Journal of Volcanology and Geothermal Research

Published by Elsevier
Online ISSN: 0377-0273
Publications
Article
West Maui’s rejuvenated-stage Lahaina Volcanics were erupted from four discrete sites. New K–Ar ages indicate two pulses of volcanism, the older about 0.6 Ma and the younger about 0.4 Ma. Compositionally the lava flows are entirely basanitic, but each pulse is diverse. The underlying postshield-stage Honolua Volcanics were emplaced by about 1.2 Ma on the basis of previously published ages. Therefore the duration of volcanic quiescence prior to rejuvenation is about 0.6 m.y. at West Maui, much longer than estimated previously.
 
Article
The 2002–03 flank eruption of Etna was characterized by two months of explosive activity that produced copious ash fallout, constituting a major source of hazard and damage over all eastern Sicily. Most of the tephra were erupted from vents at 2750 and 2800 m elevation on the S flank of the volcano, where different eruptive styles alternated. The dominant style of explosive activity consisted of discrete to pulsing magma jets mounted by wide ash plumes, which we refer to as ash-rich jets and plumes. Similarly, ash-rich explosive activity was also briefly observed during the 2001 flank eruption of Etna, but is otherwise fairly uncommon in the recent history of Etna. Here, we describe the features of the 2002–03 explosive activity and compare it with the 2001 eruption in order to characterize ash-rich jets and plumes and their transition with other eruptive styles, including Strombolian and ash explosions, mainly through chemical, componentry and morphology investigations of erupted ash. Past models explain the transition between different styles of basaltic explosive activity only in terms of flow conditions of gas and liquid. Our findings suggest that the abundant presence of a solid phase (microlites) may also control vent degassing and consequent magma fragmentation and eruptive style. In fact, in contrast with the Strombolian or Hawaiian microlite-poor, fluidal, sideromelane clasts, ash-rich jets and plumes produce crystal-rich tachylite clasts with evidence of brittle fragmentation, suggesting that high groundmass crystallinity of the very top part of the magma column may reduce bubble movement while increasing fragmentation efficiency.
 
Article
A petrological study of the eruptive products of El Reventador allowed us to infer the magmatic processes related to the 2002 and 2004–05 eruptions of this andesitic stratovolcano. On November 3, 2002, El Reventador experienced a highly explosive event, which was followed by emplacement of two lava flows in November–December 2002. Silica contents range from 62 to 58 wt.% SiO2 for the November 3 pyroclastic deposits to 58–56 and 54–53 wt.% SiO2 for the successive lava flows. In November 2004 eruptive activity resumed supplying four new lava flows (56–54 wt.% SiO2) between November 2004 and August 2005.Volatile contents in matrix glasses and glass inclusions from the November 3 pyroclastic deposits allow us to estimate the total amount of SO2 and HCl released into the atmosphere during the paroxysmal phase (i.e. 80 kT of SO2 and 280 kT of HCl). Pre-eruptive pressure-temperature conditions of the magmas range from 300 to 150 MPa and ~ 1000 °C with high water contents (~ 5 wt.%). We propose the existence of an andesitic magma body located at ~ 7–12 km depth that is frequently intruded by more primitive, hydrous magmas from a deeper source. The initial crystallization of amphibole from the hydrous primitive magma seems typical of El Reventador, as well as the historically recurrent and regular periods of eruptive activity lasting several years. This eruptive behaviour coupled with the fractionation and mixing processes inferred from the 2002 and 2004–05 petrologic data suggest that deep magmatic recharge at El Reventador is frequent, and is probably responsible for the high frequency of eruptions.
 
Article
Cathodoluminescence (CL) images of more than 300 zircons from the 1.21 Ma Ongatiti ignimbrite, Taupo Volcanic Zone (TVZ), reveal rare resorbed zircon cores surrounded by euhedral and zoned magmatic rims. U/Pb ages from in situ spot analyses of magmatic zircon cores and rims range from 1.18 to 1.44 Ma with a peak crystallisation age of 1.31±0.03 Ma (n=23, MSWD=1.7). In contrast to zircon ages from the large-magnitude Whakamaru system, age differences between magmatic cores and rims cannot be resolved for the Ongatiti system, and there is no evidence for prolonged crystallisation (>200 kyears), nor inheritance from earlier magma batches at the Mangakino caldera (>1.5 Ma). Four resorbed zircon cores produced 206Pb/238U ages of 119±2, 231±4, 315±7 and 340±6 Ma, with young (∼1.3 Ma) magmatic rims. These ages broadly correspond to the dominant detrital zircon age populations in the local Cretaceous metasedimentary basement rocks, and provide the first direct evidence for significant contributions of these basement rocks to rhyolite petrogenesis in the early TVZ.
 
Article
Quantitative X-ray diffraction analysis of about 80 rhyolite and associated lacustrine rocks has characterized previously unrecognized zeolitic alteration throughout the Valles caldera resurgent dome. The alteration assemblage consists primarily of smectite–clinoptilolite–mordenite–silica, which replaces groundmass and fills voids, especially in the tuffs and lacustrine rocks. Original rock textures are routinely preserved. Mineralization typically extends to depths of only a few tens of meters and resembles shallow “caldera-type zeolitization” as defined by Utada et al. [Utada, M., Shimizu, M., Ito, T., Inoue, A., 1999. Alteration of caldera-forming rocks related to the Sanzugawa volcanotectonic depression, northeast Honshu, Japan — with special reference to “caldera-type zeolitization.” Resource Geol. Spec. Issue No. 20, 129–140]. Geology and 40Ar/39Ar dates limit the period of extensive zeolite growth to roughly the first 30 kyr after the current caldera formed (ca. 1.25 to 1.22 Ma). Zeolitic alteration was promoted by saturation of shallow rocks with alkaline lake water (a mixture of meteoric waters and degassed hydrothermal fluids) and by high thermal gradients caused by cooling of the underlying magma body and earliest post-caldera rhyolite eruptions. Zeolitic alteration of this type is not found in the later volcanic and lacustrine rocks of the caldera moat (≤ 0.8 Ma) suggesting that later lake waters were cooler and less alkaline. The shallow zeolitic alteration does not have characteristics resembling classic, alkaline lake zeolite deposits (no analcime, erionite, or chabazite) nor does it contain zeolites common in high-temperature hydrothermal systems (laumontite or wairakite). Although aerially extensive, the early zeolitic alteration does not form laterally continuous beds and are consequently, not of economic significance.
 
Article
The Gawler Range Volcanics (GRV) of South Australia are an intracontinental, subaerial Large Igneous Province (LIP) formed during supercontinent assembly in the Mesoproterozoic. Like many LIPs, the GRV are intraplate, were erupted over a geologically short time (∼ 2 million years), and are dominated by voluminous lavas. However, the GRV are overwhelmingly dominated by felsic units. The GRV are essentially undeformed and have not been deeply buried so that their original textures are exceptionally well preserved. Furthermore, they are well exposed in very gently northward and eastward dipping sections up to 4 km thick, allowing assessment of the facies architecture and evolution of this felsic volcanic LIP. The evolution of the GRV can be clearly separated into two main stages. Initial eruptions at numerous volcanic centres produced small to moderate volume, geochemically distinct, felsic lavas and lava domes, together with ignimbrites and minor mafic and intermediate lavas, forming a sequence 0.5 to 3 km thick. Volcanic activity in this lower sequence varied from effusive to explosive and was not much different in style or products from Phanerozoic felsic volcanic provinces. However, the second stage produced at least three voluminous felsic units, each of which represents about 1000–3000 km3 of magma. Moreover, the dominance of evenly porphyritic textures and lack of pyroclastic textures (pumice, shards, broken crystal, lithic clasts) in these units suggests that they were erupted effusively and flowed as lavas. Each of these felsic lavas are generally dominated by a single uniform composition, and commonly mingled with a subordinate and compositionally distinct lava.
 
Article
The 1875-1840-Ma Great Bear magmatic zone is a 100-km wide by at least 900-km-long belt of predominantly subgreenschist facies volcanic and plutonic rocks that unconformably overlie and intrude an older sialic basement complex. The basement complex comprises older arc and back-arc rocks metamorphosed and deformed during the Calderian orogeny, 5–15 Ma before the onset of Great Bear magmatism. The Great Bear magmatic zone contains the products of two magmatic episodes, separated temporally by an oblique folding event caused by dextral transpression of the zone: (1) a 1875-1860-Ma pre-folding suite of mainly calc-alkaline rocks ranging continuously in composition from basalt to rhyolite, cut by allied biotite-hornblende-bearing epizonal plutons; and (2) a 1.85-1.84-Ga post-folding suite of discordant, epizonal, biotite syenogranitic plutons, associated dikes, and hornblende-diorites, quartz diorites, and monzodiorites. The pre-folding suite of volcanic and plutonic rocks is interpreted as a continental magmatic arc generated by eastward subduction of oceanic lithosphere. Cessation of arc magmatism and subsequent dextral transpression may have resulted from ridge subduction and resultant change in relative plate motion. Increased heat flux due to ridge subduction coupled with crustal thickening during transpression may have caused crustal melting as evidenced by the late syenogranite suite. Final closure of the western ocean by collision with a substantial continental fragment, now forming the neoautochthonous basement of the northern Canadian Cordillera, is manifested by a major swarm of transcurrent faults found throughout the Great Bear zone and the Wopmay orogen.
 
