Search

Coseismic landslides generated by strong earthquakes can substantially increase the devastation imposed on society and humanity, especially when such seismic events occur in unconsolidated pyroclastic fall deposits that are prone to destabilization. The catastrophic 2018 Hokkaido Eastern Iburi Earthquake triggered thousands of shallow liquefied landslides in pyroclastic fall deposits, 1 day after the passage of Typhoon Jebi. The landslides were highly mobile and had long runouts. We here report novel findings pertaining to distinctive properties of the widely distributed, weathered Plinian Ta-d tephra deposit from Tarumae volcano, and their impact on the spatial clustering of the Iburi landslides. Distribution of the landslides is positively correlated with the dispersal of Ta-d. Liquefaction occurred in the weathered Ta-d pumice, despite the absence of unconfined groundwater. The Ta-d pumice also has lower soil strength than other local pumice units. The volumetric soil moisture content of weathered Ta-d pumice is very high (>90%) and exceeds other soil layers, regardless of precipitation variation. The presence of hydrated halloysite was confirmed by X-ray diffraction. The halloysite enhances the shaking-triggered liquefaction, because it maintains weathered Ta-d pumice in a highly saturated and exceedingly loose state, even in the absence of unconfined groundwater. This is inconsistent with the traditional concept of liquefaction that generally occurs in sandy soils below the groundwater level.

The cataclysmic basaltic eruption of Mt. Tarawera in 1886 represents a significant cultural and scientific event for New Zealand. This review utilises published and new observations, to reinterpret eruptive parameters encompassing the entirety of the eruption. The ∼17 km eruptive fissure, active for 4+ hours, extends across Mt. Tarawera to the hydrothermally active Waimangu region. Correlating published observations of bed thickness, componentry and microtextures from Mt. Tarawera to new bed descriptions and granulometry for the Rotomahana-Waimangu rift segment allows for a re-assessment of eruption variations along the length of the fissure. Variably thick pyroclastic fall sequences at Mt. Tarawera contrast with the pyroclastic surges and an eruption plume that together deposited the 'Rotomahana Mud' erupted along the Rotomahana-Waimangu segment. Providing insight into pre-eruptive conditions, new mineral chemistry from Mt. Tarawera provides the first constraints on crystallisation pressures (

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.

The 2018 Hokkaido Eastern Iburi Earthquake triggered massive landslides in the pyroclastic fall deposits. Most of them are shallow debris slides. Based on the field reconnaissance, the shallow debris slides were further categorized into three types: steep translational sliding, gentle translational sliding, and mobilization of V-shaped convergent sliding masses. The three types of shallow landslides were investigated in depth through longitudinal sections, vertical stratigraphic sections, and in situ hardness tests. All three types of shallow landslides were found to initiate from the liquefied failure of the weak Ta-d pumice layer and further evolve to the overall mobilization of the superimposed pyroclastic fall deposits along the liquefied sliding zone. To testify the controlling role and to study the shear behavior as well as the anti-liquefaction strength of the weak Ta-d pumice layer, a series of laboratory tests (basic physical tests and triaxial tests) were conducted on the soils around the sliding zone. The test results indicate that the medium sandy Ta-d pumice MS and the fragile Ta-d pumice CS have lower shear resistance and anti-liquefaction strength than other layers and they can be easily liquefied under intense ground motion. One paleosol layer underlying the Ta-d pumice shows low permeability and enables weathering and soil erosion of the Ta-d pumice, resulting in the widespread existence of the fragile and medium sandy pumice layers in Ta-d. In addition, the positive relationship between coseismic landslide density and Ta-d pumice thickness demonstrates the controlling role of the Ta-d on Iburi landslide occurrence from a macro perspective.

The 2018 Hokkaido Eastern Iburi Earthquake caused a large number of slope failures/landslides over a wide area. In particular, the enormous damage due to slope failures was centered in the towns of Atsuma and Abira which are located to the north of the epicenter. In Atsuma, a seismic intensity (Japan Meteorological Agency) of seven was observed. This was the first time an earthquake of such a large seismic intensity was recorded in Hokkaido, Japan. The geology in this region was mainly formed by three kinds of pyroclastic fall deposits (fa) due to the erupting of Mt. Tarumae, Mt. Eniwa and Shikotsu Caldera. The most serious damage was generated in these tephra stratus. In addition, the large-scale sliding of rock slopes composed of mudstone occurred in the Hidaka-Horonai River Basin in the Horonai district of Atsuma, and its debris flowed into the river and caused the blockage of the river channel. This paper summarizes the earthquake-induced damage to natural slopes, and presents the physical features and the mechanical properties of the collapsed pyroclastic fall deposits distributed over this area.

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.

On 6 September 2018, a Mj 6.7 (Mw 6.6) earthquake with a focal depth of approximately 37 km and maximum seismic intensity of 7.0 on the Japan Meteorological Agency (JMA) scale (corresponding to approximately X on the Modified Mercalli Intensity (MMI) scale) struck the central and eastern Iburi regions of Hokkaido, Northern Japan, 1 day after the Typhoon Jebi passed through the region. Thousands of landslides were triggered and significant losses resulted from the earthquake sequence. A detailed landslide inventory map, including 5625 coseismic landslides, was delineated on the basis of 3307 published landslide sites. Most of the coseismic landslides are translational landslides of small to medium scale with high mobility and long run-out distance. Thirty-six people were killed by the landslides despite the afflicted area being sparsely populated. It is found that all the 5625 landslides spread in an elliptic area extending NNW/SSE, running approximately parallel to the strike of (active) faults in this region. The preferred aspect of the landslide-affected area is southerly, running nearly perpendicular to the NNW/SSE striking (active) faults. Most coseismic landslides are distributed in regions with seismic intensity of 7.0 to 8.0 (MMI Scale), with peak ground acceleration (PGA) of 0.4 to 0.7 g. Most of the coseismic landslides occurred at the elevation between 100 and 250 m, and the slope angle between 15° and 35°. Miocene sedimentary rock is the predominant bedrock type identified in the landslide area. Slope failures were triggered in stratified pyroclastic fall deposits, in the combination of strong seismic ground motion and intense antecedent precipitation. Sliding zone liquefaction phenomena were confirmed in the field investigation. The relationship between the old landslides (slope failures occurred prior to the Iburi earthquake) and the coseismic landslides is also discussed in this study.

