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Soil mineralogy and its effect on chemical properties of volcanic soils located in Mount Ceremai has not been studied thoroughly. The objective of the study was to assess soil mineralogy and chemical properties of volcanic soils derived from different types and ages as an integrated strategic consideration to establish nutrient management. Field research and laboratory analysis were carried out on four soil profiles derived from different parent materials, namely young lava (KM-01), young pyroclastic fall (KM-02), old lava (KM-03), and old pyroclastic fall (KM-04). Results showed that KM-04 soil had limited nutrient reserved mineral (NRM), while KM-01, KM-02, and, unexpectedly, KM-03 soil still contained high NRM. There were no apatite and K-bearing mineral found in all soils, so regular P and K fertilization were recommended. Clay composition in the surface layer of KM-01 soil was dominated by amorphous minerals, while other soils contained amorphous mineral, gibbsite, and halloysite. Although all soils contained NRM such as labradorite, augite, and hypersthene, all soils had low exchangeable cations. P retention is a serious problem for all soils, especially KM-03 which has the highest amount of allophane. Therefore, nutrient management should be focused on accelerating NRM weathering, increasing soil CEC, and improving P fertilization efficiency.

Lamongan volcano is one of the unique volcanoes in the Sunda Volcano. This volcano has side eruption centers or on the slopes of the volcano. The morphology of parasitic eruptions in this volcanoes complex includes maars and boccas. There are about 64 parasitic eruption centers consisting of 37 volcanic cones (bocca) and 27 ranu (maar). The purpose of this research is to study the characteristics of lithology and petrogenesis of this volcano complex, especially in Ranu Pakis and surrounding areas. The analytical method used is to do geological mapping and petrographic analysis. The lithology found in this research area consists of magmatic and phreatomagmatic eruption deposits. Genetically this lithology includes pyroclastic flow, pyroclastic fall (scoria fall and phreatomagmatic scoria fall/accretionary lapili), tuff (phreatic) and basaltic lava. In some pyroclastic deposits, especially in maar there are fragments of accretionary lapilli, while in bocca there are basaltic lavas. Other fragments present in pyroclastic deposits are basalt scoria blocks and bombs embedded in the groundmass of volcanic ash. The results of petrographic analysis indicate that the volcanic rocks in the study area are calc alkaline affinity consisting of pyroxene andesite, basalt and pyroxene basalt lava. The pyroxene basalt lava is composed by plagioclase, clinopyroxene and little olivine embedded in the volcanic glass. Lavas are structured scoria and textured porphyritic, intersertal, trachytic, aphyric and pilotaxitic. Trachytic texture is found in the basalt fragments of pyroxene from the pyroclastic fall deposits in Ranu Pakis and Ranu Wurung. While pyroxene andesite lavas composed by plagioclase, clinopyroxene embedded in the volcanic glass. Lavas are structured scoria and textured porphyritic, intergranular, pilotaxitic and aphyric.

Background The 2018 Hokkaido Eastern Iburi earthquake (Mj 6.7, Mw 6.6), occurred on the 6th of September 2018 and triggered thousands of landslides in pyroclastic fall deposits. The triggered landslides caused destructive damages to the structures and resulted in serious causalities. Hundreds of earthquakes persisted after the mainshock and the Iburi region is of high possibility to suffer major earthquakes in the future. An effective method to assess the seismic slope stability is of great importance for the disaster prevention and mitigation in the Iburi region. Results Based on the isopachs of different pyroclastic fall deposits mantled in the study area, GIS was employed to process the input soil layers and construct the 3D domain. By applying different horizontal pseudo-acceleration coefficients in the Scoops3D program, the factor-of-safety maps of eight cases were obtained. After validating by the coseismic landslide inventory, the performance of the computed results was evaluated. Conclusions A horizontal pseudo-acceleration coefficient between 1/2 and 2/3 of PHGA is suitable for seismic slope stability assessment in pyroclastic fall deposits. The catastrophic Tomisato landslide and Yoshinoya landslide were correctly predicted. Scoops3D proves to be an effective and efficient method for guiding disaster mitigation and management.

The tephra layers known with eruption ages play an important role in an investigation of tsunami history and archaeology in addition to volcanic history in Hokkaido, Japan. We investigated the event and tephra layers of the Late Holocene in the Pacific coast of western Hokkaido, where the stratigraphy of the Late Holocene has not been clarified. Surveys in coastal peatlands, mostly undisturbed deposits, have allowed for the discovery of thin tephra layers. The newly discovered tephra layers at the unexplored site were used to describe facies, observation under a polarization microscope, refractive index measurement of volcanic glasses, and chemical analysis, and correlated with the reported widespread tephras. We conducted wide-area field surveys and succeeded in revealing a wider distribution of tephra layers than previously known. The distribution of volcanic ash in the coastal area will contribute to the investigations of future volcanic and coastal hazards.

The Vesuvio National Park, established in June 1995, is the green area closest to Napoli megacity, which suffers the absence of urban green spaces and could hence offer to citizens the opportunity to enjoy healthy places in a peculiar environment as the landscape of an active volcano. We here propose two trails with several stops, named the Ancient Railway Track and the Valle dell’Inferno. They start from San Sebastiano al Vesuvio and Ottaviano towns, located on two opposite sides of northern Somma-Vesuvio area, and are both directed towards the Vesuvio crater. Along the trails, the visitors can enjoy several volcanic forms and products (the Somma caldera rim, dykes, lava domes, ropy lava flows, pyroclastic fall deposits) together with historical remains, such as the Cook Railway track, and the typical botanic association, the Mediterranean bush. The stops were illustrated with panels describing in detail both geological and landscape features with pictures and simple text boxes, clear and engaging for a wide set of excursionists of different ages and cultural backgrounds. The quality of the two trails was assessed through a quantitative evaluation of the single stops considering the different typologies of expected visitors. The project of promotion and fruition of green spaces in an active volcanic area here proposed contributes to encourage healthy living and raise well-being and could represent one of the means to achieve a better level of resilience for a society exposed to high volcanic risk.

