shallow lake to swamp with very low water levels, characterized by a high total organic carbon (TOC) and abundant wood fragments; and, (iii) intermittent shallow lake and alluvial deposits composed of clay minerals and sand. The electrical resistivity tomography (ERT) values and lithological features are highly consistent, which clearly reveal the presence of ca. 50 m thick lacustrine sediments, directly underlain by a ca. 70 m thick basaltic lava rather than diatreme breccia in the crater. This infill sequence implies an alternation of eruption style from phreatomagmatic to Strombolian and/or lava flow, due to high magma flux and ascent rate of the Hainan Plume during the middle Pleistocene. The ERT data also reveal the initial phreatomagmatic crater floor at ca. 120 m depth. The initial crater had a large diameter/depth ratio (ca. 17), with an elongated shape (major axis to minor axis = 0.6), implying possible lateral vent migration during the eruption. A significant erosion under tropical weathering condition during the last few hundred thousand years, accounted for the large size of the maar crater. The study provides insights into the eruptive history and post-eruptive evolution of a large maar, as well as the spatial distribution of the lacustrine sediments.
... VVF volcanic deposits, with special focus on phreatomagmatic products from carbonateseated maar-diatremes, were characterized through the detailed definition of field characteristics (e.g., deposit textures, grain size, componentry, lithofacies architecture), by means of layerby-layer thickness measurements and facies analysis, in light of well-established interpretive criteria of eruption and emplacement processes (e.g., Németh et al., 2001). In some cases, we estimated the order of magnitude of the erupted volume of individual centers, based on the thicknesses and areal distributions of the exposed deposits, also taking into account local topographic control and adding further 50% to account for fine-ash loss in the atmosphere (e.g.; Ernst et al., 1996). ...
Quaternary carbonate-seated maar-diatremes in the Volsci Range are one of the most intriguing products of the west-directed subduction of the Adriatic slab that drove the development of the Apennine mountain belt in Central Italy. The Volsci Volcanic Field is characterized by phreatomagmatic surge deposits, rich in accidental carbonate lithics, and subordinate Strombolian scoria fall deposits and lava flows, locally sourced from some tens of monogenetic eruptive centers (at least fifty tuff rings and scoria cones). We investigate the subsurface maar-diatreme processes in terms of relationships between faulting and explosive magma-water interaction, as well as the distribution pattern of the eruptive centers. With this aim, we present the following new data: i) description of the fold-and-thrust belt structure and associated eruptive centers, ii) componentry of volcanic rock-types, iii) determination of grain-size, degrees of whiteness and roundness of carbonate lithic inclusions, iv) micropaleontological analysis of carbonate lithics. We show that the clustering of eruptive centers is controlled by tectonic features. A first order control is tentatively related to crustal laceration and deep magma injection along a ENE-trending Quaternary lateral tear in the slab and to Mesozoic rift-related normal faults. A second-order control is provided by orogenic structures (mainly thrust and extensional faults). In particular, magma-water explosive interaction occurred at multiple levels (< 2.3 km depth), depending on the structural and hydrogeologic setting of the Albian-Cenomanian carbonates, which are intersected by high-angle faults. The progressive comminution, rounding and whitening of entrained carbonate lithics allows us to trace multistage diatreme processes. Finally, our study bears implications on volcanic hazard assessment in the region.
... Heat loss from magma to external water (such as groundwater, lake water or ice) is considered as one of the key driving forces for explosive magma fragmentation during phreatomagmatic (sometimes referred to as hydromagmatic or hydrovolcanic) eruptions (e.g., Németh et al., 2001;Head and Wilson, 2007;Geshi et al., 2011;White and Ross, 2011;Graettinger et al., 2013;Wohletz et al., 2013;Houghton et al., 2015;Liu et al., 2015;van Otterloo et al., 2015;Fitch et al., 2017). Magma may also come in direct contact with seawater during submarine, sublacustrine and surtseyan eruptions, where quenching and magma fragmentation form distinct lava flow morphology and pyroclasts such as pumice, hyaloclastites and Limu o Pele (e.g., Griffiths and Fink, 1992;Perfit et al., 2003;Allen et al., 2008;Chadwick et al., 2008;Clague Fig. 1. ...
The cooling rate of magma in the presence of external water during phreatomagmatic and submarine eruptions is one of the key parameters governing non-explosive to explosive magma fragmentation and eruption transitions, but remains poorly constrained. Combining results from laboratory experiments with realistic eruptive temperatures of magma cooling in ambient water of variable temperatures, and numerical modeling of transient heat transfer, we find that magma-to-water heat flux can be up to 4 × 10^6 W m^−2. The experiments exhibit two distinct water boiling regimes: A film-boiling regime defined by the presence of a coherent water vapor film between magma surface and ambient water, and a nucleate boiling regime below a critical magma surface temperature (known as the Leidenfrost temperature), where the vapor film breaks and numerous bubbles form at the magma-water interface. In general the vapor film was stable in our experiments for time scales of ≤ 5 s, indicating that this might be a limiting factor in pre-explosion magma-water mixing for energetic molten fuel-coolant interaction and explosive volcanic eruptions. The time scale of vapor film stability increases and the Leidenfrost temperature (1223 to 948 K) decreases with increasing water temperature (276 to 366 K). We show that for the empirically obtained large heat flux to external water, the cooling rate of magma can reach up to 10^6 K s^−1 at length scales of few microns, thus magma may undergo fine fragmentation due to quench-induced large thermal stresses. Our experimental and modeling results demonstrate that the time scales of various water boiling regimes, and erupting magma and ambient water temperatures determine the magma-to-water heat transfer rates, which in turn determine the transition to explosivity under subaqueous eruption conditions.
... Phreatomagmatic periods alternated with brief strombolian activity, with the alternation controlled by multiple factors such as magma flux, inhomogeneous water distribution (Valentine and White, 2012), water exhaustion, and lateral-vertical vent migration (e.g. Németh et al., 2001;White and McClintock, 2001;Sohn and Park, 2005;Auer et al., 2007;Ort and Carrasco-Núñez, 2009;Kereszturi and Németh, 2011;Ross et al., 2011;Blaikie et al., 2014;López-Rojas and Carrasco-Núñez, 2015). ...
The Aljojuca maar is located in the eastern Trans-Mexican Volcanic Belt, within the Serdán-Oriental Basin, which is characterized by Quaternary bimodal monogenetic volcanism. The Aljojuca maar has an irregular shape, with an eastern embayment structure that forms an E-W alignment with at least three older scoria cones to the east. The crater walls expose a sequence of pre-maar volcaniclastic deposits, with a lava flow linked to the older scoria cones and a paleosol at its top; the latter indicates a significant hiatus occurred between the growth of the scoria cones and the eruption of the Aljojuca maar, whose deposits cap this sequence. Changes in the local conditions produced strong interactions of the ascending magma with groundwater, shifting the strombolian eruptive style of the three older scoria cones to intense phreatomagmatic explosions of Aljojuca maar, leading to the emplacement of ca. 30-m-thick maar (tuff ring) sequence. A detailed stratigraphic study indicates that the eruption can be grouped into two main stages, comprising five eruptive phases dominated by phreatomagmatic and ephemeral strombolian eruptions, which are represented by eight stratigraphic units in total. The first stage reflects the development of the main crater and is recorded by six stratigraphic units (from A to F), and the second stage includes the occurrence of a possibly fissural E-W structure, which formed a scallop in the eastern flank of the maar (eastern embayment structure), and formed two stratigraphic units (G and H). To explain the processes involved in that evolution, a sequential model is proposed.
At the outset of the Aljojuca eruption, the feeder dike arrived at the main crater, leading to many explosions around the crater, creating a maar sensu stricto. Later, migration of the explosive loci toward the eastern flank of the maar showed a tectonic control by the dominant regional east-trending structural pattern. Several 14C paleosol ages support a late Holocene age (ranging from 4140 30 BP to 2870 30 BP.) of Aljojuca maar. This has important implications for the hazard assessment of volcanism in this area, which had not been considered previously as a potentially active system.
... A brief overview on the genesis of Plio-Pleistocene alkaline basalts in the CPR is provided below, as this topic has been covered in great detail in previous studies (e.g. Ali et al., 2013;Ali and Ntaflos, 2011;Embey-Isztin et al., 1993;Harangi et al., 2015;Kereszturi et al., 2010Kereszturi et al., , 2011Németh et al., 2001;Seghedi et al., 2004;Szabó et al., 1992). The following main alkaline basaltic volcanic fields are located in the CPR from west to east: Styrian Basin (SBVF); Burgenland; Little Hungarian Plain (LHPVF); Bakony-Balaton Highland (BBHVF); Nógrád-Gömör (NGVF) and Perşani Mts. ...
We present a new model for the formation of Plio-Pleistocene alkaline basalts in the central part of the Carpathian-Pannonian region (CPR). Based on the structural hydroxyl content of clinopyroxene megacrysts, the 'water' content of their host basalts is 2.0-2.5 wt.%, typical for island arc basalts. Likewise, the source region of the host basalts is 'water' rich (290-660 ppm), akin to the source of ocean island basalts. This high 'water' content could be the result of several subduction events from the Mesozoic onwards (e.g. Penninic, Vardar and Magura oceans), which have transported significant amounts of water back to the upper mantle, or hydrous plumes originating from the subduction graveyard beneath the Pannonian Basin. The asthenosphere with such a relatively high 'water' content beneath the CPR may have been above the 'pargasite dehydration' (< 90 km) or the 'nominally anhydrous' (> 90 km) solidi. This means that neither decompressional melting nor the presence of voluminous pyroxenite and eclogite lithologies are required to explain partial melting. While basaltic partial melts have been present in the asthenosphere for a long time, they were not extracted during the syn-rift phase, but were only emplaced at the onset of the subsequent tectonic inversion stage at ~8-5 Ma. We propose that the extraction has been facilitated by evolving vertical foliation in the asthenosphere as a response to the compression between the Adriatic indenter and the stable European platform. The vertical foliation and the prevailing compression effectively squeezed the partial basaltic melts from the asthenosphere. The overlying lithosphere may have been affected by buckling in response to compression, which was probably accompanied by formation of deep faults and deformation zones. These zones formed conduits towards the surface for melts squeezed out of the asthenosphere. This implies that basaltic partial melts could be present in the asthenosphere in cases where the bulk 'water' content is relatively high (> ~200 ppm) at temperatures exceeding ~1000-1100 °C. These melts could be extracted even under a compressional tectonic regime, where the combination of vertical foliation in the asthenosphere and deep fractures and deformation zones in the folded lithosphere provides pathways towards the surface. This model is also valid for deep seated transpressional or transtensional fault zones in the lithosphere.
... Maar formation is typical sign of phreatomagmatic eruptions. At the onset of the eruption, magma began to interact with a moderate amount of ground water in the water-saturated sand beds [Németh et al., 2001]. ...