The 2018 Hokkaido Eastern Iburi Earthquake struck the eastern Iburi region (epicenter: 42.691°N, 142.007°E, depth: 37.0 km) of Hokkaido, Japan, at 3:07.59 JST, September 6, 2018 (18:07.59, September 5, 2018 UTC). Many shallow landslides were triggered by this Mw 6.6 (Mj 6.7) earthquake. The basement complex in the affected area (sedimentary rocks) is covered with thick pyroclastic fall deposits derived from the Tarumae Volcano, etc., and the strong seismic shocks triggered shallow landsliding of them. Shallow landslides moving along valley type topography traveled greater distances than those moving along planar slope topography. Some shallow landslides occurred on relatively gentle slopes (

The 2018 Hokkaido Eastern Iburi Earthquake triggered numerous shallow landslides on slopes covered with thick pyroclastic fall deposits. These shallow landslides tended to occur on concave rather than convex slopes and their slip surfaces were very wet, indicating that water played an important role in landslide initiation. As a first step toward clarifying the role of water in these landslides, we used tensiometers to monitor pressure head dynamics on a natural hillside covered with thick pyroclastic deposits that remained in place throughout the earthquake. We found that on concave slopes, the lower part of the pyroclastic fall deposits throughout the weathered basement complex (sedimentary rock) were always wet. Notably, the interface between the pyroclastic fall deposits and weathered basement complex, which forms a potential slip surface for earthquake-induced landslides, was always at or near saturation. On convex slopes, the weathered basement complex was never saturated and showed greater pressure head fluctuation. We infer that the pyroclastic fall deposits over the basement complex tend to weather more easily and are more susceptible to intense ground motion on concave than on convex slopes and the landslide slip surface was saturated at the timing of the earthquake on concave slopes. We conclude that these factors contributed to the larger number of shallow landslides initiated on concave slopes.

The 2018 Hokkaido Eastern Iburi Earthquake caused a large amount of slope failures and landslides over a wide area. In particular, the enormous damage due to slope failures was centered in Atsuma and Abira town which are to the north of the epicenter. In Atsuma town, a seismic intensity (Japan Meteorological Agency) of seven has been observed for the first time in Hokkaido, Japan. The geology in this region was mainly formed from three kinds of pyroclastic fall deposits (fa) erupted from Tarumae volcano, Eniwa volcano, and Shikotsu Caldera. Especially, the serious damage was generated in these tephra stratus. In addition, a large scale slide of rock slopes composed of mudstone also occurred in the Hidaka-Horonai river basin in Horonai district in Atsuma town, and its debris flowed into the river and caused the blockage of the river channel. This paper summarizes earthquake-induced damages on natural slopes and mechanical properties of Tarumae pyroclastic fall deposits.

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.

Based on detailed stratigraphy, petrology and geochemistry, the initial arc magmatism of the Oman Ophiolite consisting of tholeiitic lavas followed by boninite flows and tephras is studied in the Wadi Bidi area, northern Oman Mountains. An 1110-m-thick V2 sequence is divided into the lower 970 m (LV2) and upper 140 m (UV2) thick subsequences by a 1.0-m-thick sedimentary layer. Pahoehoe flows dominate in the lower part of the LV2, while the upper part consists mainly of sheet flows with sparse interbedded pelagic sediments and a cylindrical plug. In addition to the presence of a feeder conduit, the flow-dominant lithofacies with a few thin sedimentary interbeds in the LV2 indicates that the study area was the centre of a volcano grown in a short period. The UV2 is composed of boninite sheet flows overlain by a 2.0-m-thick pyroclastic fall deposit. A small amount of boninite lavas at the end of the V2 sequence overlain by thick pelagic sediments suggests that the subduction-related arc volcanism was short lived and terminated long before the ophiolite obduction. Supplementary material: Locations, mode of occurrence, phenocryst assemblages and bulk-rock major and trace element compositions of lavas in the Wadi Bidi area are available at http://www.geolsoc.org.uk/SUP18684.

The 7.7 ka Cleetwood (Cltwd) eruption of Mount Mazama (Crater Lake, Oregon, USA) began with a Plinian phase emitting 0.5 km3 DRE of rhyodacitic pyroclastic fall material. Explosive activity then tr...

The Chemnitz Fossil Forest depicts one of the most completely preserved forest ecosystems in late Paleozoic Northern Hemisphere of tropical Pangaea. Fossil biota was preserved as a T0 taphocoenosis resulting from the instantaneous entombment by volcanic ashes of the Zeisigwald Tuff. The eruption depicts one of the late magmatic events of post-variscan rhyolitic volcanism in Central Europe. This study represents a multi-method evaluation of the pyroclastic ejecta encompassing sedimentological and (isotope) geochemical approaches to shed light on magmatic and volcanic processes, and their role in preserving the fossil assemblage. The Zeisigwald Tuff pyroclastics (ZTP) reveal a radiometric age of 291 ± 2 Ma, pointing to a late Sakmarian/early Artinskian (early Permian) stratigraphic position for the Chemnitz Fossil Forest. The initial eruption was of phreatomagmatic style producing deposits of cool, wet ashes, which deposited from pyroclastic fall out and density currents. Culmination of the eruption is reflected by massive hot and dry ignimbrites. Whole-rock geochemistry and zircon grain analysis show that pyroclastic deposits originated from a felsic, highly specialised magma, which underwent advanced fractionation, and is probably related to post-Carboniferous magmatism in the Western Erzgebirge. The ascending magma recycled old cadomic crust of the Saxo-thuringian zone, likely induced by a mantle-derived heat flow during a phase of post-variscan crustal delamination. Geochemical trends within the succession of the basal pyroclastic horizons reflect inverse zonation of the magma chamber and provide evidence for the continuous eruption and thus a simultaneous burial of the diverse ecosystem.