The Las Colinas landslide, which was triggered by the 13 January 2001, Mw = 7.7 El Salvador earthquake, was highly destructive. The local site is composed of pyroclastic flows, brown cinders, soft pyroclastic fall deposits and a thin palaeosol and is characterised by steep slopes. The extremely high ground motions recorded near the landslide location are assumed to be both produced by site effects and responsible for the landslide. To characterise the ground motion amplifications due to site effects in terms of the variation in geometrical and geological settings, parametric studies were conducted with a linear elastic slope model, which was vertically subjected to the scattering SV wave of the Gabor wavelet. The results show that a maximum amplification is obtained when the model slope angle is approximately 30° (similar to the actual slope angle), and the maximum amplification is located approximately 20 m behind the crest, where the actual movement was initiated. Additionally, a slope with a height of approximately 160 m enhances ground motion amplification. The subsurface geology is found to induce a greater effect on amplification than that of the slope topography. In particular, a soft pyroclastic fall deposit is observed to contribute most of the ground motion amplification. According to the numerical results, it can be concluded that the local site conditions induced extremely high ground motions that then contributed to the slope movement. Although the thin, buried layer of palaeosol did not cause any significant amplification, its weak cohesion enhanced movement.

For the first time; ground magnetic survey was performed which data were inverted by means of total horizontal derivative; horizontal gradient analytic signal; and hyperbolic tilt angle techniques to identify subsurface volcanic structures around Isparta city (South-Western Turkey). Here; Golcuk volcanism took place at the apex of the Isparta Angle at the intersection of the Lycian and Antalya nappes. It initiated between 4.0—4.7 my ago mainly as lava extrusions and ended with phreatoplinian eruptions during Quaternary time. The study area is covered by authochtonous and allochthonous units that are intruded by Pliocene and Quaternary Golcuk volcanics and also overlain by pyroclastic fall and flow deposits. The boundaries were revealed for the buried volcanic structure from the edge detection methods. The geometry of the trachytic dome southwestern of the Golcuk Lake and its downward continuation were studied by 2D modelling with the control of the power spectrum depth results applied to the focused anomaly. The azimuthally-averaged logarithmic power spectra plot indicates that the downward continuation of source depth of the trachytic dome reaches up to 850 m. The forward inversion results indicate that the horizontal size of the model for this trachytic dome is 1250 m beneath the surface while it’s surface extension is only about 400 m.

International audience; Turbulent volcanic jets are produced by highly-energetic explosive eruptions and may form buoyant plumes that rise many tens of kilometres into the atmosphere to form umbrella clouds or collapse to generate ground-hugging pyroclastic flows. Ash injected into the atmosphere can be transported for many hundreds of kilometres with the potential to affect climate, disrupt global air travel and cause respiratory health problems. Pyroclastic flows, by contrast, are potentially catastrophic to populations and infrastructure close to the volcano. Key to which of these two behaviours will occur is the extent to which the mechanical entrainment and mixing of ambient air into the jet by large (entraining) eddies forming the jet edge changes the density of the air–ash mixture: low entrainment rates lead to pyroclastic flows and high entrainment rates give rise to buoyant plumes. Recent experiments on particle-laden (multi-phase) volcanic jets from flared and straight-sided circular openings suggest that the likelihood for buoyant plumes will depend strongly on the shape and internal geometry of the vent region. This newly recognised sensitivity of the fate of volcanic jets to the structure of the vent is a consequence of a complex dynamic coupling between the jet and entrained solid particles, an effect that has generally been overlooked in previous studies. Building on this work, here we use an extensive series of experiments on multi-phase turbulent jets from analogue linear fissures and annular ring fractures to explore whether the restrictive vent geometry during cataclysmic caldera-forming (CCF) eruptions will ultimately lead a relatively greater frequency of pyroclastic flows than eruptions from circular vents on stratovolcanoes. Our results, understood through scaling analyses and a one-dimensional theoretical model, show that entrainment is enhanced where particle motions contribute angular momentum to entraining eddies. However, because the size of the entraining eddies scales approximately with vent width, the extent of entrainment is reduced as the vent width becomes small in comparison to its length. Consequently, our work shows that for specified mass eruption rates, the high length-to-width ratio vents typical of CCF events are more likely to produce pyroclastic flows. We suggest that the enigmatic trend in the geological record for the largest CCF eruptions to produce pyroclastic flows is an expected consequence of their being erupted through continuous or piece-wise continuous caldera ring fractures.

1 ABSTRACT. Gutâi Mts. had started to be built up in Middle Miocene, ca. 15.4 Ma ago. A series of explosive events developed starting with a major magmatic explosion and caldera collapse responsible for large volumes of ignimbrites. Successive explosions followed caldera collapse triggering a series of pyroclastic currents that underwent subsequent reworking. Mass flow has been the main transport mechanism recorded by the sedimentary structures of either ignimbrites or post-ignimbrites volcaniclastics. Multiple ignimbrite units resulted from subaerial mass flows, successively emplaced by progressive aggradation from the basal layer of a density-stratified pyroclastic current. The overlying sequence is composed of different volcaniclastics of pyroclastic origin interlayered with mudstones. They preserve the original composition of ignimbrites, but lack the evidence of hot-state deposition, recording the emplacement from more or less dilute mass flows. A syn-eruptive stage of resedimentation is suggested prior to emplacement in submarine conditions, determined by the transformation of gas- supported pyroclastic currents into water-supported mass flows after transition from subaerial to submarine conditions. The syn-eruptive resedimented volcaniclastics may be correlated with the ignimbrite-type subaerial pyroclastic flows, but they show different degrees of fluidization due to the impact of submarine environment.

International audience; The little known Tutupaca volcano (17° 01′ S, 70° 21′ W), located at the southern end of the Peruvian arc, is a dacitic dome complex that experienced a large explosive eruption during historical times. Based on historic chronicles and our radiometric data, this eruption occurred 218 ± 14 aBP, probably between 1787 and 1802 AD. This eruption was characterised by a large sector collapse that triggered a small debris avalanche (

International audience; The well-documented 1883 eruption of Krakatau volcano (Indonesia) offers an opportunity to couple the eruption’s history with the tsunami record. The aim of this paper is not to re-analyse the scenario for the 1883 eruption but to demonstrate that the study of tsunami deposits provides information for reconstructing past eruptions. Indeed, though the characteristics of volcanogenic tsunami deposits are similar to those of other tsunami deposits, they may include juvenile material (e.g. fresh pumice) or be interbedded with distal pyroclastic deposits (ash fall, surges), due to their simultaneity with the eruption. Five kinds of sedimentary and volcanic facies related to the 1883 events were identified along the coasts of Java and Sumatra: (1) bioclastic tsunami sands and (2) pumiceous tsunami sands, deposited respectively before and during the Plinian phase (26–27 August); (3) rounded pumice lapilli reworked by tsunami; (4) pumiceous ash fall deposits and (5) pyroclastic surge deposits (only in Sumatra). The stratigraphic record on the coasts of Java and Sumatra, which agrees particularly well with observations of the 1883 events, is tentatively linked to the proximal stratigraphy of the eruption.