Since the beginning of geomagnetic recording at Tihany Geophysical Observatory, baseline instability has been observed, especially in the case of the old variation house. The regularly observed annual baseline change is independent from the type of magnetometer. Common environmental effects on the instruments (for example temperature effects) are not suitable to characterize this variation. A possible reason of this instability is an unconventional geomagnetic effect on the magnetic properties of the sediment. The water saturation of a lake mud in a geyser cone shows correspondence with the variation of the base values. X-ray powder diffraction measurement detected goethite in the lake mud which, in fact makes possible the appearance of a super-ferromagnetic effect on goethite. In this study we present a possible source and the mechanism of the effect.
... The widespread of the shallow rich-water limestone aquifer in the tabular Middle-Atlas is an important aspect that generated some explosive eruptive centres, especially when precipitation and temperature oscillated persuading more complex volcanic geomorphology (Boivin et al. 1982, Traglia et al. 2009, Kshirsagar et al. 2016. Therefore, these phreatomagmatic and mixed eruptive centres play a crucial role as good sensors of the environmental variation (Wood 1980, Siebe 1986, Németh et al. 2001, mostly when superficial and ground water-table level changed (Lorenz 1984, Büchel 1993, Büchel et al. 2000. ...
Through the tabular morphology of northwestern part of the Middle-Atlas in Morocco, numerous uncovered monogenetic volcanoes arise structured of pyroclastic product layers and lava flows. Our fieldwork results witness a wide-ranging volcanic shape spectrum, as cones, maars, tuff-rings, and cone-maar mixes, generally associated with a later lava flow discharge that could develop many surfaces and appearances. There are withal sundry eruptive products such as pahoehoe lava, scoria, tuff, lapilli, peperites, base-surges, bombs, etc. This monogenetic volcanic field of practically 1000 km ² offers remarkable eruptive landforms, referred to as the largest, and the youngest volcanic field in Morocco, which consists of a large area within the Ifrane National Park. This fieldwork study provides a renewed volcanic geomorphological classification table and GIS data to be used by a wide public range for both educational and geo-touristic interest and access effectively to such a high-mountain natural museum. In the event that these volcanic structures were appropriately dealt with, the high educational scientific content and the notable touristic vocation would almost certainly create business openings and new financial wages for neighborhood populaces. This work focuses to share our outcomes and emphases the scientific value about the monogenetic volcanic field around the tabular Middle-Atlas in Morocco.
... In addition, during that time, Central Anatolia is thought to have been uplifted due to Cyprian slab break-off (e.g., Schildgen et al., 2014). All these resulted in variable hydrogeological conditions in both the Karapınar monogenetic field and the Central Anatolian volcanic province, where water probably was supplied by a combination of porous media and fracture-controlled aquifers, similar to the Tihany Maar volcanic complex in the Pannonian Basin (Németh et al., 2001). However, the link between hydrogeological conditions and the formation of various types of monogenetic volcanoes in the Central Anatolian volcanic province still needs to be resolved. ...
The Eğrikuyu monogenetic field is located in the southwestern part of the Central Anatolian volcanic province and includes numerous scoria cones and related lava flows, as well as a few maars. Eğrikuyu monogenetic field basalts are mainly olivine-nepheline (Ol-Nph) normative, with higher MgO (7.9-11.5 wt%) and Ni (up to 226 ppm) contents compared to other Central Anatolian vol canic province basalts. Enrichment in large ion lithophile elements compared to high field strength elements and depletions in Nb, Ta, P, and Ti in the multi-element diagrams are typical trace-element characteristics of all Central Anatolian volcanic province basalts. Mineral, trace element, and isotope compositions of Eğrikuyu monogenetic field basalts revealed the necessity of at least two distinct and variously enriched components responsible for their formation. Decompressional melting of metasomatized subcontinental lithospheric mantle (enriched mid-ocean-ridge basalt-like), with or without the contribution of upwelling deep asthenospheric melt (oceanic-island basalt-like), may explain the geochemical characteristics of all Central Anatolian volcanic province ba-salts. The lower 207 Pb/ 204 Pb ratios and some distinct clinopyroxene compositions (titaniferous augite and Fe-rich diopside) in Eğrikuyu monogenetic field basalts are indicators for the presence of upwelling asthenosphere, which is also evident in the low-seismic-velocity anomalies and Cyprian slab tear that underlie the field. The Eğrikuyu monogenetic field is a good example of mantle source heterogeneity in a monogenetic basaltic field and therefore constitutes a suitable region within the Central Anatolian volcanic province where different mantle source components can be traced.
... To recognize universal characteristics of craters formed by 40 subsurface phreatomagmatic explosions, a global database of young maar crater size and 41 shape was created: Maar Volcano Location and Shape (MaarVLS). The size of maars have 42 been previously described in a few studies, but the source data for larger datasets was 43 unavailable (Cas and Wright, 1987), the measurements are limited to a few isolated craters 44 (Nemeth et al., 2001), or were limited to highly eroded craters or diatremes (Martín-Serrano et 45 al., 2009). This database contains the data of maar sizes and shapes from multiple eruptive 46 fields from a range of volcanic settings. ...
A maar crater is the top of a much larger subsurface diatreme structure produced by phreatomagmatic explosions and the size and shape of the crater reflects the growth history of that structure during an eruption. Recent experimental and geophysical research has shown that crater complexity can reflect subsurface complexity. Morphometry provides a means of characterizing a global population of maar craters in order to establish the typical size and shape of features. A global database of Quaternary maar crater planform morphometry indicates that maar craters are typically not circular and frequently have compound shapes resembling overlapping circles. Maar craters occur in volcanic fields that contain both small volume and complex volcanoes. The global perspective provided by the database shows that maars are common in many volcanic and tectonic settings producing a similar diversity of size and shape within and between volcanic fields. A few exceptional populations of maars were revealed by the database, highlighting directions of future research to improve our understanding on the geometry and spacing of subsurface explosions that produce maars. These outlying populations, such as anomalously large craters (> 3000 m), chains of maars, and volcanic fields composed of mostly maar craters each represent a small portion of the database, but provide opportunities to reinvestigate fundamental questions on maar formation. Maar crater morphometry can be integrated with structural, hydrological studies to investigate lateral migration of phreatomagmatic explosion location in the subsurface. A comprehensive database of intact maar morphometry is also beneficial for the hunt for maar-diatremes on other planets.
... Subsequently, the confined aquifer located in the basement played an important role in triggering explosive highly energetic eruptions when coming into contact with the ascending magma (cf. Aramaki et al., 1986;Aranda-Gómez and Luhr, 1996;Németh et al., 2001;Buttinelli et al., 2011;Saucedo et al., 2017). Finally, because of the El Escondido pyroclastic cone is more complex than the San Diego maar as the cone is strongly eroded (Fig. 6B). ...
Monogenetic volcanic fields are commonly related to rifts and/or intraplate tectonic settings. However, they are also less commonly recognised in subduction zones, including both front and back-arc volcanoes (e.g. monogenetic volcanoes associated with the Llaima volcano in Chile or the San Agustín Volcanic Field in Colombia). Here,
we describe monogenetic volcanic fields associated with subduction-related polygenetic volcanism in the northernmost part of the Andes Northern Volcanic Zone (NVZ) (2° S to 4°30′N). These fields are associated with the main axis of the Quaternary volcanoes. They are linked to the polygenetic San Diego – Cerro Machín Volcano Tectonic
Province (~140 km long; SCVTP) in Colombia, the chain that hosts the iconic Nevado del Ruiz volcano. Presently, three monogenetic volcanic fields, with a typical calc-alkaline signature, have been identified on both sides of this province. From south to north, they are: 1) Pijaos Monogenetic Volcanic Field (PMVF), 2) Villamaría –Termales Monogenetic Volcanic Field (VTMVF), and 3) Samaná Monogenetic Volcanic Field (SMVF). PMVF is located ~25 km south of Cerro Machín volcano, the southernmost active volcano of the SCVTP. This field was formed by at least two eruptions with both effusive and explosive eruptive styles. Three cones and a maar are recognised. Previous work has defined the volcanoes as basaltic andesitic in composition, which we recognised as the most mafic expression (MgO 10–11 wt%) in the whole SCVTP. Its source is related to the same, but deeper magma that feeds the volcanoes in the SCVTP. Stratigraphic relationships show that the volcanoes are younger than the underlying alluvial and volcaniclastic Ibagué fan (< 2.58 Ma). VTMVF is located in the northwestern region of the SCVTP (N5 km of the axis of the province). This field is made up of at least 14 volcanoes aligned with
the active Villamaría – Termales fault system, as previous work has recognised. The volcanism has been mainly effusive, represented by lava domes and some lava flows. Since the 1980s, studies have framed these andesitic to dacitic volcanoes in the context of the history of the Nevado del Ruiz volcano. It is inferred that the magmatic source is a shallow magma reservoir underneath the SCVTP. Stratigraphic and field relationships have shown that the last eruption occurred b38 ka. SMVF is located ~50 km north of Romeral composite volcano, the northernmost
active volcano from the SCVTP. Previous studies have revealed that this field comprises at least two volcanoes: A maar (~20 ka years old) and a pyroclastic cone (~33 ka years old). These studies defined the volcanic products as andesitic and dacitic in composition. It is inferred that this field is a result of the same magmatism as that of the SCVTP. Overall, it is clear that monogenetic volcanism is not atypical in the area. We thus propose a SCVTP magmatic plumbing system joining both the monogenetic and polygenetic volcanoes related to the subduction arc.
... To recognize universal characteristics of craters formed by 40 subsurface phreatomagmatic explosions, a global database of young maar crater size and 41 shape was created: Maar Volcano Location and Shape (MaarVLS). The size of maars have 42 been previously described in a few studies, but the source data for larger datasets was 43 unavailable (Cas and Wright, 1987), the measurements are limited to a few isolated craters 44 (Nemeth et al., 2001), or were limited to highly eroded craters or diatremes (Martín-Serrano et 45 al., 2009). This database contains the data of maar sizes and shapes from multiple eruptive 46 fields from a range of volcanic settings. ...
A maar crater is the top of a much larger subsurface diatreme structure produced by phreatomagmatic explosions and the size and shape of the crater reflects the growth history of that structure during an eruption. Recent experimental and geophysical research has shown that crater complexity can reflect subsurface complexity. Morphometry provides a means of characterizing a global population of maar craters in order to establish the typical size and shape of features. A global database of Quaternary maar crater planform morphometry indicates that maar craters are typically not circular and frequently have compound shapes resembling overlapping circles. Maar craters occur in volcanic fields that contain both small volume and complex volcanoes. The global perspective provided by the database shows that maars are common in many volcanic and tectonic settings producing a similar diversity of size and shape within and between volcanic fields. A few exceptional populations of maars were revealed by the database, highlighting directions of future research to improve our understanding on the geometry and spacing of subsurface explosions that produce maars. These outlying populations, such as anomalously large craters (>3000 m), chains of maars, and volcanic fields composed of mostly maar craters each represent a small portion of the database, but provide opportunities to reinvestigate fundamental questions on maar formation. Maar crater morphometry can be integrated with structural, hydrological studies to investigate lateral migration of phreatomagmatic explosion location in the subsurface. A comprehensive database of intact maar morphometry is also beneficial for the hunt for maar-diatremes on other planets.