Formation and evolution of the Pannonian Basin as part of the Mediterranean region was accompanied by eruptions of compositionally diverse magmas during the Neogene to Quaternary. The long-lasting magmatic activity began with some of the most voluminous silicic eruptions in Europe for the last 20 Myr. This paper describes the eruption chronology of this volcanic activity using new, high-quality zircon U-Pb dates, and provides the first estimates on the volume and areal distribution of the volcanic products, characterizes the magma composition and discusses the silicic magmatism in a region, where the continental lithosphere underwent significant extension. A thorough zircon geochronological study was conducted on samples collected from ignimbrites and pyroclastic fall deposits exposed in the Bukkalja Volcanic Field. In-situ LA-ICP-MS analysis on zircon grains provided a fast, cheap and accurate method for such detailed geochronological work, where the volcanic products occur in scattered outcrops that often have poor stratigraphic constraints. The interpreted eruption ages were determined from the youngest zircon age population within the samples and this methodology was validated by new single zircon CA-ID-TIMS dates and sanidine Ar-Ar ages. The volcanism covers about 4 Myrs, from 18.2 Ma to 14.4 Ma and involved at least eight eruptive phases. Within this, four large eruption events were recognized at 14.358 ± 0.015 Ma (Harsany ignimbrite), 14.880 ± 0.014 Ma (Demjen ignimbrite), 16.816 ± 0.059 Ma (Bogacs unit) and 17.055 ± 0.024 Ma (Mango ignimbrite), which are found in areas across the Pannonian Basin and elsewhere in central Europe. Considering all the potential sources of silicic ash found in the Paratethys sub-basins around the Pannonian Basin and along the northern Alps and in central Italy, we suggest that they were probably derived almost exclusively from the Pannonian Basin as shown by zircon U-Pb dates presented in this paper and published comparable age data from several localities. The new eruption ages considerably refine the Early to Mid-Miocene chronostratigraphy of the Pannonian basin, where the extensive volcanoclastic horizons are used as important marker layers. The cumulative volume of the volcanic material formed during this 4 Myr long silicic volcanism is estimated to be >4000 km3, consistent with a significant ignimbrite flare-up event. Zircon crystallization ages indicate magma intrusions and formations of magma reservoirs in the continental crust for prolonged period, likely >1 Myr prior to the onset of the silicic volcanism accompanied with sporadic andesitic to dacitic volcanic activities. Mafic magmas were formed by melting of the thinned lithospheric mantle metasomatized previously by subduction-related fluids and emplaced at the crust-mantle boundary. They evolved further by assimilation and fractional crystallization to generate silicic magmas, which ascended into the pre-warmed upper crust and formed extended magma storage regions. Zircon Hf isotope and bulk rock Sr-Nd isotopic data indicate a sharp decrease of crustal and/or increase of asthenospheric mantle input after 16.2 Ma, suggesting that by this time the crust, and the lithospheric mantle was considerably thinned. This magmatism appears to have had a structural relationship to tectonic movements characterized by strike-slip and normal faults within the Mid-Hungarian Shear Zone as well as vertical axis block rotations, when the two microplates were juxtaposed. Our new zircon ages helped to refine the age of two major block-rotation phases associated with faulting. This volcanism shows many similarities with other rift-related silicic volcanic activities such as the Taupo Volcanic Zone (New Zealand) and the Basin and Range Province (USA).

As an important indicator for landslide hazard and risk assessments, landslide mobility has attracted considerable attention in the literature, yet few studies have investigated seismic earthflows. Therefore, the earthflows induced by the 2018 Mw 7.5 Palu earthquake (Indonesia) and the 2018 Mw 6.5 Eastern Iburi earthquake (Japan) and their mobility characteristics were analyzed. Long-term irrigation for cultivation of wet rice and heavy rainfall produced by Typhoon Jebi introduced substantial moisture into alluvial fans (Palu earthquake) and pyroclastic fall deposits (Eastern Iburi earthquake), respectively, and seismic shaking liquefied these moist deposits, which consequently traveled long distances. Four earthflows that were triggered on very gentle slopes of 1–3° by the Palu event exhibited very high mobility levels (H/L) of 0.0129, 0.01125, 0.0209 and 0.0271 (average H/L = 0.018), whereas 7058 earthflows triggered by the Eastern Iburi event exhibited an average mobility of 0.33. Different liquefied layers were located below or above the low permeability layer, and movement restrictions and complex final flow disturbances could be responsible for obvious mobility differences triggered by the two seismic events. However, the earthflow mobility induced by the Eastern Iburi earthquake was obviously higher than that of coseismic rock landslides worldwide and is described by the following relationship: H/L = 1.46–0.24 × log10 (earthflow_area). Furthermore, the earthflow area, peak ground acceleration (PGA) and slope angle all have increase influences on mobility.

The Mondaca Volcano comprises a thick rhyolitic lava-field and a dome of similar composition, located near the Lontué River Valley headwaters in the northern part of the Southern Andes Volcanic Zone. It reaches a total volume of ~0.85 km3, and it is formed by 4 subunits, named Mondaca 1, 2, 3 and 4, which correspond to successive rhyolitic blocky lava flows, emitted from a rounded dome structure. They present well-preserved flow structures and, in the surroundings, restricted to the south and east of the dome, pyroclastic fall, as well as block and ash deposits are also exhibited. Downstream, along the Lontué River, a laharic deposit is recognized. The lahar was produced after the collapse of an ephemeral ~0.44 km3 lake generated after the river obstruction by viscous lavas, during the 1762 first eruptive phase. Proximal lahar facies are well exposed between 5 and 30 km from their source. The profuse agricultural activity has completely obliterated the lahar’s medium facies deposits along the Central Depression, but are well identified at the mouth of the Mataquito River, 180 km downstream, as a beige-coloured layer, interbedded within dark coastal beach-sands. The identification of overflows and super-elevation deposits formed during the debris flow emplacement along the Lontué River valley, allows to determine a high flow mobility, with estimated velocities that locally reached up to 114 km/h. Petrographic characteristics in addition to chemical composition of lavas from the volcano, pyroclasts and juvenile blocks of the laharic deposit, indicate that all they correspond to high K calcoalkaline rhyolites with subalkaline affinity. These backgrounds, together with the geographical continuity between the lavas and debris deposits along the Lontué and Mataquito rivers, verify facies correlation and common origin as the result of the 1762 Mondaca Volcano eruption complex evolution. Although it was a mainly effusive eruption that could not be observed from Curicó, the collateral consequences would have been catastrophic over a vast area to the south of that city, and evidences one of the largest volcanic disasters in Chilean history. Probably because of the low density polulation at that time, the consequences could have been minor.

Timing and mechanism of volcanic tsunamis will be a key to understand the dynamics of large-scale submarine explosive volcanism. Tsunami deposits associated with the VEI 7 eruption of the Kikai Caldera at 7.3 ka are found in the Yakushima and Kuchinoerabujima Islands, ~ 40 km south -southeast of the caldera rim. The tsunami deposits distribute along the rivers in their northern coast up to ~ 4.5 km from the river exit and up to 50 m above the present sea level. The tsunami deposits in the Yakushima area consist of pumice-bearing gravels in the lower part of the section (Unit I) and pumiceous conglomerate in the upper part (Unit II). The presence of rounded pebbles of sedimentary rocks, which characterize the beach deposit, indicates a run-up current from the coastal area. The rip-up clasts of the underlying paleosol in Unit I show strong erosion during the invasion of tsunami. Compositional similarity between the pumices in the tsunami deposit and the juvenile materials erupted in the early phase of the Akahoya eruption indicates the formation of tsunami deposit during the early phase of the eruption, which produced the initial Plinian pumice fall and the lower half of the Koya pyroclastic flow. Presence of the dense volcanic components (obsidians and lava fragments) besides pumices in the tsunami deposit supports that they were carried by the Koya pyroclastic flow, and not the pumices floating on the sea surface. Sequential relationship between the Koya pyroclastic flow and the tsunami suggests that the emplacement of the pyroclastic flow into the sea surrounding the caldera is the most probable mechanism of the tsunami.

