Pyroclastic Flows Research Articles

Dynamics of large pyroclastic currents inferred by the internal architecture of the Campanian Ignimbrite

Large ignimbrites are the product of devastating explosive eruptions that have repeatedly impacted climate and life on global scale. The assemblage of vertical and lateral lithofacies variations within an ignimbrite sheet, its internal architecture, may help to determine how the parental pyroclastic current evolves in time and space. The 39 ka Campanian Ignimbrite eruption, vented from Campi Flegrei caldera, laid down a thick ignimbrite over an area of thousands of km2. A detailed reconstruction of the vertical and lateral variation of the seven lithofacies recognised in the ignimbrite medial sequence constrains the behaviour of this event. The pyroclastic current flowed over a wide area around Campi Flegrei without depositing (bypass zone), and inundated a huge area during most of the paroxysmal, waxing phase, emplacing a mainly incipiently- to strongly- welded ignimbrite. Following this waxing phase, the leading edge of the current retreated back towards the source as the current waned, impacting a progressively smaller area and leaving an unconsolidated ash and lapilli deposit, later lithified. Our study illustrates how large pyroclastic currents can evolve in time and space and the importance of both internal (eruptive and transport mechanisms) and external (topography, surficial water and rain) factors in governing their behaviour.

The Basal Friction Coefficient of Granular Flows With and Without Excess Pore Pressure: Implications for Pyroclastic Density Currents, Water‐Rich Debris Flows, and Rock and Submarine Avalanches

AbstractNumerous large‐scale geophysical flows propagate with low‐apparent basal friction coefficients, but the source of such phenomenology is poorly known. Motivated by scarce basal friction data from natural flows, we use numerical methods to investigate the interaction of granular flows with their substrate under idealized conditions. Here we investigate 3‐D monodisperse and polydisperse fluid‐particle granular flow rheology and flow‐substrate interaction using discrete element modeling and coarse‐graining techniques. This combination allows us to calculate the continuum fields of solid fraction, velocity, shear stress, and solid pressure and compare it with force measurements on the substrate. We show that the wall/basal friction coefficient is not constant. Instead, it is a function of the nondimensional slip defined as the ratio of the slip velocity over the slip velocity fluctuations. The scaling of the wall friction with nondimensional slip is independent of air viscosity and density and presence of excess pore pressure. Therefore, the reduction of the basal stress that must occur in mobile natural flows with excess pore pressure is not ascribed to the lowering of wall friction coefficient. Instead, lowering of the normal stress by fluid drag in flows with elevated pore fluid pressure justifies the definition of effective wall and internal friction coefficients to capture the geophysical flow rheology and the forcing on its substrate. These results are fundamental to understand the dynamics of geophysical mass flows including pyroclastic density currents, water‐rich debris flows, and rock and submarine avalanches.

Message from the Winner

A volcanic eruption is a phenomenon in which ballistic bombs, lapilli, volcanic ash, lava, and gas are discharged. Volcanic ash and gas are carried by the wind, and pyroclastic flows and lava flows are carried away by the force of gravity. These cause disasters of various forms in the areas around volcanoes, sometimes far from eruptive center. Accordingly, volcanic countries, particularly Asian countries such as Japan, Indonesia, and the Philippines, have been the scenes of volcanic disasters. We conducted the research project “Integrated study on mitigation of multimodal disasters caused by the ejection of volcanic products” with the Center for Volcanology and Geological Hazard Mitigation and other institutes in Indonesia under the SATREPS project from FY2013 to 2018. The aim of the project was to advance volcanic hazard mitigation, and I served as the guest editor of “Special Issue on Integrated Study on Mitigation of Multimodal Disasters Caused by Ejection of Volcanic Products” (2016) and “Special Issue on Integrated Study on Mitigation of Multimodal Disasters Caused by Ejection of Volcanic Products: Part 2” (2019) of the Journal of Disaster Research. The articles in the Special Issues have been downloaded by many researchers. The Special Issues cover many topics related to volcanic disasters, but the main theme is how to forecast real-time volcanic hazards using data monitoring, since it is this monitoring that triggers the issuing of warnings. I have studied the volcanic activity of Sakurajima, the most active volcano in Japan, for 40 years, primarily to forecast its eruptions. Forecasting the eruptions is not as important as forecasting the hazards and risks posed by volcanic actions. Research done on the mitigation of the volcanic hazards of Sakurajima as well as Indonesian volcanoes has been enhanced by interaction. The cumulative volume of magma stored in the past 100 years indicates that Sakurajima has the potential for a large-scale eruption (VEI > 4). An eruption and its dispersal of volcanic ash in particular would cause a variety of disasters over a wide area, as described in the other issues of Journal of Disaster Research. I hope that the research results will be utilized for hazard mitigation in the event of future large-scale eruptions. The research could be advanced through collaboration with studies aimed at the enhancement of resilience and recovery.