Article
Examination of the volcanic stratigraphy of deposits younger than 10,000 years on Lipari indicates four principal periods of volcanic activity related to specific centers. The products from each different volcanic center are defined as volcano-stratigraphic unit (VSU). From the oldest these are: the Canneto Dentro, Gabellotto-Fiume Bianco, Forgia Vecchia and Monte Pilato-Rocche Rosse VSUs. The study of textures and dispersal of the deposits permitted the vents to be localized and the recent volcanic history of Lipari to be reconstructed.
 
Merapi as seen from the south. Old Merapi and somma rim (far right) and New Merapi cone (center).  
(continued)
Debris avalanche deposit, Kali Boyong valley. Megaclasts of brecciated lava and stratified pyroclastic material occur in a matrix of brecciated smaller clasts, sand and clay.  
Candi Sambisari, near the Yogyakarta airport, buried by � 40 cm of fine ash and about 6 m of fluvial sediment. Photographed on 23 December 1981, during the late stages of excavation and reconstruction, before new landscaping covered the walls of the excavation. Stratigraphy similar to that of Candi Kedulan (Fig. 4, column E i ); additional stratigraphic description of Sambisari byBudianto Toha (1983).  
Article
Stratigraphy and radiocarbon dating of pyroclastic deposits at Merapi Volcano, Central Java, reveals ∼10,000 years of explosive eruptions. Highlights include:(1) Construction of an Old Merapi stratovolcano to the height of the present cone or slightly higher. Our oldest age for an explosive eruption is 9630±60 14C y B.P.; construction of Old Merapi certainly began earlier.(2) Collapse(s) of Old Merapi that left a somma rim high on its eastern slope and sent one or more debris avalanche(s) down its southern and western flanks. Impoundment of Kali Progo to form an early Lake Borobudur at ∼3400 14C y B.P. hints at a possible early collapse of Merapi. The latest somma-forming collapse occurred ∼1900 14C y B.P. The current cone, New Merapi, began to grow soon thereafter.(3) Several large and many small Buddhist and Hindu temples were constructed in Central Java between 732 and ∼900 A.D. (roughly, 1400–1000 14C y B.P.). Explosive Merapi eruptions occurred before, during and after temple construction. Some temples were destroyed and (or) buried soon after their construction, and we suspect that this destruction contributed to an abrupt shift of power and organized society to East Java in 928 A.D. Other temples sites, though, were occupied by “caretakers” for several centuries longer.(4) A partial collapse of New Merapi occurred <1130±50 14C y B.P. Eruptions ∼700–800 14C y B.P. (12–14th century A.D.) deposited ash on the floors of (still-occupied?) Candi Sambisari and Candi Kedulan. We speculate but cannot prove that these eruptions were triggered by (the same?) partial collapse of New Merapi, and that the eruptions, in turn, ended “caretaker” occupation at Candi Sambisari and Candi Kedulan. A new or raised Lake Borobudur also existed during part or all of the 12–14th centuries, probably impounded by deposits from Merapi.(5) Relatively benign lava-dome extrusion and dome-collapse pyroclastic flows have dominated activity of the 20th century, but explosive eruptions much larger than any of this century have occurred many times during Merapi's history, most recently during the 19th century.Are the relatively small eruptions of the 20th century a new style of open-vent, less hazardous activity that will persist for the foreseeable future? Or, alternatively, are they merely low-level “background” activity that could be interrupted upon relatively short notice by much larger explosive eruptions? The geologic record suggests the latter, which would place several hundred thousand people at risk. We know of no reliable method to forecast when an explosive eruption will interrupt the present interval of low-level activity. This conclusion has important implications for hazard evaluation.
 
Article
Geochemical and textural features of whole-rock samples, phenocrysts, matrix glasses, and silicate melt inclusions from five prehistoric pumiceous tephra units of Augustine volcano, Alaska, were investigated to interpret processes of magma storage and evolution. The bulk-rock compositions of the tephra (designated G, erupted ca. 2100 a.B.P.; I ca. 1700 a.B.P.; H ca. 1400 a.B.P.; and C1 and C2 ca. 1000 a.B.P.) are silicic andesite; they contain rhyolitic matrix glasses and silicate melt inclusions with 74–79 wt.% SiO2. The rocks are comprised of microlite-bearing matrix glass and phenocrysts of plagioclase, orthopyroxene, clinopyroxene, magnesio–hornblende, titanomagnetite, and ilmenite ± Al-rich amphibole with minor to trace apatite and rare sulfides and quartz. The felsic melt inclusions in plagioclase, pyroxenes, and amphibole are variably enriched in volatile components and contain 1.6–8.0 wt.% H2O, 2100–5400 ppm Cl, < 40–1330 ppm CO2, and 30–390 ppm S. Constraints from Fe–Ti oxides imply that magma evolution occurred at 796 ± 6 °C to 896 ± 8 °C and log ƒO2 of NNO + 2.2 to + 2.6. This is consistent with conditions recorded for 1976, 1986, and 2006 eruptive materials and implies that magmatic and eruptive processes have varied little during the past 2100 years.
 
Article
A detailed chemical investigation of volcanic glass fragments from volcaniclastic strata (6 tephras, 1 volcanic debris flow, 12 volcanic turbidites) of ODP Leg 107, Site 650, sedimentary sequence, leads to a varied pattern in terms of both provenance and age constraints.The six analyzed tephra strata indicate a provenance from at least three different volcanic provinces: Aeolian, Campanian, and Sicilian Channel (Pantelleria Island). The older tephra strata (021, 018, 012) have a large amount of “orogenic” rhyodacite/rhyolite deposits that may be attributed to the Aeolian province, although no subaerial coeval volcanic activity of similar composition has so far been documented in the Aeolian Arc. Tephra 007 is related to the Pantelleria Island activity and, particularly, to an ignimbrite episode dated circa 130 ka. Tephra strata 005 and 003, have a clear Campanian provenance, and are correlated with analogous tephra layers, observed in the Tyrrhenian and Ionian seas, dated circa 107 and 60 ka respectively.In the oldest portion of the sequence (from 1.3 to 0.13 Ma), the volcaniclastic sediments were only derived from the Aeolian domain whereas in the latest 130 ka, the Campanian influx becomes much more predominant. Therefore, a general K-enrichment trend is observed in the temporal sequence of all the analyzed samples (almost 700 point analyses) which may be related both to a variation in the source area and to the specific Pleistocene magmatic evolution of the peri-Tyrrhenian volcanic provinces.
 
Article
We recently reported (Boudon et al., 1984) on an eruption similar to that of May 18, 1980 at Mount St. Helens, that took place about 3100 years ago at la Soufrière, Guadeloupe. During the course of detailed geological mapping of the deposits of this event, older debris flow and blast deposits were recognized in the northern sector of the mapped area. Uncarbonized wood fragments in the debris flow have yielded ages ca. 11,500 y. B.P. The deposits extend from an amphitheater crater westward to the caribbean shore about 10 km downslope from the volcano. The deposits and crater structure suggest that they are the result of catastrophic flank failure like the event 3100 years ago. Unlike the latter activity, however, no magmatic component is found in the deposits.
 
Article
Basaltic volcanism is most typically thought to produce effusion of lava, with the most explosive manifestations ranging from mild Strombolian activity to more energetic fire fountain eruptions. However, some basaltic eruptions are now recognized as extremely violent, i.e., generating widespread phreatomagmatic, subplinian and Plinian fall deposits. We focus here on the influence of conduit processes, especially partial open-system degassing, in triggering abrupt changes in style and intensity that occurred during two examples of basaltic Plinian volcanism. We use the 1886 eruption of Tarawera, New Zealand, the youngest known basaltic Plinian eruption and the only one for which there are detailed written eyewitness accounts, and the well-documented 122 BC eruption of Mount Etna, Italy, and present new grain size and vesicularity data from the proximal deposits. These data show that even during extremely powerful basaltic eruptions, conduit processes play a critical role in modifying the form of the eruptions. Even with very high discharge, and presumably ascent, rates, partial open-system behaviour of basaltic melts becomes a critical factor that leads to development of domains of largely stagnant and outgassed melt that restricts the effective radius of the conduit. The exact path taken in the waning stages of the eruptions varied, in response to factors which included conduit geometry, efficiency and extent of outgassing and availability of ground water, but a relatively abrupt cessation to sustained high-intensity discharge was an inevitable consequence of the degassing processes.
 