Co-auteur étranger; International audience; The rhyodacitic 172 ka Lower Pumice 2 (LP2) eruption terminated the first magmatic cycle at Santorini (Greece), producing a proximal < 50 m thick succession of pyroclastic fall deposits, diffusely-stratified to massive ignimbrites and multiple lithic breccias. The eruption commenced with the development of a short-lived precursory eruption column, depositing a < 15 cm blanket of 1–2 cm sized pumice fragments at near vent localities (LP2-A1). The precursor deposits are conformably overlain by a < 30 m thick sequence of reversely-graded/ungraded pumice fall deposits that reflect opening and widening of a point-source vent, increasing mass discharge rates up to 108 kg s− 1, and the development of a 36 km high Plinian eruption column (LP2-A2, A3). The progressive increase in maximum vesicle number density (NVF) in rhyodacitic pumice, from 3.2 × 109 cm− 3 in the basal fall unit of LP2-A2-1 to 9.2 × 109 cm− 3 in LP2-A3, translates to an increase in magma decompression rate from 18 to 29 MPa s− 1 over the course of the initial Plinian phase. This is interpreted to be a consequence of progressive vent widening and a deepening of the fragmentation surface. Such interpretations are supported by the increase in lithic clast abundance vertically through LP2-A, and the occurrence of basement-derived (deep) lithic components in LP2-A3. The increasing lithic clast content and the inability to effectively entrain air into the eruption column, due to vent widening, resulted in column collapse and the development of pyroclastic density currents (PDCs; LP2-B). A major vent excavation event or the opening of new vents, possibly associated with incipient caldera collapse, facilitated the ingress of water into the magmatic system, the development of widespread PDCs and the deposition of a < 20m thick massive phreatomagmatic tuff (LP2-C). The eruption cumulated in catastrophic caldera collapse, the enlargement of a pre-existing flooded caldera and the discharge of lithic-rich PDCs, depositing proximal < 9 m thick lithic lag breccias (LP2-D).

The eruptive history and morphology of Azufral Volcano, Colombia, is explored and analyzed to provide a more complete picture of past eruptions, as well as to infer what eruption styles may occur in the future. Through the use of principal component analysis on Fe-Ti oxides, domes can be correlated to the pyroclastic deposits, enabling the identification of a full eruptive sequence. The findings suggest that eruptive activity at Azufral Volcano is largely explosive, experiencing long periods of quiescence, punctuated by short periods of pyroclastic activity and volcanic debris avalanches. Geomorphology of the dome complex is reinterpreted to better understand the sequence of dome growth. This reinterpretation, along with geochemical analysis and comparison via PCA, allows for reclassification of a major deposit, originally thought to be a juvenile block-and-ash flow, as a volcanic debris avalanche.

We studied the distribution of tephra deposits discharged by the basaltic (52–54% SiO2) explosive eruption of 1973 on Tyatya Volcano (Kunashir I., Kuril Islands). We made maps showing lines of equal tephra thickness (isopachs) and lines of maximum size of pyroclastic particles (isopleths). These data were used to find the parameters of explosive activity using the standard techniques for each of the two phases of this eruption separately. The first, phreatomagmatic, phase discharged 0.008 km3 of tephra during the generation of maars on the volcano’s northern slope. The tephra mostly consisted of fragmented host rocks with admixtures of fragments of low vesiculated juvenile basalt. The phase lasted 20 hours, the rate of pyroclastic discharge was 2 × 105 kg/s; the eruptive plume reached heights of 4–6 km with wind speeds within 10 m/s. The second, magmatic, phase discharged 0.07 km3 of tephra during the generation of the Otvazhnyi scoria cone on the volcano’s southeastern slope. The tephra mostly consisted of juvenile basaltic scoria. The highly explosive Plinian part of this phase lasted 36 hours, the rate of pyroclastic discharge was 8 × 105 kg/s; the eruptive plume reached heights of 6–8 km with wind speeds of 10–20 m/s. The total tephra volume discharged by the eruption was approximately 0.08 km3; the total amount of ejected pyroclastic material (including the resulting monogenic edifices) was 0.11 km3; the volume of erupted magma was 0.05 km3 (the conversion was based on 2800 kg/m3 density); the volcanic explosivity index, or VEI, was 3. The production rate of the Tyatya plumbing system is estimated as 3 × 105 m3 magma per annum.

A ~ 5 m thick pyroclastic and volcaniclastic sequence, never reported before, comprising a pumice fall deposit has been recognized in a disused quarry near Pollena Trocchia, on the NW slope of Somma-Vesuvius. It is composed of three stratigraphic units: a pumice fall deposit that underlies a pyroclastic density current deposit; they are overlain by a volcaniclastic unit emplaced during a quiescent period of the volcano. The pyroclastic deposits are separated by a horizon of reworked material indicating the emplacement from two distinct eruptive events. The pumice fall deposit has been subject of a detailed investigation. It consists of an ash bed overlaid by a roughly stratified pumice fall layer. The presence of ballistic clasts indicates the proximal nature of this deposit and its stratigraphic position below the Pomici di Base (22 ka) Plinian deposit allows constraining its age to the pre-caldera period (22–39 ky) of activity of Somma-Vesuvius. Samples have been collected in order to perform sedimentological (grain size and componentry), geochemical and isotopic analyses. Samples range from moderately to poorly sorted and show a trachytic composition. The comparison with literature data of compatible deposits vented from Somma-Vesuvius (Schiava, Taurano and Codola eruptions as well as borehole data) allows excluding any correlation with already known Vesuvian products suggesting that the analysed products are ascribable to a new, pre-caldera, explosive eruption. We name this new event “Carcavone eruption”. Based on thickness, maximum lithic clasts and orientation of impact sags, showing a provenance from SE, we envisage the emplacement from a Plinian style eruption vented in the northern sector of the current caldera.

