Pyroclastic Flows Research Articles

Analysis of the effect of the 2021 Semeru eruption on water vapor content and atmospheric particles using GNSS and remote sensing

Mount Semeru, an active volcano in East Java, Indonesia, erupted on December 4, 2021, following extreme rainfall that caused an avalanche of hot pyroclastic flows and lava. The tropospheric conditions and dominant particle components in the atmosphere can be monitored using Global Navigation Satellite System (GNSS) technology and remote sensing satellites. GNSS signal propagation delay in Precise Point Positioning (PPP) processing can be used to determine Zenith Tropospheric Delay (ZTD) and Precipitable Water Vapor (PWV) variables so that atmospheric conditions can be generated. In addition, by using remote sensing satellite data, it is possible to obtain rainfall data with high temporal resolution as well as the dominant particle and gas content values during eruptions. During the eruption period, the high value of PWV was dominated by the high intensity of precipitation during the rainy season. High rainfall before the eruption caused activity inside the mountain to increase, which occurred in avalanche type eruption. Apart from that, the atmosphere around Semeru was also dominated by SO2 content, which spreaded for tens of kilometers. SO2 content began to be detected significantly by remote sensing sensors on December 7, 2021. In this study, deformation and atmospheric monitoring were also carried out using low-cost GNSS at the Semeru Monitoring Station on September 9–15, 2022. The results of the ZTD and ZWD values show the dominance of the wet component, which is directly proportional to rainfall activity in this period.

Formation of undulating seafloor bedforms during the Minoan eruption and their implications for eruption dynamics and slope stability at Santorini

The Minoan eruption of Santorini is one of the largest Holocene volcanic events and produced several cubic kilometers of pyroclastic flows emplaced on the submerged flanks of the volcano. Marine geophysical surveys reveal a multitude of undulating seafloor bedforms (USBs) around Santorini. While similar structures are known from other volcanoes worldwide, Santorini offers the unique opportunity to relate USB formation with volcanic processes during one of the best-studied volcanic eruptions worldwide. In this study, we combine high-resolution seismic reflection data with multibeam echosounder bathymetry to reveal the internal architecture of USBs around Santorini and to relate their morphological characteristics to formational processes. The USBs around Santorini were formed during the Minoan eruption and represent the seafloor expression of mass transport deposits. Three types of deposits differ in composition or origin. (1) Depositional USBs, which can only be found to the north of the island, where Minoan eruption ignimbrites reach their maximum thickness and the undulating topography is the result of thrusting within the deposit. (2) USBs related to slope failures of volcaniclastics from the entire Thera Pyroclastic Formation, which can be found east, south, and west of the island. (3) USBs associated with deep-seated deformation, which occurs on the southwestern flank along an area affected by rift tectonics and extends to a depth of more than 200 m below the seafloor. In cases (2) and (3), the USBs are formed upslope by block rotation and downslope by thrusting. Our study indicates that these processes may have contributed to the generation of the devastating Minoan tsunami. Since Santorini is located in one of the most tectonically active regions in the Mediterranean, capable of producing earthquakes with magnitude M7+, our study has important implications for hazard assessment. A strong earthquake located close to the island may have the potential to reactivate slope instabilities posing a previously undetected but potentially significant tsunami hazard.

Wave Generation by Fluidized Granular Flows: Experimental Insights Into the Maximum Near‐Field Wave Amplitude

AbstractTsunamis can be generated by an impulsive displacement of water resulting from the entrance of pyroclastic density currents (PDCs). The maximum wave amplitude is of primary interest regarding tsunami modeling and applications to hazard assessment. This study explores tsunami generation by fluidized granular flows and analyzes published relationships predicting maximum wave amplitudes from PDC characteristics. A fluidized column of glass beads is released from a reservoir, flows down an inclined plane and enters a water‐filled flume, generating waves. Fluidized flows of greater mass enter the flume with greater velocities; however, all the analyzed flows impact the water with a supercritical impact Froude number. Flows of greater mass generate a single, high‐amplitude wave, followed by a longer‐period trough. The solitary‐like leading wave propagates along the flume with a nearly constant amplitude. In contrast, the leading wave is followed by a low‐amplitude trough and a second low‐amplitude crest when generated by lower mass flows. Dispersive effects are stronger for waves produced by flows of lower masses, causing the decrease of the amplitudes with distance from the shore. Increased breaking and dissipation cause decreased amplitudes of the waves generated in shallow water depths. The predictive equations, determined based on the impact Froude number and the water depth in the constant‐depth section of the flume, provide relatively good predictions of the maximum wave amplitudes. A new approach is proposed, which calculates the impact Froude number considering the water depth value where the wave generation occurs, providing an improved understanding of the wave generation process.

