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Abstract

Submarine volcanic eruptions are frequent and important events, yet they are rarely observed. Here we relate bathymetric and hydroacoustic images from the 2011-2012 El Hierro eruption with surface observations and deposits imaged and sampled by ROV. As result of the shallow submarine eruption, a new volcano named Tagoro grew from 375 to 89 m depth. The eruption consisted of two main phases of edifice construction intercalated with collapse events. Hydroacoustic images show that the eruptions ranged from explosive to effusive with variable plume types and resulting deposits, even over short time intervals. At the base of the edifice, ROV observations show large accumulations of lava balloons changing in size and type downslope, coinciding with the area where floating lava balloon fallout was observed. Peaks in eruption intensity during explosive phases generated vigorous bubbling at the surface, extensive ash,vesicular lapilli and formed high-density currents, which together with periods of edifice gravitational collapse, produced extensive deep volcaniclastic aprons. Secondary cones developed in the last stages and show evidence for effusive activity with lava ponds and lava flows that cover deposits of stacked lava balloons. Chaotic masses of heterometric boulders around the summit of the principal cone are related to progressive sealing of the vent with decreasing or variable magma supply. Hornitos represent the final eruptive activity with hydrothermal alteration and bacterial mats at the summit. Our study documents the distinct evolution of a submarine volcano and highlights the range of deposit types that may form and be rapidly destroyed in such eruptions.

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... An eruption in 2011-2012 on a volcanic ridge extending south of El Hierro with products also observed at the ocean surface led to the growth of a cone with a base at 375 m and summit at 89 m depth. According to Somoza and Gonzá (2017), the eruption was intermittently explosive. Rivera et al. (2013) and Somoza and Gonzá (2017) presented repeat multibeam sonar data showing that collapses led to a wide distribution of volcaniclastic materials extending far from the cone base to the base of the ridge, 6 km away. ...
... According to Somoza and Gonzá (2017), the eruption was intermittently explosive. Rivera et al. (2013) and Somoza and Gonzá (2017) presented repeat multibeam sonar data showing that collapses led to a wide distribution of volcaniclastic materials extending far from the cone base to the base of the ridge, 6 km away. However, the cone itself remained pointy with concave-upwards sides and a summit that Somoza and Gonzá (2017) interpreted as a hornito. ...
... Rivera et al. (2013) and Somoza and Gonzá (2017) presented repeat multibeam sonar data showing that collapses led to a wide distribution of volcaniclastic materials extending far from the cone base to the base of the ridge, 6 km away. However, the cone itself remained pointy with concave-upwards sides and a summit that Somoza and Gonzá (2017) interpreted as a hornito. Clague et al. (2000a) found volcanic cones around the Hawaiian Islands to be either pointy or flat. ...
Chapter
Sea mountains are arguably the most common large geomorphological features on Earth. Most seamounts are volcanic in origin and vary in shape with size. Small volcanic seamounts are simple, typically truncated cones, whereas seamounts taller than 3 km have more diverse forms due to multiple volcanic centers, flank rift zones and landsliding. Some other seamounts are formed by serpentinite diapirism, tectonic processes and landsliding.
... The El Hierro eruption continued during late February, when seismicity decreased drastically until 6 March 2012. As a result of this shallow submarine eruption, a new submarine volcano grew from 375 to 89 mbsl [34]. Since 2016, the new volcano appears on the official hydrographic charts as "Tagoro" (meaning "stone circle for meeting place" in the aboriginal language of Canary Islands). ...
... Previously, a similar approach has been successfully done for understanding geological and biological evolutionary stages in methane seeps displaying different scenarios of rates of fluid venting [79] and hydrodynamics [21]. Therefore, within the Macaronesia volcanic archipelagos, several recent submarine eruptions have taken place in Capelinhos (west Faial Island, Azores) in 1958-59 or south of El Hierro Island (Canary Islands) in 2011-2012 [34]. The recent discovery of soft coral gardens dominated by Alcyonacea in the Azores Archipelago [90] colonizing the volcanic substrate created from the eruption of Capelinhos in 19581-959, opens new studies of succession and survivorship of habitat-forming species in the Macaronesia volcanic areas as they have already been developed in the Hawaiian Islands [91]. ...
... The recent discovery of soft coral gardens dominated by Alcyonacea in the Azores Archipelago [90] colonizing the volcanic substrate created from the eruption of Capelinhos in 19581-959, opens new studies of succession and survivorship of habitat-forming species in the Macaronesia volcanic areas as they have already been developed in the Hawaiian Islands [91]. eral recent submarine eruptions have taken place in Capelinhos (west Faial Island Azores) in 1958-59 or south of El Hierro Island (Canary Islands) in 2011-2012 [34]. The recent discovery of soft coral gardens dominated by Alcyonacea in the Azores Archipelago [90] colonizing the volcanic substrate created from the eruption of Capelinhos in 19581-959, opens new studies of succession and survivorship of habitat-forming species in the Macaronesia volcanic areas as they have already been developed in the Hawaiian Islands [91]. ...
Article
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In this work, we integrate five case studies harboring vulnerable deep-sea benthic habitats in different geological settings from mid latitude NE Atlantic Ocean (24–42° N). Data and images of specific deep-sea habitats were acquired with Remoted Operated Vehicle (ROV) sensors (temperature, salinity, potential density, O2, CO2, and CH4). Besides documenting some key vulnerable deep-sea habitats, this study shows that the distribution of some deep-sea coral aggregations (including scleractinians, gorgonians, and antipatharians), deep-sea sponge aggregations and other deep-sea habitats are influenced by water masses’ properties. Our data support that the distribution of scleractinian reefs and aggregations of other deep-sea corals, from subtropical to north Atlantic could be dependent of the latitudinal extents of the Antarctic Intermediate Waters (AAIW) and the Mediterranean Outflow Waters (MOW). Otherwise, the distribution of some vulnerable deep-sea habitats is influenced, at the local scale, by active hydrocarbon seeps (Gulf of Cádiz) and hydrothermal vents (El Hierro, Canary Island). The co-occurrence of deep-sea corals and chemosynthesis-based communities has been identified in methane seeps of the Gulf of Cádiz. Extensive beds of living deep-sea mussels (Bathymodiolus mauritanicus) and other chemosymbiotic bivalves occur closely to deep-sea coral aggregations (e.g., gorgonians, black corals) that colonize methane-derived authigenic carbonates.
... Fe oxyhydroxides are particularly important constituents of marine sediments in volcanically active coastal areas (Hanert, 2002), such as those formed at the Tagoro eruptive event in 2011-2012 Somoza et al., 2017). During the volcanic episode, fluid emissions enriched in CO 2 , CH 4 , H 2 S, Si, Fe 2+ and other elements, affected the pH, temperature and composition of local seawater and therefore marine life (Fraile-Nuez et al., 2012;Santana-Casiano et al., 2013). ...
... Hydrothermal vents have been acting as discharge sites for warm-spring fluids and potential recharge sites for seawater. As a consequence, Fe-oxyhydroxide sediments have accumulated in the vicinity of the warm vent sites and specific vent fauna communities have developed Somoza et al., 2017;Danovaro et al., 2017). The emissions of CO 2 gas to the water column and carbonate alkalinity from El Hierro accounted for 60% and 40%, respectively, of the pH change in local seawater around the main cone of the volcano . ...
... Submersible survey SV2/D16 showed another area affected by hydrothermal venting in the region of the fissure-hosted secondary cones (213-185 m water depth) defined by Somoza et al. (2017) (Fig. 7). The area is composed of bright reddish-orange to yellow Fe oxyhydroxides forming laminated sequences of soft friable deposits on top of lava blocks and cementing brecciated lavas and scoria-lapilli deposits (Figs. ...
Article
Hydrothermal iron (Fe)-rich sediments were recovered from the Tagoro underwater volcano (Central Atlantic) that was built during the 2011–2012 volcanic event. Cruises in 2012 and 2014 enabled the monitoring and sampling of the early-stage establishment of a hydrothermal system. Degassing vents produced acoustic flares imaged on echo-sounders in June 2012, four months after the eruption. In 2014 during a ROV dive was discovered and sampled a novel hydrothermal vent system formed by hornito-like structures and chimneys showing active CO2 degassing and anomalous temperatures at 120–89 m water depth, and along the SE flank at 215–185 m water depth associated with secondary cones. Iron- and silica-rich gelatinous deposits pooled over and between basanite in the hornitos, brecciated lavas, and lapilli. The low-temperature, shallow-water hydrothermal system was discovered by venting of Fe-rich fluids that produced a seafloor draped by extensive Fe-flocculate deposits precipitated from the neutrally buoyant plumes located along the oxic/pHotic zone at 50–70 m water depths. The basanite is capped by mm- to cm-thick hydrothermally derived Fe-oxyhydroxide sediments and contain micro-cracks and degasification vesicles filled by sulfides (mostly pyrite). Mineralogically, the Fe-oxyhydroxide sediments consist of proto-ferrihydrite and ferrihydrite with scarce pyrite at their base. The Fe-rich endmember contains low concentrations of most trace elements in comparison with hydrogenetic ferromanganese deposits, and the sediments show some dilution of the Fe oxyhydroxide by volcanic ash. The Fe-oxyhydroxide phase with a mean particle size of 3–4 nm, low average La/Fe ratios of the mineralized deposits from the various sampling sites, and the positive Eu anomalies indicate rapid deposition of the Fe-oxyhydroxide near the hydrothermal vents. Electron microprobe studies show the presence of various organomineral structures, mainly twisted stalks and sheaths covered by iron-silica deposits within the mineralized samples, reflecting microbial iron-oxidation from the hydrothermal fluids. Sequencing of 16 s rRNA genes also reveals the presence of other microorganisms involved in sulfur and methane cycles. Samples collected from hornito chimneys contain silicified microorganisms coated by Fe-rich precipitates. The rapid silicification may have been indirectly promoted by microorganisms acting as nucleation sites. We suggest that this type of hydrothermal deposit might be more frequent than presently reported to occur in submarine volcanoes. On a geological scale, these volcanic eruptions and low-temperature hydrothermal vents might contribute to increased dissolved metals in seawater, and generate considerable Fe-oxyhydroxide deposits as identified in older hot-spot seamounts.
... The submarine eruption (VEI 2) occurred <2 km south of the island (e.g., Becerril et al., 2014), and explosive and effusive activity phases alternated during 4 months (e.g., Somoza et al., 2017). The eruption ended on 15 February 2012 (Sanchez-Pastor et al., 2018), and the volcanic cone, Tagoro, grew in multiple stages of growth and collapses from 375 to 89 m water depth, with a total eruptive volume of~400 ×10 6 m 3 (Somoza et al., 2017). ...
... The submarine eruption (VEI 2) occurred <2 km south of the island (e.g., Becerril et al., 2014), and explosive and effusive activity phases alternated during 4 months (e.g., Somoza et al., 2017). The eruption ended on 15 February 2012 (Sanchez-Pastor et al., 2018), and the volcanic cone, Tagoro, grew in multiple stages of growth and collapses from 375 to 89 m water depth, with a total eruptive volume of~400 ×10 6 m 3 (Somoza et al., 2017). ...
... In total, 388 ×10 6 m 3 of magma is inferred to have been intruded beneath the volcano from June 2012 to March 2014. This magma volume is comparable to the volume of pyroclastic material emitted during the 2011-2012 submarine eruption, estimated at 400 ×10 6 m 3 by oceanographic cruises (Somoza et al., 2017). Comparable intrusive volumes have also been found at other volcanoes. ...
Article
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Key Points Models of magma flow rates are presented for six post‐eruptive magmatic intrusions under El Hierro volcano from June 2012 to March 2014 Initial magma flow rates of ~300 m³/s decaying exponentially with time are inferred using GPS and InSAR, and a Bayesian inversion approach A deep magma body likely fed the inferred sill‐like intrusions with a conduit to a common feeding point under the center of the island
... The first historical eruption at El Hierro occurred at shallow water depths about 2 km off the south coast of the island (Fig. 5). While eruptive activity could not be directly observed, repeated, high-resolution bathymetric and hydroacoustic surveys during the eruption and subsequent remotely operated vehicle (ROV) observations allowed capturing the development of the submarine volcano and its associated volcaniclastic debris and lava aprons (Rivera et al., 2013(Rivera et al., , 2014Somoza et al., 2017) (Fig. 8b). The submarine cone, which was later named Volcán Tagoro, grew from initial water depths of~360 m to just 88 m below sea level. ...