As the eruptive history of Somma–Vesuvius (SV) and Campi Flegrei (CF) gives reasonable reasons to expect eruptions in the future, further analysis of the present delimitation of the Red Zones of both volcanic areas carried out by the Italian Department of Civil Protection (DCP, 1995) is warranted. For SV, the present emergency plan has been devised to protect inhabitants from the possibility of an explosive eruption similar to the ones occurring in the past, such as the 472 CE eruption. However, the new Red Zone (2014) extends up to 7 km from the crater, considered as the area of maximum invasion by pyroclastic flows. The peripheral areas of invasion coincide with the administrative limits of the municipalities, which merge, in a questionable way, with sectors that could be invaded by secondary volcanic fall products. Overall, the hazard zone delimitation mostly coincides with the limits of the areas as given in the former 2004 Red Zone delimitation. For CF, the current delimitation of the Red Zone appears overestimated for events of low magnitude, while for a Plinian event (such as the 4.1 ka Agnano–Monte Spina, Volcanic Explosivity Index 4–5 eruption), it is overestimated for pyroclastic flows and underestimated for the pyroclastic fall risk. For CF, it is appropriate to create two distinct risk maps from eruptions of different magnitudes and styles. For risk flows, the only defense for the residential population in the caldera area or at the base and along the slopes of a volcano is to mandate evacuation from the area at greatest risk. Based on this important consideration, we believe that both the models elaborated by DCP should be adjusted to better cope with the levels of risk associated with the next probable worst-case scenario eruptions, both at SV and CF. Finally, the emergency evacuation plan by DCP is completely insufficient, as it is completely missing, both at SV and CF, the building of large escape routes for millions of people to rapidly exit areas at risk. In this extent, there is the misleading message to the population that an eruption could be forecasted in days, if not weeks in advance. The DCP does not explain clearly that this is a possibility, it is not a certainty. In this case, the only way to escape from a catastrophe is, indeed, to have the availability of large escape routes.

Evidence of volcaniclastic sedimentation occurs in the first depositional sequence of the sedimentary succession of the Amantea Basin. Volcaniclastic deposits are intercalated in the upper part of a sandstone formation and these show a maximum thickness of about 8 m. The Amantea Basin is a Neogene depozone located along the Tyrrhenian margin of Calabria whose onset started during the Upper Serravallian. The source volcano to these materials had to have been located within or near to the marine basin in order to supply it with significant amounts of pyroclastic fragments emplaced by either pyroclastic fall/or flows during one or more explosive eruptions. The marine environment of volcaniclastic flows made up of pyroclastic fragments mixed with minor siliciclastic and carbonate material. The textural and structural features of the deposits and the composition of the volcanic glass fragments indicate an origin from a sub-aerial coeval explosive eruption, with initial sedimentation in a shallow marine environment, mixing with non-volcanic materials, reworking and final re-sedimentation into the basin. The age of the volcaniclastic/sedimentary sequence makes these deposits a marker for the geodynamic evolution of the area, and the lack of such horizons in the other coeval peri-Tyrrhenian basins allows us to consider the Amantea Basin as a confined elongated coastal basin area, whose tectonostratigraphic architecture denotes a structural partitioning of the eastern nascent Tyrrhenian Basin.

Rapid-moving landslides occurred in many locations during the 2009 Padang earthquake, Sumatra. We interpreted satellite images, performed field surveys, in situ dynamic cone penetration tests, and laboratory analyses for mineralogy and physical and mechanical properties. We found that landslides occurred at 159 locations in an area of 64 km2, and these areas had pumice fall deposits overlying paleosols which were heavily weathered debris flow deposits. These landslides in the investigated area occurred in areas with pumice fall deposits thicker than 350 cm; this depth was probably vital in inducing mechanical instability. The areas had sliding surfaces at the base of the pumice fall deposits, where pumice grains were mixed with the underlying paleosol and had been heavily weathered into halloysite-rich clayey materials by interaction with the percolating water from the ground surface. After the deposition of this pumice fall with mantle bedding, the beds were undercut by subsequent river erosion that loosen their downslope lateral support. This geologic history of pumice fall, weathering, and undercutting is not confined to the affected area but it is common to many volcanic areas, creating the opportunity to predict areas susceptible to earthquake-induced catastrophic debris avalanches.

Slamet volcano is the biggest volcano in Central Java, Indonesia which has stratovolcano type. Starting in 1772 until recent, Slamet volcano was erupted with short cycling so that geochemicals on rock are important to know how the history and erupted type. Method of research was conducted by geological survey (surface) and geochemical analysis of sample rocks. Geological condition is consist of lava flow, pyroclastic fall, and laharic deposits that was proven by petrography approached, meanwhile geochemical composition shows calc-alkaline and high K calc-alkaline series, genesis of magma was from continental plate with island arc tholeiitic setting. Depth of magma 155-174 km belom the earth’s surface.

International audience; The 184 ka Lower Pumice 1 eruption sequence records a complex history of eruption behaviours denoted by two significant eruptive phases: (1) a minor precursor (LP1-Pc) and (2) a major Plinian phase (LP1-A, B, C). The precursor phase produced 13 small-volume pyroclastic fallout, surge and flow deposits, which record the transition from a dominantly magmatic to a phreatomagmatic eruptive style, and exhibit a normal (dacite to andesitic-dacite) to reverse (andesitic-dacite to dacite) compositional zonation of juvenile pyroclasts in the stratigraphy. Incipient bioturbation and variability in unit thickness and lithology reflect multiple time breaks and highlight the episodic nature of volcanism prior to the main Plinian eruption phase. The Plinian magmatic eruption phase is defined by three major stratigraphic divisions, including a basal pumice fallout deposit (LP1-A), an overlying valley-confined ignimbrite (LP1-B) and a compositionally zoned (rhyodacite to basaltic andesite) lithic-rich lag breccia (LP1-C), which caps the sequence. This sequence records the initial development of a buoyant convective eruption column and the transition to eruption column and catastrophic late-stage caldera collapse events. Similarities in pyroclast properties (i.e., chemistry, density), between the Plinian fallout (LP1-A) and pyroclastic flow (LP1-B) deposits, indicate that changes in magma properties exerted no influence on the dynamics and temporal evolution of the LP1 eruption. Conversely, lithic breccias at the base of the LP1-B ignimbrite suggest that the transition from a buoyant convective column to column collapse was facilitated by mechanical erosion of the conduit system and/or the initiation of caldera collapse, leading to vent widening, an increase in magma discharge rate and the increased incorporation of lithics into the eruption column, causing mass overload. Lithic-rich lag breccia deposits (LP1-C), which cap the eruption sequence, record incremental, high-energy caldera collapse events, whereby downfaulting occurred in discrete jumps, resulting in variable magma discharge rates and the development of a fissure vent system.