Thermal remanent magnetization analyses were carried out on ceramic fragments and lithic clasts embedded in the first pumice fall deposits of the Minoan eruption. The aim of this study is to estimate the equilibrium temperature after deposition of these pyroclastic fall deposits and their thermal effect on the pre-Minoan surface. A total of 30 samples from 22 independent ceramic fragments and 20 samples from 14 lithic clasts have been studied. Samples were collected from the Megalochori Quarry, located at the southern part of Santorini island. Stepwise thermal demagnetization reveals that the ceramics were mostly re-heated at temperatures around 140–180°C; in few ceramics a higher temperature component is also present, probably related to the original heating or the use of the ceramics before the eruption. Thermal demagnetization of the lithic clasts shows similar results with slightly higher re-heating temperatures, around 180–240°C. The estimated temperatures represent the equilibrium temperatures obtained after the deposition of the pumice fall and show that the pyroclastic fall deposits at a distance of around 6 km from the eruption vent maintained a temperature high enough to re-heat the buried ceramics at temperatures around 140–180°C.

Some of detailed petrologic studies on rock samples of middle to large sized explosive pyroclastic eruptions recently revealed that the eruptions were caused by simultaneous eruption of multiple distinct magma chambers beneath the volcanoes (e.g., Nakagawa et al. 2003: Shane et al. 2007). It is very important to examine the genetic relationships among the magmas to understand the magma feeding system which caused such explosive eruptions. The explosive pyroclastic eruption stage in Shirataka volcano, NE Japan (Fig. 1) is one of potential candidates for such kind of researches. The aim of this study is to reveal the magma feeding system beneath Shirataka volcano in the explosive pyroclastic eruption stage and examine the genetic relationships among magmas involved in the explosive eruption.

We study the volcaniclastic lithofacies interbedded between siliciclastic and carbonate sediments of Cenozoic-Quaternary age (8.7 Ma to 7,000 BP) in Argamasilla and Calzada-Moral basins (Central Spain). The siliciclastic and carbonate deposits correspond to fluvio-lacustrine sedimentary environments. The volcanic materials consist of primary and reworked volcaniclastic successions sourced from the Campo de Calatrava Volcanic Field. Pyroclastic deposits are related to monogenetic and small-volume volcanic centres, such as scoria cones, tuff rings and maars, corresponding to Strombolian and phreatomagmatic eruptive styles. Taking into account sedimentological constraints seven volcaniclastic lithofacies were distinguished. Type A corresponds to subaerial pyroclastic fall deposits, as is inferred by the common disorganization of the deposit, their breccia-like aspect with presence of large bombs, poor sorting and lack of tractional sedimentary structures. Types B1, B2, B3 and B4 have different volcanic sources and are interpreted to be the product of low-density (dilute) pyroclastic surges, with textural features indicative of fluctuations in flow regime. This interpretation is based on the fabric and grain size of pyroclasts, together with the size and geometry of the internal sedimentary structures. Type C represents a secondary volcanic deposit related to volcanic sediments reworked by transitional hyperconcentrated flows and dilute fluvial processes, having subsequently accumulated in braided fluvial systems. Finally, the Type D is interpreted as an intra-maar scoria/spatter cones related to the development of maars. The most important factors that determined the sedimentation in these basins were orientation of basement faults, paleogeographic and sedimentological controls, style of eruption and volcaniclastic lithofacies type, Grupo de Investigación en Ingeniería y Medio Ambiente, Universidad de León, España, Departamento de Geología, Universidad de Salamanca, España, Departamento de Tecnología Minera, Topográfica y de Estructuras, Universidad de León, España, Unidad de Tres Cantos, Instituto Geológico y Minero de España, España

High resolution seismic reflection profiles (Sparker Multitip) offshore southern Ischia island (Naples Bay) are here presented, together with a geological interpretation of their volcanic, structural and sedimentary features. In this frame, new seismo-stratigraphic evidences on buried volcanic structures and overlying Quaternary deposits of the south-eastern offshore of Ischia island are discussed to highlight their implications on the marine geophysics and volcanology. The Ischia Bank is a large and flat relic volcanic edifice with steep slopes, merging on the continental shelf. The age of this monogenic volcano is unknown, lacking a direct datation of its basement. It represents the eruptive centre of the pyroclastic fall cropping out onshore in the eastern sector of the island, ranging in age from 8 to 6 ky B.P.. In the eastern Ischia offshore relic volcanic edifices, mostly formed by hialoclastites, have been investigated through high resolution seismics. They represent remnants of hydro-magmatic volcanic vents and suggest a subaqueous emplacement. Regional seismic sections running in the south-eastern Ischia offshore, across buried volcanic structures, are finally presented and discussed.

The Averno 2 eruption (3,700 ± 50 a B.P.) was an explosive low-magnitude event characterized by magmatic and phreatomagmatic explosions, generating mainly fall and surge beds, respectively. It occurred in the Western sector of the Campi Flegrei caldera (Campanian Region, South Italy) at the intersection of two active fault systems, oriented NE and NW. The morphologically complex crater area, largely filled by the Averno lake, resulted from vent activation and migration along the NE-trending fault system. The eruption generated a complex sequence of pyroclastic deposits, including pumice fall deposits in the lower portion, and prevailing surge beds in the intermediate-upper portion. The pyroclastic sequence has been studied through stratigraphical, morphostructural and petrological investigations, and subdivided into three members named A through C. Member A was emplaced during the first phase of the eruption mainly by magmatic explosions which generated columns reaching a maximum height of 10 km. During this phase the eruption reached its climax with a mass discharge rate of 3.2 106 kg/s. Intense fracturing and fault activation favored entry of a significant amount of water into the system, which produced explosions driven by variably efficient water-magma interaction. These explosions generated wet to dry surge deposits that emplaced Member B and C, respectively. Isopachs and isopleths maps, as well as areal distribution of ballistic fragments and facies variation of surge deposits allow definition of four vents that opened along a NE oriented, 2 km long fissure. The total volume of magma extruded during the eruption has been estimated at about 0.07 km3 (DRE). The erupted products range in composition from initial, weakly peralkaline alkali-trachyte, to last-emplaced alkali-trachyte. Isotopic data and modeling suggest that mixing occurred during the Averno 2 eruption between a more evolved, less radiogenic stored magma, and a less evolved, more radiogenic magma that entered the shallow reservoir to trigger the eruption. The early phases of the eruption, during which the vent migrated from SW to the center of the present lake, were fed by the more evolved, uppermost magma, while the following phases extruded the less evolved, lowermost magma. Integration of the geological and petrological results suggests that the Averno 2 complex eruption was fed from a dyke-shaped shallow reservoir intruded into the NE-SW fault system bordering to the west the La Starza resurgent block, within the caldera floor.