Characterizing and Mapping Volcanic Flow Deposits on Mount St. Helens via Dual-Band SAR Imagery

Mapping volcanic flow deposits can be achieved by considering backscattering characteristics as a metric of surface roughness. In this study, we developed an approach to extract a measure of surface roughness from dual-band airborne Synthetic Aperture Radar (ASAR) backscattering data to characterize and map various volcanic flow deposits—namely, debris avalanches, lahars, lava flows, and pyroclastic density currents. We employed ASAR and Indian Space Research Organization (ISRO) airborne SAR datasets, from a joint project (ASAR-ISRO), acquired in December 2019 at 2 m spatial resolution, to assess the role and importance of incorporating dual-band data, i.e., L-band and S-band, into surface roughness models. Additionally, we derived and analyzed surface roughness from a digital surface model (DSM) generated from unoccupied aircraft systems (UAS) acquisitions using Structure from Motion (SfM) photogrammetry techniques. These UAS-derived surface roughness outputs served as meter-scale calibration products to validate the radar roughness data over targeted areas. Herein, we applied our method to a region in the United States over the Mount St. Helens volcano in the Cascade Range of Washington state. Our results showed that dual-band systems can be utilized to characterize different types of volcanic deposits and range of terrain roughness. Importantly, we found that a combination of radar wavelengths (i.e., 9 and 24 cm), in tandem with high-spatial-resolution backscatter measurements, yields improved surface roughness maps, compared to single-band, satellite-based approaches at coarser resolution. The L-band (24 cm) can effectively differentiate small, medium, and large-scale structures, namely, blocks/boulders from fine-grained lahar deposits and hummocks from debris avalanche deposits. Additionally, variation in the roughness estimates of lahar and debris avalanche deposits can be identified and quantified individually. In contrast, the S-band (9 cm) can distinguish different soil moisture conditions across variable terrain; for example, identify wet active channels. In principle, this dual-band approach can also be employed with time series of various other SAR data of higher coherence (such as satellite SAR), using different wavelengths and polarizations, encompassing a wider range of surface roughness, and ultimately enabling additional applications at other volcanoes worldwide and even beyond volcanology.

Explosive sequence of La Soufrière, St Vincent, April 2021: insights into drivers and consequences via eruptive products

Abstract This paper forensically reconstructs the timings, impacts and processes that drove the sequence of explosive eruptions of La Soufrière, St Vincent in April 2021 using a combination of field-based stratigraphy and textural dissection of the deposit character together with contemporary visual observations. Explosive activity on 9 April and early on 10 April involved destruction of almost all of the 2020/2021 lava dome, c. 60% of the 1979 dome and formation of a 600 m diameter crater by 2pm UTC on 10 April. Following the initial explosion, plumes rose to altitudes of c. 15 km and pyroclastic density currents (PDCs), formed by column collapse, first occurred on 10 April, only after >24 h of explosive activity. Dense PDCs reached the sea only in the Larikai and Roseau valleys, and dilute PDCs were restricted to within 2.5 km of the Summit Crater rim. The tephra fallout deposits are stratified, composed of numerous layers of both lapilli-rich and ash-rich layers, which we have grouped into at least 7 units, based on their common characteristics (Units 1 to 7). Volume estimates, using a range of techniques to constrain uncertainties, indicate that the bulk volume of tephra (fallout and PDC) is 1.19 × 10 8 m 3 ± 20% making this a VEI 4 eruption.