We present major element glass data and correlations for the ‘Roxolany Tephra’ − a so far geochemically unconstrained volcanic ash layer previously described in last glacial (Marine Isotope Stage 2) loess deposits of the Roxolany loess–palaeosol complex in south-west Ukraine. This exceptionally well-preserved, 2–3-cm-thick tephra layer is characterized by a rhyolitic glass composition that is comparable to that of proximal tephra units from Ciomadul volcano in the East Carpathians, central Romania. The chemistry particularly matches that of the final Latest St. Ana Phreatomagmatic Activity pyroclastic fall unit of St. Ana crater that is radiocarbon dated in the proximal Mohos coring site (MOH-2) to 29.6 ± 0.62 cal ka BP. The age of the tephra correlative agrees with the newest radiocarbon and infrared optically stimulated luminescence age constraints from overlying palaeosols and tephra-embedding loess of the Roxolany sequence, respectively, which place the tephra between ca. 33 and 24 cal ka BP, and thus confirm the long-debated chronostratigraphy of this important environmental archive. The occurrence of a distal Ciomadul tephra ca. 350 km east of its source indicates great potential for further tephra and cryptotephra findings from this volcanic complex in the south-eastern Mediterranean and Black Sea region.

Oppenheimer crater is a floor-fractured crater located within the South Pole–Aitken basin on the Moon, and exhibits more than a dozen localized pyroclastic deposits associated with the fractures. Localized pyroclastic volcanism on the Moon is thought to form as a result of intermittently explosive Vulcanian eruptions under low effusion rates, in contrast to the higher-effusion rate, Hawaiian-style fire fountaining inferred to form larger regional deposits. We use Lunar Reconnaissance Orbiter Camera images and Diviner Radiometer mid-infrared data, Chandrayaan-1 orbiter Moon Mineralogy Mapper near-infrared spectra, and Clementine orbiter Ultraviolet/visible camera images to test the hypothesis that the pyroclastic deposits in Oppenheimer crater were emplaced via Vulcanian activity by constraining their composition and mineralogy. Mineralogically, we find that the deposits are variable mixtures of orthopyroxene and minor clinopyroxene sourced from the crater floor, juvenile clinopyroxene, and juvenile iron-rich glass, and that the mineralogy of the pyroclastics varies both across the Oppenheimer deposits as a whole and within individual deposits. We observe similar variability in the inferred iron content of pyroclastic glasses, and note in particular that the northwest deposit, associated with Oppenheimer U crater, contains the most iron-rich volcanic glass thus far identified on the Moon, which could be a useful future resource. We propose that this variability in mineralogy indicates variability in eruption style, and that it cannot be explained by a simple Vulcanian eruption. A Vulcanian eruption should cause significant country rock to be incorporated into the pyroclastic deposit; however, large areas within many of the deposits exhibit spectra consistent with high abundances of juvenile phases and very little floor material. Thus, we propose that at least the most recent portion of these deposits must have erupted via a Strombolian or more continuous fire fountaining eruption, and in some cases may have included an effusive component. These results suggest that localized lunar pyroclastic deposits may have a more complex origin and mode of emplacement than previously thought.

We present the first geochemical data (major and trace elements, as well as Sr, Nd, and Pb isotopes) on volcanic rocks from the Tepoztlan Formation in the central Transmexican Volcanic Belt. The Tepoztlan Formation is up to 800 m thick and comprises a wide range of primary volcanic rocks (lavas, pyroclastic density current deposits, pyroclastic fall deposits), and their secondary reworked products due to mass flow (lahars) and fluvial processes. Magnetostratigraphy combined with K/Ar and Ar/Ar geochronology suggests an age of Early Miocene (23–19 Ma) for this Formation. Lava flows, pyroclastic rocks, dykes and volcanic clasts range from basaltic andesite to rhyolite, with a clear dominance of andesites and dacites. All samples are subalkaline and hy-normative. These rocks show homogeneous REE patterns with LREE enrichment and higher LILE concentrations with respect to HFSE, notably the typical negative anomaly of Nb, Ta, and Ti, suggesting a subduction-related magma genesis. Major and trace element concentrations show that either assimilation of heterogeneous continental crust or crustal recycling by subduction erosion and fractional crystallization are important processes in the evolution of the Tepoztlan Formation magmas. Isotopic compositions of the Tepoztlan Formation samples range from (87Sr/86Sr) t = 0.703693 to 0.704355 and (143Nd/144Nd) t = 0.512751 to 0.512882, falling within the mantle array. All geochemical characteristics indicate that these rocks originated from a heterogeneous mantle, modified and evolved through assimilation of country rock and fractional crystallization in the upper crust.

The relationships between silicic volcanic and plutonic rocks have long puzzled geologists because the rich set of observations from petrology, geochronology, thermal modeling, geophysical techniques, and geochemistry have led to contradictory interpretations. Although compositional evolutionary trends leading to granite and rhyolite are congruent, it is not clear if rhyolites are formed by the extraction of melt from shallow crystal mushes that otherwise solidify to form granite plutons, or are derived from a greater depth in parallel with granite plutons, or are formed by processes separate from those which form granite plutons. Finding a consistent explanation for the silicic volcanic–plutonic relationship bears on important Earth science questions, including, “How is silicic continental crust formed?” and, “Can we predict supereruptions?” * Dacite : Relatively high-silica volcanic rock containing ~65–70 wt% SiO2. Granite, granitoids : Plutonic rocks composed predominantly of quartz, alkali feldspar, and plagioclase feldspar, typically in subequal amounts. Ignimbrite : A deposit formed from a pyroclastic flow. Magma : Although the definition of this fundamental geologic substance is disturbingly vague, the American Geosciences Institute Glossary of Geology definition is appropriate here: “naturally occurring molten or partially molten rock material, generated within the Earth and capable of intrusion and extrusion.” Plutonic : Referring to magma that crystallized at depth and is, therefore, relatively coarse-grained. Granite is a plutonic rock. Pyroclastic : Said of material ejected into the air during eruption, such as volcanic ash. Pyroclastic fall : Fine material from an explosive eruption that falls like snow. Pyroclastic fall material can circle the globe if fine enough and thrown high enough. Pyroclastic flow : A hot, fluidized, ground-hugging mass of fragmental material from an explosive eruption that moves across the ground surface at high speed. Pyroclastic flows are dominated by fine (~70 wt% SiO2. Silica : The chemical component SiO2. Silicic : Denoting a high concentration of silica (typically >66 wt%). Silicic melts are far more viscous than less-silicic ones.