... The 2011-2012 eruption was intensely monitored and was the subject of numerous multi-disciplinary studies, which we unfortunately cannot all cite here. The reader is referred elsewhere for more extensive summaries González et al., 2013;Longpré et al., 2014;Martí et al., 2013aMartí et al., , 2013bMeletlidis et al., 2015;Somoza et al., 2017). The first clear precursors were detected on 7 July 2011, 96 days prior to the onset of eruptive activity, and consisted of ground deformation measured by GPS and low-magnitude volcano-tectonic earthquakes located in the north-central part of the island (López et al., 2012) (Fig. 8a, Table A.15). ...
Article
Despite decadal–millennial repose periods, volcanoes of the Canary Islands pose significant, though poorly understood hazards to local communities and infrastructure. At least 13 volcanic eruptions forming monogenetic cones and lava flows have occurred in the archipelago since 1500 CE: six on the island of La Palma (in 1585, 1646, 1677–1678, 1712, 1949 and 1971), four on Tenerife (1704–1705, 1706, 1798 and 1909), two on Lanzarote (1730–1736 and 1824) and one on the submarine flank of El Hierro (2011−2012). In this paper, we synthesize available data on these historical eruptions, focusing on their physical characteristics and chronological development, and provide new estimates of eruption parameters, such as lava flow runout, area and volume, to inform volcanic hazard assessment in the archipelago. A companion paper reports tephra composition for the same eruptions and discusses petrogenetic implications. While incomplete and imprecise, historical records indicate that precursory seismicity began days to years prior to eruption onset, consistent with the three months of well-documented unrest for the 2011–2012 eruption. Excluding the atypical 1730–1736 event, eruptions lasted from ten days to a little under five months. Initial eruptive phases usually involved the opening of multiple vents along dike-fed fissures, with Strombolian explosive activity forming monogenetic cones. Lava flow emission generally quickly followed, and later eruptive phases were typically dominated by effusive behavior. Some eruptions (1704–1705, 1824 and 1949), however, had a complex evolution punctuated by the sequential opening of distinct vents several kilometers apart. Total lengths of vent-defined fissures range from 0.2 to 14.0 km, and maximum lava flow runout is 2.7–9.4 km, extending to the coastline in 75% of eruptions. Proximal eruptive deposits cover 1.8–7.8 km². Published estimates of subaerial eruptive volumes average between 11 and 66 × 10⁶ m³. In comparison, a new empirical relationship based on well-constrained lava flow area and volume data at other basaltic volcanoes yields volumes of 10–76 × 10⁶ m³ for Canary Island eruptions. The 1730–1736 Timanfaya eruption on Lanzarote represents an outlier in the context of historical Canary Island volcanism, with a duration of 2055 days, a total fissure length ≥ 14.4 km defined by at least ten main emission centers, a maximum lava flow length of 21.7 km, a lava flow field area of 146 km² and volume of at least 2.2–3.7 km³. Historical eruptive rates are low, at 1.0–2.1 × 10⁶ m³/year or 7.3–11.0 × 10⁶ m³/year including the 1730–1736 eruption, in agreement with long-term volcano growth rates based on geologic data. We find no evidence for time-predictable or volume-predictable behavior of the historical eruptive sequence, which has a mean recurrence interval of 39 ± 24 years. Our analysis outlines a useful framework for forecasting the onset, development and style of future eruptions in the archipelago. Further work, particularly detailed field-based studies of eruption deposits and petrologic reconstructions of eruption run-up processes, will help refine our understanding of historical volcanism and associated hazards in the Canary Islands.
... The Tagoro volcano complex (TVC, Figure 2) comprises one main cone and thirteen secondary cones, with interspersed depressions, aligned North-Northwest-South-Southeast, NNW-SSE [26,27]. The main edifice extends 88-400 m deep and the lava debris apron spreads 1-1.3 km long south-west ( Figure 2A). ...
... The formation of the Tagoro volcano complex (TVC) included extrusion of magmatic material and the formation of new hard bottoms, as well as changes in the physical-chemical characteristics of water masses in the area [6,10,26,27]. This eruptive process locally impacted pre-existing habitats through burial, mainly those conformed by antipatharians (Stichopathes, Antipathes, and Tanacetipathes), which when detected were considered survivors of the eruption and the water column anomalies [37]. ...
Article
Full-text available
Tagoro, the youngest submarine volcano of the Canary Islands, erupted in 2011 South of El Hierro Island. Pre-existing sea floor and inhabiting biological communities were buried by the newly erupted material, promoting the appearance of new habitats. The present study pursues to describe the first metazoans colonizing different new habitats formed during the eruption and to create precedent on this field. Through dredge and remote operated vehicle samplings, five main habitat types have been detected based on the substrate type and burial status after the eruption. Inside the Tagoro volcanic complex (TVC), two new habitats are located in and around the summit and main craters-hydrothermal vents with bacterial mats and sulfurous-like fields mainly colonized by small hydrozoan colonies. Two other habitats are located downslope the TVC; new hard substrate and new mixed substrate, holding the highest biodiversity of the TVC, especially at the mixed bottoms with annelids (Chloeia cf. venusta), arthropods (Monodaeus couchii and Alpheus sp.), cnidarians (Sertularella cf. tenella), and molluscs (Neopycnodonte cochlear) as the first colonizers. An impact evaluation was done comparing the communities of those habitats with the complex and well-established community described at the stable hard substrate outside the TVC, which is constituted of highly abundant hydrozoans (Aglaophenia sp.), antipatharians (Stichopates setacea and Antipathes furcata), and colonizing epibionts (e.g., Neopycnodonte cochlear). Three years after the eruption, species numbers at Tagoro were still low compared to those occurring at similar depths outside the TVC. The first dominant species at the TVC included a large proportion of common suspension feeders of the circalittoral and bathyal hard bottoms of the area, which could have exploited the uncolonized hard bottoms and the post eruptive fertilization of water masses.
... Three main origins could be established to justify the pres- ence of MTDs or volcanoclastic deposits with blanking acoustic facies between volcanic debris avalanches in the flanks of vol- canic islands and abyssal plains: (i) seafloor sediment failures and landslide propagation mechanisms triggered by volcanic flank- collapse events (e.g. as in Montserrat and Martinique, Lesser An- tilles; Le Friant et al., 2015;Brunet et al., 2016); (ii) volcanoclas- tic debris flow triggered by the loading of the slope sediments by the debris avalanches ( Urgeles et al., 1999;Masson et al., 1998Masson et al., , 2002); (iii) pyroclastic density currents ( Somoza et al., 2017;Trofimovs et al., 2008). These three options are related with active volcanic periods. ...
... These three options are related with active volcanic periods. Pyroclastic density currents have been identified only in the flanks and base of volcanic island ( Somoza et al., 2017), and local possible submarine slide deposits have been interpreted at the base of the El Golfo DA (SLB in Fig. 3a), both related with the increase of the volcanic activity. In this way, the most plausi- ble scenario for the volcanoclastic debrites could be the loading of the slope sediments by the debris avalanches ( Urgeles et al., 1999;Masson et al., 1998Masson et al., , 2002), related with the volcanic activity too. ...
Article
A new temporal history of mass wasting processes for the west of the Canary volcanic province is presented. Its onset has been estimated in the middle–upper Miocene (∼13.5 ± 1.2 Ma), matching with a critical period of construction for this volcanic province. Seismic profiles show an emplacement longevity (from the Miocene to Quaternary) in multiple events, defined by stacked lobes of debrites, linked to the flank collapses and volcanic avalanches of the volcanic edifices (islands and seamounts). An evolution of pathways and source areas has been detected from east (Miocene) to west (Quaternary); as well as a migration of the activity to the northwest (west of the Canary Islands: e.g. El Hierro and La Palma). Six connected branches (I–VI), three of them described for the first time here, of Quaternary seismic units of mass transport deposits (MTDs) have been characterized. The Pleistocene makes up a huge buried MTDs system, until now unknown, pointing a new mass transport sedimentological scenario. Finally, the two southernmost branches (V–VI), up to now unknown, are a mainly buried system of stacked and terraced lobes of debrites sourced mainly from the flank collapses of the volcanic seamounts of the Canary Island Seamount Province, apparently inactive from upper Cretaceous.
... Three main origins could be established to justify the pres- ence of MTDs or volcanoclastic deposits with blanking acoustic facies between volcanic debris avalanches in the flanks of vol- canic islands and abyssal plains: (i) seafloor sediment failures and landslide propagation mechanisms triggered by volcanic flank- collapse events (e.g. as in Montserrat and Martinique, Lesser An- tilles; Le Friant et al., 2015;Brunet et al., 2016); (ii) volcanoclas- tic debris flow triggered by the loading of the slope sediments by the debris avalanches ( Urgeles et al., 1999;Masson et al., 1998Masson et al., , 2002); (iii) pyroclastic density currents ( Somoza et al., 2017;Trofimovs et al., 2008). These three options are related with active volcanic periods. ...
... These three options are related with active volcanic periods. Pyroclastic density currents have been identified only in the flanks and base of volcanic island ( Somoza et al., 2017), and local possible submarine slide deposits have been interpreted at the base of the El Golfo DA (SLB in Fig. 3a), both related with the increase of the volcanic activity. In this way, the most plausi- ble scenario for the volcanoclastic debrites could be the loading of the slope sediments by the debris avalanches ( Urgeles et al., 1999;Masson et al., 1998Masson et al., , 2002), related with the volcanic activity too. ...
Article
A new temporal history of mass wasting processes for the west of the Canary volcanic province is presented. Its onset has been estimated in the middle–upper Miocene (∼13.5 ± 1.2 Ma), matching with a critical period of construction for this volcanic province. Seismic profiles show an emplacement longevity (from the Miocene to Quaternary) in multiple events, defined by stacked lobes of debrites, linked to the flank collapses and volcanic avalanches of the volcanic edifices (islands and seamounts). An evolution of pathways and source areas has been detected from east (Miocene) to west (Quaternary); as well as a migration of the activity to the northwest (west of the Canary Islands: e.g. El Hierro and La Palma). Six connected branches (I–VI), three of them described for the first time here, of Quaternary seismic units of mass transport deposits (MTDs) have been characterized. The Pleistocene makes up a huge buried MTDs system, until now unknown, pointing a new mass transport sedimentological scenario. Finally, the two southernmost branches (V–VI), up to now unknown, are a mainly buried system of stacked and terraced lobes of debrites sourced mainly from the flank collapses of the volcanic seamounts of the Canary Island Seamount Province, apparently inactive from upper Cretaceous.
... Intermediate-water eruption (approximately 300-600 m water depth) are rarely observed, but they can be characterized by a peculiar eruptive style characterized by floating lava balloons or pumice rafting on sea surface, as recently occurred off Terceira Island (Azores) in 1998-2001 (Casas et al., 2018; and reference therein) and El Hierro Island (Canary Islands) in 2011 (Somoza et al., 2017). In the Mediterranean Sea, a similar eruption occurred 5 km off the NW coast of Pantelleria island (Sicily Channel) in 1891. ...
Chapter
This chapter starts with a brief summary of the geological processes that resulted in the formation of the Mediterranean Sea. The main content of the chapter focuses on the description of the different processes that control recent sedimentation at the seafloor in coastal areas and in the deep sea, on how submarine volcanoes are formed and evolve and how fluid escape at the seafloor form cold seeps and related deposits. Finally, the implications of all these processes for geohazards and ecosystems are discussed.
... The eastern Canary Basin is one of the few places in the world where to study in the Quaternary the interaction and relationship among volcanism, tectonic and giant submarine landslide. Here, an intensive research has been carried out in fields such as the Quaternary or current volcanic and hydrothermal activity (Klügel et al., 2020;van den Bogaard, 2013;Medialdea et al., 2017;Somoza et al., 2017), gravitational instabilities and mass-transport deposits (MTDs) (Georgiopoulou et al., 2009(Georgiopoulou et al., , 2010Hunt et al., 2011Hunt et al., , 2013Hunt et al., , 2014Palomino et al., 2016;León et al., 2019), the relationship between MTDs and volcanic activity (Hunt et al., 2014;Hunt and Jarvis, 2017;León et al., 2019) and the presence of critical metallic elements (Marino et al., 2017). However, only a few of these studies have focused on the relationship between tectonics, volcanic activity and seafloor morphology Sánchez-Guillamón et al., 2018a, 2018b. ...