Large-scale volcanic deposit fluidization by dilute pyroclastic density currents

Large-scale volcanic deposit fluidization by dilute pyroclastic density currents

Axisymmetric column collapses of bi-frictional granular mixtures

The behaviour of granular column collapses is associated with the dynamics of geohazards, such as debris flows, landslides and pyroclastic flows, yet their underlying physics is still not well understood. In this paper, we explore granular column collapses using the sphero-polyhedral discrete element method, where the system contains two types of particles with different frictional properties. We impose three different mixing ratios and multiple different particle frictional coefficients, which lead to different run-out distances and deposition heights. Based on our previous work and a simple mixture theory, we propose a new effective initial aspect ratio for the bi-frictional granular mixture, which helps unify the description of the relative run-out distances. We analyse the kinematics of bi-frictional granular column collapses and find that deviations from classical power-law scaling in both the dimensionless terminal time and the dimensionless time when the system reaches the maximum kinetic energy may result from differences in the initial solid fraction and initial structures. To clarify the influence of initial states, we further decrease the initial solid fraction of granular column collapses, and propose a trial function to quantitatively describe its influence. Due to the utilization of a simple mixture theory of contact occurrence probability, this study can be associated with the friction-dependent rheology of granular systems and friction-induced granular segregations, and further generalized to applications with multiple species of particles in various natural and engineering mixtures.

Crystallization-controlled fusion mechanism of the amorphous fly ash from the Shell coal gasifier by particle sieving

The mineral in coal is transformed to the fly ash of different particle sizes during the entrained flow coal gasification, causing the ash deposition problem on the radiant syngas cooler. In this study, the fusion behavior of fly ash collected from a Shell coal gasifier was analyzed by particle sieving. Results indicated that the fusibility of amorphous fly ash was influenced by the anorthite crystallization at high temperature. The fusion process of fly ash particle was divided into the sintering stage, plateau stage, and melting stage, which were caused by the flow of the amorphous fly ash, anorthite crystallization, and anorthite melting, respectively. The high theoretical anorthite content and the low fly ash viscosity improved the anorthite crystallization reaction in the fly ash particles <45 μm, resulting in a wide plateau stage, narrow melting stage, and high ash fusion temperatures (AFTs). Therefore, the fusion behavior of fly ash particles <45 μm followed “melting-dissolution” mechanism. In contrast, the fusion of fly ash particles >45 μm belonged to the “softening-melting” mechanism for the weak anorthite crystallization behavior. The fly ash particles <45 μm may cause the serious ash deposition problems for its low viscosity.

MAPPING AREAS IMPACTED BY VOLCANIC FLOWS DURING AN ERUPTION USING SYNTHETIC APERTURE RADAR AND OPTICAL IMAGERY

Abstract. During volcanic disasters, the remoteness of the terrains combined with potentially incapacitated lifelines (e.g., disturbed transportation network) prevent ground-based surveys for timely assessment of damage extents. To that effect, we worked to combine satellite optical and Synthetic Aperture Radar (SAR) data to rapidly delineate the areas impacted by fast-moving volcanic flows during an eruption (e.g., Pyroclastic Density Currents (PDCs), lahars), which can in turn be used to target and organize the response efforts. We used the 2015 eruptions of Volcán de Colima (Mexico) and Volcán Calbuco (Chile) volcanoes to calibrate detection thresholds of different types of volcanic flows, from optical and SAR imagery. Optical imagery is used to calculate temporal changes of Normalized Difference Vegetation Index (NDVI) associated with the presence of erupted materials on the surface. SAR amplitude images are used to detect changes in surface roughness (sigma0) attributed to the emplacement of new volcanic flows. Classification of the respective NDVI and SAR amplitude signal changes for different types of volcanic flows is done using very-high-resolution imagery and ground-based data obtained during field work. Linear rescaling of minimal and maximal threshold signals is used to create probability maps of volcanic flow deposits extent, and then combined into a joint probability map to maximize the accuracy of the deposit extents. We tested our ability to generate volcanic flow extent maps during the April 2021 eruption of Soufrière St Vincent, using this detection method and the calibrated threshold values for PDCs and lahars.