Electrokinetic Contributions to Self‐Potential Signals From Magmatic Stressing

AbstractPre‐eruptive electrical signals at active volcanoes are generally interpreted in terms of electrokinetic processes. Spatio‐temporal self‐potential (SP) signals can be caused by strain‐induced fluid flow in volcanic aquifers, however, previous studies lack the quantitative assessments of these phenomena and the underpinning poroelastic responses. Here we use Finite‐Element Analysis to study poroelastic responses induced by subsurface stressing from sill and dike sources by jointly solving for ground displacements, pore pressure, and SP signals. We evaluate the influence of pressure source orientation on the poroelastic response in two different volcanic aquifers (pyroclastic and lava flow) to provide insights on emergent geodetic and SP signals and their sensitivity to governing parameters. Strain‐induced SP amplitudes deduced from a reference parameter set vary in both aquifer models and are of negative polarity (−0.35 and −22.6 mV) for a pressurized dike and of positive polarity (+4 and +20 mV) for a pressurized sill. Importantly, we find uniquely different SP and ground displacement patterns from either sill or dike intrusions. Our study shows that SP signals are highly sensitive to the subsurface Young's modulus, streaming potential coupling coefficient and electrical conductivity of the poroelastic domains. For the set of parameters tested, the dike model predicts SP amplitudes of up to −947 mV which are broadly representative of recorded amplitudes from active volcanoes. Our study demonstrates that electrokinetic processes reflect magma‐induced stress and strain variations and highlights the potential of joint geodetic and SP studies to gain new insights on causes of volcanic unrest.

A Confidence-Based Assessment Method for Distinguishing Pyroclastic Density Current Deposits From Other Volcaniclastic Units

Pyroclastic density currents (PDCs) are a destructive volcanic hazard. Quantifying the types, frequency and magnitudes of PDC events is essential for effective risk management, but since historical records at best extend a few hundred years this usually relies on identifying deposits in the geological record. However, small volume unconsolidated PDC deposits have low preservation potential and can be difficult to distinguish from other volcaniclastic units, especially in proximal locations. Consequently many small or poorly exposed deposits can be overlooked. Here, we introduce a structured field method for assessing volcaniclastic deposits of unknown origin with a particular focus on identifying deposits from concentrated PDCs (pyroclastic flows). The method differs from traditional identification schemes in that it does not uniquely attribute a deposit to a single depositional process, but instead assesses how confidently different volcaniclastic processes could explain the observed deposit features. Therefore, the underlying uncertainties in the assessment are explicitly addressed. The method allows consistent, rapid assessment of candidate pyroclastic flow deposits in the field, and the concept could easily be adapted for assessing other types of volcaniclastic deposit. The introduction of confidence levels in deposit interpretations should be useful for carrying though uncertainties into probabilistic assessments of volcanic hazards.