Article
The Etna 122 BC basaltic eruption had two Plinian phases, each preceded and followed by weak phreatic and phreatomagmatic activity. This study infers changing eruption dynamics from density, grain size, and microtextural data from the erupted pyroclasts. The Plinian clasts show no evidence for quenching by external water; instead, all clasts are microvesicular and have high bubble number densities relative to the products of weaker basaltic explosive eruptions, suggesting that the 122 BC magma underwent coupled degassing linked to rapid ascent and decompression. This coupled degassing was probably enhanced by crystallization of abundant microlites, which increased the magma's effective viscosity during conduit ascent.Detailed measurements of vesicles and microlites show wide variations in number densities, size distributions, and shapes among clasts collected over narrow stratigraphic intervals. For such a diversity of clasts to be expelled together, portions of melt with contrasting ascent and degassing histories must have arrived at the fragmentation surface at essentially the same time. We suggest that a parabolic velocity profile across the conduit ensured that magma near the conduit walls ascended more slowly than magma along the axis, leading to a longer residence time and more advanced degrees of outgassing and crystallization in the marginal magma. In our model, accumulation of this outgassed, viscous magma along conduit walls reduced the effective radius of the shallow conduit and led to blockages that ended the Plinian phases.
 
Article
Asososca maar is located at the western outskirts of Managua, Nicaragua, in the central part of the active, N–S trending and right-lateral Nejapa–Miraflores fault that marks an offset of the Middle America Volcanic Arc. It constitutes one of the ∼ 21 vents aligned along the fault, between the Chiltepe Volcanic Complex to the North and Ticomo vents to the South.Asososca consists of an East–West elongated crater filled by a lake, which is currently used for supplying part of Managua with drinking water (10% of the capital city demand). The crater excavated the previous topography, allowing the observation of a detailed Holocene stratigraphic record that should be taken into account for future hazard analyses. We present a geological map together with the detailed stratigraphy exposed inside and around Asososca crater aided by radiocarbon dating of paleosols. The pre-existing volcanic sequence excavated by Asososca is younger than 12,730 + 255/− 250 yr BP and is capped by the phreato–plinian Masaya Tuff (< 2000 yr BP). The pyroclastic deposits produced by Asososca maar (Asososca Tephra, in this work) display an asymmetric distribution around the crater and overlie the Masaya Tuff. The bulk of the Asososca Tephra is made of several bedsets consisting of massive to crudely stratified beds of blocks and lapilli at the base, and superimposed thinly stratified ash and lapilli beds with dune structures and impact sags. Coarser size-fractions (>− 2ϕ) are dominated by accidental clasts, including basaltic to basaltic–andesitic, olivine-bearing scoriae lapilli, porphyritic and hypocrystalline andesite blocks and lapilli, altered pumice lapilli and ash, and ignimbrite fragments. Juvenile fragments were only identified in size-fractions smaller than − 1ϕ in proportions lower than 25%, and consist of black moss-like, fused-shape, and poorly vesiculated, fresh glass fragments of basaltic composition (SiO2 ∼ 48%). The Asososca Tephra is interpreted as due to the emplacement of several pyroclastic surges originated by phreatomagmatic eruptions from Asososca crater as suggested by impact sags geometry and dune-crest migration structures. According to radiocarbon dating, these deposits were emplaced at 1245 + 125/− 120 yr BP. The stratigraphic position of the Asososca Tephra and the well-preserved morphology of the crater indicate that Asososca is the youngest vent along the Nejapa–Miraflores fault. Explosive eruptions might therefore occur again along this fault at the western outskirts of Managua. Such kind of activity, together with the strong seismicity associated to the active fault represents a serious hazard to urban infrastructure and a population of ca. 1.3 million inhabitants.
 
Article
Geostationary Operational Environmental Satellite (GOES) Imager and Sounder data were evaluated to determine the potential effects of volcanic ash detection without the use of a 12 μm infrared (IR) band, on GOES-M (12) through Q (a period of at least 10 years). Principal component analysis (PCA) images with and without 12 μm IR data were compared subjectively for six weak to moderate eruptions using pattern recognition techniques, and objectively by determining a false detection rate parameter. GOES Sounder data were also evaluated in a few instances to assess any potential contributions from the new 13.3 μm Imager band.Results indicated that, during periods of daylight, there was little apparent difference in the quality of IR detection without the 12 μm IR, likely due to a maximum in solar reflectance of silicate ash in a shortwave IR (SWIR) band centered near 3.9 μm. At night when SWIR reflectance diminished, the ash detection capability appeared to be significantly worse, evidenced by increased ambiguity between volcanic ash and meteorological clouds or surface features. The possible effects of this degradation on aviation operations are discussed. The new 13.3 μm IR band on GOES has the capability to help distinguish ash from cirrus clouds, but not from low level clouds consisting of water droplets.Multi-spectral data from higher resolution polar orbiting satellites may also be used to supplement analyses from lower resolution GOES for long-lived ash cloud events. The Advanced Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments appear to be the best options in accomplishing this, with additional satellite missions becoming available later in the decade. In summary, it will still be possible to observe and track significant volcanic ash clouds in the GOES-M through Q era (2003–2012) without the benefit of 12 μm IR data, but with some degradation that will be most significant at night.
 
Article
A complex sequence of pyroclastic flows and surges erupted by Nevado del Ruiz volcano on 13 November 1985 interacted with snow and ice on the summit ice cap to trigger catastrophic lahars (volcanic debris flows), which killed more than 23,000 people living at or beyond the base of the volcano. The rapid transfer of heat from the hot eruptive products to about 10 km² of the snowpack, combined with seismic shaking, produced large volumes of meltwater that flowed downslope, liquefied some of the new volcanic deposits, and generated avalanches of saturated snow, ice and rock debris within minutes of the 21:08 (local time) eruption. About 2 × 10⁷ m³ of water was discharged into the upper reaches of the Molinos, Nereidas, Guali, Azufrado and Lagunillas valleys, where rapid entrainment of valley-fill sediment transformed the dilute flows and avalanches to debris flows.
 
Article
The virtue of studying the chronology of an event is the insight it affords as to how man views and responds to the forces of nature. This chronology reflects the fumbling nature of mankind (as only appreciated in hindsight) when faced by an impending event of uncertain nature, in this case in a developing nation, but it might have happened anywhere. It is hoped that we as volcanologists might improve our response to such crises knowing how they have evolved previously.
 
Article
The lava dome collapse of 12–13 July 2003 was the largest of the Soufrière Hills Volcano eruption thus far (1995–2005) and the largest recorded in historical times from any volcano; 210 million m3 of dome material collapsed over 18 h and formed large pyroclastic flows, which reached the sea. The evolution of the collapse can be interpreted with reference to the complex structure of the lava dome, which comprised discrete spines and shear lobes and an apron of talus. Progressive slumping of talus for 10 h at the beginning of the collapse generated low-volume pyroclastic flows. It undermined the massive part of the lava dome and eventually prompted catastrophic failure. From 02:00 to 04:40 13 July 2003 large pyroclastic flows were generated; these reached their largest magnitude at 03:35, when the volume flux of material lost from the lava dome probably approached 16 million m3 over two minutes. The high flux of pyroclastic flows into the sea caused a tsunami and a hydrovolcanic explosion with an associated pyroclastic surge, which flowed inland. A vulcanian explosion occurred during or immediately after the largest pyroclastic flows at 03:35 13 July and four further explosions occurred at progressively longer intervals during 13–15 July 2003. The dome collapse lasted approximately 18 h, but 170 of the total 210 million m3 was removed in only 2.6 h during the most intense stage of the collapse.
 
Article
Tungurahua is a frequently active and hazardous volcano of the Ecuadorian Andes that has experienced pyroclastic flow-forming eruption in 1773, 1886, 1916–18 and 2006–08. Earlier eruptions in Late Pre-Hispanic and Early Colonial times have remained poorly known and are debated in the literature. To reconstruct the eruptive chronology in that time interval we examine relevant historical narratives recently found in Sevilla, Spain, and Rome, Italy, and we combine stratigraphic field constraints with 22 new radiocarbon age determinations. Results show that pyroclastic flow-forming eruptions and tephra falls took place repeatedly since ~ 700 ¹⁴C yr BP, when the Tungurahua region was already populated. Radiocarbon ages averaging around 625 yr BP reveal a period of notable eruptive activity in the 14th century (Late Integration cultural period). The associated andesitic eruptions produced ash and scoria falls of regional extent and left scoria flow deposits on the western flanks of the edifice. The fact that Tungurahua was known by the Puruhás Indians as a volcano at the time of the Spanish Conquest in 1533 perhaps refers to these eruptions. A group of ages ranging from 380 to 270 yr BP is attributed to younger periods of activity that also predates the 1773 event, and calibration results yield eruption dates from late 15th to late 17th centuries (i.e. Inca and Early Colonial Periods). The historical narratives mention an Early Colonial eruption between the Spanish Conquest and the end of the 16th century, followed by a distinct eruptive period in the 1640s. The descriptions are vague but point to destructive eruptions likely accompanied by pyroclastic flows. The dated tephras consist of andesitic scoria flow deposits and the contemporaneous fallout layers occur to the west.
 