Article
This paper integrates sedimentary, tectonic and volcanic geological processes inside a model of volcano-tectonic activity in oceanic intraplate domains related to rifted continental margins. The study case, the eastern Canary Basin (NE Atlantic), is one of the few places in the world where giant MDTs and Quaternary volcanic and hydrothermal edifices take place in intraplate domains. In this paper, we analyse how two structural systems (WNW-ESE and NNE-SSW) matching with the oceanic fabric control the location of volcanic systems, seafloor tectonic reliefs and subsequently the distribution of main sedimentary systems. Linear turbidite channels, debris flow lobes and the lateral continuity of structural and volcanic reliefs follow a WNW-ESE trend matching the tracks of the oceanic fracture zones. Furthermore, escarpments, anticline axes and volcanic ridges follow a NNE-SSW trend matching normal faults delimiting blocks of oceanic basement. The morpho-structural analysis of all the above geomorphological features shows evidence of a volcanic and tectonic activity from the middle–upper Miocene to the Lower–Middle Pleistocene spread over the whole of the eastern Canary Basin that reached the western Canary Islands. This reactivation changes the paradigm in the seamount province of Canary Islands reported inactive since Cretaceous. A tecto-sedimentary model is proposed for this period of time that can be applied in other intraplate domains of the world. A tectonic uplift in the study area with a thermal anomaly triggered volcanic and hydrothermal activity and the subsequent flank collapse and emplacement of mass transport deposits on the Western Canary Slope. Furthermore, this uplift reactivated the normal basement faults, both trending WNW-ESE and NNE-SSW, generating folds and faults that control the location of turbidite channels, escarpments, mass transport deposits and volcanic edifices.
... The integration of repeated multibeam surveys with hydroacoustic monitoring has resulted in a powerful tool for the detection of active submarine volcanoes (especially given that volcanic eruptions only occasionally reach the sea surface) and to identify submarine eruptive processes (Somoza et al., 2017;Tepp et al., 2019). ...
Book
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The publication presents an overview of the type, distribution and impact of marine geohazards in European coastal regions and on several Blue Economy sectors. It highlights novel scientific approaches that broaden our understanding of these hazards. The document points towards relevant actions that would ensure the development of effective risk-mitigation and science-based management practices and policies, such as mapping of the seabed and including geohazards in maritime spatial planning policies, thereby contributing to protect coastal population and economic activities at sea.
... Elevated concentrations of volatiles (H 2 = 550 nM, CH 4 = 831 nM, CO 2 = 34 µM), high turbidity and high total alkalinity values were associated with temperature and pH anomalies (respectively, 0.2 °C and 1 pH unit 27 anomalies are characteristic of submarine eruptions and may reflect magma degassing 28 , molten lava interaction with seawater 29 or fluid/ water discharge from subsurface storage zones in the crust or sedimentary cover 30 . The height and the strong backscatter signature of the acoustic plume suggest that a mixture of solid particles (pyroclastic/hyaloclastic jet 28 ) and/or differentiated fluid phases (droplets, hydrate-coated bubbles or free gas 31 ) are driven upwards through the water column from the NVE summit 32 . High turbidity measured at water depths below 2,500 m, on the northern flank of the NVE, probably indicates the presence of these particles 33 . ...
Article
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Volcanic eruptions shape Earth’s surface and provide a window into deep Earth processes. How the primary asthenospheric melts form, pond and ascend through the lithosphere is, however, still poorly understood. Since 10 May 2018, magmatic activity has occurred offshore eastern Mayotte (North Mozambique channel), associated with large surface displacements, very-low-frequency earthquakes and exceptionally deep earthquake swarms. Here we present geophysical and marine data from the MAYOBS1 cruise, which reveal that by May 2019, this activity formed an 820-m-tall, ~5 km³ volcanic edifice on the seafloor. This is the largest active submarine eruption ever documented. Seismic and deformation data indicate that deep (>55 km depth) magma reservoirs were rapidly drained through dykes that intruded the entire lithosphere and that pre-existing subvertical faults in the mantle were reactivated beneath an ancient caldera structure. We locate the new volcanic edifice at the tip of a 50-km-long ridge composed of many other recent edifices and lava flows. This volcanic ridge is an extensional feature inside a wide transtensional boundary that transfers strain between the East African and Madagascar rifts. We propose that the massive eruption originated from hot asthenosphere at the base of a thick, old, damaged lithosphere. An ~5 km³ volcanic edifice offshore Mayotte formed between May 2018 and May 2019 by rapid magma intrusion through the entire lithosphere, according to an analysis of marine observations and geophysical data.
... At the Mid-Atlantic Ridge, the seafloor massive sulfides deposits, are enriched in the ore metals (Cu, Zn, As, Au, Ag, U, etc.), whose concentrations are much higher than those in the land-based volcanogenic massive sulfide [15,16]. The hydrothermal-derived oxyhydroxide sediments have been recently associated with the 2011-2012 underwater volcano eruption and the hydrothermal system established in the Canary Islands [17,18]. The hydrothermal micro-layers have been discovered within thick ferromanganese crusts in seamounts from the Atlantic Ocean, showing the influence of hydrothermal plumes during the growth process of ferromanganese deposits [19]. ...
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In this study, to better understand the influence of hydrothermal processes on ore metal accumulation in bottom sediments, we examined distribution of Fe, Mn, Cu, Zn, As, and Pb in core of metalliferous sediments from the Pobeda hydrothermal cluster, and in core of non-mineralized (background) carbonate sediments (located 69 km northwards). Mechanisms of Fe, Mn, Cu, and Zn accumulation in sediments (12 samples) were evaluated based on sequential extraction of geochemical fractions, including a conditional mobile (F-1, exchangeable complex; F-2, authigenic Fe-Mn oxyhydroxides and associated metals; F-3, metals bound to organic matter/sulfides), and residual (F-4), fixed in crystalline lattices ones. The element contents were determined by the XRF and AAS methods, total carbon (TC) and total organic carbon (TOC) were determined using a Shimadzu TOC-L-CPN. Mineral composition and maps of element distribution in sediment components were obtained using the XRD and SEM-micro-X-ray spectrometry methods, respectively. In metalliferous sediments, according to our data, the major Fe mineral phase was goethite FeOOH (37–44% on a carbonate-free basis, cfb). In the metalliferous core, average contents (cfb), of Fe and Mn were 32.1% and 0.29%, whereas those of Cu, Zn, Pb, and As, were 0.74%, 0.27%, 0.03%, and 0.02%, respectively. Metalliferous sediments are enriched in Fe, Cu, Zn, Pb, and As, relatively to background ones. The exception was Mn, for which no increased accumulation in metalliferous core was recorded. Essential mass of Fe (up to 70% of total content) was represented by the residual fraction composed of crystallized goethite, aluminosilicates, the minerals derived from bedrock destruction processes mineral debris. Among geochemically mobile fractions, to 80% Fe of the (F-1 + F-2 + F-3) sum was determined in the form of F-2, authigenic oxyhydroxides. The same fraction was a predominant host for Mn in both metalliferous and background sediments (to 85%). With these Fe and Mn fractions, a major portion of Cu, Zn, and Pb was associated, while a less their amount was found in sulfide/organic fraction. In the metalliferous sediment core, maximal concentrations of metals and their geochemically mobile fractions were recorded in the deeper core sediment layers, an observation that might be attributed to influence of hydrothermal diffused fluids. Our data suggested that ore metals are mostly accumulated in sediment cores in their contact zone with the underlying serpentinized peridotites.
... Many concepts are still based on the interpretation of ancient deposits and on theory (e.g., [114] and references therein). However, the growing availability of detailed digital elevation models (also used to depict seafloor changes associated with eruptions through repeated surveys) integrated with hydroacoustic monitoring and in situ observations of volcanic settings will exponentially increase their detection (considering that volcanic eruptions only occasionally reach the sea surface) and our knowledge of submarine eruptive processes (e.g., [115][116][117][118][119][120]). ...
Article
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Offshore geological hazards can occur in any marine domain or environment and represent a serious threat to society, the economy, and the environment. Seismicity, slope sedimentary instabilities, submarine volcanism, fluid flow processes, and bottom currents are considered here because they are the most common hazardous processes; tsunamis are also examined because they are a secondary hazard generated mostly by earthquakes, slope instabilities, or volcanic eruptions. The hazards can co-occur and interact, inducing a cascading sequence of events, especially in certain contexts, such as tectonic indentations, volcanic islands, and canyon heads close to the coast. We analyze the key characteristics and main shortcomings of offshore geological hazards to identify their present and future directions for marine geoscience investigations of their identification and characterization. This review establishes that future research will rely on studies including a high level of multidisciplinarity. This approach, which also involves scientific and technological challenges, will require effective integration and interplay between multiscale analysis, mapping, direct deep-sea observations and testing, modelling, and linking offshore observations with onshore observations.
... 129 A ~1900-m high, vertical acoustic plume, rising through the water column from the summit of and may reflect magma degassing 30 , molten lava interaction with seawater 31 or fluid/water 138 discharge from subsurface storage zones in the crust or sedimentary cover 32 . The height and 139 the strong backscatter signature of the acoustic plume suggest that a mixture of solid particles 140 (pyroclastic/hyaloclastic jet 30 ) and/or differentiated fluid phases (droplets, hydrate-coated 141 bubbles or free gas 33 ) are driven upward through the water column from the summit of the 142 NVE 34 . High turbidity measured, below 2500 m, on the northern flank of the NVE, likely 143 indicates the presence of these particles 35,36 . ...
... This type of habitat, one composed of a high abundance of soft corals and that lacks carbonate skeletons, may represent the first stages of colonization by octocorals above an acidic low-temperature hydrothermal environment with continuous degasification emissions of CO 2 after the cessation of magmatic activity. The evolution of this habitat, colonized in only 50 years, may be useful as a comparison for other recent eruptions that developed in the Macaronesia, as, for example, with the one that occurred on the El Hierro Island, Canary Islands, in 2011-2012 (Somoza et al., 2017). ...
Article
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This work presents the preliminary result of the multidisciplinary cruise EXPLOSEA2 surveying the northern Mid-Atlantic Ridge and Azores Archipelago from 46 • 30 N to 38 • 30 N aboard the R/V Sarmiento de Gamboa and ROV Luso over 54 days (June 11 to July 27, 2019). In this cruise report, we detail the geophysical, hydrographic, geological, oceanographic, ecological, and microbiological data acquired and a brief of main findings. The cruise addressed the exploration and comprehensive characterization of venting sites, including the water column, the sediments and rocks that host the hydrothermal activity, and the associated mineralizations, biology, and microbiology. Deep hydrothermal chimneys and massive sulfide deposits (up 3,000 m in depth) within the Moytirra hydrothermal active field were identified on slopes that had not been explored previously. Another striking finding made during the EXPLOSEA2 cruise was the field of carbonate chimneys named the "Magallanes-Elcano" field, a potentially relict ultramafic-hosted hydrothermal site sourced by abiotic methane. This field is related to a serpentinite and gabbro rock outcropping on a dome-shaped massif named the "Iberian Massif." An outstanding finding of the EXPLOSEA2 survey was the identification of the first garden of soft corals growing after active submarine eruptions were reported in the Azores Archipelago composed by a high density of soft corals the suborder Alcyoniina at the summit and flanks of a recent volcanic cone at 160 m water depth developed during the 1957-1958 eruption of Capelinhos. Several cold-water coral habitats formed by colonial scleractinians (e.g., Lophelia pertusa and Madrepora oculata), coral gardens composed of mixed assemblages of black corals (Leiopathes sp.), and octocorals and dense aggregations of the glass sponge Pheronema carpenteri that may be classified Frontiers in Marine Science | www.frontiersin.org 1 November 2020 | Volume 7 | Article 568035 Somoza et al. Mid-Atlantic Ridge and Azores Multidisciplinary Cruise as vulnerable marine ecosystems (VMEs) have been discovered during the EXPLOSEA2 cruise along the northern Mid-Atlantic Ridge. This work reveals the importance of multidisciplinary surveys to the knowledge of deep-sea environments.