Decrypting silicic magma/plug fragmentation at Azufral crater lake, Northern Andes: insights from fine to extremely fine ash morpho-chemistry

Azufral (SW Colombia) is a dangerous silicic volcano hosting a crater lake, which serves as an excellent example of an incipient plug disruption through phreatomagmatism. We studied the youngest succession of dilute pyroclastic density currents (PDCs) onlapping the north-eastern crater rim. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy was used to carry out an automated single-particle analysis of fine to extremely fine ash. We were able to obtain fast and accurate chemical analysis and imaging of 15,098 particles within the 250–63-μm and the 63–32-μm size ranges. The 2D form and roughness parameters were determined for 4895 juvenile glassy particles and validated by 3D micro-X ray computer tomography. There are two end members of high (group 1) and low (group 2) roughness juvenile glassy particles. Group 1 comprises high-roughness glass particles with solidity values as low as 0.34 in 2D and 0.33 in 3D, and convexity values as low as 0.33 in 2D and 0.26 in 3D. Group 2 comprises low-roughness glass particles with 2D solidity values > 0.79 and 3D solidity values typically > 0.58. In this group, 2D convexity values are > 0.68 and 3D convexity values are > 0.71. Both end members are mostly discriminated by the 2D Concavity Index (0.14 to 0.77 in group 1 vs. 0.05–0.35 in group 2). The remaining group 3 comprises particles of intermediate roughness values. In this study, we show how an incipient plug developed over a short repose time might be subjected to only a few cycles of vesicle nucleation, collapse and densification, retaining the characteristics of juvenile glass. Each glassy juvenile ash type, defined by a particular morphology, roughness and microtexture can be linked to a density “stratified” conduit model. In Azufral, the capping and conduit lining dense regions and the permeable zones of the incipient plug likely cracked. The newly formed cracks could allow hydraulic forcing caused by external water and induce phreatomagmatic interaction. This interaction favoured the fine fragmentation of the plug while enhancing ongoing magmatic processes. Finally, the variations of bulk componentry provided clues on dilute pyroclastic density current transport and physical fractionation processes by secondary fragmentation, elutriation and interaction with the crater rim.

Modelling pyroclastic density currents from a subplinian eruption at La Soufri\xe8re de Guadeloupe (West Indies, France)

We have used a three-dimensional, non-equilibrium multiphase flow numerical model to simulate subplinian eruption scenarios at La Soufrière de Guadeloupe (Lesser Antilles, France). Initial and boundary conditions for computer simulations were set on the basis of independent estimates of eruption source parameters (i.e. mass eruption rate, volatile content, temperature, grain size distribution) from a field reconstruction of the 1530 CE subplinian eruption. This event is here taken as a reference scenario for hazard assessment at La Soufrière de Guadeloupe. A parametric study on eruption source parameters allowed us to quantify their influence on the simulated dynamics and, in particular, the increase of the percentage of column collapse and pyroclastic density current (PDC) intensity, at constant mass eruption rate, with variable vent diameter. Numerical results enabled us to quantify the effects of the proximal morphology on distributing the collapsing mass around the volcano and into deep and long valleys and to estimate the areas invaded by PDCs, their associated temperature and dynamic pressure. Significant impact (temperature > 300 °C and dynamic pressure > 1 kPa) in the inhabited region around the volcano is expected for fully collapsing conditions and mass eruption rates > 2 × 107 kg/s. We thus combine this spatial distribution of temperature and dynamic pressure with an objective consideration of model-related uncertainty to produce preliminary PDC hazard maps for the reference scenario. In such a representation, we identify three areas of varying degree of susceptibility to invasion by PDCs—very likely to be invaded (and highly impacted), susceptible to invasion (and moderately impacted), and unlikely to be invaded (or marginally impacted). The study also raises some key questions about the use of deterministic scenario simulations for hazard assessment, where probability distributions and uncertainties are difficult to estimate. Use of high-performance computing techniques will in part allow us to overcome such difficulties, but the problem remains open in a scientific context where validation of numerical models is still, necessarily, an incomplete and ongoing process. Nevertheless, our findings provide an important contribution to the quantitative assessment of volcanic hazard and risk at La Soufrière de Guadeloupe particularly in the context of the current unrest of the volcano and the need to prepare for a possible future reawakening of the volcano that could culminate in a magmatic explosive eruption.