Article
Water and molecular carbon dioxide concentrations, the speciation of water, and hydrogen isotope ratios have been measured in a series of obsidians from the ca. 1340 A.D. eruption of the Mono Craters chain in central California. Obsidians were collected from domes and pyroclastic deposits. The maximum water contents of the obsidian clasts from the pyroclastic deposits generally declined as the eruption proceeded, but at most stratigraphic levels the obsidians display a range of water contents. The water contents of the obsidians from domes are lower than those from the pyroclastic beds. The D/H ratio varies monotonically with the total water content. The proportions of water dissolved in these glasses as hydroxyl groups and as molecules of water vary smoothly with total water content. Dissolved molecular carbon dioxide contents are low, but roughly proportional to total water content.
 
Article
The explosive rhyolitic eruption of Öræfajökull volcano, Iceland, in AD 1362 is described and interpreted based on the sequence of pyroclastic fall and flow deposits at 10 proximal locations around the south side of the volcano. Öræfajökull is an ice-clad stratovolcano in south central Iceland which has an ice-filled caldera (4–5 km diameter) of uncertain origin. The main phase of the eruption took place over a few days in June and proceeded in three main phases that produced widely dispersed fallout deposits and a pyroclastic flow deposit. An initial phase of phreatomagmatic eruptive activity produced a volumetrically minor, coarse ash fall deposit (unit A) with a bi-lobate dispersal. This was followed by a second phreatomagmatic, possibly phreatoplinian, phase that deposited more fine ash beds (unit B), dispersed to the SSE. Phases A and B were followed by an intense, climactic Plinian phase that lasted ∼ 8–12 h and produced unit C, a coarse-lapilli, pumice-clast-dominated fall deposit in the proximal region. At the end of Plinian activity, pyroclastic flows formed a poorly-sorted deposit, unit D, presently of very limited thickness and exposed distribution. Much of Eastern Iceland is covered with a very fine distal ash layer, dispersed to the NE. This was probably deposited from an umbrella cloud and is the distal representation of the Plinian fallout. A total bulk fall deposit volume of ∼ 2.3 km3 is calculated (∼ 1.2 km3 DRE). Pyroclastic flow deposit volumes have been crudely estimated to be < 0.1 km3. Maximum clast size data interpreted by 1-D models suggests an eruption column ∼ 30 km high and mass discharge rates of ∼ 108 kg s− 1. Ash fall may have taken place from heights around 15 km, above the local tropopause (∼ 10 km), with coarser clasts dispersed below that under a different wind regime. Analyses of glass inclusions and matrix glasses suggest that the syn-eruptive SO2 release was only ∼ 1 Mt. This result is supported by published Greenland ice-core acidity peak data that also suggest very minor sulphate deposition and thus SO2 release. The small sulphur release reflects the low sulphur solubility in the 1362 rhyolitic melt. The low tropopause over Iceland and the 30-km-high eruption column certainly led to stratospheric injection of gas and ash but little sulphate aerosol was generated. Moreover, pre-eruptive and degassed halogen concentrations (Cl, F) indicate that these volatiles were not efficiently released during the eruption. Besides the local pyroclastic flow (and related lahar) hazard, the impact of the Öræfajökull 1362 eruption was perhaps restricted to widespread ash fall across Eastern Iceland and parts of northern Europe.
 
Article
The ice-covered Öræfajökull stratovolcano is composed mostly of subglacial pillow lava and hyaloclastite tuff, ranging from basalt to rhyolite. A large devastating plinian eruption in 1362 AD produced 10 km3 (2 km3 DRE) rhyolitic ash and pumice from a vent within the summit caldera, with fallout mainly towards ESE. The ejected rhyolite magma with 0.5–1% crystals of oligoclase, fayalite, hedenbergite, ilmenite and magnetite was remarkably homogenous throughout the eruption.A 1.8 m thick tephra section on the SE flank of the volcano has 14 recognizable units. The tephra is dominated by fine-grained vesicular glass with bubble wall thickness of 1–5 μm. The high and even vesiculation of the glass indicates fast magma ascent and explains the extreme mechanical fragmentation within the eruptive column. The grain-size distribution indicates time-variable intensity of the plinian eruption with three evenly spaced phases of maximum fragmentation. An initial vent-clearing explosion produced phreatomagmatic debris with up to 35% lithic fragments. The low abundance (< 3%) of lithic fragments during the subsequent eruption indicates that the conduit and vent remained stable. The tephra fallout deposit is characterized by upwards increasing pumice dimensions and occasional bomb-like pumice blocks, indicating less mechanical fragmentation during contraction and lowering of the plinian column.A conservative estimate of 20–40 km3 for the total volume of the magma reservoir is based on the erupted volume of highly differentiated and homogeneous rhyolite. The 365-year period between 1362 and a minor benmoreitic eruption in 1727, and the absence of currently detectable magma reservoirs in the crust below Öræfajökull show that differentiated crustal magma chambers feeding large plinian eruptions can be established and disappear on a 100–500 year timescale.
 
Article
Six volcanologists and three tourists were killed in the crater of Galeras Volcano, Colombia, when it erupted without warning. The scientists were attending the United Nations International Decade for Natural Disaster Reduction Workshop which had been convened to improve monitoring, research and disaster mitigation at Galeras, at the time the most active and one of the most hazardous volcanoes in South America. Information on the events surrounding the eruption was obtained by sending a questionnaire to twelve scientists who had been inside the caldera at the time of the eruption or who had assisted in the search and rescue operation. The autopsy reports on the five corpses, and the few pieces of equipment and clothing retrieved from the crater area, were also studied. The main causes of death and injury were the forces at the eruptive vent and the bombardment by hot rocks ejected in the first 15 min of the eruption, ranging from blocks over 1 m in size to pea-sized lapilli which fell last. Some conclusions can be drawn for the future safety of volcanologists working in craters at high altitude. Hard hats would protect against concussion from blows to the head during escape from the danger area, and a lightweight, heat-resistant and water-repellent coverall would limit the skin burns and the risk of clothing being ignited from contact with incandescent, falling ejecta. The coverall could also be life saving by protecting immobilised casualties from hypothermia due to the rain and wind whilst waiting to be rescued, especially as the volcanic activity, cloud cover or nightfall could curtail rescue efforts. Work in hazardous craters should be strictly limited to essential tasks and periods of good visibility, and a climbing team should leave the area at least four hours before nightfall in case rescue is needed. Tourists must be warned against visiting active crater areas.
 
Article
In the Seventh cruise of R/V “Professor Logatchev” anomalies of natural electric field (EF), Eh and pS were discovered using a towed instrument package (RIFT) at 14°45′N on the MAR (Logatchev hydrothermal field). The anomalous zone (AZ) is situated close (10–35 m) to two low-temperature venting areas of degrading sulphides and a black smoker (Irina-Microsmoke) forming a distinct buoyant plume. Over or close to the main area of high-temperature venting situated to the south-east from the AZ, no EF or Eh anomalies were observed. According to the results of Mir dives the highly mineralised solutions from smoking craters at the main mound mostly form non-buoyant plumes (reverse-plumes). The buoyant plume structure shows the differentiation of the electrical and Eh fields within the plume. Maxima of the EF, Eh and EH2S anomalies were revealed in the lower part (∼15 m) of the plume. The negative redox potential plume coupled with a sulphide anomaly is more localized in comparison with the EF. This observation indicates a distinct change in the composition of buoyant plume water, which may be due to the formation and fallout of early formed Fe sulphide particles soon after venting.
 
Article
The Cretaceous Fort à la Corne (FALC) kimberlite field was active over a time span of ~ 20 Ma with contemporaneous terrestrial (Mannville Group) to marine (Lower Colorado Group) background sedimentation. Steep-sided pipes, craters and positive landform volcanoes such as scoria or tuff cones are thought to have formed during that period.The 147 Kimberlite is located in the SE section of the field's main cluster and is part of the large (~ 377.5 ha) Orion North volcanic complex. Based on logging of 25 drill cores, the morphology of the country rock/kimberlite interface suggests excavation of a complex crater field down to the upper portion of the Mannville Group sedimentary deposits. At least two types of volcaniclastic deposits are identified: a main kimberlite unit that is typically characterized by crustal xenolith-poor (1–2%), normal graded beds possibly deposited as turbidites in a subaqueous environment, originating from the nearby 148 tephra cone and infilling the adjacent 147 crater, and a second unit, located on the NE margin of the 147 Kimberlite, that represents a thick (~ 60 m) sequence of large (up to 22 m) sedimentary country rock blocks located at least 60 m above their original stratigraphic position.We suggest the following time sequence of events: Crater excavation as a consequence of a shallow magma fragmentation level within the uppermost country rock sequences, together with several closely spaced eruptive centres initially formed the complex, intercalated crater field. Subsequently, ongoing eruptions with a fragmentation level above the country rock produced the lithic fragment poor main infill of the 148 Kimberlite. Resedimentation from the outer flanks of the 148 tephra cone resulted in the deposition of turbidites in the 147 area. A consolidation phase solidified the lowermost portion of the main infill in 147. A subsequent explosion(s) occurred within the Mannville Group in the 147 area, ejecting large blocks of sedimentary country rocks and fracturing the overlying volcaniclastic main infill. Finally, blocks of the main infill tilted and possibly slumped into the subsidence structure developed above the emptied explosion chamber of 147.The different volcanic deposits reflect a change in eruption style and fragmentation level from highly explosive to spatter activity with little fragmentation potential. Cap rocks to build up the volatile overpressure necessary to blast the craters were not present at the time of emplacement. No diatremes were observed in the study area. Assuming that the magma properties remained constant over time, the change in eruption style has to be attributed to external factors, such as water access to the rising magma. The volcanic behaviour of the kimberlite magma appears to be comparable to that of other magmatic systems, both in eruptive style and production rate. No evidence was found for a high, possibly Plinian production rate or dispersion.
 