Scenario-based probabilistic hazard assessment for explosive events at the San Salvador volcanic complex, El Salvador

We present a scenario-based, probabilistic hazard assessment for the San Salvador volcanic complex (SSVC), a volcanic field located in the vicinity of San Salvador that includes the El Boquerón stratovolcano and 25 monogenetic vents. We define a set of likely eruption scenarios for tephra fallout and pyroclastic density currents (PDCs). The eruption scenarios range from violent Strombolian eruptions with a significant uncertainty in source position to sub-Plinian and Plinian activity fed from the central cone. The adopted methodology is mainly based on numerical modeling using Tephra2 (adopting the software TephraProb) to study tephra fallout and the branching box model and the branching energy cone model (adopting the programs BoxMapProb 2.0 and ECMapProb 2.0) to describe inertial and frictional PDCs, respectively. Despite the dominant W-WSW-trending winds, numerical results show that Plinian eruptions at El Boquerón volcano are able to deposit thick tephra layers in the metropolitan area of San Salvador city, likely reaching mass loads of the order of 100 kg/m2 (conditional probability of 50%). The simulated sub-Plinian events highlight the seasonal influence of wind patterns. In fact, the conditional probability of significant tephra sedimentation in San Salvador city is strongly reduced when eruptions occur during the rainy season. Numerical modeling of violent Strombolian eruptions is performed considering uncertainty in vent position. Results show that the conditional probability of depositing tephra mass loads higher than 10 kg/m2 at a given point reaches a maximum value of ∼7% on the NW flank of the volcano, at about 8 km from the central crater. On the other hand, very low conditional probabilities (<1%) are obtained for San Salvador city for any relevant threshold (10 kg/m2 or more) of tephra mass load during violent Strombolian events. Regarding PDCs, results show that those produced during large-scale Plinian eruptions are able to invade significant areas of the volcano surroundings, including San Salvador city. PDCs generated from the partial collapse of a sub-Plinian eruption column exhibit maximum inundation probabilities on the N, W and S flanks of the volcano. Cerro El Picacho exerts a significant shield effect on the propagation of these PDCs, with low inundation probabilities for San Salvador city (<3%). Finally, coupling published vent opening probability maps and numerical modeling of small-scale PDCs yields maximum inundation probabilities on the NW flank of the volcano, reaching maximum conditional probabilities of the order of ∼10% and values of about 5% near the village of Nuevo Sitio del Niño.

Coastal sedimentation and topographic changes in the Mataram Plain, Lombok (Indonesia) following the 1257 CE eruption of Samalas volcano

AbstractThe 1257 CE eruption of Samalas volcano, Indonesia, buried the entire island of Lombok beneath various thicknesses of pyroclastic material during this Volcanic Explosivity Index (VEI) 7 event. This study aims to reconstruct the paleo‐topography of western Lombok before the Samalas eruption in 1257 CE and analyse the sedimentation processes that led to its landscape evolution over the last 700 years. Stratigraphic data were collected from various surveys, such as outcrops, coring, drilling, hand auger and wells observation. Electrical resistivity tomography (ERT) measurements were performed to complement the stratigraphic data. A combination of stratigraphy, ERT and topographic data from various sources (topographic map, Digital Elevation Model Nasional [DEMNAS] and Real Time Kinematic [RTK] measurement) is employed to determine the depth of the paleo‐surface. Topographic modelling was performed by subtracting the delta‐DEM (DDEM) from the current‐DEM (CDEM). The result of this operation is a paleo‐DEM, which is used to reconstruct the paleo‐hydrographic features such as shoreline positions and river channels. Modelling results demonstrate that the relief has not been significantly modified, except in lowland areas, which is the sediment accumulation zone. River channels have experienced minor changes, except for the location of the river mouth and the degree of meandering. Significant changes occurred at the shoreline that has prograded by approximately 1.6 km during the last 700 years. A schematic model is built to illustrate the evolution processes of the study area, consisting of the pre‐eruption condition, the immediate post‐eruption condition and development of the current condition. This model further develops the previously proposed model with a higher resolution and simultaneously revises the estimated boundary of the pyroclastic density current (PDC) deposit from previous work.