The occurrence of pyroclastic flow deposits is not restricted to polygenetic and/or felsic volcanic systems, but can also occur at mafic monogenetic volcanic centres. At the c. 5 ka Mt Gambier Volcanic Complex, Australia, two small-volume pyroclastic flow deposits resulted from phreatomagmatic eruptive phases of the Blue Lake East and the Valley Lake maar craters. The facies descriptions of the two massive, poorly sorted lapilli tuff and tuff breccia deposits are given. Low-grade carbonized wood fragments in the deposits mark low emplacement temperatures (180–270°C) for these deposits with only c. 12–23% of the total thermal energy of the original magma preserved at the time of deposition. The Blue Lake East vent erupted by forming a short-lived vertical eruption column, which could not be sustained and collapsed. The Valley Lake pyroclastic flow deposit has a highly asymmetric dispersal to the west, indicating that this deposit was formed during an eruptive phase with a large westward-directed lateral component. Such massive, poorly sorted deposits outside the maar crater indicate that some similar deposits in diatremes may have originated from surface eruptions and not just from subsurface debris jets.

The Campanian Ignimbrite eruption (39 ka) was the most powerful eruptive event of the Campi Flegrei caldera (southern Italy). This event coincided with the onset of a cold climatic phase and the Paleolithic transition from Neanderthals to modern humans. The eruption started with a sustained column that emplaced a widespread pyroclastic fall deposit covering an area >4000 km2 within the 15 cm isopach. For the first time, we present the complete longitudinal variation from the coarse and 10-m-thick proximal (down to 15 km) sequence, through the well-stratified pumice lapilli deposit in medial areas (30−80 km), to the distal tephra (hundreds to thousands of kilometers distant). The Plinian pumice fall deposit shows a strong lateral heterogeneity due to variations in stratification, grading, and abundance of components. All Campanian Ignimbrite fall layers display Plinian dispersal. Variation of grain size with stratigraphic height suggests that the convective plume was far from steady state. Initially, the plume dispersed 1.3 km3 of tephra toward the ENE (N75°E) from a height of 29 km (layer A). A gradual increase in intensity resulted in inverse grading of layer B. Column height increased from 26 to 37 km at a vertical velocity of 3.6 m/s. It had a main dispersal axis to the east (N97°E) and a secondary lobe to the southeast (N137°E). During this phase, a maximum volume of 1.73 km3 of tephra was emplaced. Accessory lithics concentrated in layer C are possibly due to vent clearing after partial blockage of the vent. The 33-km-high column dispersed ejecta to the east (N95°E), with only 0.2 km3 of tephra erupted during this phase. During the successive gradual decline in eruption intensity (column height decreased from 38 to 32 km at a velocity of 4.2 m/s), a normally graded layer (D) with a volume of 1 km3 accumulated to the east (N95°E). The sustained column phase ended with a pulsating and partially collapsing column that reached 23 km in height and dispersed 1.1 km3 of a stratified and lithic-rich succession (layer E) to the southeast (N112°E). If we include the distal co-Plinian deposit, a total volume of 7.8 km3 (dense rock equivalent [DRE]) of magma was released (containing 0.09 km3 of accessory lithics). Tephra mass for the single layers is on the order of 1011 kg, and the total mass is ∼2 × 1012 kg (2 × 1013 kg including the co-Plinian ash). Mass discharge rates ranged from 0.9 to 6.7 × 108 kg/s. The calculated magnitude of the sustained column phase is 6.3. The duration of the Plinian phase of this eruption, based on the ratio of two parameters, erupted mass divided by discharge rate, is estimated to have been ∼20 h (including co-Plinian ash). This study shows that Plinian deposits are not always homogeneous and, as for pyroclastic current deposits, can show an articulate architecture. Only the complete reconstruction of vertical and lateral variations in components, stratification, and grading might provide insights into the temporal and spatial evolution of the sustained plume.

Co-auteur étranger; International audience; Cubilche Volcanic Complex (Imbabura Province, Ecuador) includes three morphologically well-preserved eruptive centers: in increasing size, Cunrru Dome Complex (3300 m above sea level, m asl), Panga Ladera (3420 m asl) and Cubilche (3836 m asl). As this complex is poorly known, we conducted a volcanological study of its evolution by combining geomorphological, lithostratigraphic, radiocarbon (14C), and petrological analyses, along with eruption size determinations. Cunrru Dome Complex shows an eastward-opening scarp formed during a dome collapse event that emplaced a small-volume debris avalanche deposit and a pumice-rich layer from an accompanying directed explosion. The higher Panga Ladera edifice is breached towards the north, and the emplacement of the resulting debris avalanche deposit was also accompanied by a blast-forming eruption of ash and pumice. The post-collapse vent subsequently produced dilute pyroclastic density currents (PDCs) that built a low cone. The Cubilche eruptive center comprises old and young edifices. The Old Cubilche edifice emitted lavas from a summit crater and flank vents before being partly destroyed during a flank failure event associated with an explosive eruption that produced a widespread pyroclastic density current deposit dated at ca 44 ka and an associated pyroclastic fall deposit. The Young Cubilche cone grew inside the Old Cubilche avalanche crater during ~14–19 ka over five eruptive episodes that included early effusive eruptions, a dome growth period that terminated with a PDC that emplaced scoria flow deposits at ca 29.6 ka, an explosive eruption at ca 26.3 ka, and final Strombolian activity emitting more mafic products. As the adjacent Imbabura Volcanic Complex erupted in early Holocene times and the two complexes seem to share common reservoirs and plumbing systems, we cannot fully discard a possible reactivation at Cubilche. Other more short-term hazards are debris flows and landslides potentially triggered by heavy rain fall and/or seismic events.

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.

Earthquake-induced landslides of pyroclastic fall deposits are special because they occur on gentle slopes and are highly mobile with long runout distance; even one landslide could have hundreds of fatalities when it occurs in a populated area. We have been examining such landslides induced by 6 earthquakes in Japan and one in Indonesia with field surveys, and here summarize their geological features to establish a methodology of prediction. These case histories strongly suggest that pumice deposits and a clay mineral, halloysite, are very susceptible to earthquake shaking and those susceptible beds can be identified from the view point of volcanic stratigraphy. Landslides of pyroclastic fall deposits may occur repeatedly by earthquakes in a certain area until unstable beds are removed, so we need to consider the potential of earthquake-induced landslide is high in an area with buried pumice fall deposits at least where previous earthquakes induced such type of landslides.