Article
Experimental studies have been performed on the thermal properties of an olivine-melilitite in solid and partly molten states in a temperature range between 288 and 1470 K. Densities (ρ), heat capacities (Cp), and thermal diffusivities (α) were measured by dilatometry, heat flux differential scanning calorimetry, and laser flash analysis and used to calculate the thermal conductivities (λ). In the solid state (288 to 1220 K) ρ decreased from 3091 to 2993 kg/m3, Cp increased from 0.76 to 1.41 J g−1 K−1, α varied between 5.1 and 8.7 10−3 cm2/s, and λ varied between 1.75 and 2.54 W m−1 K−1. In the partly molten state (1300 to 1470 K) Cp increased from 1.56 to 1.70 J g−1 K−1, α decreased from 2.5 to 2.2 10−3 cm2/s, and λ decreased from 1.16 to 1.09 W m−1 K−1. The importance of these data for the physical description of processes acting during explosive volcanic eruptions is discussed.
 
Article
New 40Ar/39Ar and 14C ages have been found for the Albano multiple maar pyroclastic units and underlying paleosols to document the most recent explosive activity in the Colli Albani Volcanic District (CAVD) near Rome, Italy, consisting of seven eruptions (Albano 1 = oldest). Both dating methodologies have been applied on several proximal units and on four mid-distal fall/surge deposits, the latter correlated, according to two current different views, to either the Albano or the Campi di Annibale hydromagmatic center. The 40Ar/39Ar ages on leucite phenocrysts from the mid-distal units yielded ages of ca. 72 ka, 73 ka, 41 ka and 36 ka BP, which are indistinguishable from the previously determined 40Ar/39Ar ages of the proximal Albano units 1, 2, 5 and 7, thus confirming their stratigraphic correspondence.Twenty-one 14C ages of the paleosols beneath Albano units 3, 5, 6 and 7 were found for samples collected from 13 proximal and distal sections, some of which were the same sections sampled for 40Ar/39Ar measurements. The 14C ages were found to be stratigraphically inconsistent and highly scattered, and were systematically younger than the 40Ar/39Ar ages, ranging from 35 ka to 3 ka. Considering the significant consistence of the 40Ar/39Ar chronological framework, we interpret the scattered and contradictory 14C ages to be the result of a variable contamination of the paleosols by younger organic carbon deriving from the superficial soil horizons.These results suggest that multiple isotopic systems anchored to a robust stratigraphic framework may need to be employed to determine accurately the geochronology of the CAVD as well as other volcanic districts.
 
Article
The Ochre Pumice (OP) Plinian fallout was produced by Popocatépetl volcano in central Mexico, during a major Plinian eruption that occurred 4965 ± 65 ¹⁴C yr BP (3700 BC). The OP is part of the Ochre Pumice Sequence (OPS), that consists of surge, fall, and pyroclastic flow deposits. The OP Plinian fallout shows a bimodal grain size distribution with poor to moderate sorting that improves progressively towards the upper beds. The juvenile component is mainly pumice (>83 wt.%), whereas the accidental components consist of igneous, sedimentary, and metamorphic clasts from the walls of the magma chamber and/or conduit. The vesicularity of the pumice decreases from bottom to top of the stratigraphic sequence while the crystal and glass contents increase. This suggests increasing magma degassing prior and during the eruption. The chemical composition of the pumice varies insignificantly; at the base it is less evolved (SiO2 = 61 wt.%) and it becomes slightly more silicic towards the top (SiO2 = 63 wt.%). Pumice clasts have a crystallinity index that ranges between 10 and 25 vol.% and display a seriate texture with phenocrysts of euhedral plagioclase (Pl) + clinopyroxene (Cpx) + orthopyroxene (Opx) + olivine (Ol) ± oxide (Ox) ± apatite (Ap).
 
Article
Caldera collapse changes volcanic eruption behavior and mass flux Many models of caldera formation predict that those changes in eruption dynamics result from changes in conduit and vent structure during and after collapse Unfortunately no previous studies have quantified or described how conduits change in response to caldera collapse Changes in pumice texture coincident with caldera formation during the 1800 C-14 yr BP KS, eruption of Ksudach Volcano Kamchatka provide an opportunity to constrain magma decompression rates before and after collapse and thus estimate changes in conduit geometry Prior to caldera collapse only white rhyodacite pumice with few microlites and elongate vesicles were erupted Following collapse only gray rhyodacite pumice containing abundant microlites and round vesicles were erupted Bulk compositions phase assemblages phenocryst compositions and geothermometry of the two pumice types are indistinguishable thus the two pumice types originated from the same magma Geothermobarometry and phase equilibria experiments indicate that magma was stored at 100-125 MPa and 895 +/- 5 C pnor to eruption Decompression experiments suggest microlite textures observed in the white pumice require decompression rates of> 0 01 MPa s(-1) whereas the textures of gray pumice require decompression at similar to 0 0025 MPa s(-1) Balancing those decompression rates with eruptive mass fluxes requires conduit size to have increased by a factor of similar to 4 during caldera collapse Slower ascent through a broader conduit following collapse is also consistent with the change from highly stretched vesicles present in white pumice and to round vesicles in gray pumice Numerical modeling suggests that the mass flux and low decompression rates during the Gray phase can be accommodated by the post collapse conduit developing a very broad base and narrow upper region (c) 2010 Elsevier BV All rights reserved
 
Article
The 7600 14C-year-old Kurile Lake caldera-forming eruption (KO) in southern Kamchatka, Russia, produced a 7-km-wide caldera now mostly filled by the Kurile Lake. The KO eruption has a conservatively estimated tephra volume of 140–170 km3 making it the largest Holocene eruption in the Kurile–Kamchatka volcanic arc and ranking it among the Earth's largest Holocene explosive eruptions. The eruptive sequence consists of three main units: (I) initial phreatoplinian deposits; (II) plinian fall deposits, and (III) a voluminous and extensive ignimbrite sheet and accompanying surge beds and co-ignimbrite fallout. The KO fall tephra was dispersed over an area of >3 million km2, mostly in a northwest direction. It is a valuable stratigraphic marker for southern Kamchatka, the Sea of Okhotsk, and a large part of the Asia mainland, where it has been identified as a ∼6 to 0.1 cm thick layer in terrestrial and lake sediments, 1000–1700 km from source. The ignimbrite, which constitutes a significant volume of the KO deposits, extends to the Sea of Okhotsk and the Pacific Ocean on either side of the peninsula, a distance of over 50 km from source. Fine co-ignimbrite ash was likely formed when the ignimbrite entered the sea and could account for the wide dispersal of the KO fall unit. Individual pumice clasts from the fall and surge deposits range from dacite to rhyolite, whereas pumice and scoria clasts in the ignimbrite range from basaltic andesite to rhyolite. Ignimbrite exposed west and south of the caldera is dominantly rhyolite, whereas north, east and southeast of the caldera it has a strong vertical compositional zonation from rhyolite at the base to basaltic andesite in the middle, and back to rhyolite at the top. Following the KO eruption, Iliinsky volcano formed within the northeastern part of the caldera producing basalt to dacite lavas and pyroclastic rocks compositionally related to the KO erupted products. Other post-caldera features include several extrusive domes, which form islands in Kurile Lake, submerged cinder cones and the huge silicic extrusive massif of Dikii Greben' volcano.
 
Article
The eruptive history of Kuju volcano on Kyushu, Japan, during the past 15,000 years has been determined by tephrochronology and 14C dating. Kuju volcano comprises isolated lava domes and cones of hornblende andesite together with aprons of pyroclastic-flow deposits on its flanks. Kuju volcano produced tephras at roughly 1000-yr intervals during the past 5000 years and 70% of the domes and cones have formed during the past 15,000 years. The youngest magmatic activity of Kuju volcano was the 1.6 km3 andesite eruption about 1600 years ago which emplaced a lava dome and block-and-ash flow. Kuju volcano shows a nearly constant long-term eruption rate (0.7–0.4 km3 for 1000 years) during the past 15,000 years. This rate is within the range of estimated average eruption rates of late Quaternary volcanoes in the Japanese Arc, but is about one order of magnitude higher than the eruption rate of Unzen volcano. Kuju volcano has been in phreatic eruption since October 1995. The late Quaternary history of Kuju indicates that it poses a significant volcanic hazard, primarily due to block-and-ash flows from collapsing lava domes.
 