The Atacazo-Ninahuilca Volcanic Complex (ANVC) is located in the Western Cordillera of Ecuador, 10 km southwest of Quito. At least six periods of Pleistocene to Holocene activity (N1 to N6) have been preserved in the geologic record as tephra fallouts and pyroclastic flow deposits. New field data, including petrographic and whole-rock geochemical analyses of over forty soil and tephra sections, 100 pumice and lithic samples, and 10 new C-14 ages allow us to constrain: (1) the tephra fall isopachs and detailed characteristics of the last two events (N5-N6) including volume estimates of the tephra and pyroclastic flow deposits and the corresponding volcanic explosivity index (VEI); (2) the petrographical and geochemical correlations between domes, tephras, and pyroclastic flow deposits; and, (3) the timing of the last 4 eruptive events and a period of quiescence that endured a few thousand years (1000-4000).The last two eruptive events (N5 and N6) took place at around 4400 +/- 35 yr BP and 2270 +/- 15 yr BP, producing huge plinian and pyroclastic flow deposits. Taking into account the widely spread deposits of these VEI 5 eruptions, the present population of about 70000 people, and the current infrastructure; the development of mitigation plans and deployment of monitoring systems at ANVC is highly recommended. (C) 2008 Elsevier B.V. All rights reserved.

International audience; La Soufrière of Guadeloupe is a dangerous volcano characterized over the last decade by moderate seismic and fumarolic unrest. In the last 15,000 years it has experienced phreatic and magmatic eruptions and unusually numerous flank collapse events sometimes associated with a magmatic eruption. We propose a new age of 1530 A.D. and a new eruptive scenario for the last magmatic eruption on the basis of a novel statistical analysis of radiocarbon age dates, and new field and geochemical data. This eruption is the only magmatic eruption likely to have occurred in Guadeloupe during the last 1400 years. The eruption mainly involved an andesitic magma which, in the first phase of the eruption, partially mixed with a slightly more differentiated magma stored in a small and shallow magma chamber. Ascent of magma to the surface generated a partial collapse of the hydrothermally altered edifice that increased the magma discharge and led to a sub-plinian phase with scoria fallout and column-collapse pyroclastic flows followed by near-vent pyroclastic scoria fountains. The eruption ended with growth of a lava dome. Our revised interpretation of the last magmatic eruption of La Soufrière constitutes the most likely key to a future magmatic eruption scenario for this volcano which displays strong evidence of unrest since 1992.

Geological surveys, tephrostratigraphic study, and 40Ar/39Ar age determinations have allowed us to chronologically constrain the geological evolution of the lower NW flank of Etna volcano and to reconstruct the eruptive style of the Mt Barca flank eruption. This peripheral sector of the Mt Etna edifice, corresponding to the upper Simeto valley, was invaded by the Ellittico volcano lava flows between 41 and 29 ka ago when the Mt Barca eruption occurred. The vent of this flank eruption is located at about 15 km away from the summit craters, close to the town of Bronte. The Mt Barca eruption was characterized by a vigorous explosive activity that produced pyroclastic deposits dispersed eastward and minor effusive activity with the emission of a 1.1-km-long lava flow. Explosive activity was characterized by a phreatomagmatic phase followed by a magmatic one. The geological setting of this peripheral sector of the volcano favors the interaction between the rising magma and the shallow groundwater hosted in the volcanic pile resting on the impermeable sedimentary basement. This process produced phreatomagmatic activity in the first phase of the eruption, forming a pyroclastic fall deposit made of high-density, poorly vesicular scoria lapilli and lithic clasts. Conversely, during the second phase, a typical strombolian fall deposit formed. In terms of hazard assessment, the possible occurrence of this type of highly explosive flank eruption, at lower elevation in the densely inhabited areas, increases the volcanic risk in the Etnean region and widens the already known hazard scenario.

A partial dome collapse with concurrent pyroclastic flow (PF) activity occurred at Soufrière Hills Volcano (SHV), Montserrat on 8 January 2007. Pyroclastic density currents were observed to propagate from the Northwest and West sectors of the summit dome into the heads of Tyres Ghaut and Gages Valley, respectively. Between 10:00 and 10:15 UTC pyroclastic flows entered Tyres Ghaut and from there descended into the Belham Valley reaching a distance of about 5 km from the source. Pyroclastic flow activity on the Northwest and West side of the edifice continued at high levels over the following 1.5 h, although run-out distances of individual flows did not exceed 1.5 km. Subsequent observations showed that material had been removed from the lower Northwest side of the dome leaving an amphitheatre-like structure cutting through the old crater rim. The seismic waves excited by the propagation of pyroclastic flows were recorded by the Montserrat Volcano Observatory's network of broadband seismometers. The seismic records show the onset of a continuous signal before 09:30 UTC with gradually increasing amplitudes and spectral energy in the 1–8 Hz band. The signal rapidly increased in amplitude and a characteristic spindle-shaped waveform with broadband energy (1–25 Hz) was observed accompanying large PF that descended along the slopes of the volcano. The main phase was followed by a sequence of individual seismic pulses which correlated well with visual observations of PF. PF are a major hazard at SHV and pose significant risk for the population living in the proximity of the volcano. They can occur with little or no warning and have the potential to reach inhabited areas to the Northwest. The study of the seismic activity associated with the generation and propagation of pyroclastic flows can help to identify characteristic precursory seismic sequences providing valuable information to improve the understanding of the hazards posed by the SHV and to allow better warning to be given to the authorities.