The fragmentation-induced fluidisation of pyroclastic density currents

Pyroclastic density currents (PDCs) are the most lethal volcanic process on Earth. Forecasting their inundation area is essential to mitigate their risk, but existing models are limited by our poor understanding of their dynamics. Here, we explore the role of evolving grain-size distribution in controlling the runout of the most common PDCs, known as block-and-ash flows (BAFs). Through a combination of theory, analysis of deposits and experiments of natural mixtures, we show that rapid changes of the grain-size distribution transported in BAFs result in the reduction of pore volume (compaction) within the first kilometres of their runout. We then use a multiphase flow model to show how the compressibility of granular mixtures leads to fragmentation-induced fluidisation (FIF) and excess pore-fluid pressure in BAFs. This process dominates the first ~2 km of their runout, where the effective friction coefficient is progressively reduced. Beyond that distance, transport is modulated by diffusion of the excess pore pressure. Fragmentation-induced fluidisation provides a physical basis to explain the decades-long use of low effective friction coefficients used in depth-averaged simulations required to match observed flow inundation.

Silicic volcanic rocks, a main regional source of geogenic arsenic in waters: Insights from the Altiplano-Puna plateau, Central Andes

Volcanic rocks are a common, worldwide source of geogenic arsenic (As) that can affect water quality detrimentally. Nonetheless, variations of As concentration within different types of volcanic rocks and questions related to the original source of As in magma are not yet fully understood. We compiled published As data from the abundant Cenozoic volcanic rocks of the Altiplano-Puna plateau, considered the main source of As for waters in the region. These data indicates that volcanic rocks in the Altiplano-Puna have a mean As concentration of 9.1 mg/kg, which is almost 2 times higher than the upper continental crust. Arsenic increases within the more silicic compositions such as dacites and rhyolites as well as from mafic monogenetic volcanic edifices to stratovolcanoes of intermediate composition, silicic calderas and ignimbrite fields. The rate and composition of crustal assimilation by the magmas (enhanced by the crustal thickness up to >70 km) strongly influence the As concentration in volcanic rocks. The assimilation of argillaceous shale-type sediments represents the most important source of As in the magmas. The eruption dynamics has an enormous effect on As concentration. The higher the explosivity of an eruption, the higher the amount of ash that will be formed. Arsenic can be sorb onto ash particles so that fall deposits produced during explosive volcanic eruptions are prone to high As concentrations. Large volume ignimbrites formed after caldera collapses in the Altiplano-Puna are often the result of sustained explosive eruptions related to low, dense pyroclastic fountaining eruptions where highly concentrated pyroclastic density currents (PDC, flowing pyroclastic mixtures of particles and gas) are able to maintain high temperatures for long periods. Then As released from volatiles may remain for longer time in the emplacing PDC and can be sorbed onto ash particles, resulting in deposits with a higher As concentration. Post eruption hydrothermal alteration and sulfide mineralization produce As enrichment up to 100 times in the volcanic rocks (957 mg/kg) of the region, but can be very heterogeneous. Volcanism and its related products are the main source of As in the region. Once As is released from the volcanic sources, the semiarid climate, the occurrence of Na-HCO3 water types, and alkaline pH further enhance As concentrations in surface water and groundwater.

A 200-year snapshot of soil development in pyroclastic deposits derived from the 1815 super explosive eruption of Mount Tambora in Indonesia