Article
Two holes were drilled to depths of 150 m and 70 m from the surface about 200 m from the active crater of Aso Volcano and quartz thermometers were installed in the holes at depth intervals of 30 m and 35 m, respectively. This series of observations is one of the first measurements of temperature at depth so close to an active crater. The ground temperature at a depth of 2 m had an annual variation with a range of about 10°C, as expected, clearly corresponding to the atmospheric temperature variation, but delayed by about 1 month. Temperatures measured at depths from 30 m to 70 m had very small annual temperature variations. The range of temperature at 30 m depth was about 0.04°C. The temperature at a depth of 60 m, however, was particularly stable, probably because at this depth the hole is in the middle of a massive lava flow. At depths of 70 m or more, small (less than 0.2°C) annual temperature variations were again observed. These variations are probably due to the effects of surface water descending to these levels through cracks and fissures. At 120 m depth, the average temperature is about 17.5°C, over 5°C above the surface average temperature, and the annual temperature variation has a range of about 2°C, out of phase with the atmospheric changes. This is probably due to the interaction of rainfall descending from the surface with convecting hotter fluids from below. The temperature gradient below 100 m depth is very high, with the average temperature at a depth of 150 m being about 31°C. The temperature variations at this depth are dominated by long-period variations, with a steady decline after a peak in November–December 1989, overlain by a rather irregular seasonal variation, with a range of about 0.5°C. October 1989 was the time of most active volcanic activity, with Strombolian eruptions depositing ash to a distance of 50 km from the crater, accompanied by very high amplitude volcanic tremor. So the temperature changes at 150 m seem to be mainly the result of volcanic activity. The maximum temperature at this depth occurred 1 or 2 months after the peak of observed volcanic activity. So it is likely that the temperature variations show a delayed influence of the level of volcanic activity. These results show that in the unconsolidated materials often found by active volcanic craters, the effects of seasonal atmospheric variations are carried to substantial depths by groundwater flows, so that at Aso Volcano, only at the maximum depth of 150 m are the temperature variations clearly dominated by the level of volcanic activity.
 
Article
Volcán de Colima (103°37′W, 19°30′45″N) has had significant eruptive activity over the last five centuries, leading to its designation as the most active volcano in Mexico. This activity has manifested itself through a variety of eruptive processes, culminating in explosive events rated VEI 4. Much of our knowledge of the earlier volcanic events is from non-scientific writings and as such is only an interpretation of sometimes ambiguous information. The most recent eruptions of the 19th and 20th centuries are, however, well documented, scientifically allowing for more detailed understanding of these events.
 
Article
The last magmatic eruption of Soufrière of Guadeloupe dated at 1530 A.D. (Soufrière eruption) is characterized by an onset with a partial flank-collapse and emplacement of a debris-avalanche that was followed by a sub-plinian VEI 2–3 explosive short-lived eruption (Phase-1) with a column that reached a height between 9 and 12 km producing about 3.9 × 106 m3 DRE (16.3 × 106 m3 bulk) of juvenile products. The column recurrently collapsed generating scoriaceous pyroclastic flows in radiating valleys up to a distance of 5–6 km with a maximum interpolated bulk deposit volume of 11.7 × 106 m3 (5 × 106 m3 DRE). We have used HAZMAP, a numerical simple first-order model of tephra dispersal [Macedonio, G., Costa, A., Longo, A., 2005. A computer model for volcanic ash fallout and assessment of subsequent hazard. Comput. Geosci. 31, 837–845] to reconstruct to a first approximation the potential dispersal of tephra and associated tephra mass loadings generated by the sub-plinian Phase 1 of the 1530 A.D. eruption. We have tested our model on a deterministic average dry season wind profile that best-fits the available data as well as on a set of randomly selected wind profiles over a 5 year interval that allows the elaboration of probabilistic maps for the exceedance of specific tephra mass load thresholds. Results show that in the hypothesis of a future 1530 A.D. scenario, populated areas to a distance of 3–4 km west–southwest of the vent could be subjected to a static load pressure between 2 and 10 kPa in case of wet tephra, susceptible to cause variable degrees of roof damage. Our results provide volcanological input parameters for scenario and event-tree definition, for assessing volcanic risks and evaluating their impact in case of a future sub-plinian eruption which could affect up to 70 000 people in southern Basse-Terre island and the region. They also provide a framework to aid decision-making concerning land management and development. A sub-plinian eruption is the most likely magmatic scenario in case of a future eruption of this volcano which has shown, since 1992, increasing signs of low-energy seismic, thermal, and acid degassing unrest without significant deformation.
 
Article
The record of felt earthquakes around Naples Bay in southern Italy is probably complete since the mid-15th century. According to this record, intense earthquake swarms originating beneath Campi Flegrei, an explosive caldera located along the north coast of Naples Bay, have occurred only twice: (1) before the only historical eruption in Campi Flegrei in 1538; and (2) from mid-1983 to December 1984. Earthquake activity during the earlier period, which began at least a few years, and possibly as many as 30 years, before the 1538 eruption, damaged many buildings in the city of Pozzuoli, located near the center of Campi Flegrei. Minor seismic activity, which consisted of only a few felt earthquakes, occurred from 1970 to 1971. The second period of intense earthquake swarms lasted from mid-1983 to 1984, again damaging many buildings in Pozzuoli. Two periods of uplift along the shoreline within Campi Flegrei have also been noted since the mid-15th century: (1) during the few decades before the 1538 eruption; and (2) as two distinct episodes since 1968. Uplift of a few meters probably occurred a few decades before the 1538 eruption; uplift of as much as 3.0 m has occurred in Pozzuoli since 1968.These similarities strongly suggest that, for the first time in 440 years, the same process that caused intense local earthquake swarms and uplift in the early 1500's and led to an eruption in 1538, has again occurred beneath Campi Flegrei. Though no major seismicity or uplift has occurred since December 1984, because of the large amount of extensional strain accumulated during the past two decades, if a third episode of seismicity and rapid uplift occurs, it may lead to an eruption within several months after the resumption of activity.
 
Article
The Azores archipelago occupies a lateral branch of the Mid-Atlantic Ridge near the triple junction of three large tectonic plates, the North American, the Eurasian and the African plates. The tectonic setting is even more complex because of the existence of the Azores hotspot and hotspot–ridge interaction. However, the hotspot origin at depth as a plume and its lateral extent are controversial subjects. High-resolution tomographic models, through the mapping of low-velocity and anisotropy anomalies, can provide an important hint to evaluate the depth and lateral extent of plumes when they exist. Therefore, we present a review of the Azores deep seismic structure as inferred from recent global and regional studies. The mapping of S-wave negative velocity anomalies in various models reveals a negative anomaly beneath the Azores confined within the upper 250–300 km. Considering the time evolution of a plume, this low-velocity anomaly might be the signature of a present-day dying plume, which created the Azores plateau 20 Ma ago. However, tomographic investigations have reached the limit of resolution provided by the global and regional seismic coverage available today. Only a long-term deployment (several years) of several broadband seismic stations in the Archipelago and on the surrounding seafloor will provide the increased resolution to better characterize plume geometry.
 
Article
In a recently published manuscript [Guidoboni, E., Boschi, E., 2006. Vesuvius before the 1631 eruption, EOS, 87(40), 417 and 423]; [Guidoboni, E. (Ed.), 2006. Pirro Ligorio, Libro di diversi terremoti (1571), volume 28, codex Ja II 15, Archivio di Stato di Torino, Edizione Nazionale delle Opere di Pirro Ligorio, Roma, De Luca, 261 pp], Pirro Ligorio gives a detailed description of the phenomena occurring in the crater area of Vesuvius volcano, in 1570–1571 and previous years. Here, these phenomena are interpreted as the first clearly documented signals of unrest of this volcanic system caused by the shallow emplacement of a magma batch and leading to the 1631 eruption. Our interpretation is mainly based on the present understanding of the fluid geochemistry of magmatic-hydrothermal systems. In this way, it is possible to conclude that: (i) incandescent rocks were present at the surface, with temperatures > 500 °C approximately and (ii) either a magmatic-dominated or a magmatic-hydrothermal-type of conceptual geochemical model applies to Vesuvius in 1570–1571 and preceding years.The Ligorio's picture represents the first clear evidence that the magma involved in the 1631 eruption was present under the volcano more than sixty years before the eruption. Moreover, its emplacement produced a series of phenomena which were clearly observed although not understood at that time. A similar phenomenological pattern should be easily detected and correctly interpreted at present or in the future.
 