A model for permeability evolution during volcanic welding

Volcanic ash and pyroclasts can weld when deposited hot by pyroclastic density currents, in near-vent fall deposits, or in fractures in volcano interiors. Welding progressively decreases the permeability of the particle packs, influencing a range of magmatic and volcanic processes, including magma outgassing, which is an important control on eruption dynamics. Consequently, there is a need for a quantitative model for permeability evolution during welding of ash and pyroclasts under the range of conditions encountered in nature. Here we present in situ experiments in which hydrous, crystal-free, glassy pyroclasts are imaged via x-ray tomography during welding at high temperature. For each 3D dataset acquired, we determine the porosity, Darcian gas permeability, specific surface area, and pore connectivity. We find that all of these quantities decrease as a critical percolation threshold is approached. We develop a constitutive mathematical model for the evolution of permeability in welding volcanic systems based on percolation theory, and validate the model against our experimental data. Importantly, our model accounts for polydispersivity of the grainsize in the particle pack, the pressures acting on the pack, and changes in particle viscosity arising from degassing of dissolved H2O during welding. Our model is theoretically grounded and has no fitting parameters, hence it should be valid across all magma compositions. The model can be used to predict whether a cooling pyroclast pack will have sufficient time to weld and to degas, the scenarios under which a final deposit will retain a permeable network, the timescales over which sealing occurs, and whether a welded deposit will have disequilibrium or equilibrium H2O content. A user-friendly implementation of the model is provided.

Characterization and Geotourist Resources of the Campo de Calatrava Volcanic Region (Ciudad Real, Castilla-La Mancha, Spain) to Develop a UNESCO Global Geopark Project

The Campo de Calatrava Volcanic Region is located in Central Spain (Ciudad Real province, Castilla-La Mancha) where some eruptions of different intensity and spatial location took place throughout a period of more than 8 million years. As a result, more than 360 volcanic edifices spread over 5000 km2. Eruptions of this volcanic system were derived from alkaline magmas with events of low explosivity (Hawaiian and Strombolian). These events are characterized by three different manifestations: the emission of pyroclasts (cinder and spatter cones) and lava flows; some hydromagmatic events, which lead to the formation of wide craters (maars) and pyroclastic flows; and remnant volcanic activity related to gas emission (CO2), hot springs (hervideros) and carbonic water fountains (fuentes agrias). The methods used for this study are based on analytical studies of geography, geomorphology and geoheritage to identify volcanoes and their resources and attractions linked to the historical-cultural heritage. These volcanoes are a potential economic resource and attraction for the promotion of volcano tourism (geotourism), and they are the basis for achieving a UNESCO Global Geopark Project, as a sustainable territorial and economic management model, to be part of the international networks of conservation and protection of nature and, especially, that of volcanoes.

Characteristic of the Mount Colo Volcano, Una-Una Island, Central Sulawesi Province: Tectonic Evolution and Disaster Mitigation

The Una-Una Island is in the Gulf of Tomini, Central Sulawesi Province. This island is a soliter active volcano island with Mount Colo as volcano name. The island is located between the North Arm and East Arm of Sulawesi, which are having complex tectonic regime, situated between two subduction zones. Volcanic rocks from Una-Una Island are basaltic-trachyandesite until trachydasite composition with magma affinity is calk-alkaline, high-K calk-alkaline and shoshonite. Tectonic reconstruction in this area started at Miocene (15 Ma) where the Celebes Sea Plate subducted below the North Arm of Sulawesi with a gentle slope produced adakite-type volcanic rocks. Along with the continuous subduction process and increasingly steep angle of subduction, the magma source then underwent. Intensive movement of the Banggai-Sula microcontinent, resulted in obduction of the ophiolite during collision, whereas volcanic activity in Una-Una Island and surrounding islands are still ongoing. Recent eruption of the Mount Colo in 1983 produced abundant of pyroclastic material with acid silica and still adakite type composition with mineralogical assemblages consist of hornblende-phlogophite-biotite, gives the impression that it originated from the same magma sources. According to composition of magma and eruption history which were produced magmatic explosion followed by pyroclastic surge, flow and fall, the disaster mitigation focus to eruption forecasting through visual and instrumental monitoring provide by Centre for Volcanology and Geological Hazard Mitigation, Geological Agency, Ministry of Energy and Mineral Resources Republic of Indonesia.