... Elevated concentrations of volatiles (H 2 = 550 nM, CH 4 = 831 nM, CO 2 = 34 µM), high turbidity and high total alkalinity values were associated with temperature and pH anomalies (respectively, 0.2 °C and 1 pH unit 27 anomalies are characteristic of submarine eruptions and may reflect magma degassing 28 , molten lava interaction with seawater 29 or fluid/ water discharge from subsurface storage zones in the crust or sedimentary cover 30 . The height and the strong backscatter signature of the acoustic plume suggest that a mixture of solid particles (pyroclastic/hyaloclastic jet 28 ) and/or differentiated fluid phases (droplets, hydrate-coated bubbles or free gas 31 ) are driven upwards through the water column from the NVE summit 32 . High turbidity measured at water depths below 2,500 m, on the northern flank of the NVE, probably indicates the presence of these particles 33 . ...
Conference Paper
Volcanic eruptions are foundational events shaping the Earth's surface and providing a window into deep Earth processes and composition. Most eruptions occur on established volcanoes, exploiting longstanding magma reservoirs and pathways. Those creating new volcanoes are rare and usually too small or too remote to be well monitored, particularly in the offshore domain. We document here a lithosphere-scale magmatic event giving birth to a 5km3 submarine volcano offshore Mayotte island (Western Indian Ocean). This event is associated with large surface displacements and unusually long-lasting and intense seismic activity. Starting in May 2018, hundreds of earthquakes were a felt by the population, whose anxiety increased by the day. As part of a response program for crisis management, high-resolution geophysical, seismological and geodetic data were acquired onshore and offshore. The newborn volcano was discovered by comparing multibeam bathymetry acquired in 2019 to older data. The volcano has only been growing for less than a year and is already 820m tall. Popping rocks dredged on its flank suggest that the melt transferred rapidly from the upper mantle, without storage in intermediate reservoirs. Four main fluid plumes more than 2000 m-high emanate from the volcano summit, attesting to its intense activity. The volcano lies at the eastern tip of a N110° E striking volcanic ridge, made of dozens of older volcanic edifices. An ocean bottom seismometer deployment improved earthquake and tremor locations, revealing two unusually deep (25 to 50 km) seismic swarms along the ridge, and, at shallower depths, the source of many very long period (15s) seismic signals showing an exceptionally long duration (1000s). The new volcano may have erupted as a result of lithosphere-scale rifting process involving the drainage of a large asthenospheric reservoir, possibly confined at the base of the lithosphere.
... This vent location is 1.5 km northwest from the supposed 2001 eruption site and situated on the same broad bathymetric high and on the caldera rim ( Figure S9). The two rings strongly resemble breaching of billowing underwater eruption columns or steam cupolas generated during shallow submarine eruptions (Kokelaar & Durant, 1983;Somoza et al., 2017). No pumice raft is visible in the satellite image of the rings (pixel size 10 m), therefore pumice raft formation occurred subsequently. ...
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Plain Language Summary Although 70% of volcanism occurs underwater, submarine eruptions are seldom witnessed owing to their remoteness and absence of technologies enabling their detection. On the 7 August 2019, a submarine volcanic eruption 200 m below sea level in the Tonga Islands formed a 195 km² pumice raft. The raft was first encountered and sampled by yacht crews, and is visible on satellite images. Pumice rafts are dispersed by ocean currents, wind, and waves, and can cross entire oceans or get stranded on coasts. After 7 weeks of dispersal, the pumice raft reached the Fiji Islands, and a fraction continued its westward route toward Vanuatu and eastern Australia. Excellent imaging of the raft by satellites permitted reconstruction of daily raft dispersal for the first 8 weeks. Here we show that drift calculations, including components of ocean current, wind, and wave action, can usefully forecast raft dispersal. We tested and tuned these drift calculations by comparing the simulated drift with daily satellite images of the raft. Further, a combination of satellite images and drift calculations based on oceanographic models were used for maritime hazard mitigation in near‐real time.
... La Palma and El Hierro have suffer volcanic eruption recently in the last 50 years. As for example, the volcanic eruption of Teneguia (La Palma) in 1971 or the underwater volcanic eruption of Tagoro (El Hierro) in 2011 (Samoza et al. 2017). ...
Article
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Fluoride is a widely distributed ion in the environment and, consequently, in water as well. High levels of fluoride in waters can be found in the Canary Islands because of their volcanic origin. Due to the risk and detrimental effects associated with a high fluoride intake, the content of this ion has been potentiometrically determined in 256 supply water samples from the islands of Tenerife, El Hierro, and La Palma, using a fluoride selective ion electrode. Fluoride mean concentration found on Tenerife is 4.22 mg/L, exceeding the parametric value of 1.5 mg/L set out in Spanish legislation. The consumption of 2 L of water from the studied municipalities of Tenerife would mean there is an excessive fluoride intake. The consumption of this water poses a serious risk to health. It is necessary to take action aimed at reducing the level of fluoride in the north of the island of Tenerife.
... Subsequent to the Beaulieu et al. (2013) review, work on El Hierro Island in the North Atlantic, associated with the Canary hotspot, suggests that it may be another relevant analogue. Evidence for gas venting has been observed in water 88 to 350 m deep around El Hierro (Beaulieu et al., 2013;Pérez et al., 2012;Pérez et al., 2014;Somoza et al., 2017). Flares were recorded along with CO 2 and H 2 S degassing and pyroclastic plumes during Earth and Space Science CO 2 continuing after the eruption (Santana-Casiano et al., 2016). ...
Article
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Abstract Bubble emission mechanisms from submerged large igneous provinces remains enigmatic. The Kerguelen Plateau, a large igneous province in the southern Indian Ocean, has a long sustained history of active volcanism and glacial/interglacial cycles of sedimentation, both of which may cause seafloor bubble production. We present the results of hydroacoustic flare observations around the underexplored volcanically active Heard Island and McDonald Islands on the Central Kerguelen Plateau. Flares were observed with a split‐beam echosounder and characterized using multifrequency decibel differencing. Deep‐tow camera footage, water properties, water column δ3He, subbottom profile, and sediment δ13C and δ34S data were analyzed to consider flare mechanisms. Excess δ3He near McDonald Islands seeps, indicating mantle‐derived input, suggests proximal hydrothermal activity; McDonald Islands flares may thus indicate CO2, methane, and other minor gas bubbles associated with shallow diffuse hydrothermal venting. The Heard Island seep environment, with subbottom acoustic blanking in thick sediment, muted 3He signal, and δ13C and δ34S fractionation factors, suggest that Heard Island seeps may either be methane gas (possibly both shallow biogenic methane and deeper‐sourced thermogenic methane related to geothermal heat from onshore volcanism) or a combination of methane and CO2, such as seen in sediment‐hosted geothermal systems. These data provide the first evidence of submarine gas escape on the Central Kerguelen Plateau and expand our understanding of seafloor processes and carbon cycling in the data‐poor southern Indian Ocean. Extensive sedimentation of the Kerguelen Plateau and additional zones of submarine volcanic activity mean additional seeps or vents may lie outside the small survey area proximal to the islands.
... As an alternative hypothesis, the hummocky morphology might be the result of a slope failure affecting the southern submarine flank of Linosa and related to slide scars carving the shelf edge (Fig. 3), producing a blocky field of debris or a debris avalanche deposit (similarly to what observed in other volcanic contexts; Watts and Masson, 1995;Romagnoli et al., 2009a and2009b), although these deposits commonly show a more widespread extension and larger scales. Further investigations (such as the acquisition of extremely high-resolution bathymetric data through AUV or ROV images, see for instance Clague et al., 2019 andSomoza et al., 2017) and samplings could allow to better characterize the nature and source area of submarine lava flows/volcaniclastic deposits at Linosa. ...
Article
Linosa Island represents the emergent tip of a mostly submarine, much wider volcanic edifice, with at least 96% of its areal extent lying below sea level. Marine geological surveys carried out in 2016 and 2017 allowed to reconstruct the submarine portions of Linosa and to characterize the main volcanic features, providing new, unexpected insights on the evolution of this little-explored volcanic complex. In particular, the submarine setting of the NW offshore is represented by a ~10-km long volcanic belt punctuated by a number of small eruptive cones, appearing more recent with respect to the assumed Mid/Late-Quaternary age of volcanism on the island. This evidence suggests that the growth of the volcanic edifice has likely been more complex than that claimed on the base of subaerial volcanism only, and supports a north-westward migration of the activity over time. The submarine southern flank of the volcanic edifice is also characterized by eccentric eruptive cones, but mostly without evidences of recent activity. The main processes responsible for the growth and evolution of Linosa volcano and their possible relative chronology are discussed in the framework of what previously known on the base of the limited subaerial portions, with implications on the potential hazard of the volcanic edifice (considered as not-active in recent times). Similarity with the Pantelleria volcano, located in the NW Sicily Channel, are also evidenced, especially for what regards the distribution and morphometric characteristics of eruptive cones occurring in the submarine portions of both islands.
... By collecting high-resolution quantitative data on the morphology of modern volcanic edifices and surrounding lava flows from airborne-shuttle radar topography or time-lapse multibeam bathymetry, we can estimate erupted volumes, at least for individual eruptive episodes (e.g. Holcomb et al., 1988;Walker, 1993;Goto and McPhie, 2004;Cocchi et al., 2016;Somoza et al., 2017;Allen et al., 2018;Chadwick et al., 2018;Grosse and Kervyn, 2018). Whilst remote sensing data capture the external morphology of volcanoes and lava flows both before, during, and after eruptions, they do not image their basal surface or internal architecture. ...
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Submarine volcanism accounts for ca. 75 % of the Earth's volcanic activity. Yet difficulties with imaging their exteriors and interiors mean that the extrusion dynamics and erupted volumes of deepwater volcanoes remain poorly understood. Here, we use high-resolution 3-D seismic reflection data to examine the external and internal geometry and extrusion dynamics of two late Miocene–Quaternary deepwater (> 2 km emplacement depth) volcanoes buried beneath 55–330 m of sedimentary strata in the South China Sea. The volcanoes have crater-like bases, which truncate underlying strata and suggest extrusion was initially explosive, and erupted lava flows that feed lobate lava fans. The lava flows are > 9 km long and contain lava tubes that have rugged basal contacts defined by ∼90±23 m high erosional ramps. We suggest the lava flows eroded down into and were emplaced within wet, unconsolidated, near-seafloor sediments. Extrusion dynamics were likely controlled by low magma viscosities as a result of increased dissolved H2O due to high hydrostatic pressure and soft, near-seabed sediments, which are collectively characteristic of deepwater environments. We calculate that long-runout lava flows account for 50 %–97 % of the total erupted volume, with a surprisingly minor component (∼3 %–50 %) being preserved in the main volcanic edifice. Accurate estimates of erupted volumes therefore require knowledge of volcano and lava basal surface morphology. We conclude that 3-D seismic reflection data are a powerful tool for constraining the geometry, volumes, and extrusion dynamics of ancient or active deepwater volcanoes and lava flows.
... The main edifice extends from 88 to 400 m below sea level (mbsl; Fig. 51.2C) and is 1À1.3 km in (elongated) length and width. It has an irregular base comprising a main cone and 13 secondary cones, related to fissure volcanic vents distributed in a NNWÀSSE trend (Fig. 51.2A;Vázquez et al., 2016;Somoza et al., 2017). ...
Chapter
The Canary Islands are a volcanic alignment of seven islands that conforms an archipelago located in the northwestern part of the still active Nubian (African) tectonic plate. The archipelago showed its latest volcanic activity south off El Hierro Island in 2011, resulting in the formation of the newest underwater volcano, known as Tagoro, for the Canary Islands.
... Other authors (e.g. Somoza et al., 2017) suggest a different origin to these xeno-pumices to be a mingling between Cretaceous to Pliocene sedimentary oceanic sequence and the ascending magma. After some weeks of eruption, the volcano emitted lava balloons, consisting of an internal gas-filled cavity surrounded by a few centimeters-thick crust of quenched vesicular lava . ...
Article
Six different magmatic intrusions were detected around El Hierro Island in the two years that followed the end of the 2011–2012 submarine eruption. Each intrusion lasted between few days to three weeks and produced intense seismic swarms and rapid ground deformation. We performed a hypoDD relocation of >6000 earthquakes and inverted the GPS data in order to obtain the location of the magma source of each intrusion. Each episode presents a spatial gap between seismicity and magma source of 3–8 km with the earthquakes located always deeper than the deformation sources. We propose a magma plumbing system consisting on a deep structure injecting magma to a more ductile shallower location beneath El Hierro crust. While the seismicity is associated with the deeper structure, the ascent and accumulation of magma at shallower level deforms the crust aseismically. The mechanism of most of these episodes consists of an initial injection of magma producing most of the ground deformation and high b-values of the seismicity indicating fluid fractures during the first days and finishes with high magnitude earthquakes and low b-values indicating an overpressure of the injection process. There is a correlation between the seismic and geodetic moment ratio and the direction of propagation of each intrusion towards one of the volcanic rifts of the island, suggesting the possible existence of a deep structure beneath the island related with to the triaxial origin of the island. This work presents important advances in the knowledge of monogenetic magmatic intrusions and, specifically, in those occurred in El Hierro Island between 2011 and 2014, with important implications for future volcano monitoring in the Canary Islands.
