Pyroclastic Surge Research Articles

Detecting Geothermal Phenomena at Sikidang Crater Area Based on Ground Penetrating Radar Method

Abstract Sikidang Crater (2000 masl) is one of the leading tourist sites in the Dieng area. However, not many people realise that Sikidang Crater is located in the Dieng Volcanic Complex where most of the volcanoes belong to the type A category. Sikidang Crater is one of the main geothermal manifestations occupied by mud pools, solfatara, fumaroles, and altered rocks. These manifestations have potential geological hazards such as toxic gases, base surge, and mud explosions. On the other hand, it has a high level of human activity that increases the risk of disasters. As an effort to prevent and mitigate disasters, it is necessary to know the subsurface geological conditions of the crater. This study aims to determine the subsurface geological conditions of the crater. This research uses the methods of detailed geological mapping, manifestation observation, and Ground Penetrating Radar (GPR) geophysical survey. The tool used is Akula Geoscanner 9000C running at 64.75 Hz frequency, capable of penetrating 50 meters deep, and has a vertical resolution of > 0.85 meters. Sikidang Crater is located at the southeastern foot of Mount Pangonan and it forms semicircular like a horseshoe. According to Van Zuidam, the crater is classified as a solfatara and fumarole field geomorphology unit. The lithology of this area is dominated by the eruption products of Mount Pangonan. In general, radargrams resulting from GPR surveys show various amplitudes of reflected electromagnetic waves. This is consistent when correlated with the variation in rock density of the research area. At some points, there is a decrease in electromagnetic wave velocity due to contrast in dielectric constant values, which is interpreted as geothermal fluid flow towards the surface. The potential level of geothermal fluid flow is classified into high, medium, low, and none based on the density of potential points seen in the radargram.

IMEX_SfloW2D v2: a depth-averaged numerical flow model for volcanic gas–particle flows over complex topographies and water

Abstract. We present developments to the physical model and the open-source numerical code IMEX_SfloW2D (de' Michieli Vitturi et al., 2019). These developments consist of a generalization of the depth-averaged (shallow-water) fluid equations to describe a polydisperse fluid–solid mixture, including terms for sedimentation and entrainment, transport equations for solid particles of different sizes, transport equations for different components of the carrier phase, and an equation for temperature/energy. Of relevance for the simulation of volcanic mass flows, vaporization and entrainment of water are implemented in the new model. The model can be easily adapted to simulate a wide range of volcanic mass flows (pyroclastic avalanches, lahars, pyroclastic surges), and here we present its application to transient dilute pyroclastic density currents (PDCs). The numerical algorithm and the code have been improved to allow for simulation of sub- to supercritical regimes and to simplify the setting of initial and boundary conditions. The code is open-source. The results of synthetic numerical benchmarks demonstrate the robustness of the numerical code in simulating transcritical flows interacting with the topography. Moreover, they highlight the importance of simulating transient in comparison to steady-state flows and flows in 2D versus 1D. Finally, we demonstrate the model capabilities to simulate a complex natural case involving the propagation of PDCs over the sea surface and across topographic obstacles, through application to Krakatau volcano, showing the relevance, at a large scale, of non-linear fluid dynamic features, such as hydraulic jumps and von Kármán vortices, to flow conditions such as velocity and runout.

Temporal change in eruption style during the basaltic explosive An’ei eruption of the Izu-Oshima volcano, Japan: insights from stratigraphy and chemical composition analyses