The Influence of Rock Resistance for Geomorphology of Krakatau Islands, South Lampung District, Lampung Province

Krakatoa Islands is one of the results of high activity volcanic islands located in the Sunda Strait, Indonesia. Volcanic activity of the research area is highly influential on the typical morphological conditions. Rocks produced from this volcano activity a role in the formation of geomorphology that is typical of areas with high volcanic activity. Rocks in the study area were the result of volcanic activity such as lava, pyroclastic alluvial. Geomorphology analysis was conducted by analyzing river flow pattern, slope criteria analysis and shoreline analysis since 1984. East Anak Krakatoa island which is dominated by lava, in contrast to the krakatoa west of which the rock formers are dominantly pyroclastic fall. Unconsolidated rocks form west Sertung island, east Panjang island and south Rakata island which the rock formers are dominantly pyroclastic flow. Evidence of 1883 catastrophic eruption is highly visible on the north Rakata island, east Sertung island and west Panjang island shown by vertical high cliff which is indicated as a caldera structure. The results of the geomorphological analysis are poured into geomorphological maps. Geomorphology unit in research area consist of 9 (nine) geomorphology units of Krakatoa Islands. Krakatoa Islands in this geomorphological case, is still controlled by climate change, erosional of sea water wave, 1883 catastrophic eruption which produces rock in the form of lava and pyroclastic and volcanic activity still continues to this day.

The 15 March 2019 Bezymianny Volcano Explosive Eruption and Its Products

Bezymianny Volcano is one of the most active volcanoes in Kamchatka and in the world. This paper describes the preparation, behavior, products, dynamics, and the geological effect of the March 15, 2019 explosive eruption of the volcano, which was predicted 6.5 h before it began. The sequence of eruptive events was analyzed using data provided by video and satellite-based monitoring of the volcano; the quantitative characteristics for the distribution of pyroclastic deposits were obtained in the information system “Remote Monitoring of Activity of Volcanoes in Kamchatka and the Kurile Islands”. The explosions lifted ash to heights of 15 km above sea level (up to 12 km above the volcano), the eruptive cloud was moving northeastward and east from the volcano, the main ashfall area was 210 400 km2, including 15 000 km2 on land. Apart from tephra, the eruption produced pyroclastic flows and pyroclastic surges covering an area of 30 km2. The total volume of explosive products is estimated as 0.1–0.2 km3. The eruptive rocks are calc-alkaline moderate-K basaltic andesites (SiO2 = 54.84–56.29 wt %), they are the most mafic among all rocks of the current Bezymianny eruption cycle.

The interaction between concentrated pyroclastic density currents and snow: a case study from the 2008 mixed-avalanche from Volcán Llaima (Chile)

The incorporation of snow and ice by pyroclastic density currents (PDCs) can generate mixed-avalanches and pose significant hazards at snow-clad volcanoes. Commonly, the poor preservation of these thin deposits, combined with the subtle characteristics of PDC-snow interaction, has limited their recognition in the geological record. A small-volume (2.5 × 105 m3), basaltic-andesite, mixed-avalanche deposit formed during the 2008 eruption of Volcan Llaima (Chile) provides insight into PDC and snow interactions. Pyroclasts accumulated on the crater rim and collapsed to form a flow that swept up to 2.8 km from source and spread across 6.09 × 105 m2 of the snow-clad slopes. The PDC-snow interaction at the crater rim or during flow propagation resulted in distinct deposit and pyroclast textures. These included abundant blocky non-vesicular cauliflower clasts and blocky poorly vesicular scoria. The thin and sheet-like mixed-avalanche deposit had a lumpy surface, lacked marginal levees, was very loose, and fine ash depleted. Although the flow likely incorporated snow and/or ice mechanically, the overall coarseness of the mixture precluded effective fluidization related to vaporization. Many of the features described herein are distinctive features of other mixed-avalanche deposits worldwide and should be considered key indicators of PDC-snow interaction.