... Basalt volcanism in the Little Hungarian Plain and the nearby Bakony-Balaton Highland Volcanic Field involved large range of eruption styles and associated volcanic forms, from maars through lava lake-filled tuff rings and scoria cones to shield volcanoes (Harangi et al. 1994;Németh and Martin 1999;Németh et al. 2001;Martin and Németh 2004;Németh 2012). Shallow, but broad tuff ring volcanoes in LHPVF have been formed due to the phreatomagmatic explosive eruption caused by mixing between uprising hot basaltic magma and water-saturated clastic sediments in areas where thick Neogene siliciclastic units build-up shallow pre-volcanic strata (Harangi and Harangi 1995;Németh 2004, 2005). ...
Three-dimensional geophysical modelling of the early Late Miocene Pásztori volcano (ca. 11–10 Ma) and adjacent area in the Little Hungarian Plain Volcanic Field of the Danube Basin was carried out to get an insight into the most prominent intra-crustal structures here. We have used gridded gravity and magnetic data, interpreted seismic reflection sections and borehole data combined with re-evaluated geological constraints. Based on petrological analysis of core samples from available six exploration boreholes, the volcanic rocks consist of a series of alkaline trachytic and trachyandesitic volcanoclastic and effusive rocks. The measured magnetic susceptibilities of these samples are generally very low suggesting a deeper magnetic source. The age of the modelled Pásztori volcano, buried beneath a 2 km-thick Late Miocene-to-Quaternary sedimentary sequence, is 10.4 +/− 0.3 Ma belonging to the dominantly normal C5 chron. Our model includes crustal domains with different effective induced magnetizations and densities: uppermost 0.3–1.8 km thick layer of volcanoclastics underlain by a trachytic-trachyandesitic coherent and volcanoclastic rock units of a maximum 2 km thickness, with a top situated at minimal depth of 2.3 km, and a deeper magmatic pluton in a depth range of 5–15 km. The 3D model of the Danube Basin is consistent with observed high ΔZ magnetic anomalies above the volcano, while the observed Bouguer gravity anomalies correlate better with the crystalline basement depth. Our analysis contributes to deeper understanding of the crustal architecture and the evolution of the basin accompanied by alkaline intraplate volcanism.
... Azonban sajnos nem ismert a teljes freatomagmás piroklasz tit-rétegsor, így nem tudjuk, hogy milyen más típusú piroklasztitot tartalmazhat. Mindenesetre figyelemreméltó, hogy egyik feltárásban sem találunk olyan típusú, jelentős vastagságú piroklasztitösszletet, amely gazdag lenne dur va hamunál nagyobb méretű feltépett litoklasztokban (mint ahogy ezt a jól ismert tihanyi piroklasztitokban dokumen -tálták [NÉMETH et al. 2001]). Ez utalhat arra, hogy a robbanások a felső, kevésbé konszolidált rétegsorban történtek, és onnan nem migráltak mélyebbre (így nem tépték fel a mélyebben található keményebb kőzeteket). ...
A tanulmányban a Bakony–Balaton-felvidéki Vulkáni Terület (BBVT) legismertebb tanúhegyén, a Badacsonyon kibukkanó freatomagmás piroklasztit-sorozat első kvantitatív leírását és vulkanológiai értelmezését mutatjuk be. A piroklasztitok juvenilis / litikus törmelékeinek arányát pontszámlálásos módszerrel vizsgáltuk vágott kézipéldány-felszíneken. A felület%-ban kapott eredményeket a kőzetminták teljes térfogatára vonatkozónak vettük. E módszer segítségével meghatároztuk a freatomagmás robbanások relatív mélységét a szinvulkáni felszínhez képest, következtetéseket vontunk le a lehetséges szineruptív vulkánmorfológiára, valamint a terepi megfigyelések és korábbi tanulmányok alapján rekonstuáltuk a vulkán működésének teljes fejlődéstörténetét. A képelemzés során megállapítottuk litikus elegyrészek minimális arányát. Ebből, valamint a piroklasztitok térbeli elterjedéséből és rétegtani helyzetéből valószínűsíthető, hogy a Badacsony egy monogenetikus (esetleg policiklikus) tufagyűrű vagy sekély maar vulkán volt, amelynek kialakulásában a víz-magma kölcsönhatás következtében történt sekély mélységű freatomagmás robbanások játszották a fő szerepet. A tufagyűrű vulkáni forma a litoklasztok kis mennyiségével alátámasztható. Viszonylag kevés litoklasztot tartalmazó freatomagmás kitörési termékek nem csak tufagyűrűk, hanem puha, konszolidálatlan kőzeten kialakuló sekély maarok képződményei is lehetnek, amely modell a Badacsony esetében is valószínűsíthető. A terepi megfigyelések, valamint a képelemzés eredménye alapján a vulkanizmus freatomagmás robbanásos, lávaöntő és magmás robbanásos fázisokra osztható. Ezen adatok alapján vulkáni fejlődéstörténeti modellt állítottunk fel. A kevés korábbi, célzott vulkanológiai szemléletű munka miatt e „kezdeti” adatok megfelelő alapot adhatnak a további badacsonyi vulkanológiai kutatásoknak.
... Understanding the effects of climate change on flow patterns and recharge-discharge relationships with surface water bodies can nevertheless help to better mitigate or prepare for the consequences, e.g. with improved water management plans and policies in order to protect these vulnerable water resources or to develop them in a sustainable manner. Balogh and Németh (2005), Faragó (1990), Kundzewicz et al. (2008), Leith and Whitfield (1998), Molson et al. (1992), Németh et al. (2001), Singh (2014), Tullner (2002), Weast (1980), Winter (1999a,b). ...
Climate change can directly influence groundwater systems through modification of recharge. Affecting not only groundwater levels and flow dynamics, climate change can also modify the fragmentation and hierarchy of groundwater flow systems. In this study, the influence of climate change - impacted recharge on groundwater levels and on inter-connected groundwater flow patterns is evaluated. Special emphasis is placed on how flow system hierarchy may change, to examine possible consequences on groundwater-related shallow surface water bodies and on groundwater – surface water interaction. As a test site with no significant anthropogenic impacts, the Tihany Peninsula in Hungary was an ideal area for the study. We address the following issues: i) How might a groundwater system, including groundwater-surface water interaction, be modified by predicted climate change?, ii) Given the variable groundwater levels and flow patterns, how will the water levels and fluxes be impacted around surface water bodies?, and iii) How sensitive are groundwater-related wetlands to these changes, and will they be maintained or will they eventually disappear? In order to answer these questions, two-dimensional transient numerical simulations were performed based on site-specific measurements and climatic prediction at the Tihany Peninsula. Results show that future climate trends can cause dynamic evolution and dissipation of transient groundwater flow systems, and the characteristic flow system hierarchy can change from nested flow systems to a set of single flow cells. Preservation of associated groundwater-dependent ecosystems would be challenging under these conditions since long-term climate change could potentially have serious consequences, including wetland disappearance. Understanding these transient processes in two-dimensions can also help to set-up three-dimensional site-specific models.
... This is usually attributed to high particle concentration rather than turbulence [28]. Sagging in unit 3 by mud stone fragments is an indication of abundant moisture and wetness of the environment [29] [30] [31] [32]. The mudstone lumps are intact, but slightly deformed and marginally altered within this deposit. ...
The Bambili maars are twin contemporaneous maars embedded in trachytic rocks. The two maars are separated by a low lying inter
... Granitoid basement rocks are exposed in the erosionally enlarged maar crater (gr) Fig. 4.37 Panoramic views of the tuff ring succession [27°10′ 41.86″N; 42°17′ 17.88″E] in the eastern sector of the tuff ring of Jubb with its pyroclastic units (u1, u2, u3 and u4) (a-c). On c and d yellow circles locate the well-developed dunes/anti-dunes of the PDC deposit pyroclastic units resemble textural features typical to diatreme filling successions similar as it has been reported from Hopi Buttes, Arizona (Lefebvre et al. 2013;, Waipiata, New Zealand (Németh and White 2003), or the Pannonian Basin, mostly in Hungary (Németh et al. 2001). In this respect the exposed pyroclastic rocks could represent an exposure level of volcanoes near or even below the syn-eruptive surface. ...
This book records the geoheritage values of globally significant, yet little-known, volcanic geosites in Saudi Arabia. It is the first of its kind to focus on the Middle East, clearly showing the hidden geoheritage value of the volcanic Arabian Peninsula’s harrats and demonstrating why the Saudi Arabian volcanic fields are unique. Along with the systematic geosite description, the book introduces scientifically founded geoeducational programs that can be used to develop our understanding of volcanic geoheritage values of volcanic fields. It offers a detailed and comprehensive research-based description of four of the most accessible volcanic harratts in Saudi Arabia and an additional summary of other more remote fields. Additionally, it discusses geoeducational programs that could be used to link these volcanic areas and use them in volcanic hazard education.
The mobility of rare-earth elements (REE) in low-grade diagenetic regimes, potentially leading to their clay-mediated fractionation, remains poorly understood. This study draws evidence from the argillitized Miocene tuff of the Southwestern Pannonian Basin (SPB) and adjacent Dinarides intramontane basins (DIB) to investigate the role of illite-smectite (I-S) in controlling early diagenetic REE behavior. The present research relies on detailed mineralogical, geochemical, and gas adsorption characterization of altered tuff, focusing on comparative analyses of the REE chemistry obtained by in situ laser ablation inductively coupled plasma mass spectrometry of glass shards and that of spatially related authigenic clay minerals. The depositional environment, in which the volcanic glass alteration took place, gave rise to the composition of secondary paragenesis, revealing a dominance of IS. The normalized REE geochemistry of clay separates show similarities to unaltered glass, but notable differences indicate fluctuations in fluid/rock ratio environments. The redox conditions during glass alteration are reflected in Ce and Eu anomalies and indicate the ranges from oxic to anoxic across the analyzed tuffs. The results showed that IS , formed through volcanic glass diagenesis, inherits magmatic REE signatures but also fractionates REE based on more reducing physiochemical conditions. The strong correlation between smectite content of IS and a total budget of fractionated REE posits the smectite interlayers as prime factors controlling the REE fractionation during volcanic ash diagenesis. Furthermore, greater specific surface area values and development of slit-shaped porosity along the non-basal edges of IS particles contributed to REE adsorption. These findings contribute to our understanding of REE behavior in low-temperature diagenetic environments, emphasizing the significance of clay minerals in retaining and fractionating these elements which may lead ultimately to the formation of economically viable ion-adsorption clay deposits.