Early-stage pedogenic processes and formation rates on completely obliterated volcanic landscapes, such as the super explosive 1815 Mount Tambora eruption, have not previously been robustly explored. The objectives of this study were to determine (i) the mineralogical composition of the sand fraction, selected physical and chemical soil properties and potential nutrient reserves after 200 years of pedogenesis, and (ii) chemical weathering indices, rate of soil formation, and rates of C and N accretion. Soil formation was examined for five soil profiles on stable plain/foot slope positions representing the diversity of soils in these landscape positions, which are important for agricultural production. Results showed that the soil mineralogical composition of the sand fraction was dominated by easily weatherable minerals (e.g., labradorite and augite volcanic glass) indicating high potential nutrient reserves (e.g., Ca2+, Mg2+, K+, P) as confirmed by X-ray fluorescence (XRF) analyses. Allophanic material formation was minimal (<2.3%) owing to the preferential accumulation of Al3+ into Al-humic complexes. The low contents of allophanic materials and metal-humus complexes resulted in low P-retention (17.5–43.4%) within the soil solum, with the highest value in surface horizons (33–43%). Morphological features showed rapid solum (A + B horizons) development of 22 to 107 cm. Shallow soils occurred on shallow eruption deposits (consisting of pyroclastic flow underlain by pumice), whereas the deepest soils were found on thick deposit consisting of either trachyandesite pyroclastic or basaltic andesite materials. The chemical index of alteration (CIA) followed the order of A horizons (48.4 ± 4.6) > B horizons (45.4 ± 2.4) > C horizons (43.8 ± 4.2) ≈ tephra/lava (43.1), indicating accumulation of Al oxides and depletion of base cations in the upper horizons. Similarly, the base depletion index (BDI) showed a trend of A horizons (1.13 ± 0.18) < B horizons (1.25 ± 0.09) < C horizons (1.34 ± 0.20) ≈ tephra/lava (1.35), indicating depletion of base cations (Ca2+, Mg2+, K+, Na+) from the soil surface to C horizons. Based on solum depths (A + B horizons) and 200 years of post-eruption soil development, the solum formation rate ranged from 1.2 to 5.3 mm yr−1. Appreciable stocks of SOC (2.3–12.8 kg C m−2) and SON (0.21–0.77 kg m−2) accumulated over the 200 year period. Eruption materials from the Mt. Tambora eruption with a precisely known timescale contributed new pedological insights documenting rapid soil formation rates from pyroclastic materials leading to a rapid recovery of soil functions to support agricultural production.

A new hazard scenario at Vesuvius: deadly thermal impact of detached ash cloud surges in 79CE at Herculaneum

Diluted pyroclastic density currents are capable to cause huge devastation and mortality around volcanoes, and temperature is a crucial parameter in assessing their lethal power. Reflectance analysis on carbonized wood from ancient Herculaneum allowed a new reconstruction of the thermal events that affected buildings and humans during the 79CE Vesuvius eruption. Here we show that the first PDC entered the town was a short-lived, ash cloud surge, with temperatures of 555–495 °C, capable of causing instant death of people, while leaving only a few decimeters of ash on ground, which we interpret as detached from high concentration currents. The subsequent pyroclastic currents that progressively buried the town were mostly higher concentration PDCs at lower temperatures, between 465 and 390 and 350–315 °C. Charcoal proved to be the only proxy capable of recording multiple, ephemeral extreme thermal events, thus revealing for the first time the real thermal impact of the 79CE eruption. The lethal impact documented for diluted PDC produced during ancient and recent volcanic eruptions suggests that such hazard deserves greater consideration at Vesuvius and elsewhere, especially the underestimated hazard associated with hot detached ash cloud surges, which, though short lived, may expose buildings to severe heat damages and people to death.

An Eocene leaf flora from the northern Peruvian Andes

The fossil forest known as El Bosque Petrificado Piedra Chamana lies in close proximity to the village of Sexi in the Department of Cajamarca in northern Peru. The forest was deposited in either a lahar or pyroclastic flow, and ashfall deposits, as mineralized wood and leaf impressions 39 million years ago (late Middle Eocene). More than 30 types of non-monocot angiosperms have been described from the fossil wood, which is densely embedded in rock outcrops, scattered across the ground, and occasionally found in situ. Anatomical characteristics and identifications of the woods suggest a seasonally flooded lowland tropical forest with a dry period. This site also preserves a small leaf flora which has not received a full treatment in earlier works and is the focus of the present study. The leaves are described in detail using standard leaf architecture terminology. The flora has 31 non-monocot leaf morphotypes. The presence of more than 30 morphotypes suggests high diversity based on having only ∼210 non-monocot leaf specimens. The leaf collection also includes ∼10 monocot specimens. One of the leaf morphotypes shows similarities to the extant mangrove genus Avicennia, possibly confirming one of the fossil wood identifications. Most of the leaves are incomplete, but when the margin is preserved, it is untoothed. The lack of teeth indicates a warm, tropical climate (estimated mean annual temperature of >25 °C based on leaf margin analysis). Leaves in the collection are small with 28 of 31 morphotypes inferred as microphyll or notophyll in laminar size, providing support for the seasonal dryness indicated by the fossil woods. Despite the small size of the collection, this leaf flora is important to document as there are few Eocene plant macrofossil localities in Peru; it provides some insight into the Cenozoic forests in this understudied region.