The 2360 BP eruption of Mount Meager, Canada featured an explosive subplinian onset resulting in dacitic fallout tephra and associated pumiceous pyroclastic flow deposits, followed by the effusion of dacite lava and the deposition of a thick sequence of block and ash flow deposits. Fall deposits are distributed to the NE of the vent onto a rugged, deeply incised landscape. The central axis of deposition is ~ 063° Az; the lateral margins of the fall deposit are massive to unbedded whereas deposits underlying the plume axis feature complex bedding relationships. We present componentry and granulometry data for eight outcroppings of the fall deposit (four on plume axis and four off plume axis). Vertical cross-sections, based on surface outcrops and drill core logs from local commercial drilling programs, are used to relate the accessory lithics to their source depth in the underlying subvolcanic basement. These combined datasets inform on the dynamics of this explosive phase of the eruption including variations in column height, eruption intensity, atmospheric conditions, and depth to fragmentation front. The lateral variations within the fall strata reflect the effects of the prevailing atmospheric conditions on the form and dispersal pattern of the subplinian plume. Vertical variations in granulometry and componentry of the fall deposits are used to track temporal changes in eruption intensity and column height and the transient influence of the jetstream on the dispersal pattern of the plume. Lastly, vertical variations in lithic componentry, combined with our knowledge of the subsurface geology, are used to quantitatively track the deepening of the fragmentation front. Our computed results show that the fragmentation front migrated from ~ 640 m to ~ 1160 m below the vent over the course of the 2360 BP Mount Meager eruption.

Pyroclastic flow eruption large-scale experiment (PELE) is a large-scale facility for experimental studies of pyroclastic density currents (PDCs). It is used to generate high-energy currents involving 500–6500 m3 natural volcanic material and air that achieve velocities of 7–30 m s−1, flow thicknesses of 2–4.5 m, and runouts of >35 m. The experimental PDCs are synthesized by a controlled “eruption column collapse” of ash-lapilli suspensions onto an instrumented channel. The first set of experiments are documented here and used to elucidate the main flow regimes that influence PDC dynamic structure. Four phases are identified: (1) mixture acceleration during eruption column collapse, (2) column-slope impact, (3) PDC generation, and (4) ash cloud diffusion. The currents produced are fully turbulent flows and scale well to natural PDCs including small to large scales of turbulent transport. PELE is capable of generating short, pulsed, and sustained currents over periods of several tens of seconds, and dilute surge-like PDCs through to highly concentrated pyroclastic flow-like currents. The surge-like variants develop a basal

We reported detailed investigation of the pumiceous deposits reside in the western part of Slamet Volcano that are found as both primary and secondary product. Pyroclastic fall, flow and surge deposits represent those of the primary products, whereas lahar and fluvial deposits represent those of the secondary products. The tephra fall deposits are separated by pyroclastic flow and surge deposits as typical of sub-plinian to plinian eruption type. The secondary deposits of fluvial deposits occurred in between the primary deposits indicating repose time of the explosive events, whereas lahar deposits occurred as the youngest deposits concluding these pumiceous events. Petrographic observation show that pumice deposit is extremely vesicular with various bubble sizes, vitrophyric in texture, and contains subhedral phenocryst of plagioclase, orthopyroxene, clinopyroxene, opaque mineral and minor biotite. Chemical compositions of major and trace elements were obtained using ICP-MS-AES. SiO2 range from 58,7 to 63,9 wt.% and classified as andesite to dacite with LOI number range from -0,04 to 3,06. Ratios of incompatible elements (e.g. Ba/Zr, Rb/Zr, Zr/Nb, and Hf/Nb) consistently separate rocks of Old and Young Slamet. In these ratios, pumiceous samples are plotted within the range of Young Slamet implying for genetic relationship. These explosive events are “unique” considering typical recent basaltic activities of Slamet volcano and need to be carefully considered in the volcanic hazard mitigation.We reported detailed investigation of the pumiceous deposits reside in the western part of Slamet Volcano that are found as both primary and secondary product. Pyroclastic fall, flow and surge deposits represent those of the primary products, whereas lahar and fluvial deposits represent those of the secondary products. The tephra fall deposits are separated by pyroclastic flow and surge deposits as typical of sub-plinian to plinian eruption type. The secondary deposits of fluvial deposits occurred in between the primary deposits indicating repose time of the explosive events, whereas lahar deposits occurred as the youngest deposits concluding these pumiceous events. Petrographic observation show that pumice deposit is extremely vesicular with various bubble sizes, vitrophyric in texture, and contains subhedral phenocryst of plagioclase, orthopyroxene, clinopyroxene, opaque mineral and minor biotite. Chemical compositions of major and trace elements were obtained using ICP-MS-AES. SiO2 range from 58,7 to 6...

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.

Alluvial fans and terraces develop in diverse regions responding to different tectonic and climatic conditions. The Motozintla basin is located in the State of Chiapas, southern Mexico and has an E–W orientation following the trace of the left-lateral Polochic Fault. The evolution of the Motozintla basin and the alluvial plain is related to several factors, such as fault movement, intense erosion by hydrometeorological events, and anthropogenic activity. This study presents the geomorphology of the alluvial plain that between the villages of Motozintla and Mazapa de Juarez exposes 31 alluvial fans, 5 hanging terraces and 13 ramps. Fourteen of these alluvial fans have been truncated by the Polochic fault, exposing maximum uplifts of ~ 12 m. The internal structure of truncated fans consists of single massive beds (monolithologic fans) or stacked beds (polygenetic fans). The fans' stratigraphy is made of debris flow deposits separated by paleosols and minor hyperconcentrated flows, fluviatile beds, and pyroclastic fall deposits. The reconstruction of the stratigraphy assisted by radiocarbon geochronology suggests that these fans have been active since late Pleistocene (25 ka) to the present. This record suggests that at least 10 events have been recorded at the fan interior during the past ~ 1840 years. One of these events at 355 ± 65 14 C yrs. BP (cal yrs. AD 1438 to 1652) can be correlated across the fans and is likely associated with an extreme hydrometeorologic event. The presence of a 165 ± 60 14 C yrs. BP (cal yrs. AD 1652–1949) debris flow deposit within the fans suggests that movement along the Polochic fault formed the fans' scarp afterwards. In fact, a historic earthquake along the fault occurred east of Motozintla on July 22, 1816 with a M w of 7.5–7.75. Recent catastrophic floods have affected Motozintla in 1998 and 2005 induced by extreme hydrometeorological events and anthropogenic factors. Therefore, scenarios for Motozintla involved several types of mass movement processes that pose a serious hazard and threat to the inhabitants of the region.