Basaltic eruptions sometimes show an explosive and complex nature; thus, clarifying the sequence and controlling parameters is essential for understanding their causes. The An’ei eruption of the Izu-Oshima volcano during 1777–1792 was a complex basaltic eruption producing lava flows, pyroclastic falls, and ash plumes. We reconstructed the transition of the eruption style based on geological data combined with comparisons with data from historical documents and used chemical analyses to develop a magma plumbing model. The An’ei eruption started in August 1777 with scoria ejection. The scoria deposit was classified into Units A–C. Unit A scoria was produced by early weak explosions and more intense subsequent explosions. Unit B scoria marked a return to weak plumes before the summit eruption reached its climactic phase in November 1778 and explosively ejected Unit C scoria. Several lava flows were also effused from the foot of the scoria cone during these periods of scoria ejection. After a 5-year hiatus, the eruption ultimately shifted to persistent, weak ash ejection and pyroclastic surges. The tephra volumes of Units A, B, and C were estimated at 1.9–4.3 × 107, 0.6–4.5 × 106, and 1.3–3.2 × 107 m3, respectively. Associated column heights of 8–11, 3–10, and 9–12 km were obtained for Units A, B, and C, respectively, resulting in sub-Plinian classification. Chemical analyses have shown that the plagioclase phenocryst content increased as the eruption progressed. The transition from relatively weak activity with Strombolian and sub-Plinian explosions, caused by aphyric magma, to short-period activity with more intense sub-Plinian explosions, caused by porphyritic magma, can be explained by evacuation of magma from multiple reservoirs with different contents of plagioclase phenocrysts. Simultaneous lava flows that have different petrological features from those of the scoria eruptions also suggest multiple magma reservoirs and pathways. This view of the temporal change in eruptive style, corresponding to change in magma type, is essential for understanding the eruptive processes of large-scale basaltic eruptions of the Izu-Oshima volcano and contributes to clarifying the nature and hazards of basaltic eruptions which turn into explosive activities in general.

Possible geological interpretation of the volcanic seismic facies based on volcanostratigraphy elements: A case analysis of the Yingcheng Formation in the Changling Fault Depression, Songliao Basin, NE China

Volcanic rocks in faulted depressions are one of the most interested areas for hydrocarbon exploration. In a frontier basin exploration, integrated interpretation of the seismic facies of volcanic rocks is a key success. The key information of boundary system and deposited unit in the volcanostratigraphy did not attract sufficient attention during the process of seismic stratigraphic interpretation of volcanic rocks. In this paper, the volcanic rocks of the Yingcheng Formation in the Changling Fault Depression of the Songliao Basin are taken as an example. According to the maximum average slope, the volcanic seismic facies were divided into three types: mounded seismic facies unit (MSFU), tabular seismic facies unit (TSFU), and mounded-tabular seismic facies unit (M-TSFU). MSFU consists of lava dome and simple lava flows, which has fewer reservoir layers, medium to poor reservoir quality with limited extension. The TSFU comprises more complex component of simple lava flow and base surges, and contains more layers, with good-medium reservoir quality and a large reservoir extension. The M-TSFU has numerous reservoir layers with good reservoir quality and a significant reservoir extension, as well as a higher proportion of braided lava flows and pyroclastic flows. Going from the most favorable reservoir targets to the least favorable, the following units were deposited in the Changling Fault Depression: pyroclastic flow, braided lava flow, base surge, simple lava flow, lava dome, and reworked volcanic clastic flow. The study suggested that mounded-tabular facies units are potential favorable exploration targets in the Songliao Basin. This paper provides a technical route for seismic facies interpretation of volcanic rocks and the analysis of favorable volcanic exploration targets in faulted volcanic basins.

Ash aggregation processes in a basaltic tuff ring (Songaksan, Jeju Island, Korea): Controls of diatreme conditions and transport processes