Article
Mt. Etna in Sicily (Italy) is one of the best monitored basaltic volcanoes in the world due to the frequent eruptions from its summit and flanks. Routine monitoring carried out by Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania, for surveillance purposes permits following the evolution of volcanic events. In this paper, a description of the ash monitoring system as occurred during the August–December 2006 summit eruption at the Southeast Crater (SEC) is shown. This eruption was characterized by lava flow effusions and vigorous Strombolian activity. Eighteen paroxysmal episodes occurred up to the end of November, forming weak ash plumes accompanied by moderate tephra fallout over Etna's slopes. During these events, we applied a multidisciplinary approach to promptly monitor the paroxysmal activity and the associated tephra fallout, through analysis from seismic tremor and observation from live-cameras, sampling operations, mapping and analysis of the deposit. During the most significant episodes, we carried out textural and grain-size analysis on tephra samples and evaluated the total grain-size deposit and the erupted volume, while numerical simulations of tephra dispersal allowed better understanding eruptive dynamics. An example of this methodology is applied to the 16 November episode, during which seismic tremor furnished important constraints on the chronology. This paroxysmal eruption produced light fallout on the north-east sector of the volcano for about ten hours and a number of debris-avalanches over the slopes of the SEC cone. The erupted deposit was composed for the most part of lithic components and characterized by a total-size distribution centered on 2.2 Φ, while its total mass was evaluated 7 × 106 kg. On the whole, such integrated studies help to obtain information on magma fragmentation and eruptive mechanisms, to characterize the explosive styles shown by Etna and finally, to better approach the monitoring of imminent eruptions.
 
Article
On October 16, 1955, at 10:45 a.m. (local time), after three days of intense rain (140 mm) that was twice the monthly average precipitation, a devastating flood surge formed a volcaniclastic debris flow on the eastern slopes of Nevado de Colima Volcano. Nearly simultaneous flood surges formed in the Arroyo Seco, Los Platanos, and Dos Volcanes ravines that coalesced with the larger flow in the Atenquique ravine. At each confluence with a tributary, the flow was diluted. The texture and structure of the preserved 1955 deposits near high water marks indicate that the downstream flow was mainly in the lower range of debris flow concentration (60% sediment concentration by weight). Downstream the tributaries, the flood encountered a ∼ 0.06 × 106 m3 water reservoir that failed, significantly increasing the surge volume. Additional entrained sediment also increased the flow volume. Downstream, the flood wave reached the town of Atenquique as an 8–9 m catastrophic wave causing the death of more than 23 people, the partial destruction of the town, and losses of ∼ 13,000,000 pesos (∼ 1 million US dollars today) to a paper mill and company facilities. According to eyewitness accounts the flood wave had a peak discharge that lasted ca. 10 to 15 minutes at Atenquique. Deposits at the site and the high-water marks observed from photographs of the town's church indicate that sediment concentration was ca. 60 wt.%. The flood continued for about 1 km to its junction with the Tuxpan River where it was diluted by mixing with normal flood flow. The deposits covered an area of ∼ 1.2 km2 and had a minimum volume of ∼ 3.2 × 106 m3. The main deposit consists of a single unit, averaging 4 m in thickness, with weak textural variations that suggest surging within the flood wave. The deposit is heterolithologic and consists of boulders set in a matrix of sand-size sediment, with polymodal or bimodal distributions and normal grading varying with distance from source. The town of Atenquique has been reconstructed largely within the area inundated by the 1955 flood wave, thus creating the conditions for a future disaster. A rainfall-intensity warning system and an educational program for inhabitants are strategies to mitigate this risk.
 
Article
Uniform maps of circumpacific convergence zones constructed by the same projection and scale reveal three main associations between intermediate depth seismicity and contemporaneous volcanic activity. First, in areas of high seismicity there are usually few active volcanoes. Second, in areas of low to moderate seismicity aseismic domains can often be recognized beneath the active volcanoes. Third, adjacent to the aseismic domains there are nests of seismicity located a few 10's of km away from the active volcanoes usually in the direction of the trench. More than 40 such nests are identified in the circumpacific and Indonesian arcs. These three associations may be related to melting near the upper surface of the underthrust slab. A fluid phase, either silicate melt or a hydrous fluid released by dehydration of the slab, would lower the strength of the slab and create aseismic zones beneath the active volcanoes. Nests of earthquakes can develop by stress concentration at the margins of the weak zones. Areas not volcanically active have little or no fluid phase and a higher level of seismicity.
 
Article
The oxygen isotope composition of calcite veins and vugs in basalts from a drill site on the island of Sao Miguel show near-equilibration with fresh water at observed temperatures only at a depth of 600–700 m. This is interpreted to mean that the greatest flow of hot water may be occurring in this depth interval.
 
Article
The largest historical eruption (VEI 6) in the Andes began on February 19 and continued until March 6 or 15, AD 1600 at Huaynaputina, a dacitic stratovolcano located on a high volcanic plateau in south Peru. Tephra falls, pyroclastic flows and surges disrupted life in an area of ∼4900 km2 around the volcano, and ash-fall was reported 200–500 km away in south Peru, west Bolivia, and north Chile. The aftermath of the large-scale eruption was severe and protracted for the people and colonial economy of south Peru. By linking up the series of events inferred from Spanish chronicles with the lithofacies and composition of the tephra (bulk volume 11.4–12.1 km3, dense rock equivalent (DRE) 4.6–4.95 km3), we distinguish five eruptive phases. (1) During the plinian phase, a sustained plinian column 27–35 km high on February 19–20 delivered a dacitic pumice fall of ∼3.1 km3 DRE volume. The plinian pumice formed a widespread lobe of ∼95 000 km2 within the 1-cm isopach; strong winds carried fine ash >500 km to the west, and west-northwest into the Pacific Ocean. The computed volumetric eruption rate was in the range of 5.4–6.6×104 to 1×105 m3/s and the mass eruption rate 1.3–1.6×108 kg/s. The onset and high discharge of the sustained plinian eruption was fueled by the disruption of an active hydrothermal system enclosed in the pre-AD 1600 amphitheater. The plinian column shut off as the vent was choked when the fragmentation focus deepened to beneath the weathered bedrock, >1600 m below the vent area. (2) During the second phase, a dwindling column sent ash-falls on proximal to medial areas and possibly pyroclastic surges on proximal slopes. (3) During the third ignimbrite-forming phase with interspersed hydromagmatic events, pyroclastic flows 1.5–2 km3 in volume were channeled into the Rı́o Tambo canyon and tributaries. The flows with interbedded base-surge deposits in proximal tributaries probably produced vigorous columns over high, rugged relief around the Huaynaputina plateau. Winds winnowing the columns dispersed a widespread co-ignimbrite ash, probably mixed with co-plinian ash, over an area of ∼265 000 km2. (4) During the fourth phase, an unusual crystal ash-fall was deposited when the residual magma with a crystal content as high as 80% was tapped near the end of the eruption. (5) During the fifth phase, ash-flows produced surge deposits and lag-fall breccias near vent, small-volume ash-flow deposits in proximal catchments, and a thin ash-fall layer in medial to distal areas. The proximal deposits were also produced by diluted flows able to surmount ridges 1000 m high as far as 15 km east from the vent. The ignimbritic and hydromagmatic phases greatly modified the ≤400-m-diameter plinian vent. Tapping of the crystal-rich magma and ash flows towards the end of the eruption led to the formation of two youthful vents in domes. Geochemistry and mineralogy of the plinian and post-plinian units point to an unusual zoned magma sequence. The ignimbrite-forming phase tapped a magma batch richer in silica than the less differentiated plinian magma. The crystal-rich magma of unit 4 was fed by ‘crystal mush’ in a layered magma reservoir and (or) from two magma reservoirs at distinct depths. The geochemical and mineralogical trend throughout the eruption, and preliminary measurements of geobarometers suggest a complex model linking a shallow (6–7 km) magma reservoir to a deeper (∼15 km) reservoir. The total DRE volume (4.6–4.95 km3) of erupted tephra did not lead to caldera collapse. Ring fractures cutting multiple vents are associated with a dyke swarm intruding the weathered volcanic bedrock. This suggests the onset of a funnel-type or piecemeal collapse.
 
Article
While major explosive eruptions of anhydrite-bearing silicic magma have been known to influence earth's climate through the release of sulfate aerosols, quantifying the atmospheric loading of these eruptions remains an elusive goal. The eruptions that have had the most impact on climate typically erupted oxidized and anhydrite-bearing magma. The > 9 km3 of dacite magma erupted during the VEI 6 eruption of Huaynaputina (Peru) in 1600 is oxidized (ƒO2 NNO + 1.4) but does not contain magmatic anhydrite. Yet it is thought to have a significant impact on climate. Herein we follow the approach that S contents in magmatic apatite grains can be used to provide an independent estimate of the magnitude and source of the atmospheric sulfur loading. Apatite SO3 concentrations of 0.09 to 0.17 wt.% yield an estimate of ~0.8 Mt of total erupted sulfur derived from degassing of the melt. This is considerably less than the stratospheric sulfur input of 16–55 Mt of S estimated from ice core data and requires that much of the stratospheric sulfur load from Huaynaputina was from other sources than the melt. While a fluid phase in equilibrium with the melt is a likely source, a significant contribution from combustion of sulfur from a fossil hydrothermal system excavated during eruption is evidenced by comminuted hydrothermal debris and lithics that make up to 2.5 to 10 wt.% of erupted material. We calculate that up to 22% of the total S budget of the eruption could reasonably be attributed to combusted hydrothermal sulfur. Thus, three sources of sulfur: the melt, a coexisting fluid phase, and external hydrothermal sulfur, appear to explain the atmospheric input from this eruption. Our work confirms that unraveling the S budget of large silicic eruptions is extremely complex and requires a multi-faceted approach based on a detailed understanding of the eruption.
 