Detailed descriptions of the effects of explosive eruptions on urban settlements available to volcanologists are relatively rare. Apart from disease and starvation, the largest number of human deaths caused by explosive eruptions in the twentieth century are due to pyroclastic flows. The relationship between the number of victims related to a specific hazard and the presence of urban settlements in the area covered by the eruption has been shown. However, pyroclastic falls are also extremely dangerous under certain conditions. These conclusions are based on archaeological and volcanological studies carried out on the victims of the well-known AD 79 eruption of Vesuvius that destroyed and buried the Roman city of Pompeii. The stratigraphic level in the pyroclastic deposit and the location of all the casualties found are described and discussed. The total number of victims recovered during the archaeological excavations amounts to 1150. Of these, 1044 well recognisable bodies plus an additional group of 100 individuals were identified based on the analysis of several groups of scattered bones. Of the former, 394 were found in the lower pumice lapilli fall deposit and 650 in the upper stratified ash and pumice lapilli pyroclastic density currents (PDCs) deposits. In addition, a tentative evaluation suggests that 464 corpses may still be buried in the unexcavated part of the city. According to the reconstruction presented in this paper, during the first phase of the eruption (August 24, AD 79) a huge quantity of pumice lapilli fell on Pompeii burying the city under 3 m of pyroclastic material. During this eruptive phase, most of the inhabitants managed to leave the city. However, 38% of the known victims were killed during this phase mainly as a consequence of roofs and walls collapsing under the increasing weight of the pumice lapilli deposit. During the second phase of the eruption (August 25, AD 79) 49% of the total victims were on the roadways and 51% inside buildings. All of these inhabitants, regardless of their location, were killed by the unanticipated PDCs overrunning the city. New data concerning the stratigraphic level of the victims in the pyroclastic succession allow us to discriminate between the sequential events responsible for their deaths. In fact, casts of some recently excavated corpses lay well above the lower PDCs deposit, testifying that some of the inhabitants survived the first pyroclastic current. Finally, during the PDCs phase the victims died quite rapidly by ash asphyxiation. From the attitude of some casts, it seems that some people survived the initial impact of the second pyroclastic current and tried to support head and bust during the progressive aggradation of the deposit at the base of the current.

The Soufriere Hills volcano, Montserrat, West Indies, has undergone a series of dome growth and collapse events since the eruption began in 1995. Over 90% of the pyroclastic material produced has been deposited into the ocean. Sampling of these submarine deposits reveals that the pyroclastic flows mix rapidly and violently with the water as they enter the sea. The coarse components (pebbles to boulders) are deposited proximally from dense basal slurries to form steep-sided, near-linear ridges that intercalate to form a submarine fan. The finer ash-grade components are mixed into the overlying water column to form turbidity currents that flow over distances >30 km from the source. The total volume of pyroclastic material off the east coast of Montserrat exceeds 280 × 106 m3, with 65% deposited in proximal lobes and 35% deposited as distal turbidites.

The Onano explosive eruption of the Latera Volcanic Complex (Vulsini Volcanoes, Quaternary potassic Roman Comagmatic Region, Italy) provides an interesting example of multiple changes of eruptive style that were concomitant with a late phase of collapse of the polygenetic Latera Caldera. This paper reports a reconstruction of the event based on field analysis, laboratory studies of grain size and density of juvenile clasts, and re-interpretation of available subsurface geology data. The Onano eruption took place in a structurally weak area, corresponding to a carbonate substrate high bordered by the pre-existing Latera caldera and Bolsena volcano-tectonic depression, which controlled the ascent and eruption of a shoshonitic-phonotephritic magma through intersecting rim fault systems. Temporal changes of magma vesiculation, fragmentation and discharge rate, and consequent eruptive dynamics, were strongly controlled by pressure evolution in the magma chamber and changing vent geometry. Initially, pumice-rich pyroclastic flows were emplaced, followed by spatter- and lithic-rich flows and fallout from energetic fire-fountaining. The decline of magma pressure due to the partial evacuation of the magma chamber induced trapdoor collapse of the chamber roof, which involved part of the pre-existing caldera and external volcano slopes and eventually led to the present-day caldera. The widening of the vent system and the emplacement of the main pyroclastic flow and associated co-ignimbrite lag breccia marked the eruption climax. A sudden drop of the confining pressure, which is attributed to a pseudo-rigid behaviour of the magma chamber wall rocks during a phase of rapid magma drainage, led to extensive magma vesiculation and fragmentation. The disruption of the magma chamber roof and waning magma pressure in the late eruption stage favoured the explosive interaction of residual magma with groundwater from the confined carbonate aquifer. Pulsating hydrostatic and magma pressures produced alternating hydromagmatic pyroclastic surges, strombolian fallout and spatter flows.

In 472 A.D. an explosive eruption took place on November 6 from the summit caldera of the Somma. The stratigraphy of the pyroclastic deposits suggests that the eruption involved a complex series of events, which may be grouped into four main phases. The first phase was a small magmatic explosion that resulted in a well vesiculated pumice fall layer ( La ) in the north-northeast. La products contain ∼20% lithic fragments and represent the vent opening stage of the eruption. Subsequent activity resulted in layered fall deposits, subdivided into layers Lb and Lmax . The products contain a much higher proportion of lithic fragments (∼50%) and are inversely graded, coarse-grained, poorly vesiculated and interbedded with thin, lithic-rich fine ash beds. These characteristics indicate that the Lb – Lmax events were most likely phreatomagmatic, caused by influx of groundwater in the magma chamber–conduit system. They resulted in a fall deposit to the north-northeast ( Lb ) and northeast–southeast ( Lmax ) of the volcano. The volume of this deposit is estimated at 1.2 km 3 (0.52 km 3 DRE). Component analysis indicates that lithics make up about 0.22 km 3 of the deposit. Therefore the magma emplaced as tephra fall is ∼0.3 km 3 . The fall phase was ended by block and ash flow of the second phase, emplaced on the northern flanks of the Somma edifice. The largest block and ash flow descended to the northwest, reaching a distance of 5 km from the summit. Increasing pressure due to strong magma–water interaction is the most likely cause of the volcaniclastic debris flow of the third phase. The deposits, identified in the northern and eastern sectors of Mt Somma, comprise a large volume of lithic breccia containing a high proportion of tephritic–phonolitic xenolithic blocks up to 0.5 m across, in a grey, poorly sorted, coarse, sandy matrix, containing only a trace of juvenile pumice. The fourth phase represents the final activity, producing surge deposits, rich in accretionary lapilli and ash fall deposits, that are clearly related by phreatic–phreatomagmatic interaction of water table and magma in the chamber–conduit system. The reconstruction of the A.D. 472 eruptive phases shows that a violent explosive eruption took place in historic times. Based on these data conclusions may be drawn on explosive eruptions which may occur in the future at Somma-Vesuvio.