... These were defined as "xenopumices" and described as decametric fragments that exhibit cores of white and porous pumice-like material. The xenopumices were interpreted as recycled sedimentary layers picked up and heated by the ascending magma (Meletlidis et al., 2012;Troll et al., 2012;Somoza et al., 2017). During the final phase of the eruption, basanitic lava balloons, exceeding 1 m in size, were observed temporarily floating above the emission centre (Berg et al., 2016). ...
Article
High-resolution bathymetric data and seafloor sampling were used to characterize the most recent volcanic eruption in the Azores region, the 1998–2001 Serreta submarine eruption. The vent of the eruption is proposed to be an asymmetric topographic high, composed of two coalescing volcanic cones, underlying the location where lava balloons had been observed at the sea surface during the eruption. The volcanic products related to the 1998–2001 eruption are constrained to an area of ~0.5 km² around the proposed vent position. A submarine Strombolian-style eruption producing basaltic lava balloons, ash and coarse scoriaceous materials with limited lateral dispersion led to the buildup of the cones. The 1998–2001 Serreta eruption shares many similarities with other intermediate-depth lava balloon-forming eruptions (e.g., the 1891 eruption offshore Pantelleria and the 2011–2012 eruption south of El Hierro), revealing the particular conditions needed for the production of this unusual and scarcely documented volcanic product.
Article
The Cretaceous was an important period of manganese deposition in Iran, as evidenced by a series of medium-sized manganese deposits along the edge of the Neotethys ocean. This study characterizes representative example that occurs in Late Cretaceous volcanic rocks in the Goft deposit. This manganese deposit is typically volcanic hosted, with manganese-containing minerals, such as pyrolusite, psilomelane, cryptomelane, braunite, and manganite. The ore bodies hosted by red tuff are predominantly layered and usually have nodular structures. Replacement of Cretaceous foraminifers and radiolarians fossils by manganese minerals, are also frequently observed in the Goft deposit. This deposit is a high-quality ore characterized by low P and Fe grades and an average Mn grade of approximately 14%. The average Mn/Fe, Co/Ni, Co/Zn, and V/(V+Ni) ratios in the Goft manganese deposit are 9.73, 0.24, 0.18, and 50, respectively. The overall REE contents are among 17.7 to 181 ppm, with an average of 87 ppm. The Ce/Ce* values of manganese ores vary from 0.26 to 0.99, with the mean of 0.53. The Eu/Eu* anomalies of the manganese oxide-hydroxide ores are close to 1 with a range of 0.70 to 1.22. Most manganese samples show negative Ce anomalies, indicating that the ore formation environment was predominantly oxide and cold conditions. The geochemical behavior of trace elements, including the REEs of the manganese oxide provides clear evidence a low-temperature hydrothermal origin. The mineralogical and geochemical characteristics presented in this study strongly suggest a volcanogenic exhalative genesis for Goft manganese deposit.
Article
This study summarizes the compilation and cartographic works of seabed mineral deposit types in pan-European seas developed under the GeoERA-MINDeSEA project. In total , 692 occurrences and 1194 individual mineral samples of volcanogenic massive sulphides and hydrothermal mineralisation; ferromanganese crusts; phosphorites; marine placer deposits; polymetallic nodules and their associated strategic and critical elements (CRM) are characterised. The GeoERA-MINDeSEA project has been built based on extensive studies carried out previously, which include geophysical surveys, sampling stations, underwater photography and ROV surveys, and mineralogical, geochemical and isotopic studies. The study currently develops pan-European and national databases, and expand the strategic and CRM knowledge through a compilation of mineral potential and metallogenic studies of CRM resources in European seas. GeoERA-MINDeSEA portal, for the first time, publish harmonised marine mineral resource information, case studies and maps; identify potential areas for responsible resource exploration and extraction; strategic management and Marine Spatial Planning. The study is also providing recommendations for future target areas, studies and standards to be used across Europe as part of this project.
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On the 15th of January 2022, a massive hydrovolcanic eruption at Hunga Tonga-Hunga Ha'apai in Tonga (SW Pacific) sent shockwaves in the near-field regime, close to the volcano. The far-field disturbances that encircled the globe were of a slower velocity. The most prominent disturbance was the Lamb wave, with the rest of the disturbances being a variety of gravity waves travelled around the globe and instantly became an international headline story. The eruption generated atmospheric pressure waves recorded multiple times across the globe, triggered a tsunami, and injected highly fragmented pyroclasts up to 55 km into the atmosphere. Enduring several hours, a series of individual large blasts generated an unprecedented lightning “show” recorded by the lightning detection networks, such as Vaisala. Consequences were devastating to the local community and the tsunami was felt across the Pacific and beyond. The impact of the eruption was truly global and comparable to the Krakatau 1883 eruption. A question we pose here is which geoheritage elements were created and preserved after the eruption. First reports confirmed that while fine ash was reported on land about 100 km from the source, most deposits were thin (mm-cm thick). This indicates that it is unlikely that any major section will be preserved, especially in the years following the event given the tropical setting. In addition, most of the ash fell into the Pacific Ocean, leaving no visible mark of this catastrophe. Unfortunately, the proximal region (e.g., the vent site) has also been destroyed, leaving only limited in-situ geoheritage elements likely to be accessible in the future. This poses a problem for human societal memory, as major catastrophic events in the collective memory of a community may only persist for a few decades, even when significant eruptive features may be preserved. Without “visible” geoheritage elements, this time will likely be much shorter. Geocultural elements (oral traditions or cultural activities) are likely to preserve and transmit information within the local communities for a longer period, but their accessibility and decoding may face difficulties in the absence of physically preserved evidence. Therefore, we consider it is important to trace and explore these geocultural elements through a mix of traditional and western approaches of community engaged activities. For example, the Pacific region has experienced several similar large-scale eruptions in historic times, and a few of them resulted in preserved geoheritage elements such as superb sections of the 1452–53 CE Kuwae eruption in Vanuatu. While these sites are locally known, their appearance and their geological context are not evidently and immediately considered as part of a major volcanic system, as they do not fit the common human perception of volcanoes as large conical mountains. Such visual perceptions do not align with the common near-sea level/shallow subaqueous caldera-dominated systems such as the location of the recent Tonga event. In achieving a better understanding in local communities of this type of geohazard, the geoheritage and geoeducation values of those rare geosites will increase significantly over time.
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The formation of isolated seamounts distant from active plate boundaries and mantle plumes remains unsolved. The solitary intraplate volcano Vesteris Seamount is located in the Central Greenland Basin and rises ∼3,000 m above the seafloor with a total eruptive volume of ∼800 km3. Here, we present a new high-resolution bathymetry of Vesteris Seamount and a detailed raster terrain analysis, distinguishing cones, irregular volcanic ridges, volcanic debris fans, U-shaped channels and lava flows. The slope angles, ruggedness index and slope direction were combined with backscatter images to aid geologic interpretation. The new data show that the entire structure is a northeast to southwest elongated stellar-shaped seamount with an elongated, narrow summit surrounded by irregular volcanic ridges, separated by volcanic debris fans. Whole-rock geochemical data of 78 lava samples form tight liquid lines of descent with MgO concentrations ranging from 12.6 to 0.1 wt%, implying that all lavas evolved from a similar parental magma composition. Video footage from Remotely Operated Vehicle (ROV) dives shows abundant pyroclastic and hyaloclastite deposits on the summit and on the upper flanks, whereas lavas are restricted to flank cones. The seamount likely formed above a weak zone of the lithosphere possibly related to initial rifting parallel to the nearby Mohns Ridge, but the local stress field increasingly affected the structure of the volcano as it grew larger. Thus, we conclude that the evolution of Vesteris Seamount reflects the transition from deep, regional lithospheric stresses in the older structures to shallower, local stresses within the younger volcanic structures similar to other oceanic intraplate volcanoes. Our study shows how the combination of bathymetric, visual and geochemical data can be used to decipher the geological evolution of oceanic intraplate volcanoes.
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Manganese nodules are a potential source of critical metals such as Cu, Ni, and Co and are widely distributed on the abyssal plains of the global oceans. A polymetallic nodule metallogenic belt with a heterogeneous and spatially clustered nodule distribution was recently discovered in NW Pacific inter-seamount basin (NPIB) areas. However, the geological processes that regulate the nodule occurrence in that region are unresolved. Here, we report on the characteristics of a high-density field of manganese nodules in the abyssal plain north of Suda Seamount. Ship-borne multibeam bathymetric data reveal a typical seamount sector-collapse topography characterized by radial lineaments of debris channels and ridges formed by rapid debris-avalanche flow. Backscatter data linked with underwater observation indicate that manganese nodules are more concentrated (50%–80% areal coverage) along the main body of the debris apron compared to adjacent neighboring areas (<30%). The extremely high concentrations (∼80% areal coverage) characterized by overlapping nodules are apparently associated with downslope movement, possibly triggered by block movement along the fault slip plane or by gravity processes. Our results indicate that seamount sector-collapse may have provided sufficient nucleus material for nodule growth and contributed to high nodule concentrations locally. The destruction of submarine volcanic edifices is universal, and the debris aprons and plains around such seamounts are potential prospecting areas for manganese nodule resources throughout the NPIB.
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Four pure hydrogenetic, mixed hydrogenetic-diagenetic and hydrogenetic-hydrothermal Fe-Mn Crusts from the Canary Islands Seamount Province have been studied by Micro X-Ray Diffraction, Raman and Fourier-transform infrared spectroscopy together with high resolution Electron Probe Micro Analyzer and Laser Ablation Inductively Coupled Plasma Mass Spectrometry in order to find the correlation of mineralogy and geochemistry with the three genetic processes and their influence in the metal recovery rate using an hydrometallurgical method. The main mineralogy and geochemistry affect the contents of the different critical metals, diagenetic influenced crusts show high Ni and Cu (up to 6 and 2 wt. %, respectively) (and less Co and REY) enriched in very bright laminae. Hydrogenetic crusts on the contrary show High Co and REY (up to 1 and 0.5 wt. %) with also high contents of Ni, Mo and V (average 2500, 600 and 1300 μg/g). Finally, the hydrothermal microlayers from crust 107-11H show their enrichment in Fe (up to 50 wt. %) and depletion in almost all the critical elements. One hydrometallurgical method has been used in Canary Islands Seamount Province crusts in order to quantify the recovery rate of valuable elements in all the studied crusts except the 107-11H, whose hydrothermal critical metals’ poor lamina were too thin to separate from the whole crust. Digestion treatment with hydrochloric acid and ethanol show a high recovery rate for Mn (between 75% and 81%) with respect to Fe (49% to 58%). The total recovery rate on valuable elements (Co, Ni, Cu, V, Mo and rare earth elements plus yttrium (REY)) for the studied crusts range between 67 and 92% with the best results for Co, Ni and V (up to 80%). The genetic process and the associated mineralogy seem to influence the recovery rate. Mixed diagenetic/hydrogenetic crust show the lower recovery rate for Mn (75%) and Ni (52.5%) both enriched in diagenetic minerals (respectively up to 40 wt. % and up to 6 wt. %). On the other hand, the presence of high contents of undigested Fe minerals (i.e., Mn-feroxyhyte) in hydrogenetic crusts give back low recovery rate for Co (63%) and Mo (42%). Finally, REY as by-product elements, are enriched in the hydrometallurgical solution with a recovery rate of 70–90% for all the studied crusts.