The GIS-based geomorphological and morphometric approaches were combined with field- and tephrostratigraphic analyses to reconstruct the history of the Mt Manengouba volcano including the Eboga maars in the southwestern part of the Cameroon Volcanic Line (CVL). The elevation, slope, relative relief, topographic position and terrain ruggedness indexes from the Digital Elevation Model (DEM, 12.5 m) were determined to constrain two main geomorphic units corresponding to the Elengoum and Eboga nested stratovolcanoes which were affected by differential erosional processes. The studied grain size, shape, vesicularity, structure, degree of lithification, sorting, thickness, grading patterns, sedimentary features, spatial distribution revealed three tephrostratigraphic units: U1 (U1-1, lithic and juvenile; U1-2 dominantly juvenile), U2 (U2-1 ash- and juvenile richdeposits; U2-2, juvenile-scoria with few lithic) and U3 (scoria cone deposits). The total volume of ~0.199 km3 of tephra deposits ranges the Eboga maars volcanoes within the small-volume monogenetic types. These results revealed dry/wet phreatomagmatism and strombolian activity as a contribution to the seven phases-eruptive history of the Mt Manengouba volcano: the pre-Manengouba; emplacement of Elengoum stratovolcano; collapse of Elengoum summit and formation of Elengoum caldera; emplacement of Eboga stratovolcano; the collapse of Eboga summit and formation of Eboga caldera; a phreatomagmatic phase and emplacement of Female and Male maars ending with an explosive stage associated with the formation of scoria and parasitic cones.
A természetközeli ökoszisztémák a kis változásokra azonnal és érzékenyen reagálnak. Az antropogenitás növekedésével párhuzamosan az előhelyek mozaikossága is fokozódik, ami az élőhelyek állapotromlásához vezethet. Éppen ezért a vizes területek megőrzésére, védelmére, fenntartására kiemelkedő hangsúlyt kell fektetni. A Nagyfelbontású Repülőgépes Monitoring Hálózat (NRMH) alkalmas a változások követésére, így a nád monitorozására is. A módszer fejlesztését a táj térszerkezetében végbemenő gyors változások indokolták. A változásokra való reagálás igénye a nehezen megközelíthető terepen megtalálható területek gyors és költséghatékony felmérését tette szükségessé. A szubcentiméteres (centiméter alatti felbontású) részletességű ortofotók kis, pár négyzetkilométeres területek térképezését teszik lehetővé gazdaságosan, így a tájrészletek ilyen mélységű értékelése mintaterületek kijelölésével oldható meg. A tihanyi Külső-tó területének felszínborítása jelentős változásokon ment keresztül az elmúlt években, a tó felszínének jelentős részét az egybefüggő nádas foglalja el. Az NRMH vizes élőhelyekre vonatkozó felszínborítási kategóriarendszere hat új kategóriával bővült a tó vizsgálatán keresztül.
This paper presents the results from a geographic information systems (GIS) workflow, which was used to analyze the spatial distribution and temporal evolution of volcanoes in the Mio-Pleistocene monogenetic Bakony-Balaton Highland Volcanic Field (BBHVF), located in the Pannonian Basin, Hungary. Volcanism occurred during the tectonic inversion in a back-arc setting and a compressive/transpressive tectonic regime on the hottest and thinnest lithosphere of continental Europe. The main goal of this study is to clarify the effect of the pre-existing structure of the upper lithosphere in the distribution of the volcanic centers across the volcanic field using an innovative GIS methodology. Orientation of the volcanic field was compared to the orientation of the faults in the BBHVF, and in its larger vicinity, which resulted in correspondence, suggesting the dominance of the SW-NE direction. The directions of the volcanic lineaments fit well to the two main fault directions. The fault-volcano proximity analysis suggests that the fault plane of a thrust fault was an important structural feature during the lifespan of the volcanism. All results suggest that the fault plane of a regionally significant Cretaceous thrust fault (Litér Fault) might have served as a temporary pathway for the ascending magma, whereby (similarly to other, smaller faults) redirecting the magmas causing clustering of the volcanoes. This highlights the importance of major upper crustal structural heterogeneities for magma transport in a compressive tectonic system, especially in the case of active, monogenetic volcanic fields from a volcanic hazard perspective. The present GIS workflow can be effective in analyzing the spatial patterns of the volcanism and its connection with crustal structures at monogenetic volcanic fields worldwide.
Maar-diatreme volcanoes are the second-most common type on land, occurring in volcanic fields within all major tectonic environments. Their deposits typically contain an abundance of lithic fragments quarried from the substrate, and many contain large, deep-sourced lithic fragments that were erupted to the surface. Primary volcaniclastic deposits fill the diatreme structure formed during eruption. There is negligible inelastic deformation of diatreme-adjacent country rock, indicating that country rock is removed to create the diatreme structures, either by being shifting downward below observable levels, ejected upward to contribute to surficial deposits, or dissolved and hidden in magma erupted or intruded at depth. No previous study has systematically reviewed and analysed the reported lithic fragments of maar-diatreme systems. We present a comprehensive compilation from published work of lithic characteristics in maar ejecta rings and in diatreme deposits of both common and kimberlite maar-diatremes. For maar-diatremes and their tephra ring deposits, we find no correlations among lithic clast sizes, shapes, depositional sites, and excavation depths. This is difficult to reconcile with models involving systematic diatreme deepening coupled with tephra-ring growth, but consistent with those involving chaotic explosions and mixing. Larger amounts of data are needed to further examine how these types of volcanoes operate.
Clinoforms and clinothems are important and common architectural elements in the sedimentary record of many basins worldwide. The influence that they exert on chronostratigraphic interpretations, however, is often underestimated. This is especially true in non-marine basins, such as the Central European to Central Asian Neogene Paratethyan basins, where chronostratigraphic division and correlation is usually based on fossils of environmentally sensitive molluscs recovered from outcrops of shallow-water deposits. In the subsurface, the diachronous boundary between the foreset and topset parts of the shelf-edge scale clinoforms, where significant lithological and paleontological changes can be observed with the transition from deep to shallow water, was routinely identified with one of the regional stage or substage boundaries, inflicting serious confusion in chronostratigraphy. In the late Neogene brackish lacustrine basin fill of the Pannonian basin (Pannonian Stage, 11.6 to 2.6 Ma), where extended endemic radiation and long-term gradual morphological change in various groups of the biota offer good marker species for high-resolution biostratigraphy, molluscs and dinoflagellate algae are used to establish a clinothem chronostratigraphy. The biozone and clinothem boundaries are correlated with the geological time scale through mammal stratigraphic considerations, magnetostratigraphy, and radiometric dating. For the time being, the beginning of lacustrine deposition at 11.6 Ma and the intervals between 8.8 and 7.1 Ma and 4.6–2.6 Ma are accurately dated in drill cores. These time intervals can be correlated through the dense seismic network across the basin. For other time intervals of the late Miocene and Pliocene, the uncertainty of dating remains high on the order of several 100 kys.
The Holocene tuff ring of Songaksan, Jeju Island, Korea, is intercalated with wave-worked deposits at the base and in the middle parts of the tuff sequence, which are interpreted to have resulted from fair-weather wave action at the beginning of the eruption and storm wave action during a storm surge event in the middle of the eruption, respectively. The tuff ring is overlain by another marine volcaniclastic formation, suggesting erosion and reworking by marine processes because of post-eruption changes of the sea level. Dramatic changes of the chemistry, accidental componentry, and ash-accretion texture of the pyroclasts are also observed between the tuff beds deposited before and after the storm invasion. The ascent of a new magma batch, related to the chemical change, could not be linked with either the Earth and ocean tides or the meteorological event. However, the changes of the pyroclasts texture suggest a sudden change of the diatreme fill from water-undersaturated to supersaturated because of an increased supply of external water into the diatreme. Heavy rainfall associated with the storm is inferred to have changed the water saturation in the diatreme. Songaksan demonstrates that there was intimate interaction between the volcano and the environment.
Cenozoic geological evolution of New Zealand centres around the formation of Zealandia, a new continent that became detached from the eastern margin of Gondwana around 105 Ma. Spreading opened the Tasman Sea leaving a fragment of continental lithosphere, largely submerged, in the SW Pacific. Throughout the Cenozoic history, volcanism became an integral part of Zealandia. Continental lithosphere provided the basement for the volcanism, both onshore and offshore. Monogenetic volcanism was common throughout the Cenozoic. The availability of water was ubiquitous through surface water bodies (oceans and lakes) and various other terrestrial hydrous systems provided by the humid temperate climate of Zealandia. Hydrovolcanism, both explosive and non-explosive, has played a significant role in Zealandia's volcanic history resulting in volcano mega-architecture involving edifice geology and volcanic hazards. However, hydrovolcanism has commonly been overlooked in Zealandia's monogenetic volcanism context. Cenozoic monogenetic fields of Zealandia provide a unique laboratory and comparative analogy for other volcanic fields on Earth that are associated with low-lying terrestrial settings or shallow marine environments in a humid temperate climate.
Bahariya monogenetic volcanic field is characterized by important geomorphological features (geomorphosites), namely, sub-circular maar-tuff ring, scoria cones, and domal-shaped tumuli. These geomorphosites constitute an asset for geoeducation, geotourism and miscellaneous social activities. They offer important knowledge into the paleoenvironmental and climatic factors that affected the style of volcanism at the occasion, and eventually shaped the diverse landforms found in the volcanic field. Bahariya Oasis is exclusive for its excellent locations where many volcanic heritages of high value give evidence of phreatomagmatic and effusive-controlled phases which formed volcanic landscapes under humid to dry climate. The geoheritage and archeological sites of early settlements are abundant in the Bahariya Oasis, accentuating the scientific magnitude of this region. There have been seven geosites recognized such as (1) the scoria cone, (2) the lava flows and their surface morphological features, (3) the pseudopillow fractures, (4) columnar joints, (5) peperites, (6) tumuli, and (7) rootless cones. These geosites coupled with other unique sites define the Oasis as global geopark. The latter will consider as an excellent logistical network to endorse volcanic geosciences and raise the economic growth in this part of Bahariya Oasis. The diverse geological characteristics at the Bahariya make this area a high volcanic geodiversity that can be used for geoeducational programs and geotourism. Excursions and research programs carried out by universities will contribute to enhanced geoconservation for local sustainable development. Currently, in the Bahariya region, tourism is not well developed, but it is recommended that, roads be improved to give better accessibility to the geomorphosites, and interpretative panels, informative brochures, multi-media presentations, seminars and workshops, scientific lectures, and postcards be produced to inform tourists about the geology of the region.