The paper explores the potential of tsunami generation by pyroclastic flows travelling down the flank of the volcano Vesuvius that is found south of Naples in Italy. The eruption history of Vesuvius shows that it is characterised by large explosive eruptions of plinian or subplinian type during which large volume of pyroclastic flows can be produced. The most remarkable examples of such eruptions occurred in 79 AD and in 1631 and were catastrophic. Presently Vesuvius is in a repose time that, according to volcanologists, could be interrupted by a large eruption, and consequently proper plans of preparedness and emergency management have been devised by civil authorities based on a scenario envisaging a large eruption. Recently, numerical models of magma ascent and of eruptive column formation and collapse have been published for the Vesuvius volcano, and propagation of pyroclastic flows down the slope of the volcanic edifice up to the close shoreline have been computed. These flows can reach the sea in the Gulf of Naples: the denser slow part will enter the waters, while the lighter and faster part of the flow can travel on the water surface exerting a pressure on it. This paper studies the tsunami produced by the pressure pulse associated with the transit of the low-density phase of the pyroclastic flow on the sea surface by means of numerical simulations. The study is divided into two parts. First the hydrodynamic characteristics of the Gulf of Naples as regards the propagation of long waves are analysed by studying the waves radiating from a source that is a static initial depression of the sea level localised within the gulf. Then the tsunami produced by a pressure pulse moving from the Vesuvius toward the open sea is simulated: the forcing pulse features are derived from the recent studies on Vesuvian pyroclastic flows in the literature. The tsunami resulting from the computations is a perturbation involving the whole Gulf of Naples, but it is negligible outside, and persists within the gulf long after the transit of the excitation pulse. The size of the tsunami is modest. The largest calculated oscillations are found along the innermost coasts of the gulf at Naples and at Castellammare. The main conclusion of the study is that the light component of the pyroclastic flows produced by future large eruptions of Vesuvius are not expected to set up catastrophic tsunamis.

A core drilled within the northern part of the city of Napoli has offered the unique opportunity to observe in one single sequence the superposition of the four pyroclastic flow units emplaced during the Campanian Ignimbrite (CI) eruption. Such a stratigraphic succession has never been encountered before in natural or in man made exposures. Therefore the CI sequence was reconstructed only on the basis of stratigraphic correlations and compositional data (in literature). The occurrence of four superposed CI flows, together with all the data available (in literature) allowed us to better constrain the chemical stratigraphy of the deposit and the compositional structure of the CI magma chamber. The CI magma chamber includes two cogenetic magma layers, separated by a compositional gap. The upper magma layer was contaminated by interaction with radiogenic fluids. The two magma layers were extruded either individually or simultaneously during the course of the eruption. In the latter case they produced a hybrid magma. But no evidence of input of new geochemically and isotopically distinct magma batches just prior or during the eruption has been found. Comparison with the exposed CI deposits has permitted reconstruction of variable eruption phases and related magma withdrawal and caldera collapse episodes. The eruption was likely to have began with phreatomagmatic explosions followed by the formation of a sustained plinian eruption column fed by the simultaneous extraction from both magma layers. Towards the end of this phase the upward migration of the fragmentation surface and the decrease in magma eruption rate and/or activation of fractures formed an unstable pulsating column that was fed only by the most-evolved magma layer. This plinian phase was followed by the collapse of the eruption column and the beginning of caldera formation. At this stage expanded pyroclastic flows fed by the upper magma layer in the chamber generated. During the following major caldera collapse episode, the maximum mass discharge rate was reached and both magma layers were tapped, generating expanded pyroclastic flows. Towards the end of the eruption, only the deeper and less differentiated magma layer was tapped producing more concentrated pyroclastic flows that traveled short distances.

This paper deals with ground-hugging, gas–pyroclast currents from explosive volcanic eruptions and their deposits. Key field observations and laboratory determinations are proposed to relate specific deposit types with flow regimes and particle concentration in the transport and depositional systems. Three relevant flow scenarios and corresponding deposit types have been recognized from a survey of pyroclastic successions of the Vulsini Volcanic District (central Italy): (1) dilute, turbulent, pyroclastic currents producing normally or multiply graded beds by direct suspension sedimentation; (2) concentrated bedload regions beneath suspension currents, depositing inversely graded beds by traction carpet sedimentation; (3) self-sustained, high particle concentration, laminar, mass flows developing massive, poorly sorted bodies, with opposite grading of coarse lithic and pumice clasts, overlying fine-grained, inversely graded, basal layers. Main distinguishing criteria include the occurrence and pattern of clast grading, clast–thickness relationships, grain size, ash matrix componentry and pyroclast size–density relationships. Downcurrent and temporal transitions among identified flow scenarios are likely to occur for changing energy conditions and gas–pyroclast ratio both on regional and local scales. The nature and efficiency of magma fragmentation, volatile content, conduit geometry (which determine the characteristics of the erupted mixture and possible lateral blast component at the vent), and the angle of incidence of the column collapse, are suggested as the main factors controlling the generation of one type over the other at flow inception. Dilute, fine-grained, overpressured eruption clouds are thought to favor the formation of low particle concentration turbulent currents. Column collapse over slightly inclined volcano slopes, causing a high degree of compression of the collapsing mixture and of gas expulsion, would favor the generation of high particle concentration pyroclastic currents.

On 25 June 1997, an unsteady, retrogressive, partial collapse of the lava dome at Soufrière Hills Volcano lasted 25 minutes and generated a major pulsatory block-and-ash flow, associated pyroclastic surges and a surge-derived pyroclastic flow that inundated an area of 4 km2 on the north and NE flanks of the volcano. Three main pulses are estimated to have involved 0.78, 2.36 and 2.36 x 106m3 of debris and the average velocities of the fronts of the related block-and-ash flow pulses were calculated to be 15 ms-1, 16.1 ms-1 and 21.9 ms-1 respectively.Deposits of block-and-ash flow pulses 1 and 2 partially filled the main drainage channel so that material of the third pulse spilled out of the channel at several places, inundating villages on the eastern coastal plain. Bends and constrictions in the main drainage channel, together with depositional filling of the channel, assisted detachment of pyroclastic surges from the pulsatory block-and-ash flow. The most extensive pyroclastic surge detached at an early stage from the third block-and-ash flow pulse, swept down the north flank of the volcano and then climbed 70 m in elevation before dissipating. Rapid sedimentation from this surge generated a high-concentration granular flow (surge-derived pyroclastic flow) that drained westwards into a valley not anticipated to be at high risk.Observations support the hypothesis that the interior of the Soufrière Hills Volcano lava dome was pressurized and that pyroclastic surge development became more substantial as deeper, more highly pressurized parts of the dome were incorporated into the pyroclastic flow. Surge development was at times so violent that expanded clouds detached from the block-and-ash flow within a few tens of metres of the lava dome. © 2002 The Geological Society of London.