Characterization of Acoustic Infrasound Signals at Volcán de Fuego, Guatemala: A Baseline for Volcano Monitoring

Monitoring volcanic unrest and understanding seismic and acoustic signals associated with eruptive activity is key to mitigate its impacts on population and infrastructure. On June 3, 2018, Volcan de Fuego, Guatemala, produced a violent eruption with very little warning. The paroxysmal phase of this event generated pyroclastic density currents (PDC) that impacted nearby settlements resulting in 169 fatalities, 256 missing, and nearly 13,000 permanently displaced from their homes. Since then, Volcan de Fuego has been instrumented with an extensive network of seismic and infrasound sensors. Infrasound is a new monitoring tool in Guatemala. A key step toward its effective use in volcano monitoring at Volcan de Fuego is establishing a baseline for the interpretation of the recorded signals. Here, we present the first comprehensive characterization of acoustic signals at Volcan de Fuego for the whole range of surface activity observed at the volcano. We use data collected during temporary deployments in 2018 and from the permanent infrasound network. Infrasound at Fuego is dominated by the occurrence of short-duration acoustic transients linked to both ash-rich and gas-rich explosions, at times associated with the generation of shock waves. The rich acoustic record at Fuego includes broadband and harmonic tremor, and episodes of chugging. We explore the occurrence of these signals in relation to visual observations of surface activity, and we investigate their source mechanisms within the shallow conduit system. This study provides a reference for the interpretation of acoustic signals at Volcan de Fuego and a baseline for real-time monitoring of its eruptive activity using infrasound data. Our results suggest that changes in the style of activity and morphology of the summit crater are reflected in the acoustic signature of eruption; as such our study provides a reference for the interpretation of acoustic signals at Volcan de Fuego and a baseline for real-time monitoring of its eruptive activity using infrasound.

Evidence for a large-magnitude Holocene eruption of Mount Rittmann (Antarctica): A volcanological reconstruction using the marine tephra record

In Antarctica, the near-source exposures of volcanic eruption deposits are often limited as they are not well preserved in the dynamic glacial environment, thus making volcanological reconstructions of explosive eruptions extremely challenging. Fortunately, pyroclastic deposits from explosive eruptions are preserved in Southern Ocean sediments surrounding Antarctica, and the tephrostratigraphy of these sequences offers crucial volcanological information including the timing and tempo of past eruptions, their magnitude, and eruption dynamics. Here we report the results of a tephrostratigraphy and tephrochronology study focused on four sediment cores recovered from the Wood Bay area in the western Ross Sea, Antarctica. In all these sedimentary sequences, we found a well-stratified primary tephra of considerable thickness, up to 80 cm, hereafter named the Aviator Tephra (AVT). According to the characteristics of the tephra deposit and its distribution, the AVT was associated with an eruption of considerable intensity, potentially representing one of the largest Holocene eruptions recorded in Antarctica. Based on the major and trace element geochemistry and the mineral assemblage of the tephra, Mount Rittmann was identified as the source of the AVT. A Holocene age of ∼11 ka was determined by radiocarbon dating organic material within the sediments and 40Ar-39Ar dating of alkali-feldspar crystals included in the tephra. Eruption dynamics were initially dominated by hydromagmatic magma fragmentation conditions producing a sustained, relatively wet and ash-rich eruptive cloud. The eruption then evolved into a highly energetic, relatively dry magmatic Plinian eruption. The last phase was characterized by renewed efficient magma-water interaction and/or collapse of the eruptive column producing pyroclastic density currents and associated co-ignimbritic plumes. The distal tephra deposits might be linked to the widespread lag breccia layer previously identified on the rim of the Mount Rittmann caldera which share the same geochemical composition. Diatoms found in the sediments surrounding the AVT and the primary characteristics of the tephra indicate that the Wood Bay area was open sea at the time of the eruption, which is much earlier than previously thought. AVT is also an excellent tephrostratigraphic marker for the Wood Bay area, in the Ross Sea, and a useful marker for future synchronization of continental ice and marine archives in the region.