Monogenetic basaltic volcanic systems, despite their considerable smaller size and shorter lifetime compared to polygenetic volcanoes, can have complex pre-eruptive histories and composite volcanic facies architectures. Their source-to-surface investigation is essential for our better understanding of monogenetic volcanism and requires high-resolution mineral-scale analyses. In this study, we focus on diversely zoned olivine crystals and their spinel inclusions from alkaline basaltic volcanics that are the result of mixing of numerous magmas, crystals and fragments of various origins. The Fekete-hegy volcanic complex is one of the largest and most composite eruptive centers in the intracontinental monogenetic Bakony–Balaton Highland Volcanic Field (western Pannonian Basin, Eastern Central Europe). It is a compound multi-vent system built up by multiple eruption episodes: initial maar-forming phreatomagmatic eruptions were followed by massive lava flows and magmatic explosive activity. We performed stratigraphically controlled sampling in order to reveal the history of the successively erupted magma batches represented by the distinct eruptive units, as well as to discover the petrogenetic processes that controlled the evolution of the magmatic system. The juvenile pyroclasts of the phreatomagmatic eruption products (unit 1) contain a remarkably diverse mineral assemblage including five different olivine types and three distinct spinel groups. In addition, they comprise various xenoliths. Based on detailed textural investigations combined with in situ electron microprobe analyses, high-resolution laser ablation ICP-MS trace element mapping and single spot measurements on the variably zoned olivines of unit 1 samples, eight distinct environments are inferred to have been involved in their formation. Four of these environments account for the significant compositional variation of the olivine-hosted spinel inclusions. A complex set of open- and closed-system petrogenetic processes operated during the evolution of the magmatic system: magma stalling, accumulation, storage, fractionation, mixing, replenishments, cumulate remobilization, incorporation of foreign fragments and crystals from the wall rocks. All these diverse environments and processes resulted in the mixed character of the erupted magmas during the initial phreatomagmatic eruptive phase. In contrast, the uniform petrological features and the small variations shown by the olivines and spinels from unit 2–3 indicate that the later magmatic explosive – effusive phase was preceded by a considerable change in the magmatic system; it experienced a simple evolution through olivine + spinel fractional crystallization without any of the complexities seen during the initial phase. The present study emphasizes the importance of high-resolution mineral-scale textural and chemical investigations to unravel the complexity of the sub-volcanic magmatic systems feeding monogenetic basaltic volcanoes. Compared to the application of whole-rock geochemistry alone, this approach enables a direct and more detailed insight into the architecture and evolution of these systems.
Maars and diatremes as associated with any type of magma involved in volcanic activity, i.e. acid to ultrabasic, non-alkalic and alkalic magmas. Most maars and diatremes are the result of phreatomagmatic activity, i.e. a complex magma/external water (mostly groundwater) interaction, giving rise to powerful water vapour explosions. These explosions are responsible for hydraulic fragmentation not only of the magma, but also of large amounts of country rocks which form the wall rocks of the diatremes. The wall rock fragments characteristically make up a very high proportion of the produced pyroclastic rocks. The hydrostatic pressure of the water column above the explosion site and the availability or influx capacity of groundwater is assumed to control propagation or prevention of downward penetration of diatremes. Explosive eruptions in shallow-marine and in diverse continental environments are discussed in relation to a model of hydrostatically controlled phreatomagmatism. (M.A. 87M/3318)-R.A.H.
This paper deals with various methods of solving the complex problems of the hydrological transformation of rainfall into runoff in karst terrains. As an example of a typical karst catchment, the Crnojevića spring, located in deep Dinaric karst, is used to illustrate, explain and solve several hydrological problems in karst. The introduction deals with the geographical, geological and meteorological factors which conditioned a specific system of surface and underground flows, typical for karst terrains. The paper also explains some basic activities related to the identification of such a system. Special attention has been paid to the karst terrain of the Cetinje polje and its flooding, which occurred in February 1986. This flood initiated numerous intensive investigations which made it possible to define the catchment area of Crnojevića spring and the volume of the underground karst reservoir.
The Miocene-Pliocene Pannonian Lake formed in an extensional basin system behind the compressional arc of the Carpathians. Its size and depth were comparable to those of the Caspian Sea. Subsidence began in Middle Miocene times, forming deep, pelagic basins, separated by reef-bearing ridges. Clastic influx filled the marginal basins during Middle Miocene time. Prograding deltas dissected the lake and completed the infilling of the basin system by the end of the Pliocene. Basin plain, prodelta, delta front, delta plain, beach, fluviatile, and marsh environments can be recognized.
Eleven basaltic volcanoes from a variety of geologic settings were studied in order to compare vent morphology, deposit stratigraphy, and emplacement mechanisms at tuff rings with those at tuff cones. The tuff rings consist of thinly bedded, poorly indurated, relatively fresh pyroclasts deposited with bedding angles less than 12. The tuff cones consist of massive, thickly bedded, high indurated, and hydrated pyroclasts deposited at bedding angles up to 30. This massive tuff contains ash-fall layers interspersed with nearly equal volumes of base-surge beds. Stratigraphic data and models of pyroclastic surge suggest that the massive bedding of tuff cones results from a cool (below 100 C), wet emplacement. In contrast, the thinly-bedded deposits of tuff rings are typically emplaced while hot (above 100 C) and relatively dry. As the volume of water that explosively mixed with magma increases, the amount of steam produced increases, but the level of superheating of that steam decreases. This leads to an increased wetness of the resulting surge blasts. With increasing ratios of water to magma, activity changes from lava fountains to dry surges to wet surges. The resulting volcanic landforms are respectively cinder cones, tuff rings, and tuff cones. Accordingly, a dry environment would contain cinder cones; abundant ground water promotes tuff rings; and a shallow body of standing water favors development of tuff cones. 48 references, 19 figures, 2 tables.
Copyright - GeoRef, Copyright 2012, American Geosciences Institute. Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe, Hanover, Germany, Date revised - 2001-01-01, Language of summary - English, Pages - 417-438, ProQuest ID - 52210129, Document feature - illus. incl. sects., 3 tables, geol. sketch maps, SubjectsTermNotLitGenreText - alkali basalts; aquifers; Bakony Mountains; Balaton region; basalts; basement; Cenozoic; Central Europe; Central Transdanubia; clastic rocks; craters; Europe; ground water; Hungary; igneous rocks; karst; Miocene; Neogene; paleogeography; paleorelief; phreatomagmatism; sandstone; sedimentary rocks; Tertiary; Transdanubia; upper Miocene; volcanic features; volcanic fields; volcanic rocks; volcanoes, Last updated - 2012-06-07, CODEN - ZGMPAG, Corporate institution author - Nemeth, Karoly; Martin, Ulrike, DOI - 2001-052130; 0372-8854; ZGMPAG
Conference title - IUGG99, Copyright - GeoRef, Copyright 2012, American Geosciences Institute., Date revised - 2009-01-01, Language of summary - English, Pages - 171, ProQuest ID - 50396247, SubjectsTermNotLitGenreText - Bakony Mountains; Balaton Highland; Balaton region; Cenozoic; Central Europe; Europe; explosive eruptions; glasses; Hungary; igneous rocks; maars; Miocene; Neogene; Pannonian Basin; phreatomagmatism; pyroclastics; Tertiary; tihany-type eruptions; upper Miocene; volcanic rocks; volcanism, Last updated - 2012-06-07, CODEN - IGABAX, Corporate institution author - Nemeth, Karoly; Martin, Ulrike; Anonymous, DOI - 2009-068510; IGABAX
Copyright - GeoRef, Copyright 2012, American Geosciences Institute. Reference includes data supplied by CNR, Comitato Scienze Geologiche e Minerarie, Rome, Italy, Date revised - 2001-01-01, Language of summary - English, Pages - 271-282, ProQuest ID - 52238925, Document feature - illus. incl. 1 table, sketch maps, SubjectsTermNotLitGenreText - Bakony Mountains; Balaton region; Central Europe; craters; Europe; Hungary; igneous rocks; landform description; maars; Pannonian Basin; phreatomagmatism; pyroclastics; scoria; volcanic features; volcanic fields; volcanic rocks; volcaniclastics, Last updated - 2012-06-07, Corporate institution author - Nemeth, K; Martin, U, DOI - 2001-035881; 1121-9114
Copyright - GeoRef, Copyright 2012, American Geosciences Institute. Reference includes data supplied by Hungarian Geological Library, Budapest, Hungary, Date revised - 2000-01-01, Language of summary - English, Pages - 251-266, ProQuest ID - 52296013, SubjectsTermNotLitGenreText - aquifers; Boglar; Central Europe; controls; erosion; Europe; ground water; Hungary; Lake Balaton; Pannonian Basin; porous materials; Veszprem Hungary; volcanic features; volcanoes, Last updated - 2012-06-07, Corporate institution author - Nemeth, K; Martin, U; Philippe, M, DOI - 2000-075211; 0236-5278; 1588-2594
A new view is presented of the Bakony-Balaton Highland Volcanic Field (BBHVF), Hungary, active in late Miocene and built up of ca. 100 mostly alkaline basaltic eruptive centers, scoria cones, tuff rings, maar volcanic complexes and shield volcanoes. A detailed map shows the physical volcanology of the monogenetic volcanic field. In areas where thick Pannonian Sandstone beds build up the pre-volcanic strata normal maar volcanic centers have formed with usually thick late magmatic infill in the maar basins. In areas, where relatively thin Pannonian Sandstone beds resting on thick Mesozoic or Paleozoic fracture-controlled, karstwater-bearing aquifer, large unusual maar volcanic sequences appear (Tihany type maar volcanoes). In the northern part of the field large former scoria cones and shield volcanoes give evidence for a smaller impact of the ground and surface water causing phreatomagmatic explosive activity. The Tihany type maar volcanic centers are usually filled by thick maar lake deposits, building up Gilbert type gravelly, scoria rich deltas in the northern side of the maar basins, suggesting a mostly north to south fluvial system in the pre-volcanic surface. Calculating paleosurface elevation for the eruptive centers, two paleo-geomorphology maps are drawn for a younger (4-2.8 Ma) and an older (7.54-4 Ma) scenario. The erosion rate of the volcanic field is estimated to vary between 96 m/Ma and 18 m/Ma. In the western site of BBHVF the erosion rate is higher (more than 60 m/Ma, Tapolca Basin), and an average 50 m/Ma in the center and eastern side.