The 8-10 May 1997 eruption of Bezymianny volcano began with extrusion of a crystallized plug from the vent in the upper part of the dome. Progressive gravi- tational collapses of the plug caused decompression of highly crystalline magma in the upper conduit, leading at 13:12 local time on 9 May to a powerful, vertical Vulcanian explosion. The dense pyroclastic mixture col- lapsed in boil-over style to generate a pyroclastic surge which was focused toward the southeast by the steep- walled, 1956 horseshoe-shaped crater. This surge, with a temperature 30 km 2 with deposits as much as 30 cm thick and extending 7 km from the vent. The surge deposits comprised mas- sive to vaguely laminated, gravelly sand (Md -1.2 to 3.7φ; sorting 1.2 to 3φ) of poorly vesiculated andesite (mean density 1.82 g cm -3 ; vesicularity 30 vol%; SiO2 content ~58.0 wt%). The deposits, with a volume of 5-15×106 m3, became finer grained and better sorted with distance; the maximal diameter of juvenile clasts decreased from 46 to 4 cm. The transport and deposition of the surge over a snowy landscape generated extensive lahars which traveled >30 km. Immediately following the surge, semi-vesiculated block-and-ash flows were emplaced as far as 4.7 km from the vent. Over time the juvenile lava in clasts of these flows became progres- sively less crystallized, apparently more silicic (59.0 to 59.9 wt% SiO 2 ) and more vesiculated (density 1.64 to 1.12 g cm-3; vesicularity 37 to 57 vol%). At this stage the eruption showed transitional behavior, with mass di- vided between collapsing fountain and buoyant column. The youngest pumice-and-ash flows were accompanied by a sustained sub-Plinian eruption column ~14 km high, from which platy fallout clasts were deposited (~59.7% SiO 2 ; density 1.09 g cm-3; vesicularity 58 vol%). The explosive activity lasted about 37 min and produced a to- tal of ~0.026 km 3 dense rock equivalent of magma, with an average discharge of ~1.2×104 m3 s-1. A lava flow ~200 m long terminated the eruption. The evolutionary succession of different eruptive styles during the explo- sive eruption was caused by vertical gradients in crystal- lization and volatile content of the conduit magma, which produced significant changes in the properties of the erupting mixture.

This paper deals with the magnetic fabric and remanent magnetization of welded scoriae fall deposits. Four scoriae blankets were emplaced on Vulcano (Aeolian Islands) from about 50 to 8 ka. Their detailed chronostratigraphic position has been debated in the literature and they have therefore been given a different interpretation in the reconstruction of the Vulcano's eruptive history. The aims of the study were a better understanding of the magnetic features of the scoriae fall deposits, which have so far been given little attention, and to set the chronostratigraphic relationships of the sampled deposits on the ground of their palaeomagnetic directions. Overall, the magnetic properties of the four deposits are alike. Investigation of isothermal remanence and susceptibility versus temperature measurements point to low-Ti titanomagnetite as the main ferromagnetic mineral. Magnetic foliation is well developed, moderately dispersed and in most cases close to horizontal. Lineation is either clustered or dispersed within the foliation plane. Stepwise thermal and alternating field demagnetization shows that secondary components are negligible in two units. In the other two, they are always completely removed in the first steps, below 20 mT or 400°C. Thereafter, the characteristic component (ChRM) is clearly isolated and the within-site dispersion of its direction is small ( α 95 α 95 The palaeomagnetic results corroborate the hypothesis that the investigated scoriae deposits correspond to different volcanic phases, related to recurrent arrival of mafic magma, and show that those of Spiaggia Lunga and Quadrara were produced during two distinct periods of volcanic activity with little time separation between them.

Of 1.1 million people living on the flanks of the active Merapi volcano, 440,000 are at relatively high risk in areas prone to pyroclastic flows, surges, and lahars. For the last two centuries, the activity of Merapi has alternated regularly between long periods of viscous lava dome extrusion, and brief explosive episodes at 8–15 year intervals, which generated dome-collapse pyroclastic flows and destroyed part of the pre-existing domes. Violent explosive episodes on an average recurrence of 26–54 years have generated pyroclastic flows, surges, tephra-falls, and subsequent lahars. The 61 reported eruptions since the mid-1500s killed about 7000 people. The current hazard-zone map of Merapi (Pardyanto et al., 1978) portrays three areas, termed ‘forbidden zone’, ‘first danger zone’ and ‘second danger zone’, based on successively declining hazards. Revision of the hazard map is desirable, because it lacks details necessary to outline hazard zones with accuracy, in particular the valleys likely to be swept by lahars, and excludes some areas likely to be devastated by pyroclastic gravity-currents such as the 22 November 1994 surge. In addition, risk maps should be developed to incorporate social, technical, and economic factors of vulnerability. Eruptive hazard assessment at Merapi is based on reconstructed eruptive history, on eruptive behavior and scenarios, and on existing models and preliminary numerical modeling. Firstly, the reconstructed eruptive activity, in particular for the past 7000 years and from historical accounts of eruptions, helps to define the extent and recurrence frequency of the most hazardous phenomena (Newhall et al., 2000; Camus et al., 2000). Pyroclastic flows traveled as far as 9–15 km from the source, pyroclastic surges swept the flanks as far as 9–20 km away from the vent, thick tephra fall buried temples in the vicinity of Yogyakarta 25 km to the south, and subsequent lahars spilled down the radial valleys as far as 30 km to the west and south. At least one large edifice collapse has occurred in the past 7000 years (Newhall et al., 2000; Camus et al., 2000). Secondly, four eruption scenarios are portrayed as hazardous zones on two maps and derived from the past eruptive behavior of Merapi and from the most affected areas in the past. Thirdly, simple numerical simulation, based on a Digital Elevation Model, a stereo-pair of SPOT satellite images, and one 2D-orthoimage helps to simulate pyroclastic and lahar flowage on the flanks and in radial valley channels, and to outline areas likely to be devastated. Three major threats are identified: (1) a collapse of the summit dome in the short-to mid-term, that can release large-volume pyroclastic flows and high-energy surges towards the south–southwest sector of the volcano; (2) an explosive eruption, much larger than any since 1930, may sweep all the flanks of Merapi at least once every century; (3) a potential collapse of the summit area, involving the fumarolic field of Gendol and part of the southern flank, which can contribute to moderate-scale debris avalanches and debris flows.