Hazards Mitigation of Lahar Flows on Semeru Volcano after the 4 December 2021 Eruption Based on PS-InSAR

Volcanic eruption is one of the phenomena that can change the volcanic landscape drastically. Monitoring of volcanic edifices after eruptions should be considered to further understand the potential hazards in the future. Satellite monitoring is a reliable technique for assessing deformation in a volcano. InSAR was applied to detect material build-up after the eruption phase of Semeru Volcano in December 2022. As a consequence of the opening crater along with the InSAR result, a lahar product after the eruption was deposited in the southwest direction. Significant deformations were indicated by PS-InSAR near the crater, which was characterized by a LOS displacement of -10 to -40 mm/year, indicating scouring of the pyroclastic material moving down the slope. The accumulation of pyroclastic flows from the abrading process below was detected in the proximal zone of Semeru, as shown by the positive LOS displacement ranging from 10 to 40 mm/year. The field survey conforms to the PS InSAR results, where unconsolidated material, ranging in size from gravel to boulders, piles up approximately 4-5 m in Curah Kobokan. Highly unconsolidated material tends to move easily by water and threaten the surrounding settlements. Overlying PS InSAR and drainage pattern in the flank of Semeru, concluding several locations that have a high-risk potential of being affected by lahar flows are Curah Kobokan, Supiturang Village, Pronojiwo District, then Tulungrejo, Pasropan Village, Pasrujambe District, Lumajang Regency.

Micronutrient Mineral and Nutrient Content of Volcanic Soils and Creeks from the Montserrat Soufriere Hills Volcano. Nature’s Fertilizer: Mineral Nutrient Content of Volcanic Soils

Agricultural soils and potable water supplies provide a major source of minerals known to be essential for plant and animal health. After several hundred years of relative quiescence, the Soufriere Hills Volcano of Montserrat roared back to life in 1995 through 1997, wreaking severe havoc and severe damage to the geography and ecosystems and serious immediate and chronic health risks to the remaining inhabitants of the Island. The pyroclastic ash flow reached temperatures of 1500 °F and progressed down the hillsides at speeds of 80 mph, causing incineration and virtual destruction of everything in its path, while the gaseous and particulate laden plume reached altitudes of 7 miles (10.7 km), impacting air quality and aircraft navigation in the region. A total of 19 individuals became entrapped in the lava flow, and perished quickly as a direct result of the volcanic eruption. Volcanic soils derive from deeper layers of the earths surfaces and are notoriously rich in mineral nutrients representative of those deep mineral deposits. While virtually all combustible objects in the path of the raging ash flow become incinerated within minutes, the aftermath of the eruptions delivers the mineral rich constituents over a wide swath of the surrounding geography often reaching miles from the volcanic origin. Soils and consumable water sources are well known to provide a reliable community source of essential minerals in human nutrition, and in their chronic absence, numerous pathologic sequela may develop. To determine the mineral content of surrounding surface soils, samples of surface ash layers and nearby creeks were obtained from 7 regions and 3 free-flowing creeks and subjected mineral analysis. The surface ash specimens contained abundant amounts of the nutrients Iron, Calcium, Sodium, Magnesium, Sulfur, and non-nutrient Aluminum, intermediate amounts of potassium, Phosphorous, and Manganese, and small amounts of Boron, Copper and Zinc. Creek water runoff originating from higher elevations was consistently acidic with a healthy mean pH of 5.1, and contained smaller proportions of the same minerals, reflective of their relative effective solubility in the acidic water. Thus, the volcanic ash flow while devastating to the environment and public health in the immediate aftermath, provided numerous minerals important to plant and animal nutrition and to human health and health water sources which contributed to the longer-term reinstitution of edible plants and to the recovery of the vibrant lush greenery of the Emerald Isle of the Caribbean.