The volcanic centers next to Balatonboglar township represent 3.5 Ma old products of post-extensional alkaline basaltic volcanism in the Pannonian Basin (eastern Central Europe). They are small, eroded volcanic centers located on the southern shore of Lake Balaton and genetically related to the Bakony-Balaton Highland Volcanic Field eruptive centers. The relatively small area (500 m x 500 m) contains at least 2 eruptive centers, which are probably related to each other and have built up a complex volcano, called the Boglar Volcano. The volcanic rocks overlie the older Pannonian clastic sedimentary sequence and represent the topographic highs in this area. The areas of lower elevation around the eruptive centers are covered by Pleistocene to Holocene swamp, lake and river clastic sediments, which strongly suggest intense erosion during the last few million years. All volcanic rocks around Balatonboglar are volcaniclastic. There is no evidence of lava flow occurrence. The volcaniclastic sediments have been divided into two lithofacies associations. The largest amount of volcaniclastic rocks is located in the center of the local hills and has been interpreted as a phreatomagmatic crater fill lapilli tuff. They contain large amphibole megacrysts and small olivine crystals. The second lithofacies association is interpreted as lahar deposits. This sequence contains an unusually large amount of fossil tree trunks, which are identified as Abies species. Within a small area in the western hills small outcrops show evidence of maar-lake clastic sediment occurrence. On the hilltops debris shows intimate interaction processes between clastic sediments and basaltic melt. We interpret this to mean that the eruptive centers of Boglar Volcano were formed under subaerial conditions, with explosions fueled by intensive interaction between water-saturated Pannonian sand and uprising basaltic magma.
The Suwolbong pyroclastic sequence in the western part of Cheju Island, Korea, comprises partly preserved rim beds of a Quaternary basaltic tuff ring whose vent lies about 1 km seaward of the present shoreline. The sequence consists of breccia, lapillistone, lapilli tuff and tuff. Eighteen sedimentary facies are established and organized into six lateral facies sequences (LFS) and seven vertical facies sequences (VFS).
The LFS 1, 4 and 5 begin with massive lapilli tuff which transforms downcurrent into either planar-bedded (LFS 1), undulatory-bedded (LFS 4) or climbing dune-bedded (LFS 5) (lapilli) tuff units. They are representative of relatively ‘dry’ base surge whose particle concentration decreases downcurrent with a progressive increase in both tractional processes and sorting. The LFS 2 begins with disorganized and massive lapilli tuff and transforms into crudely stratified units downcurrent. It results from relatively ‘wet’ base surge in which sorting is poor due to the cohesion of damp ash. The LFS 3 comprises well-sorted lapilli tuff and stratified tuff further downcurrent, suggestive of deposition from combined fall and surge of relatively ‘dry’ hydroclastic eruption. All seven vertical facies sequences generally comprise two facies units of coarse-grained fines-depleted lapilli tuff and an overlying fine-grained tuff. These sequences are suggestive of deposition from base surge that consists of a turbulent head and a low-concentration tail.
Depositional processes in the Suwolbong tuff ring were dominated by a relatively ‘dry’ base surge. The base surge comprises turbulent and high-concentration suspension near the vent whose deposits are generally unstratified due to the lack of tractional transport. As the base surge becomes diluted downcurrent through fallout of clasts and mixing of ambient air, it develops large-scale turbulent eddies and is segregated into coarse-grained bedload and overlying fine-grained suspension forming thinly stratified units. Further downcurrent, the base surge may be either cooled and deflated or pushed up into the air, depending on its temperature. The Suwolbong tuff ring comprises an overall wet-to-dry cycle with several dry-to-wet cycles in it, suggestive of overall decrease in abundance of external water and fluctuation in the rate of magma rise.
A large diameter borehole core from an epiclastic kimberlite remnant on the farm Stompoor in the Prieska district, Cape Province, contains a continuous 76 m section of fossiliferous sediments interpreted as having accumulated within a crater-lake during the Late Cretaceous. Three distinct facies associations reflect depositional processes that prevailed in offshore areas of the original lake. Facies Association A: matrix-supported pebble conglomerates comprising a chaotic assemblage of pyroclastic, basement and country rocks set in a fine-grained matrix. Flat, non-erosional basal surfaces with ‘frozen’ rip-up clasts, the protrusion of matrix-supported clasts above the upper surfaces and a direct relationship between maximum clast size and bed thickness suggest deposition from debris flows that originated subaerially on pyroclastic talus cones surrounding the crater. Facies Association B: alternating thin beds of matrix-supported granule conglomerate, structureless fine-grained sandstone and parallel laminated mudrock. Small fining-upward sequences within these beds are comparable to turbidite Bouma Tade, Tde. Numerous partings display petrified fish and frog skeletons, as well as bivalve, gastropod and ostracode shells, leaf impressions, insect wings and a possible bird bone. These beds were deposited by thin debris-flows and turbidity underflows interspersed with periods of ‘pelagic’ sedimentation. Facies Association C: microlaminated mudstone beds containing scattered ‘dropstone lapilli’. The lamination is imparted by alternating Ca-rich/Ca-poor layers which may reflect climatic seasonality. They are interpreted as the result of seasonally influenced suspension settling through a thermally stratified water column.
The Middle Jurassic Kirkpatrick flood basalts and comagmatic Ferrar intrusions in the Transantarctic Mountains represent
a major pulse of tholeiitic magmatism related to early stages in the breakup of Gondwana. A record of the volcano-tectonic
events leading to formation of this continental flood-basalt province is provided by strata underlying and only slightly predating
the Kirkpatrick lavas. In the central Transantarctic Mountains, the lavas rest on widespread (≥7500 km2) tholeiitic pyroclastic deposits of the Prebble Formation. The Prebble Formation is dominated by lahar deposits and is an
unusual example of a regionally developed basaltic lahar field. Related, partly fault-controlled pyroclastic intrusions cut
underlying strata, and vents are represented by the preserved flanks of two small tephra cones associated with a volcanic
neck. Lahar and air-fall deposits typically contain 50–60% accidental lithic fragments and sand grains derived from underlying
Triassic – Lower Jurassic strata in the upper part of the Beacon Supergroup. Juvenile basaltic ash and fine lapilli consist
of nonvesicular to scoriaceous tachylite, sideromelane, and palagonite, and have characteristics indicating derivation from
hydrovolcanic eruptions. The abundance of accidental debris from underlying Beacon strata points to explosive phreatomagmatic
interaction of basaltic magma with wet sediment and groundwater, which appears to have occurred in particular where rising
magma intersected upper Beacon sand aquifers. Composite clasts in the lahar deposits exhibit complex peperitic textures formed
during fine-scale intermixing of basaltic magma with wet sand and record steps in subsurface fuel-coolant interactions leading
to explosive eruption.
The widespread, sustained phreatomagmatic activity is inferred to have occurred in a groundwater-rich topographic basin linked
to an evolving Jurassic rift zone in the Transantarctic Mountains. Coeval basaltic phreatomagmatic deposits of the Mawson
and Exposure Hill Formations, which underlie exposures of the Kirkpatrick Basalt up to 1500 km to the north along strike in
Victoria Land, appear to represent other parts of a regional, extension-related Middle Jurassic phreatomagmatic province which
developed immediately prior to rapid outpouring of the flood basalts. This is consistent with models which assign an important
role to lithospheric stretching in the generation of flood-basalt provinces.
Small and large maars exist associated with small and large diatremes, respectively, their subsurface feeder structures. The problem of size and growth of maar-diatreme volcanoes is discussed from a phreatomagmatic point of view from field data, some geophysical data, and short-lived historic maar eruptions. A hydrostatic pressure barrier of usually about 20–30 bars is assumed to control the maximum depth level of explosive magma/groundwater interactions. Similar to the situation in submarine and subglacial volcanism, initial maar-forming water vapour explosions are therefore assumed to occur at shallow depth and to produce a small maar with a shallow diatreme. Because of limited availability of groundwater and ejection of groundwater in the form of steam, the confining pressure barrier is displaced downward. Consequently, water vapour explosions can take place at consecutively deeper levels with the result that the diatreme penetrates downward and grows in size. Since maars are collapse craters resulting from ejection of wallrocks fragmented by water vapour explosions at the level of the diatreme root zone, downward penetration of a diatreme not only results in increase in size of a diatreme but also in increase in size of the overlying maar. As availability of groundwater in limited amounts controls formation of diatremes and their downward penetration, lack of groundwater enables magma to rise within a diatreme and to form a scoria cone or lava lake within the maar, as is frequently found in volcanic fields such as the Eifel area in Germany. In contrast, availability of large amounts of water in near surface environments such as shallow marine, lake, water-rich coastal plains, or water-rich fluviatile gravel beds prevents formation of maars and deep diatremes but causes formation of tuff rings.
Sampling frequency is one of the most crucial factors in the design of groundwater quality monitoring systems. Monitoring systems in general have two major objectives: (1) to describe natural processes and long-term changes and (2) to serve as alarm-systems and detect single pollution events. A comparison between two data sequences of different sampling frequency - weekly and monthly - is made through an example of the groundwater quality monitoring system in the karstic region of the Transdanubian Mountains in Hungary. Hydrogeochemical time series were first decomposed into their components: trend, periodicity, autocorrelation, and rough in succession. In order to identify outliers within the rough, Exploratory Data Analysis (EDA) was applied. Optimal sampling frequency was determined based on the analysis of the above components. Results have shown that (1) seasons shorter than two months do exist in the studied time series which cannot be captured by monthly sampling; (2) for monitoring seasonal processes samples should be collected at the Nyquist frequency (at least two samples per period); for pollution detection autocorrelation lag-time (or semi-variogram range in time) should determine the sampling distance; in the lack of autocorrelation property the analysis of outliers should guide the sampling design; (3) cross-correlation analysis between precipitation and the observed parameters indicative of pollutant travel time yields valuable additional information on the pollution sensitivity of the hydrogeological system.
This Quaternary volcanic field is located on the Rhenish Massif, W Germany, which is presently rising above an anomalous mantle structure. Magmas of nephelinitic, leucititic, basanitic, tephritic and phonolitic composition reached the surface in approx 240 volcanoes. About 60 maars occur in this classic region and the remaining 180 volcanoes are mostly scoria cones. Nearly all maars formed in valleys where abundant ground-water was able to circulate through zones of structural weakness in bedrock beneath the valley floors. The rising magma generally had access to this ground-water during the entire period of phreatomagmatic maar eruptions. In contrast most of the scoria cones erupted within small maars (initial maars), which suggests that the magma rising underneath these volcanoes must have met only limited amounts of ground-water circulating along hydraulically less active zones of structural weakness. The available water was shut off when the initial maar collapsed and the magma could then rise, intrude the diatreme and erupt on the maar floor forming a scoria cone in a second eruptive phase.-J.M.H.
Volcanic activity takes many forms, ranging from quiet lava emissions to extremely violent and explosive bursts, many of which can be related to magma composition as discussed in Chapter 3. The kinds of eruptions can be correlated to volcano shapes and sizes, and in this chapter we explore the connection between pyroclastic systems, eruptive mechanisms and their influences upon juvenile particles.