We present a model of fountain collapse for small-scale (Soufrière-type) explosive eruptions that relates the asymmetry of a volcanic crater (e.g., the presence of crater notches) with the emplacement direction of pyroclastic flows. Analysis of two-dimensional simulations of compressible fluids emanating from asymmetric nozzles shows that under sonic to supersonic conditions, the streamline of a jet can become tilted. The inclination of the streamline increases with greater slant angle of the nozzle and with increasing exit pressure. Using the two-dimensional simulations as analogues to volcanic eruptions, we propose that pyroclastic ejecta within the inner core of an erupting jet column can become asymmetrically focused before collapsing at fountain heights of a few hundred meters above the crater exit. The ensuing pyroclastic flows associated with fountain collapse thus become directional in character with flow orientation controlled by crater geometry and eruption exit pressure. The model applies to volcanoes with vertical conduits and crater to vent geometries that act as effective sonic to supersonic jet nozzles. We propose that the 1984 eruption of Mayon volcano fits this model. In the second phase of this eruption a prominent crater notch imparted a southeastward tilt to the basal gas thrust region of the eruption column. In turn, this led to the discharge of pyroclastic flows onto the southeast flank of the volcano. Copyright 1999 by the American Geophysical Union.

The most recent eruption at the Mono Craters occurred in the fourteenth century A.D. Evidence for this event includes 0.2 km 3 of pyroclastic fall, flow, and surge deposits and 0.4 km3 of lava domesa nd flows. These rhyolitic deposits emanated from aligned vents at the northern end of the volcanic chain. Hence we have named this volcanic episode the North Mono eruption. Initial explosions were Plinian to sub-Plinian events whose products form overlapping blankets of air fall tephra. Pyroclastic flow and surge deposits lie upon these undisturbed fall beds within several kilometers of the source vents. Extrusion of five domes and coulees, including Northern Coulee and Panurn Dome, completed the North Mono eruption. Radiocarbon dates and dendrochronological considerations constrain the eruption to a period between A.D. 1325 and 1365. The lack of lacustrine laminae or aeolian and fluvial beds between individual pyroclastic beds suggests that the explosive phases of the eruption took place over a period of not more than several months. Within the resolution of the available radiocarbon and dendrochronologic dates, the North Mono eruption is contemporaneous with the latest eruption of the Inyo volcanic chain, about 20 km to the south. However, the Inyo tephra blanket clearly overlies, and thus postdates, all North Mono tephra. Minor disturbance of the North Mono tephra prior to deposition of the Inyo tephra indicates that the period of time between the North Mono and Inyo eruptions was probably no more than a year or two. This near contemporaneity of the two eruptions suggests a genetic relationship. Liquefaction of North Mono sands on the floor of Mono Lake occurred twice during the waning stages of the North Mono eruption and 3 times immediately before and after pulses of the Inyo eruption. This is evidence that five earthquakes of M L > 5.5 occurred during the North Mono and Inyo eruptions. The chemical and textural similarity of the erupted products and their nearly simultaneous evacuation from aligned vents indicates that the North Mono eruption resulted from intrusion of a dike beneath the northern 6 km of the volcanic chain. Several observations suggest that dike intrusion beneath the Mono Craters has replaced normal faulting as the mechanism for elastic rebound and permanent extension of the crust at this latitude. However, dike widths compatible with relief of purely tectonic strains (

The Tertiary volcano-sedimentary sequence of the Feres basin (Thrace, NE Greece), includes lavas of andesitic–rhyolitic composition as well as volcaniclastic rocks, pyroclastic flows and pyroclastic fall deposits principally of dacitic–rhyodacitic composition. The pyroclastic flow deposits frequently show intense devitrification, vapour-phase crystallization and evidence of fumarolic activity, which involves deposition of scapolite in pore spaces. The Feres basin can be subdivided on the basis of mineral alteration assemblages: (1) the Pefka region; characterized by intense hydrothermal alteration of the volcanic rocks and mineral zoning(silicic, argillic, sericitic and propylitic zones) with polymetallic mineralization, and (2) the remainder of the basin; where the volcaniclastic rocks are characterized by the alteration of volcanic glass to zeolites (clinoptilolite, heulandite, mordenite, analcime), clay minerals (smectite, illite, celadonite, chlorite), SiO2polymorphs (cristobalite, opal-CT, quartz), K-feldspar and calcite. Laumontite is also present as an alteration product of plagioclase, with stilbite sporadically occurringin veinlets. Locally, rhyolites are also altered to zeolites (clinoptilolite and/or mordenite). The zeolitization process has occurred rapidly with the depositional environment, temperature, rate of cooling(of the volcanic rocks), nature and temperature of the mineral-forming fluids and composition of the parent material controllingthe formation of zeolites.

A phreatic eruption at Mount Ontake (3067 m) on September 27, 2014, led to 64 casualties, including missing people. In this paper, we clarify the eruption sequence of the 2014 eruption from recorded images (photographs and videos obtained by climbers) and interviews with mountain guides and workers in mountain huts. The onset of eruption was sudden, without any clear precursory surface phenomena (such as ground rumbling or strong smell of sulfide). Our data indicate that the eruption sequence can be divided into three phases. Phase 1: The eruption started with dry pyroclastic density currents (PDCs) caused by ash column collapse. The PDCs flowed down 2.5 km SW and 2 km NW from the craters. In addition, PDCs moved horizontally by approximately 1.5 km toward N and E beyond summit ridges. The temperature of PDCs at the summit area partially exceeded 100 °C, and an analysis of interview results suggested that the temperature of PDCs was mostly in the range of 30–100 °C. At the summit area, there were violent falling ballistic rocks. Phase 2: When the outflow of PDCs stopped, the altitude of the eruption column increased; tephra with muddy rain started to fall; and ambient air temperature decreased. Falling ballistic rocks were almost absent during this phase. Phase 3: Finally, muddy hot water flowed out from the craters. These models reconstructed from observations are consistent with the phreatic eruption models and typical eruption sequences recorded at similar volcanoes., Article, Earth, Planets and Space. 68:79 (2016)