Unravelling the dynamics and hazards of the June 3rd, 2018, pyroclastic density currents at Fuego volcano (Guatemala)

The June 3rd, 2018, eruption of Fuego volcano (Guatemala) produced a complex sequence of small-volume pyroclastic density currents (PDCs) that inundated all sectors around the volcano and propagated >12 km on the southeastern flank, deposited ~50 million m3 of pyroclastic material, and killed at least 430 people in the village of San Miguel de Los Lotes and along the RN-14 road. This eruption has illustrated once again that the behavior of small-volume PDCs remains difficult to predict, demonstrating the need for an improved physical understanding of their generation, transport and depositional processes to ultimately improve assessment of their local hazard potential. In this work, we present preliminary results of an interdisciplinary study of the 2018 PDC deposits of Fuego, integrating: (1) field data of the pristine deposit characteristics recorded immediately after the eruption and after one rainy season, (2) sedimentological data (including grain size distributions and componentry) from samples collected at each lobe front and several exposed stratigraphic sections inside three principal ravines draining the volcano and affected by the eruption (Seca, Ceniza and Las Lajas), (3) preliminary quantification of the observed range of different clast surface textures, shape and vesicularities, as determined by SEM analyses, (4) surface morphological data from high-resolution satellite and aerial photography, and (5) advanced digital terrain model analysis correlated with sedimentological data to reconstruct the sequence of events on June 3rd and propose a conceptual model of PDC generation and emplacement on the SE flank of Fuego. In this model, a sequence of packages of material involved in discrete failure events of a perched mass of pyroclastic material accumulated within an old collapse structure on the upper SE flank, corresponds to the emplacement of a series of pulses of valley-confined PDCs down the Las Lajas channel. Headwall failures and gravitational collapses correlate with specific stratigraphic, sedimentological and textural characteristics of the valley-confined PDC units. The duration of individual granular collapse events serves as a proxy for the mobility of the triggered series of PDCs. Also, our detailed stratigraphic work shows evidence of stacked, massive flow units deposited by rapid stepwise aggradation of successive block-and-ash flow (BAF) pulses and their distribution along the southeastern flank supports the interpretation that the June 3rd PDCs, including the dilute parts of the currents, were largely controlled by the topography. The lack of strong changes in the grain size distributions of the fine sub-populations inside the seven valley-confined BAF lobate front units, together with their high content of fines, imply the presence of a self-limiting attrition process, decreasing the bulk porosity of such long-runout BAFs and lowering their effective friction coefficient during transport to reach longer runout distances. This multi-faceted approach completes previous studies already performed on small-volume PDCs at other volcanoes (Merapi, Colima, Unzen) and opens a unique perspective that will provide a significant step forward in our understanding of how such currents are emplaced.

Emplacement history of volcaniclastic turbidites around the central Azores volcanic islands: Frequencies of slope landslides and eruptions

Volcanic islands export clastic material to their surrounding oceans by explosive eruptions, lava emissions, biogenic production on their shelves, and failure of their slopes, amongst other processes. This raises the question of whether geological events (in particular, eruptions and landslides) can be detected offshore and dated, and whether any relationships (for example, with climate changes) can be revealed using sediment cores. The volcanically active central Azorean islands (Faial, Pico, São Jorge, and Terceira), with their neighboring submarine basins, are potentially good candidates for such an analysis. Here, chronostratigraphies of four gravity cores collected amongst the islands are constructed based on twelve radiocarbon dates and two dates derived by geochemically correlating primary volcaniclastic turbidites with ignimbrites on Faial and Terceira Islands. Age-depth models are built from the hemipelagic intervals to estimate individual turbidite dates. Volumes of turbidites are modeled by multiplying basin areas with bed thickness, allowing for various turbidite thinning rates and directions. The volumes of landslide-generated turbidites are only comparable with the largest volumes of their adjacent upper-slope submarine landslide valleys; therefore, such turbidites in the cores likely derive from these largest landslides. Emplacement intervals between turbidites originating from both landslides and pyroclastic density currents are found to be mostly a few thousand years. Frequencies of landslide-generated turbidites and hemipelagic sedimentation rates were both highest in the past 8 k.y. compared to preceding periods up to 50 k.y. High hemipelagic sedimentation rates are interpreted to be related to sea-level rise, allowing more shelf bioproduction and release of particles by coastal erosion. The coincident increased frequencies of submarine landslides may also be associated with the increased sediment supply from the islands, resulting in a more rapid build-up of unstable sediments on submarine slopes. Notably, the emplacement frequencies of turbidites of pyroclastic density current origins do not suggest the decreased eruption frequency toward the Holocene that has been found elsewhere.