Maar craters of the Mio-Pliocene Hopi Buttes volcanic field of Arizona formed within a broad playa system, and accumulated a variety of lacustrine sedimentary deposits. Many craters initially held isolated, groundwater-fed lakes. Ephemeral streams crossing the playa entered some of the lake-filled craters, and built coarse grained Gilbert-type deltas and subaqueous fans along the margins of these craters. The small, coarse grained fans and deltas have many features in common with much larger coarse grained deltaic and fan deltaic deposits. However, the local production of coarse grained volcanic sediment, low gradients in the local stream catchment, steep subaqueous relief and the small size of the receiving ‘basins’resulted in a unique combination of features. Cone-shaped subaqueous fans initially formed at the mouths of incised feeder streams. The fans are small accumulations of steeply dipping gravelly tephra that consist almost entirely of overlapping lobes constructed by density-modified grain flows. Gravelly Gilbert-type tephra deltas formed in brimfull craters fed by a freely migrating feeder stream. They are concave lakeward, mimicking the underlying crater wall topography. Complex deltaic geometries are defined by topset strata that steeply onlap tall foreset beds. They suggest that feeding stream floods caused rapid and comparatively large variations in lake level within the small crater lakes. Bed-specific carbonate alteration is common, and probably resulted from both influx of detrital carbonate across the playa and alteration of tephra beds by carbonate-saturated lakewaters during between flood periods of high net evaporation.
The pyroclastic deposits of many basaltic volcanic centres show abrupt
transitions between contrasting eruptive styles, e.g., Hawaiian versus
Strombolian, or `dry' magmatic versus `wet' phreatomagmatic. These
transitions are controlled dominantly by variations in degassing
patterns, magma ascent rates and degrees of interaction with external
water. We use Crater Hill, a 29 ka explosive/effusive monogenetic centre
in the Auckland volcanic field, New Zealand, as a case study of the
transitions between these end-member eruptive styles. The Crater Hill
eruption took place from at least 4 vents spaced along a NNE-trending,
600-m-long fissure that is contained entirely within a tuff ring
generated during the earliest eruption phases. Early explosive phases at
Crater Hill were characterised by eruption from multiple unstable and
short-lived vents; later, dominantly extrusive, volcanism took place
from a more stable point source. Most of the Crater Hill pyroclastic
deposits were formed in 3 phreatomagmatic (P) and 4 `dry' magmatic (M)
episodes, forming in turn the outer tuff ring and maar crater (P1, M1,
P2) and scoria cone 1 (M2-M4). This activity was followed by formation
of a lava shield and scoria cone 2. Purely `wet' activity is represented
by the bulk of P1 and P2, and purely `dry' activity by much of M2-M4.
However, M1 and parts of M2 and M4 show evidence for simultaneous
eruptions of differing style from adjacent vents and rapid variations in
the extent and timing of magma:water interaction at each vent. The
nature of the wall-rock lithics, and these rapid variations in inferred
water/magma ratios imply interaction was occurring mostly at depths of
≤80 m, and the vesicularity patterns in juvenile clasts from these
and the P beds imply that rapid degassing occurred at these shallow
levels. We suggest that abrupt transitions between eruptive styles, in
time and space, at Crater Hill were linked to changes in the local magma
supply rate and patterns and vigour of degassing during the final metres
of ascent.
The pyroclastic deposits of many basaltic volcanic centres show abrupt transitions between contrasting eruptive styles, e.g., Hawaiian versus Strombolian, or `dry' magmatic versus `wet' phreatomagmatic. These transitions are controlled dominantly by variations in degassing patterns, magma ascent rates and degrees of interaction with external water. We use Crater Hill, a 29 ka explosive/effusive monogenetic centre in the Auckland volcanic field, New Zealand, as a case study of the transitions between these end-member eruptive styles. The Crater Hill eruption took place from at least 4 vents spaced along a NNE-trending, 600-m-long fissure that is contained entirely within a tuff ring generated during the earliest eruption phases. Early explosive phases at Crater Hill were characterised by eruption from multiple unstable and short-lived vents; later, dominantly extrusive, volcanism took place from a more stable point source. Most of the Crater Hill pyroclastic deposits were formed in 3 phreatomagmatic (P) and 4 `dry' magmatic (M) episodes, forming in turn the outer tuff ring and maar crater (P1, M1, P2) and scoria cone 1 (M2–M4). This activity was followed by formation of a lava shield and scoria cone 2. Purely `wet' activity is represented by the bulk of P1 and P2, and purely `dry' activity by much of M2–M4. However, M1 and parts of M2 and M4 show evidence for simultaneous eruptions of differing style from adjacent vents and rapid variations in the extent and timing of magma:water interaction at each vent. The nature of the wall-rock lithics, and these rapid variations in inferred water/magma ratios imply interaction was occurring mostly at depths of ≤80 m, and the vesicularity patterns in juvenile clasts from these and the P beds imply that rapid degassing occurred at these shallow levels. We suggest that abrupt transitions between eruptive styles, in time and space, at Crater Hill were linked to changes in the local magma supply rate and patterns and vigour of degassing during the final metres of ascent.
The Xalapaxco tuff cone is located on the northeast flank of La Malinche stratovolcano in central Mexico. An unusually large number (10) of explosion craters, concentrated on the central and on the uphill side of the cone, expose alternating beds of stratified surge deposits and massive fall deposits. The morphology of the cone and the characteristics of its deposits point to the involvement of significant quantities of groundwater during its eruption. The phreatomagmatic eruptions which led to the cone's formation pierced an alluvial fan, whose source is a glacially carved canyon near the summit of La Malinche volcano. The large canyon was cut during repeated glacial episodes, the last of which ended ca. 8500 years ago. The present alluvial fan mostly consists of reworked glacio-fluviatile andesite/dacite material from La Malinche. Rising magma encountered substantial amounts of groundwater within the limestone basement and in overlying intercalated pyroclastic and glacio-fluviatile deposits of the alluvial fan. Short-lived phreatomagmatic eruptions produced surge and airfall deposits. Xenoliths found in the cone beds are composed of dacite and andesite clasts, limestone, chert, and rare ignimbrite fragments. No juvenile material could be unequivocally identified, but is represented most probably by porphyritic dacite similar in texture and composition to La Malinche lavas. The multiple craters were formed as a response to changes in water and magma supply during the short-lived eruption. Hence, the locations where ideal magma/water ratios existed to fuel phreatomagmatic explosions shifted in time and space. Analysis of diameter/depth ratios of the craters indicates that the activity shifted from the center of the cone to its periphery in the west. Due to the configuration of the hydrographic environment, more groundwater flowing from La Malinche was available from the fan on the uphill side than below the cone at later stages of the eruption. The apparently anomalous position of the tuff cone on the slopes of a stratovolcano in a presently dry environment can be explained by more humid climatic conditions prevailing at the time of eruption.
Four principal mechanisms of deposition are effective in the formation of sediment gravity flow deposits. Grains deposited by traction sedimentation and suspension sedimentation respond invidually and accumulate directly from bed and suspended loads, respectively. Those deposited by frictional freezing and cohesive freezing interact through either frictional contact or cohesive forces, respectively, and are deposited collectively, usually by plug formation. Sediment deposition from individual sediment flows commonly involves more than one of these mechanisms acting either serially as the flow evolves or simultaneously on different grain populations. -from Author
This paper is included in the Special Publication entitled 'The physics of explosive volcanic eruptions', edited by J.S. Gilbert and R.S.J. Sparks. High-speed, gravity-driven flows of hot particles and gas are a common and highly destructive product of explosive volcanism. They range widely in nature from expanded, turbulent suspension currents formed by lateral blasts or by the fountaining of vertical eruption columns, to highly concentrated granular avalanches formed by lava dome collapse or as dense underflows beneath suspension currents. The deposits from these flows, here called pyroclastic density currents, range in volume from much less than 1 km 3 to thousands of cubic kilometres, and may extend over 100 km from their source. This chapter reviews the eruption, transport and deposition of pyroclastic density currents from both geological and physical perspectives, focussing on some recent advances.
The IUGS Subcommission on the Systematics of Igneous Rocks herein presents its recommendations on the nomenclature and classification of pyroclastic and mixed pyroclastic-epiclastic deposits using descriptive, mainly granulometric, criteria. The recommendations are the result of an international inquiry by means of questionnaires during the last four years.
Two new palaeobotanical sites, Gérce and Pula from western Hungary, found in volcanic craters are characterized in terms of floristic composition, vegetation, and palaeoclimate. Radiometric dating of adjacent volcanic bodies indicates the age of the fossiliferous deposits near the Lower/Upper Pliocene boundary. Deciduous broad-leaved, woody plants prevail in both localities (Quercus, Ulmus, Zelkova, Acer, Salicaceae) and are associated with some rare exotic elements (Ginkgo, Torreya, Engelhardia, Eucommia, Sassafras) and Buxus. The climatic conditions inferred from the reconstructed vegetation indicate a Cf-type of climate with a mean annual temperature of 10–13°C and some dry periods during the year.
The paleogeographic evolution of Lake Pannon within the Pannonian basin is reconstructed with eight maps, ranging from the Middle Miocene to the Early Pliocene. The maps are based on the distribution of selected biozones and specific fossils, and on complementary sedimentological and seismic information. Our reconstruction shows that the history of Lake Pannon can be divided into three distinct intervals: an initial stage with low water level, which resulted in isolation from the sea at about 12 Ma and might have led to temporary fragmentation of the lake; an interval of gradual transgression lasting until ca. 9.5 Ma; and a long late interval of shrinkage and infilling of sediments that persisted into the Early Pliocene. The deep subbasins of the lake formed during the transgressive interval, in more basinward locations than the deep basins of the preceding Sarmatian age. The southern shoreline, running parallel with the Sava and Danube rivers along the northern foot of the Dinarides, changed very little during the lifetime of the lake, while the northern shoreline underwent profound changes.
In central Anatolia, the Late Pleistocene Narköy maar formed on a fault zone. A 5-m-thick pyroclastic succession erupted from a crater 900 m in diameter. The presence of gas fumeroles, hot springs, and hydrothermal alteration zones indicates that the area is geothermally active. The products of the maar are large blocks and lapilli to coarse ash. Planar bedding and cross-stratification are well developed within coarse ash beds. The maar deposits were generated by a single period of phreatomagmatic explosion with two episodes. The first episode produced wet eruption clouds, while the second one was relatively dry in nature. The estimate of the volume of pyroclastic ejecta compared with the dimensions of the maar demonstrates a material deficiency, which is attributed to a large volume of gas emanated during the phreatomagmatic explosion along a fault presently cross-cutting the maar. In addition, a relatively small volume of magma intruded along the fault and mixed with meteoric water in the fault zone to produce the phreatomagmatic eruption. The existence of a hydrothermal system in the fault zone is important in affecting the eruption style and evolution of Narköy maar.