Observations of lightning in relation to transitions in volcanic activity during the 3 June 2018 Fuego Eruption

Satellite and ground-based remote sensing are combined to characterize lightning occurrence during the 3 June 2018 Volcán de Fuego eruption in Guatemala. The combination of the space-based Geostationary Lightning Mapper (GLM) and ground-based Earth Networks Total Lightning Network observed two distinct periods of lightning during this eruption totaling 75 unique lightning flash occurrences over five hours (57 in cloud, 18 cloud-to-ground). The first period of lightning coincided with the rapid growth of the ash cloud, while the second maxima occurred near the time of a deadly pyroclastic density current (PDC) and thunderstorm. Ninety-one percent of the lightning during the event was observed by only one of the lightning sensors, thus showing the importance of combining lightning datasets across multiple frequencies to characterize electrical activity in volcanic eruptions. GLM flashes during the event had a median total optical energy and flash length of 16 fJ, and 12 km, respectively. These median GLM flash energies and lengths observed in the volcanic plume are on the lower end of the flash spectrum because flashes observed in surrounding thunderstorms on 3 June had larger median total optical energy values (130 fJ) and longer median flash lengths (20 km). All 18 cloud-to-ground flashes were negative polarity, supportive of net negative charge within the plume. Mechanisms for the generation of the secondary lightning maxima are discussed based on the presence and potential interaction between ash plume, thunderstorm, and PDC transport during this secondary period of observed lightning.

Postseismic deformation following the 2016 Kumamoto earthquake detected by ALOS-2/PALSAR-2

I have been conducting a study of postseismic deformation following the 2016 Kumamoto earthquake using ALOS-2/PALSAR-2 acquired till 2018. I apply ionospheric correction to interferograms of ALOS-2/PALSAR-2. L-band SAR gives us high coherence enough to reveal surface deformation even in vegetated or mountainous area for pairs of images acquired more than 2 years. Postseismic deformation following the Kumamoto earthquake exceeds 10 cm during 2 years at some spots in and around Kumamoto city and Aso caldera. Westward motion of ~ 6 cm/year was dominant on the southeast side of the Hinagu fault, while westward shift was detected on both sides of the Futagawa fault. The area of latter deformation seems to have correlation with distribution of pyroclastic flow deposits. Significant uplift was found around the eastern Futagawa fault and on the southwestern frank of Aso caldera, whose rate reaches 4 cm/year. There are sharp changes across several coseismic surface ruptures such as Futagawa, Hinagu, and Idenokuchi faults. Rapid subsidence between Futagawa and Idenokuchi faults also found. It is confirmed that local subsidence continued along the Suizenji fault, which newly appeared during the mainshock in Kumamoto City. Subsidence with westward shift of up to 4 cm/year was also found in Aso caldera. Time constant of postseismic decay ranges from 1 month to 600 days at selected points, but that postseismic deformation during the first epochs or two is dominant at point in the Kumamoto Plain. This result suggests multiple source of deformation. Westward motion around the Hinagu fault may be explained with right lateral afterslip on the shallow part of this fault. Subsidence along the Suizenji fault can be attributed to normal faulting on dipping westward. Deformation around the Hinagu and Idenokuchi faults cannot be explained with right lateral afterslip of Futagawa fault, which requires other sources. Deformation in northern part of Aso caldera might be the result of right lateral afterslip on a possible buried fault.

Paleomagnetic constraints on a time-stratigraphic framework for the evolution of Ohachidaira volcano and the summit caldera, central Hokkaido, Japan