Article
The 1630 AD eruption on the island of São Miguel in the Azores took place from a vent in the southern part of the 7 × 5 km caldera of Furnas volcano. Precursory seismic activity occurred at least 8 hours before the eruption began and was felt over 30 km away. This seismic activity caused extensive damage destroying almost all buildings within a 10 km radius and probably triggered landslides on the southern coast.The explosive activity lasted ~ 3 days and ashfall occurred as far as 550 km away. Published models yield a volume of 0.65 km3 (DRE) for the explosive products. Throughout the course of the eruption more than six discrete airfall lapilli layers, each of subplinian magnitude, were generated by magmatic explosive activity. Dispersal directions initially to the west and finally northeast of the vent indicate a change in wind direction during the eruption. Isopleth maps suggest column heights of up to 14 km and wind speeds varying between < 5 and 30 m/s when compared to published plume models. On steep southern slopes (> 20°) at least one lapilli layer (L2) shows pinch and swell thickness variations, and rounded pumice clasts suggesting instant remobilisation as grain flows.Ash-rich layers with abundant accretionary lapilli and vesicular textures are interbedded with the lapilli layers and represent the deposits formed by phreatomagmatic phases that punctuated the purely magmatic activity. The ash-rich layers show lateral thickness variations, as well as cross-bedding and sand-wave structures suggesting that low-concentration, turbulent flows (surges) deposited material on topographic highs. These pyroclastic surges were probably responsible for the 80 people reported burned to death 4 km southwest of the vent. High-particle-concentration, non-turbulent pyroclastic flows were channelled down steep valleys to the southern coast contemporaneously with the low-concentration surges. The massive flow deposits (~ 2 m thick) pass laterally into thin, stratified, accretionary lapilli-rich ashes (~ 20 cm thick) over 100 m horizontally. Lateral transition between thick massive and thin stratified facies occurs on a flat surface unconfined by topography indicating that the flows had an effective yield strength.Effusive activity followed the explosive activity building a trachytic lava dome with a volume of ~20 × 106 m3 (0.02 km3 DRE) within the confines of the tuff/pumice cone formed during the explosive phase. Historic records suggest that dome building occurred over a period of at least two months. Calculated durations for eruptive phases and the fluctuation in eruptive style suggest that the eruption was pulsatory which may have been controlled by variable magma supply to the surface.
 
Article
The 1631 Vesuvius eruption is one of its best known and most studied of its type. However, the historical approach performed within the framework of the Exploris project highlighted new evidence from previously unused or unknown historical sources. These consist of three treatises that were contemporary to the event; although written in Latin, they have been fully translated and analysed. To guarantee systematic use and open access to the large amount of information they contain, they have been provided as a small database. These treatises have provided new information on phenomena that preceded and accompanied the eruption of 1631, making possible the formation of a complex chronological profile, starting from around 6 months before the eruption. The anthropic impact is also outlined. The method applied has produced a chronology of “cold data”, which are not interpreted from the volcanological standpoint, but only derived directly from the analysed history and sequence of the texts. The analysis of the three treatises has not, however, solved all of the problems connected with the detailed knowledge of the event in 1631. Indeed, problems of two kinds persist: a) linguistic correspondence between the volcanological terms of today and those used in the texts; b) the lack of precision of the measures indicated. Here, the main results obtained from this analysis method are presented, along with a discussion of their limitations and some new perspectives.
 
Palaeomagnetic results from Vesuvius
Article
The 1631 eruption of Mount Vesuvius was the most destructive episode in the recent volcanic history of Vesuvius and the last in which large pyroclastic flows were emitted. The controversy about whether lava flows were also generated in this eruption, as sustained in the mapping by Le Hon (1866) and by the interpretation by some authors (Burri et al., 1975; Rolandi et al., 1991) of eyewitness accounts, is important not only for a better understanding of the eruption but also for the implications in the prediction of volcanic hazards of this volcano, set in an overpopulated area with more than 3 million people potentially at risk.
 
Article
Silicate-melt inclusions from lavas and pyroclastics from a selected suite of pre-A.D. 1631 interplinian Mt. Somma–Vesuvius lavas and scoria have been experimentally homogenized and studied by microthermometry, electron microprobe (EMPA) and secondary-ion mass spectrometry (SIMS) to examine pre-eruptive volatile content and magma evolution. The melt inclusions have a bubble about 0.06% their volume, uncommonly contain non-condensable gas but do not contain any dense fluid phases. Clinopyroxene-hosted inclusions yield homogenization temperatures (Th) from 1170 to 1260°C, most between 1220 and 1240°C; plagioclase-hosted inclusions have Th from 1210 to 1230°C; these values are typical for the Vesuvius environment. The dominant factor controlling major element variability in the inclusions is clinopyroxene fractionation; MgO varies from 5 to 3 wt%, SiO2 varies from 60 to 48 wt%, total alkalis vary from 15 to 4 wt%, and CaO varies from 13 to 5 wt%. H2O varies from 2.7 to 0.6 wt% and is decoupled from incompatible element evolution suggesting vapor saturation during trapping. Chlorine and F vary from 1.0 wt% to 0 and 0.63 to 0 wt%, respectively. Bulk rock and limited matrix glass analyses show that the lavas lost about half of their F and Cl content except for the A.D. 472–1631 lava which contains similar Cl abundances as the bulk rock. SO3 varies from 0.5 to 0 wt% and compared with matrix glass and bulk rock demonstrate that the lavas have lost essentially all sulfur. The samples can be classified into three age groups, >25,000 yr B.P., 25,000–17,000 yr B.P., and A.D. 472–1631. There is a systematic increase in some components, e.g., total alkalis, SO3, Cl, Li, B, and Sr with the youth of the sample and a decrease in others, e.g., Zr and Y. However, on average these samples seem less evolved than later A.D. 1631–1944 lavas.
 
Article
The eruption of 1631 A.D. was the most violent and destructive event in the recent history of Vesuvius. More than fifty primary documents, written in either Italian or Latin, were critically examined, with preference given to the authors who eyewitnessed volcanic phenomena. The eruption started at 7 a.m. on December 16 with the formation of an eruptive column and was followed by block and lapilli fallout east and northeast of the volcano until 6 p.m. of the same day. At 10 a.m. on December 17, several nuées ardentes were observed to issue from the central crater, rapidly descending the flanks of the cone and devastating the villages at the foot of Vesuvius. In the night between the 16th and 17th and on the afternoon of the 17th, extensive lahars and floods, resulting from rainstorms, struck the radial valleys of the volcano as well as the plain north and northeast.
 
Article
During the period 1631–1944, Vesuvius was in persistent activity with alternating mild strombolian explosions, quiet effusive eruptions, and violent strombolian eruptions. The major difference between the predominant style of activity and the violent strombolian stages is the effusion rate. The lava effusion rate during major eruptions was in the range 20–100 m3/s, higher than during mild activity and quiet effusion (0.1–1 m3/s). The products erupted during the mild activity and major paroxysms have different degree of crystallization. Highly porphyritic lava flows are slowly erupted during years-long period of mild activity. This activity is fed by a magma accumulating at shallow depth within the volcanic edifice. Conversely, during the major paroxysms, a fast lava flow precedes the eruption of a volatile-rich, crystal-poor magma. We show that the more energetic eruptions are fed by episodic, multiple arrival of discrete batches of magma rising faster and not degassing during the ascent. The rapidly ascending magma pushes up the liquid residing in the shallow reservoir and eventually reaches the surface with its full complement of volatiles, producing kilometer-high lava fountains. Rapid drainage of the shallow reservoir occasionally caused small caldera collapses. The major eruptions act to unplug the upper part of the feeding system, erupting the cooling and crystallizing magma. This pattern of activity lasted for 313 y, but with a progressive decrease in the number of more energetic eruptions. As a consequence, a cooling plug blocked the volcano until it eventually prevented the eruption of new magma. The yearly probability of having at least one violent strombolian eruption has decreased from 0.12 to 0.10 from 1944 to 2007, but episodic seismic crises since 1979 may be indicative of new episodic intrusions of magma batches.
 
Top-cited authors
Giovanni Orsi
  • University of Naples Federico II
Colin Wilson
  • Victoria University of Wellington
Sandro de Vita
  • National Institute of Geophysics and Volcanology
William I Rose
  • Michigan Technological University
Clive Oppenheimer
  • University of Cambridge