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Two Fe–Mn crusts among 35 samples, from six seamounts in the Canary Island Seamount Province, were selected as representatives of the endpoint members of two distinct types of genetic processes, i.e., mixed diagenetic/hydrogenetic and purely hydrogenetic. High-resolution analyses pursued the main aim of distinguishing the critical elements and their association with mineral phases and genetic processes forming a long-lived Fe–Mn crust. The Fe–Mn crust collected on the Tropic Seamount is composed of dense laminations of Fe-vernadite (>90%) and goethite group minerals, reflecting the predominance of the hydrogenetic process during their formation. Based on high-resolution age calculation, this purely hydrogenetic crust yielded an age of 99 Ma. The Fe–Mn crust collected on the Paps Seamount shows a typical botryoidal surface yielding an age of 30 Ma. electron probe microanalyzer (EPMA) spot analyses show two main types of manganese oxides, indicating their origin: (i) hydrogenetic Fe-vernadite, the main Mn oxide, and (ii) laminations of interlayered buserite and asbolane. Additionally, the occurrence of calcite, authigenic carbonate fluor-apatite (CFA) and palygorskite suggests early diagenesis and pervasive phosphatization events. Sequential leaching analysis indicated that Co, Ni, Cu, Ba and Ce are linked to Mn minerals. Therefore, Mn-oxides are enriched in Ni and Cu by diagenetic processes or in Co and Ce by hydrogenetic processes. On the other hand, Fe-oxides concentrate V, Zn, As and Pb. Moreover, the evidence of HREE enrichment related to Fe-hydroxides is confirmed in the mixed hydrogenetic/diagenetic crust.
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Between October 2011 and March 2012 a submarine volcanic eruption took place at the offshore of El Hierro Island. The extensive study of the eruption and subsequent degassing process has allowed monitoring the newly generated volcanic edifice. Multibeam bathymetric has enabled building a digital high-resolution bathymetric model (grid 1x1 m). The preliminary analysis of the geomorphology of this volcanic eruption displays four main features: i) the edifice consists of a principal and a series of secondary cones distributed in NW-SE trend; ii) two escarpments NE-SW directed that partially match with inherited flanks of the previously existing valley; iii) three crests, one of them interpreted as the prolongation of a NE-SW scarp and the other as the head of gravitational instabilities of NE-SW and N-S direction at the main hill; and iv) mixed lava and dense pyroclastic flows extended from the volcanic edifice to the southwest and characterized by a high slope front, that probably represents the maximum distance reached by the main lava products.
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The eruption of South Sarigan Seamount in the southern Mariana arc in May 2010 is a reminder of how little we know about the hazards associated with submarine explosive eruptions or how to predict these types of eruptions. Monitored by local seismometers and distant hydrophones, the eruption from ~ 200 m water depth produced a gas and ash plume that breached the sea surface and rose ~ 12 km into the atmosphere. This is one of the first instances for which a wide range of preand post-eruption observations allow characterization of such an event on a shallow submarine volcanic arc volcano. Comparison of bathymetric surveys before and after the eruptions of the South Sarigan Seamount reveals the eruption produced a 350 m diameter crater, deeply breached on the west side, and a broad apron downslope with deposits > 50 m thick. The breached summit crater formed within a pre-eruption dome-shaped summit composed of andesite lavas. Dives with the Japan Agency for Marine-Earth Science and Technology Hyper-Dolphin remotely operated vehicle sampled the wall of the crater and the downslope deposits, which consist of andesite lava blocks lying on pumiceous gravel and sand. Chemical analyses show that the andesite pumice is probably juvenile material from the eruption. The unexpected eruption of this seamount, one of many poorly studied shallow seamounts of comparable size along the Mariana and other volcanic arcs, underscores our lack of understanding of submarine hazards associated with submarine volcanism.
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We report precursory geophysical, geodetic, and geochemical signatures of a new submarine volcanic activity observed off the western coast of El Hierro, Canary Islands. Submarine manifestation of this activity has been revealed through acoustic imaging of submarine plumes detected on the 20-kHz chirp parasound subbottom profiler (TOPAS PS18) mounted aboard the Spanish RV Hespérides on June 28, 2012. Five distinct “filament-shaped” acoustic plumes emanating from the flanks of mounds have been recognized at water depth between 64 and 88 m on a submarine platform located NW El Hierro. These plumes were well imaged on TOPAS profiles as “flares” of high acoustic contrast of impedance within the water column. Moreover, visible plumes composed of white rafts floating on the sea surface and sourcing from the location of the submarine plumes were reported by aerial photographs on July 3, 2012, 5 days after acoustic plumes were recorded. In addition, several geophysical and geochemical data support the fact that these submarine vents were preceded by several precursory signatures: (i) a sharp increase of the seismic energy release and the number of daily earthquakes of magnitude ≥2.5 on June 25, 2012, (ii) significant vertical and horizontal displacements observed at the Canary Islands GPS network (Nagoya University-ITER-GRAFCAN) with uplifts up to 3 cm from June 25 to 26, 2012, (iii) an anomalous increase of the soil gas radon activity, from the end of April until the beginning of June reaching peak values of 2.7 kBq/m3 on June 3, 2012, and (iv) observed positive peak in the air-corrected value of 3He/4He ratio monitored in ground waters (8.5 atmospheric 3He/4He ratio (R A)) at the northwestern El Hierro on June 16, 2012. Combining these submarine and subaerial information, we suggest these plumes are the consequence of submarine vents exhaling volcanic gas mixed with fine ash as consequence of an event of rapid rise of volatile-rich magma beneath the NW submarine ridge of El Hierro. These precursory signals have revealed important to improve and optimize the detection of early warning signals of volcanic unrest episodes at El Hierro.
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We present multiple lines of evidence for years- to decade-long changes in the location and character of volcanic activity at West Mata seamount in the NE Lau Basin over a 16 year period, and a hiatus in summit eruptions from early 2011 through at least September 2012. Boninite lava and pyroclasts were observed erupting from its summit in 2009 and hydroacoustic data from a succession of hydrophones moored nearby show near-continuous eruptive activity from January 2009 to early 2011. Successive differencing of seven multibeam bathymetric surveys of the volcano made in the 1996-2012 period reveal a pattern of extended constructional volcanism on the summit and northwest flank punctuated by eruptions along the volcano's WSW rift zone (WSWRZ). Away from the summit, the volumetrically largest eruption during the observational period occurred between May 2010 and November 2011 at ~2920 m depth near the base of the WSWRZ. The (nearly) equally long ENE rift zone did not experience any volcanic activity during the 1996-2012 period. The cessation of summit volcanism recorded on the moored hydrophone was accompanied or followed by the formation of a small summit crater and a landslide on the eastern flank. Water column sensors, analysis of gas samples in the overlying hydrothermal plume and dives with a remotely operated vehicle in September 2012 confirmed that the summit eruption had ceased. Based on the historical eruption rates calculated using the bathymetric differencing technique, the volcano could be as young as several thousand years.
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Release of dissolved volatiles during submarine fire fountaining eruptions can profoundly influence the buoyancy flux at the vent. Theoretical considerations indicate that in some cases buoyant magma can be erupted prior to fragmentation (~75% vesicle volume threshold). Laboratory simulations using immiscible fluids of contrasting density indicate that the structure of the source flow at the vent depends critically on the relative magnitudes of buoyancy and momentum fluxes as reflected in the Richardson number (Ri). Analogue laboratory experiments of buoyant discharges demonstrate a variety of complex flow structures with the potential for greatly enhanced entrainment of surrounding seawater. Such conditions are likely to favor a positive feedback between phreatomagmatic explosions and volatile degassing that will contribute to explosive volcanism. The value of the Richardson number for any set of eruption parameters (magma discharge rate and volatile content) will depend on water depth as a result of the extent to which the exsolved volatile components can expand.
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Understanding magmatic systems feeding volcanoes is critical for accurate interpretation of monitoring data and, ultimately, eruption forecasting. Following 3 months of precursory unrest, the first historical eruption at El Hierro, Canary Islands, took place ~2 km offshore from October 2011 to March 2012. Our detailed petrological analysis of lava samples reveals that at least two distinct magmas initially supplied from reservoirs in the mantle underwent hybridization at 15–25 km depth, i.e., also largely within the upper mantle beneath El Hierro. Diffusion chronometry applied to zoned olivine crystals indicates that magma mixing began during the period of preeruptive seismicity and continued for weeks after the eruption onset. Our data also capture a magma stagnation level at 10–15 km depth in the lower crust, consis- tent with lateral propagation of an intrusion over substantial distances before rapid magma transit to the seafloor. The remarkable spatial and temporal correlation of petrological and geophysical data at El Hierro suggests that the observed seismicity records magma mixing and forceful intrusion as well as subsequent reservoir dynamics. These results demonstrate that eruptions at El Hierro are controlled principally by deep-seated processes, with little influ- ence from shallow crustal levels, and have important implications for monitoring of renewed unrest at long-dormant volcanoes.
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In December 1998 a volcanic eruption started about 10 km W of Terceira Island, Azores, on the so-called Terceira Rift. The eruptive vents were located in the Serreta Submarine Ridge, at depths ranging from 300 to 1000 meters. The observed eruption was preceded by a small seismic crisis, and lasted for more than two years. The tectonic setting of the eruption site, the alignment of the eruptive vents and the type of volcanic products point towards a basaltic fissure eruption. The most striking features formed during this eruption were "lava balloons". These hollow structures, spherical to ellipsoidal in shape, are interpreted as the result of puffing up of gas under the plastic surface of lava at vent level. Degassing of a very fluid, gas-rich magma within or beneath submarine lava lakes and/or during lava fountaining episodes is believed to be the process that generates such structures.
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The application of petrography, mineral chemistry, geochemistry, and experimental petrology, including mineral^melt thermodynamic and diffusion modelling, on quenched basanitic magma samples from the recent (2011^2012) submarine eruption of El Hierro (Canary Islands) has permitted the identification of major physico-chemical variations prior to and during magma eruption that correlate in time with monitored geophysical changes. After nearly 3 months of seismic unrest the eruption of El Hierro started on October 10, 2011 and ended by late February 2012.We studied 10 lava balloons and pyroclastic fragments collected floating on the sea surface between October 15 and lateJanuary. Based on petrological and geophysical data we distinguish two main eruptive episodes. Magma erupted from the beginning of the eruption until late November 2011 was an evolved basanite (�5 wt%MgO), changing to more primitive compositions (�8^9 wt%MgO) with time, thus suggesting extraction from a compositionally zoned magma system. Experimental data and mineral^melt thermodynamic modelling indicate that the erupted magma equilibrated at a pressure of about 400MPa, which corresponds to a depth of 12^15 km. This depth is consistent with the location of the crust^mantle discontinuity beneath El Hierro and with the hypocentral location of seismicity during the unrest episode. Preliminary modelling of the olivine chemical zoning of crystals erupted in this first episode suggests that the time scale for basanite fractionation and magma replenishment in the shallower reservoir was of the order of a few months.This is within the same time frame as the duration of the unrest episode preceding the eruption. The first eruption episode coincided with intense seismicity mostly located north of the island, first at a depth of 20^25 km and a few days later also at 10^15 km depth, with strong seismic tremor beneath the vent site. An abrupt change in magma composition and crystal content was observed at the end of November 2011. After that, more primitive and less viscous magma erupted contemporaneously with a change in the frequency and intensity of seismic events. During this period, seismicity was mostly north of the island at depths of 10^15 km. At the same time the tremor intensity at the eruption site significantly dropped. This marked the onset of the second eruption episode, which is correlated with an intrusion of fresh, more primitive magma into the shallow magmatic system that raised the temperature of the remaining magma. Experiments reveal that subtle changes in temperature of about 508C (i.e. 1100^11508C) were enough to produce large changes in the crystal content (10^60 wt %). This non-linear behaviour between crystal contentand temperature had important effects on magma dynamics during transport and cooling. Our results suggest the existence of two interconnected mafic magma reservoirs during the El Hierro eruption, which agrees with the pattern shown by the seismicity. Stress readjustments of the plumbing system, caused by decompression during the eruption, influenced the thermodynamic evolution of the erupting magma and facilitated the intrusion of the deeper magma into the shallow reservoir, thus forcing a change in its rheological characteristics and eruption dynamics.
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Many submarine caldera volcanoes are blanketed with deposits of highly vesicular pumice, typically attributed to vigorous explosive activity. However, it is challenging to relate volcanic products to specific eruptive styles in submarine volcanism. Here we document vesicularity and textural characteristics of pumice clasts dredged from the submarine Macauley volcano in the Kermadec arc, southwest Pacific Ocean. We find that clasts show a bimodal distribution, with corresponding differences in vesicle abundances and shapes. Specifically, we find a sharp mode at 91% vesicularity and a broad mode at 65-80%. Subordinate clasts show gradients in vesicularity. We attribute the bimodality to a previously undocumented eruptive style that is neither effusive nor explosive. The eruption rate is insufficient to cause magma to fragment explosively, yet too high to passively feed a lava dome. Instead, the magma foam buoyantly detaches at the vent and rises as discrete magma parcels, or blebs, while continuing to vesiculate internally. The blebs are widely distributed by ocean currents before they disintegrate or become waterlogged. This disintegration creates individual clasts from interior and rim fragments, yielding the bimodal vesicularity characteristics. We conclude that the generation and widespread dispersal of highly vesicular pumice in the marine environment does not require highly explosive activity.