We present a revised stratigraphy of the proximal deposits around Ohachidaira volcano and their paleomagnetic directions obtained from 21 sites (193 samples). We identify four proximal pyroclastic members from Ohachidaira volcano that were produced after the early edifice-building effusive volcanism, from older to younger: (1) vent-opening mafic pyroclastic density current (PDC) deposits (Kobachidaira ignimbrite); (2) maar-forming mafic tephra-ring deposits (Mamiyadake tephra ring); (3) mafic to silicic caldera-forming deposits (Sounkyo Member); and (4) mafic PDC deposits (Kumonotaira ignimbrite). Well-grouped paleomagnetic directions obtained from the Kobachidaira ignimbrite and the Sounkyo Member indicate that each deposit was formed over a short time interval compared to geomagnetic secular variation―that is, less than a century. Conversely, scattered paleomagnetic directions of the Mamiyadake tephra ring record the secular variation of the geomagnetic field that took place over a longer time interval―that is, at least 750 yr, probably more. The Kumonotaira ignimbrite, which has a similar paleomagnetic direction to the underlying Sounkyo Member, may have been produced during the Sounkyo eruption. From comparison between our data and the previously reported paleomagnetic directions of two petrologically distinct distal ignimbrites, we conclude that the Sounkyo Member is a proximal correlative of the distal pyroxene-rich ignimbrite, and that the distal hornblende-rich ignimbrite may not be of an Ohachidaira origin. The revised stratigraphy suggests that Ohachidaira volcano is a maar-caldera complex volcano, and that the summit caldera is a flaring funnel formed incrementally by explosive erosion and syn-eruptive collapse of the vent walls. Volume estimates imply that the Sounkyo eruption fundamentally enlarged the vent and formed the caldera. Our data confirm that the comparison of paleomagnetic directions can offer a useful identification and correlation tool for the Ohachidaira pyroclastic sequences.

Fireside tales: understanding experiences of previous eruptions and factors influencing the decision to evacuate from activity of Volcán de Fuego

Volcán de Fuego (Guatemala) is capable of large (VEI?2) explosive eruptions like that of June 2018, which triggered pyroclastic flows that devastated the community of San Miguel Los Lotes, causing hundreds of fatalities and severe long-term socio-economic impacts. Future volcanic risk mitigation efforts are likely to involve temporary evacuation of local communities, the success of which requires co-operation between locals, scientists, and decision-makers. However, how locals' experiences of eruptive activity influence their responses to evacuation has not been studied in detail. We investigated these themes through semi-structured interviews that focussed on direct experience as opposed to volcanic risk perception, revealing substantial differences between scientists' and locals' observations of Fuego’s activity. Furthermore, a disparity emerged between communities on Fuego's west and east flanks in terms of direct prior eruption experience and communication with authorities. These findings have serious implications for future evacuation efforts at Fuego and at other highly populated volcanoes.

Mineralogical characterization and diagenetic history of Permian marine tuffaceous deposits in Guangyuan area, northern Sichuan basin, China

Based on thin section identification, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis of samples from cuttings and cores in drillings, tuffaceous deposits were identified to intercalate in marine carbonate rocks and mudstones in the upper part of Maokou Formation and the middle to lower part of the Wujiaping Formation in Guangyuan area, northern Sichuan basin, China. These tuffaceous deposits are of significance to understand the influence range of magmatic activity of the Emeishan Large Igneous Provinces (ELIP), and explore and exploit oil and gas reservoirs in Permian strata in the Sichuan basin. The research results indicated that tuffs formed 0.1–10 mm-thick laminae, and they formed lamellar interbedding with organic mudstones and carbonaceous mudstones, which were sandwiched among bioclast limestones and marls. Tuffaceous deposits in the study area include tuff, sedimentary tuff and tuffaceous sedimentary rock. Under the influence of sulfate reduction, acidic hydrotherm and alkaline fluid, tuffaceous deposits were altered by diagenesis such as dolomitization, argillization, pyritization and dissolution, and formed a variety of secondary rocks and pores which characterized by the micron-scale solution pores in tuff components and the nanometer-scale intercrystal pores among authigenic clay minerals. In addition, the primary directional sedimentary structure of tuffs and sedimentary tuffs and developed laminae in the rocks are conducive to the formation of fissures parallel to laminae, and effectively improve the reservoir property of rocks. The tuffaceous deposits in the study area are mainly the products of subaqueous pyroclastic flow that were dominated by acidic magmatism and indicated that they may not be directly related to the ELIP, which is located in the southwest Sichuan-Yunnan provinces and dominated by continental eruption of basalt.