The sedimentary infill of the Acigöl maar lake, one of the volcanic centres in the Cappadocia district of Anatolia, contains unusual, high-calorific sub-Recent peat deposits, of which the origin is attributed to geothermal processes. The sedimentary facies record is analyzed to reconstruct the lake's depositional history and to disentangle the combined signal of climatic and geothermal factors. The facies succession comprises: a lake-fringe clastic apron shed from the maar walls; early-stage, coarse-grained tuffaceous deposits of the lake proper, intercalated with brecciated mudstones and limestones; and final-stage, fine-grained tuffaceous deposits of the lake proper, intercalated with peats and plant-bearing clastics and with some terminal travertines. The closed lake was highly dependent on climate, particularly precipitation, and the depositional conditions were further controlled by a connective hydrothermal system which itself was driven by the input of meteoric water. The associated heat flow played an important role by creating a microclimatic niche, where even the impoverished late-Quaternary (cold regional climate) vegetation could flourish and form substantial peats. The varying hydrological budget of the lake was the main “switching” mechanism for the peat-forming conditions, with two water-depth thresholds involved. If the lake level rose too high, the low vegetation was drowned and hemipelagic clastic sedimentation prevailed. If the lake level fell too low, the vegetation was killed and formation of travertine took place. The heat flow through the pore water and clastic sediments was crucial to the high maturation of the peat deposits.
Ubehebe craters, Death Valley, California, include over a dozen maar volcanoes formed primarily by phreatic eruptions of trachybasalt through a thick and permeable fanglomeratic sequence on the north slope of Tin Mountain. Tuff derived from Ubehebe Crater, the largest crater in the area, is characteristically thinly bedded or laminated and was deposited by airfall and base-surge processes. Thick-bedded deposits showing evidence of mass flow occur where base surges were concentrated within, and followed gullies which had been carved into the fanglomerate prior to eruption. Cross-bedded sequences were deposited by base surges that moved radially outward from Ubehebe Crater. They occur in the form of relatively small and large dunelike structures with spacing and morphologic features similar to antidunes and migration patterns somewhat similar to climbing ripples. The largest dunes in the area are composite structures that preserve a sequence of bed forms deposited in the high flow regime. Deposition apparently began in the antidune phase of the upper flow regime, progressing in time through sinuous lamination to plane beds as flow power decreased. Laminations are well developed and bed forms are preserved at each level within the composite structures because of a high rate of deposition and high sediment cohesion during flow of the base surges.
Vesiculated tuffs are tuffs that contain vesicles between the ash particles. Formation of the vesicles is the result of trapping of steam, the transporting agent of volcanic base surges, in wet, muddy or sticky ash deposited by the base surges. Vesiculated tuffs are described from various maars and tuff-rings in Europe (Iceland, France, Germany) and USA together with associated surface features such as: gravity flowage ripples, mud flow channels, current ripples, and current ridges. Other features described are: plastering of ash against obstacles and vesiculated accretionary lapilli, the latter containing vesicles in the outer layer.
Vesiculated base surge deposits probably contained as much as 20–30% of interstitial water and fell out of the base surge clouds en masse owing to non-free flow and consequent accretion.
Remnants of an extensive maar-diatreme volcanic field are magnificently exposed at various depths of erosion in the Hopi Buttes volcanic field of northeastern Arizona. Field and petrographic studies of both the maar and diatreme elements of a selection of volcanoes within the field show that: (1) lower sections of the maar rim sequences are typically rich in sandy mudrock derived from the pre-eruptive Mio-Pliocene Bidahochi Formation, and the muddy Bidahochi sediment was soft and wet at the time of maar eruptions; (2) beds higher within the rims contain generally increased proportions of sandstone clasts from the Triassic Wingate Formation. In the diatremes, late-emplaced breccia has deeper-seated lithics than more marginal breccia emplaced earlier; and (3) many vents are topped by megacryst-enriched scoria and spatter, and deep-seated xenoliths are known only from upper diatreme and craterfilling tephra. These observations show that: (1) eruptions at Hopi Buttes involved interaction of magma with unconsolidated mudrock at shallow levels, and the phreatomagmatic processes that provided the bulk of the energy involved in the violent eruptions were driven by the interaction of magma and wet sediment; (2) the locus of explosive activity migrated downward as eruptions progressed; and (3) the closing stage of many eruptions was characterized by rapid magma rise and relative depletion of water.
Repeated small eruptions of basaltic to intermediate magma produce monogenetic volcanic fields, which are common worldwide. The variety of volcanic landforms produced in such fields is controlled by whether or not water is present at or near the surface at the time of eruption. Basinal settings are typically "wetter', and hydrovolcanic eruptions produce tuff cones, maars and tuff rings instead of the scoria cone fields developed in dry, upland settings. Hydrovolcanic fields produce less lava and relatively more clastic debris than scoria cone fields and often contain large craters excavated by maar eruptions. Tephra eroded from volcanoes within hydrovolcanic fields tends to be reworked and redistributed within the basin in sheetform deposits and as crater filling sequences, whereas the tephra eroded from scoria cone fields is largely carried from the fields in deeply incised streams skirting the fields' lava flows. -from Author
Grey tuffs of late Pleistocene age form broad fans radiating from the Laacher See basin. They were derived from phreatomagmatic outbursts, and transported in turbulent pyroclastic flows, in contrast with the underlying white pumice tuffs of air fall origin. Flow origin of the grey tuffs is inferred from the well-bedded plane parallel to cross-bedded tephra characteristic of base surge deposits, and a variety of other sedimentary structures, as well as grain size distributions. We recognize a tentative sequence of five main kinds of dune structures or cross-bedded strata. With some reservations these may be compared with the high flow-regime alluvial bedforms produced experimentally in flumes.
Most of the cross-bedded structures in the Laacher See deposits resemble antidunes, with steep stoss sides and very low-dipping lee sides. Upcurrent migration of antidune crests is dominant close to the source, but changes to downcurrent migration at greater distances, presumably because of decay in flow energy.
The most spectacular cross-bedding is somewhat similar to chute and pool structures formed under experimental condition in alluvial flumes, but not recognized in ancient sedimentary rocks. We suggest that these structures of the Laacher See tuffs formed during deposition from phreatic pyroclastic flows of very high flow energy and high sediment concentration. The antidunes apparently formed at lesser flow velocity than chute and pool structures, although interpretation of velocity conditions by examination of the deposits is difficult because of other factors such as the cohesiveness of wet material erupted by explosive phreatic volcanic activity. The large wave lengths of the dune-like structures, however, suggest unusually high velocities. The Laacher See magmas were of phonolitic to tephritic composition, and may have erupted with greater explosive energy and in greater volume than comparable basaltic eruptions.
Rothenberg scoria cone Eifel formed by an alternation of three Strombolian and three phreatomagmatic eruptive phases. Eruptions took place from up to six vents on a 600 m-long fissure, building an early tuff ring and then two coalescing scoria cones. Strombolian volcanism dominated volumetrically, as the supply of external water was severely limited. Magma/water interaction only occurred during the opening stages of eruption at any vent, when discharge rates were low and the fragmentation surface was below the water table. The phreatomagmatic deposits consist of relatively well-sorted fall beds and only minor surge deposits. They contain juvenile clasts with a wide range of vesicularity and grain size, implying considerable heterogeneity in the assemblage of material ejected by the phreatomagmatic explosions. the transition from phreatomagmatic to Strombolian eruption at any vent was rapid and irreversible, and Strombolian volcanism persisted even when eruption rates are inferred to have waned at the close of each eruptive phase as, by then, the fragmentation surfaces were high in the growing cones and water was denied access to the magma. The Strombolian deposits are relatively homogenous, consisting of alternating coarser- and finer-grained, well-sorted fall beds erupted during periods of open-vent eruption and partial blockage of the vent respectively. The intervals of Strombolian eruption were always a delicate balance between discharge of freely degassing magma and processes such as ponding of degassed magma in the vent, collapse of the growing cones, and repeated recycling of clasts through the vent. Clear evidence of the instability of the Rothenberg cones is preserved in numerous unconformities within deposits of the inner walls of the cones. The close of Strombolian phases was probably marked by a decreasing supply of magma to the vents accompanied by ponding and stagnation of lava in the craters.
Accretionary lapilli are common in fine-grained pyroclastic flow and surge deposits and related co-ignimbrite/co-surge ash layers of Laacher See volcano. Two morphologically different types are distin-guished: (1) Rim-type lapilli are composed of a coarse-grained core surrounded by a fine-grained rim. Rims are internally graded or made up of several layers of alternating fine and very-fine grained ash. (2) Core-type lapilli lack fine-grained rims. Field relationships, internal, and grain-size characteristics are specific to accretionary lapilli from different types of tephra deposits. Accretionary lapilli may therefore be a helpful tool to infer the origin of tephra of different origin. In co-ignimbrite ashfall, accretionary lapilli are generally concentrated at the base, whereas pyroclastic flow and surge deposits contain lapilli in the upper parts of individual, thin-bedded layers. Rim-type lapilli are found in pyroclastic flow and surge deposits up to 4 km from the source. Core-type lapilli occur at greater distances or are associated with vesiculated tuffs where they are within 1 km from the vent. Accretionary lapilli from co-ignimbrite/co-surge ash show open framework textures and edge-to-face contacts of individual ash particles. Vesicularity is generally low but the overall porosity of 40% to 50% results in an average density of 1200 kg/m3. Accretionary lapilli in pyroclastic flow and surge deposits are more densely packed and platy particles are often in face-to-face contacts. Vesicularity of those from pyroclastic flow deposits is significantly higher; the overall porosity is about 30% to 40% and the average density 1600 kg/m3. Grain-size analyses show that the accretionary lapilli in co-ignimbrite/co-surge ashfall deposits are the most fine-grained with a median (Md) of 20 to 30 m and a maximum grain size of 250 to 350 m. Accretionary lapilli from pyroclastic flow deposits have intermediate Md-values of 30 to 50 m and a maximum grain size of 350 to 500 m. Those of surge deposits are the coarsest grained with Md-values of 30 to >63 m and a maximum grain size up to 2 mm.
The juvenile content of phreatomagmatic deposits contains both first-cycle juvenile clasts derived from magma at the instant of eruption, and recycled juvenile clasts, which were fragmented and first ejected by earlier explosions during the eruption, but fell back or collapsed into the vent. Recycled juvenile clasts are similar to accessory and accidental lithics in that they contribute no heat to further magma: water interaction, but previously no effective criteria have been defined to separate them from first-cycle juvenile clasts. We have investigated componentry parameters (vesicularity, clast morphology and extent of mud-coating) which, in specific circumstances, can distinguish between first-cycle juvenile clasts, involved in only one explosion, and such recycled juvenile clasts. Phreatomagmatic fall deposits commonly show gross grainsize and sorting characteristics identical to deposits of purely dry or magmatic eruptions. However the abundance of non-juvenile clasts in pyroclastic deposits is a sensitive indicator of the involvement of external water. If this component is calculated including recycled juvenile clasts with accidental and accessory clasts the contrast is even more striking. Data from a Holocene maar deposit in Taupo Volcanic Zone, New Zealand, suggest that the first-cycle juvenile component of the deposits is less than one-third of that determined by simple juvenile:lithic:crystal componentry.