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Most of Earth's volcanoes are under water. As a result of their relative inaccessibility, little is known of the structure and evolution of submarine volcanoes. Advances in navigation and sonar imaging techniques have made it possible to map submarine volcanoes in detail, and repeat surveys allow the identification of regions where the depth of the sea floor is actively changing. Here we report the results of a bathymetric survey of Monowai submarine volcano in the Tonga-Kermadec Arc, which we mapped twice within 14 days. We found marked differences in bathymetry between the two surveys, including an increase in seafloor depth up to 18.8m and a decrease in depth up to 71.9m. We attribute the depth increase to collapse of the volcano summit region and the decrease to growth of new lava cones and debris flows. Hydroacoustic T-wave data reveal a 5-day-long swarm of seismic events with unusually high amplitude between the surveys, which directly link the depth changes to explosive activity at the volcano. The collapse and growth rates implied by our data are extremely high, compared with measured long-term growth rates of the volcano, demonstrating the pulsating nature of submarine volcanism and highlighting the dynamic nature of the sea floor.
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On 10 October 2011, a submarine volcanic eruption started 2 km south from El Hierro Island (Spain). Since July 2011 a dense multiparametric monitoring network was deployed all over the island by Instituto Geografico Nacional (IGN). By the time the eruption started, almost 10000 earthquakes had been located and the deformation analyses showed a maximum deformation of more than 5 cm. Earthquake migration from the north to the south of the island and acceleration of seismicity are in good correlation with changes in the deformation pattern as well as with some anomalies in geochemical and geomagnetic parameters. An earthquake of local magnitude 4.3 at 12 km depth (8 October 2011) and shallower seismicity a day after, preceded the onset of the eruption. This is the first time that a volcanic eruption is fully monitored in the Canary Islands. Data recorded during this unrest episode at El Hierro will contribute to understand reawakening of volcanic activity in this region and others of similar characteristics. Citation: Lopez, C., et al. (2012), Monitoring the volcanic unrest of El Hierro (Canary Islands) before the onset of the 2011-2012 submarine eruption, Geophys. Res. Lett., 39, L13303, doi:10.1029/2012GL051846.
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We present here a bathymetric map of a new underwater volcano which began its growth on 10 October 2011 to the south of El Hierro Island (Canary Is., Spain). The map scale is 1:25,000 and the map covers 210.9sq. km. In July 2011, the seismic monitoring network of Spanish National Geographic Institute (IGN), began to detect an increase in low-intensity earthquakes around El Hierro Island along with ground deformation. This seismic crisis culminated on 10th October with a submarine eruption 2km south of the small port of La Restinga, and lasted until March 2012 when IGN determined the end of the eruption process. After eight surveys monitoring the morphological and bathymetric evolution during the eruptive phase that ended in March 2012, Spanish Oceanographic Institute and the Hydrographic Institute of the Navy, carried out a survey from the 6th to the 8th of December 2012 to map the bathymetric and morphologic situation after the 2011-2012 eruptive period. The map presented here is based on full seafloor coverage by multibeam swath data echosounder carried out when the submarine volcano was in a quiet phase, using a grid mesh size of 12x12meters.
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Many volcanic hazard factors - such as the likelihood and duration of an eruption, the eruption style, and the probability of its triggering large landslides or caldera collapses - relate to the depth of the magma source. Yet, the magma source depths are commonly poorly known, even in frequently erupting volcanoes such as Hekla in Iceland and Etna in Italy. Here we show how the length-thickness ratios of feeder dykes can be used to estimate the depth to the source magma chamber. Using this method, accurately measured volcanic fissures/feeder-dykes in El Hierro (Canary Islands) indicate a source depth of 11-15 km, which coincides with the main cloud of earthquake foci surrounding the magma chamber associated with the 2011-2012 eruption of El Hierro. The method can be used on widely available GPS and InSAR data to calculate the depths to the source magma chambers of active volcanoes worldwide.
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The geochemistry of pyroclasts sampled from four volcanoes along the Kermadec arc in the SW Pacific is used to investigate the genesis of silicic magmas in a young (< 2 Myr), archetypical intra-oceanic arc setting. Raoul, Macauley and Raoul SW volcanoes in the northern Kermadec arc, and Healy volcano in the southern Kermadec arc have all recently erupted dacitic to rhyolitic crystal-poor pumice. In addition to whole-rock analyses, we present a detailed study of mineral and glass chemistries to highlight the complex structure of the Kermadec magmatic systems. Major and trace element bulk-rock compositions mostly fall into relatively narrow compositional ranges, forming discrete groups by eruption for Raoul, and varying with relative crystal contents for Healy. In contrast, pumices from Macauley cover a wide range of compositions, between 66 and 72 center dot 5 wt % SiO2. At all four volcanoes the trace element patterns of pumice are subparallel to both those of previously erupted basalts and/or whole mafic blebs found both as discrete pyroclasts and as inclusions within pumices. Pb and Sr isotopic compositions have limited ranges within single volcanoes, but vary considerably along the arc, being more radiogenic in the southern volcanoes. Distinctive crystal populations and zonation patterns in pumices, mafic blebs and plutonic xenoliths indicate that many crystals did not grow in the evolved magmas, but are instead mixed from other sources including gabbros and hydrothermally altered tonalites. Such open-system mixing is ubiquitous at the four volcanoes. Oxygen isotope compositions of both phenocrysts (silicic origin) and xenocrysts or antecrysts (mafic origin) are typical for mantle-derived melts. Whole-rock, glass and mineral chemistries are consistent with evolved magmas being generated at each volcano through similar to 70-80% crystal fractionation of a basaltic parent. Our results are not consistent with silicic magma generation via crustal anatexis, as previously suggested for these Kermadec arc volcanoes. Although crystallization is the dominant process driving melt evolution in the Kermadec volcanoes, we show that the magmatic systems are open to contributions from both newly arriving melts and wholly crystalline plutonic bodies. Such processes occur in variable proportions between magma batches, and are largely reflected in small-scale chemical variations between eruption units.
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Pyroclastic deposits from four caldera volcanoes in the Kermadec arc have been sampled from subaerial sections (Raoul and Macauley) and by dredging from the submerged volcano flanks (Macauley, Healy, and the newly discovered Raoul SW). Suites of 16–32 mm sized clasts have been analyzed for density and shape, and larger clasts have been analyzed for major element compositions. Density spectra for subaerial dry-type eruptions on Raoul Island have narrow unimodal distributions peaking at vesicularities of 80–85%, whereas ingress of external water (wet-type eruption) or extended timescales for degassing generate broader distributions, including denser clasts. Submarine-erupted pyroclasts show two different patterns. Healy and Raoul SW dredge samples and Macauley Island subaerial-emplaced samples are dominated by modes at ~80–85%, implying that submarine explosive volcanism at high eruption rates can generate clasts with similar vesicularities to their subaerial counterparts. A minor proportion of Healy and Raoul SW clasts also show a pink oxidation color, suggesting that hot clasts met air despite 0.5 to >1 km of intervening water. In contrast, Macauley dredged samples have a bimodal density spectrum dominated by clasts formed in a submarine-eruptive style that is not highly explosive. Macauley dredged pyroclasts are also the mixed products of multiple eruptions, as shown by pumice major-element chemistry, and the sea-floor deposits reflect complex volcanic and sedimentation histories. The Kermadec calderas are composite features, and wide dispersal of pumice does not require large single eruptions. When coupled with chemical constraints and textural observations, density spectra are useful for interpreting both eruptive style and the diversity of samples collected from the submarine environment.
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Extraordinary video and hydrophone observations of a submarine explosive eruption were made with a remotely operated vehicle in April 2006 at a depth of 550–560 m on NW Rota-1 volcano in the Mariana arc. The observed eruption evolved from effusive to explosive, while the eruption rate increased from near zero to 10–100 m3/h. During the peak in activity, cyclic explosive bursts 2–6 min long were separated by shorter non-eruptive pauses lasting 10–100 s. The size of the ejecta increased with the vigor of the explosions. A portable hydrophone deployed near the vent recorded sounds correlated with the explosive bursts; the highest amplitudes were ∼50 dB higher than ambient noise at frequencies between 10 and 50 Hz. The acoustic data allow us to quantify the durations, amplitudes, and evolution of the eruptive events over time. The low eruption rate, high gas/lava ratio, and rhythmic eruptive behavior at NW Rota-1 are most consistent with a Strombolian eruptive style. We interpret that the eruption was primarily driven by the venting of magmatic gases, which was also the primary source of the sound recorded during the explosive bursts. The rhythmic nature of the bursts can be explained by partial gas segregation in the conduit and upward migration in a transitional regime between bubbly flow and fully developed slug flow. The strongest explosive bursts were accompanied by flashes of red glow and oscillating eruption plumes in the vent, apparently caused by magma-seawater interaction and rapid steam formation and condensation. This is the first time submarine explosive eruptions have been witnessed with simultaneous near-field acoustic recordings.
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We present some of the results of a geophysical and hydroacoustic exploration survey achieved in November-December 2011 in the El Hierro Island (Canarian Archipelago) aboard the RV “Sarmiento de Gamboa”. We used different geophysical techniques like multichannel seismic reflection and wide angle reflection, gravity measurements and parametric sounding, together with high resolution bathymetry mapping. The broad frequency range of the acoustic systems allows imaging the injection of buoyant volcanic plumes driven by gas bubbles exsolved from magma during the long lasting eruption of the submarine volcano.
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West Rota Volcano (WRV) is a recently discovered extinct submarine volcano in the southern Mariana Arc. It is large (25 km diameter base), shallow (up to 300 m below sealevel), and contains a large caldera (6 x 10 km, with up to 1 km relief). The WRV lies near the northern termination of a major NNE-trending normal fault. This and a second, parallel fault just west of the volcano separate uplifted, thick frontal are crust to the east from subsiding, thin back-arc basin crust to the west. The WRV is distinct from other Mariana Arc volcanoes: (i) it consists of a lower, predominantly andesite section overlain by a bimodal rhyolite-basalt layered sequence; (ii) andesitic rocks are locally intensely altered and mineralized; (iii) it has a large caldera; and (iv) WRV is built on a major fault. Submarine felsic calderas are common in the Izu and Kermadec Arcs but are otherwise unknown from the Marianas and other primitive, intraoceanic arcs. Ar-40-Ar-39 dating indicates that andesitic volcanism comprising the lower volcanic section occurred 0.33-0.55 my ago, whereas eruption of the upper rhyolites and basalts occurred 37-51 thousand years ago. Four sequences of rhyolite pyroclastics each are 20-75 m thick, unwelded and show reverse grading, indicating submarine eruption. The youngest unit consists of 1-2 m diameter spheroids of rhyolite pumice, interpreted as magmatic balloons, formed by relatively quiet effusion and inflation of rhyolite into the overlying seawater. Geochemical studies indicate that felsic magmas were generated by anatexis of amphibolite-facies meta-andesites, perhaps in the middle are crust. The presence of a large felsic volcano and caldera in the southern Marianas might indicate interaction of large normal faults with a mid-crustal magma body at depth, providing a way for viscous felsic melts to reach the surface.
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High-resolution bathymetry and seafloor sampling have been used to characterize the 1891 submarine eruption of the Pantelleria volcanic complex. This submarine eruption has been documented mainly by historical reports, describing basaltic scoria bombs floating on the sea surface (i.e., lava balloons). In this study, the 1891 eruptive vent has been identified as a small cone (volume of ~700,000 m3) rising ~90 m from 350 m w.d., and located within a newly discovered submarine volcanic field covering a wide area offshore from the NW coast of Pantelleria; recently, Kelly et al. [2012] confirmed this location by a multibeam and ROV survey. Pyroclasts from the 1891 eruption crop out directly on the seafloor and are fresh scoria clasts (i.e. small bombs, bomb fragments and lapilli) and glass ash-sized grains; both have been characterized in their morphology, textures, and geochemistry. The distinctive vesicularity and crystallization characteristics displayed by the scoriaceous pyroclasts reflect modes of degassing in both syn- and post-eruptive regimes; these characteristics, along with the distribution of deposits suggest for the strongest eruptive phase of the 1891 eruption a style analogous to Hawaiian fountaining. Glass grains from a buoyant plume were dispersed northward from the vent, up to distances of 1.5 km, redirected by the Levantine Intermediate Water. The identification of the 1891 submarine eruptive vent offshore Pantelleria, as well as the features of erupted pyroclasts improve our knowledge of submarine explosive eruptions that occur at shallow-intermediate depths and, among these, of the rare eruptions producing lava balloons.
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[1] Starting in July 2011, anomalous seismicity was observed at El Hierro Island, a young oceanic island volcano. On 12 October 2011, the process led to the beginning of a submarine NW-SE fissural eruption at ~15 km from the initial earthquake loci, indicative of significant lateral magma migration. Here we conduct a multifrequency, multisensor interferometric analysis of spaceborne radar images acquired using three different satellite systems (RADARSAT-2, ENVISAT, and COSMO-SkyMed (Constellation of Small Satellites for Mediterranean Basin Observation)). The data fully captures both the pre-eruptive and coeruptive phases. Elastic modeling of the ground deformation is employed to constrain the dynamics associated with the magmatic activity. This study represents the first geodetically constrained active magmatic plumbing system model for any of the Canary Islands volcanoes, and one of the few examples of submarine volcanic activity to date. Geodetic results reveal two spatially distinct shallow (crustal) magma reservoirs, a deeper central source (9.5 ± 4.0 km), and a shallower magma reservoir at the flank of the southern rift (4.5 ± 2.0 km). The deeper source was recharged, explaining the relatively long basaltic eruption, contributing to the observed island-wide uplift processes, and validating proposed active magma underplating. The shallowest source may be an incipient reservoir that facilitates fractional crystallization as observed at other Canary Islands. Data from this eruption supports a relationship between the depth of the shallow crustal magmatic systems and the long-term magma supply rate and oceanic lithospheric age. Such a relationship implies that a factor controlling the existence/depth of shallow (crustal) magmatic systems in oceanic island volcanoes is the lithosphere thermomechanical behavior.
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El Hierro Island, located at the Canary Islands Archipelago in the Atlantic coast of North Africa, has been rocked by thousands of tremors and earthquakes since July 2011. Finally, an underwater volcanic eruption started 300 m below sea level on October 10, 2011. Since then, regular multidisciplinary monitoring has been carried out in order to quantify the environmental impacts caused by the submarine eruption. Thanks to this natural tracer release, multisensorial satellite imagery obtained from MODIS and MERIS sensors have been processed to monitor the volcano activity and to provide information on the concentration of biological, chemical and physical marine parameters. Specifically, low resolution satellite estimations of optimal diffuse attenuation coefficient (Kd) and chlorophyll-a (Chl-a) concentration under these abnormal conditions have been assessed. These remote sensing data have played a fundamental role during field campaigns guiding the oceanographic vessel to the appropriate sampling areas. In addition, to analyze El Hierro submarine volcano area, WorldView-2 high resolution satellite spectral bands were atmospherically and deglinted processed prior to obtain a high-resolution optimal diffuse attenuation coefficient model. This novel algorithm was developed using a matchup data set with MERIS and MODIS data, in situ transmittances measurements and a seawater radiative transfer model. Multisensor and multitemporal imagery processed from satellite remote sensing sensors have demonstrated to be a powerful tool for monitoring the submarine volcanic activities, such as discolored seawater, floating material and volcanic plume, having shown the capabilities to improve the understanding of submarine volcanic processes.
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Compositionally variable limu o Pele occurs in widely distributed sediments collected during ROV Tiburon dives along the Gorda Ridge axis. The fragments formed deeper than the critical depth of seawater and are unlikely to be formed by supercritical expansion of seawater upon heating in contact with hot lava. Discharge of CO2 through erupting lava is the most likely way to make such bubbles at >298 bars pressure. The distribution and composition of limu o Pele fragments indicate that low-energy strombolian activity is a common, although minor, component of eruptions along mid-ocean ridges. Combined dissolved and exsolved volatile contents of N-MORB from the Gorda Ridge with 12.8-15.6% spherical vesicles are about 0.78% CO2 and 0.18 wt% H2O and exceed estimates of primary CO2 of only 0.07 to 0.095 wt% calculated from whole rock Nb concentrations. This discrepancy suggests that the magmas accumulated an exsolved volatile phase prior to eruption. The evidence that a separated volatile phase drives strombolian eruptions on the seafloor also implies that volatile bubbles coalesce during storage or transport to the surface. The combination of large bubbles in otherwise dense magma suggests nearly complete coalescence of small bubbles and is most consistent with accumulation of the exsolved volatile phase, most likely near the tops of crustal magma chambers, prior to upward transport in shallow conduits to the eruptive vents on the seafloor. A portion of this CO2-rich separated fluid phase is released in brief bursts during eruptions where it becomes part of event plumes.
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Layered volcaniclastic deposits up to 11-m thick crop out along caldera-bounding faults on the summit of Loihi Seamount. The layers include unconsolidated volcanic sands and gravels and volcanic silt-to-mudstone. Fragments in volcaniclastic units include fluidal clasts, bubble-wall fragments (limu-o Pele), highly vesicular to scoriaceous fragments, and Pele's hair formed during pyroclastic eruptions, and lithic fragments coated in lava, coarse-grained basalt fragments, hydrothermally altered basalt and glass fragments, and hydrothermal stockwork fragments of pyrite and barite formed during hydromagmatic (phreatic and phreatomagmatic) eruptions. Pyroclasts of tholeiitic and transitional compositions tend to be dense and probably formed during strombolian activity whereas those of alkalic compositions are highly vesicular to scoriaceous and could have formed during strombolian or Hawaiian eruptions. Scoria fragments from subaerial eruptions of Kilauea, intercalated with locally derived volcaniclastic deposits, are most likely from the ca. 1790 A.D. Keanakakoi eruption, and suggest that the volcaniclastic units on Loihi are younger than a few thousand years. Exposed sections decrease in thickness to the north on the summit, suggesting sources located mainly in the southern part of the summit platform. Based on analogy with Kilauea, we infer that hydrovolcanic eruptions are linked to pit crater formation, as occurred in 1996, and to earlier caldera formation. The bottom of the deepest pit crater is at 1356 m depth, so explosive hydrovolcanic activity can occur at least this deep. Loihi Seamount is an unparalleled natural laboratory to study the eruptive style of submarine basaltic explosive eruptions, deposition of the ejecta, and its redistribution and winnowing by currents.
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Hierro eruption started on 10 October 2011 after an unrest episode that initiated on 17 July 2011. This is the first eruption in the Canary Islands that has been tracked in real time. Although being submarine and not directly observable, the data recorded allowed its reconstruction and to identify its causes and mechanisms. Seismicity, surface deformation, and petrological data indicate that a batch of basanitic magma coming from a reservoir located at a depth of about 25 km below the El Hierro Island was emplaced at shallower depth creating a new reservoir about 10-12 km above, where magma evolved until the initiation of the eruption. The characteristics of seismicity and surface deformation suggest that the necessary space to accumulate magma at this shallower position, which coincides with the crust/mantle boundary beneath El Hierro, was created in about 2 months by elastic deformation and magma-driven fracturing of the crust. After this first intrusion episode, part of the magma started to migrate laterally toward the SE for nearly 20 km, always keeping the same depth and following a path apparently controlled by stress barriers created by tectonic and rheological contrasts in the upper lithosphere. This lateral migration of magma ended with a submarine eruption at about 5 km offshore from the southern corner of El Hierro Island. The total seismic energy released during the unrest episode was of 8.1 × 1011 J, and the total uplift previous to the onset of the eruption was of 40 mm. Combining geological, geophysical, and petrological data and numerical modeling, we propose a volcanological model of the causes and mechanisms of El Hierro eruption that shows how the stress distribution in the crust beneath El Hierro, which was influenced by rheological contrasts, tectonic stresses, and gravitational loading, controlled the movement and eruption of magma. We also discuss the implications of this model in terms of eruption forecast in the Canary Islands.
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High-resolution (1.5 m) mapping from the autonomous underwater vehicle (AUV) D. Allan B. of West Mata Volcano in the northern Lau Basin is used to identify the processes that construct and modify the volcano. The surface consists largely of volcaniclastic debris that forms smooth slopes to the NW and SE, with smaller lava flows forming gently sloping plateaus concentrated along the ENE and WSW rift zones, and more elongate flows radiating from the summit. Two active volcanic vents, Prometheus and Hades, are located ˜50 and ˜150 m WSW of the 1159 m summit, respectively, and are slightly NW of the ridgeline so the most abundant clastic deposits are emplaced on the NW flank. This eruptive activity and the location of vents appears to have been persistent for more than a decade, based on comparison of ship-based bathymetric surveys in 1996 and 2008-2010, which show positive depth changes up to 96 m on the summit and north flank of the volcano. The widespread distribution of clastic deposits downslope from the rift zones, as well as from the current vents, suggests that pyroclastic activity occurs at least as deep as 2200 m. The similar morphology of additional nearby volcanoes suggests that they too have abundant pyroclastic deposits.
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The purpose of this work is to gain insights into the 2011-2012 eruption of El Hierro (Canary Islands) by mapping the evolution of the seismic b-value. The El Hierro seismic sequence offers a rather unique opportunity to investigate the process of reawakening of an oceanic intraplate volcano after a long period of repose. The 2011-2012 eruption is a submarine volcanic event that took place about 2 km off of the southern coast of El Hierro. The eruption was accompanied by an intense seismic swarm and surface manifestations of activity. The earthquake catalogue during the period of unrest includes over 12 000 events, the largest with magnitude 4.6. The seismic sequence can be grouped into three distinct phases, which correspond to well-separated spatial clusters and distinct earthquake regimes. The estimated b-value is of 1.18 ± 0.03, and a magnitude of completeness of 1.3, for the entire catalogue. B is very close to 1.0, which indicates completeness of the earthquake catalogue with only minor departures from the linearity of Gutenberg-Richter frequency-magnitude distribution. The most straightforward interpretation of this result is that the seismic swarm reached its final stages, and no additional large magnitude events should be anticipated, similarly to what one would expect for non-volcanic earthquake sequences. The results, dividing the activity in different phases, illustrate remarkable differences in the estimate of b-value during the early and late stages of the eruption. The early pre-eruptive activity was characterized by a b-value of 2.25. In contrast, the b-value was 1.25 during the eruptive phase. Based on our analyses, and the results of other studies, we propose a scenario that may account for the observations reported in this work. We infer that the earthquakes that occurred in the first phase reflect magma migration from the upper mantle to crustal depths. The area where magma initially intruded into the crust, because of its transitional nature is characterized by high fracturing, thus favours anomalously high b-values. The larger magnitude earthquakes recorded in the second phase may reflect relaxation around the magma reservoir that had fed the eruption and, thus, lower b-values.
Article
We present the first-ever quantitative analysis of pyroclast textures from subaqueous deposits of a Surtseyan emergent volcano. The volcano, Black Point, formed in Mono Lake's Pleistocene precursor, Lake Russell, at ~13,300 ± 500 BP, from an explosive basaltic eruption involving the interaction of shallow lake water (~105 m) with vesiculating magma. The bulk of the edifice comprises unconsolidated tephra and represents submerged stages of eruption. Thin summit deposits formed during a final phase of emergent eruption and produced a group of low tuff rings. Lapillus clasts (16 mm to 32 mm) and fine ash grains (4 Φ, 0.0625 mm) from the subaqueous deposits have textures that reveal a conduit history of bubble nucleation, growth, collapse, intense microlite crystallization, and magma-water interaction. Lapilli vesicularity ranges broadly to high values (up to 89%), while vesicle number densities (5.4 x 102-4.8 x 104 vesicles per mm3) are comparable to those published for Strombolian and Plinian basaltic eruptions (>1 x 104 vesicles per mm3). Vesicle size and volume distributions suggest continuous bubble nucleation, but the suite of data as a whole indicates that a late-stage nucleation event played a significant role in shaping the eruption. Ash grain morphology and surface features indicative of magma-water interactions attest to water's role in fragmentation. Overall the pyroclast textures are consistent with water modification of a rather intense basaltic eruption, which might have been of a violent Strombolian or Plinian style if the eruption had been “dry” and occurred subaerially.
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