Aggregation of ash generated by explosive volcanic eruptions controls the dispersal and residence time of ash in the atmosphere and, therefore, the hazard to aviation. Ash aggregation is particularly common in hydromagmatic volcanoes produced by explosive magma-water interactions. Nevertheless, few studies have been done on this process because of the lower risk of volcanic hazards posed by these volcanoes in comparison to classical stratovolcanoes. Observations of the microscopic textures of the tuff samples from a Holocene tuff ring in Jeju Island, Korea, show that the ash particles occur mainly in the form of coated particles and ash lumps, which are either rich or poor in clay minerals derived from the substrate. The clay-rich aggregates formed in the diatreme by cohesive and capillary bonding of clay-rich and water-undersaturated debris. When the diatreme was filled with clay-poor and water-saturated debris, particles were ejected mainly without ash coats and aggregation. Once emitted from the diatreme, the aggregates and uncoated/solitary particles could be further aggregated together or accreted on larger particles by liquid bonding, producing clay-poor aggregates, multiple-coated particles, and composite ash lumps. The ash aggregation occurred mainly in co-surge ash clouds and ash plumes but not in pyroclastic surges, in which the time available for ash aggregation was too short (a few tens of seconds or less). This study demonstrates that the substrate characteristics and environmental factors that can influence the material properties of the diatreme fill, such as the clay mineral and water contents, are the prime controls of ash aggregation in hydromagmatic volcanoes.

Lateral Extent of Pyroclastic Surge Deposits at Ubehebe Crater (Death Valley, California) and Implications for Hazards in Monogenetic Volcanic Fields

AbstractHazard assessments in monogenetic volcanic fields require estimates of the runout of pyroclastic surges that result from phreatomagmatic explosive activity. Previous assessments used runout distances of 1–4 km, with large cases up to 6 km. Surge deposits at Ubehebe Crater (∼2100 y.b.p., Death Valley, California) have been traced ∼9 km from the crater center, and likely originally extended 1–3 km farther. There is no evidence that the Ubehebe Crater activity was unusually energetic; rather, its distal deposits are better preserved than those at most maar volcanoes because of its young age and the arid environment. Numerical simulations illustrate how low temperatures facilitate long runout of phreatomagmatic surges due to reduced expansion of entrained air compared to hot surges, allowing cool surges to retain higher densities than ambient air. We suggest that hazard assessments for volcanic fields with phreatomagmatic, maar‐forming eruptions should consider runout distances in the range of 10–15 km.

Pyroclastic deposits of Ubehebe Crater, Death Valley, California, USA: Ballistics, pyroclastic surges, and dry granular flows

Abstract We describe and interpret deposits associated with the final Ubehebe Crater-forming, phreatomagmatic explosive phase of the multivent, monogenetic Ubehebe volcanic center. Ubehebe volcano is located in Death Valley, California, USA. Pyroclastic deposits occur in four main facies: (1) lapilli- and blockdominated beds, (2) thinly bedded lapilli tuff, (3) laminated and cross-laminated ash, and (4) massive lapilli ash/tuff. Lapilli- and block-dominated beds are found mostly within several hundred meters of the crater and transition outward into discontinuous lenses of lapilli and blocks; they are interpreted to have been deposited by ballistic processes associated with crater-forming explosions. Thinly bedded lapilli tuff is found mainly within several hundred meters, and laminated and cross-laminated ash extends at least 9 km from the crater center. Dune forms are common within ~2 km of the crater center, while finer-grained, distal deposits tend to exhibit planar lamination. These two facies (thinly bedded lapilli tuff and laminated and cross-laminated ash) are interpreted to record multiple pyroclastic surges (dilute pyroclastic currents). Repeated couplets of coarse layers overlain by finer-grained, laminated horizons suggest that many or most of the surges were transient, likely recording individual explosions, and they traveled over complex topography in some areas. These two factors complicate the application of classical sediment-transport theory to quantify surge properties. However, dune-form data provide possible constraints on the relationships between suspended load sedimentation and bed-load transport that are consistent using two independent approaches. Massive lapilli ash/tuff beds occur in drainages below steep slopes and can extend up to ~1 km onto adjacent valley floors beneath large catchments. Although they are massive in texture, their grain-size characteristics are shared with laminated and cross-laminated ash facies, with which they are locally interbedded. These are interpreted to record concentrated granular flows sourced by remobilized pyroclastic surge deposits, either during surge transport or shortly after, while the surge deposits retained their elevated initial pore-gas pressures. Although similar surge-derived concentrated flows have been described elsewhere (e.g., Mount St. Helens, Washington, USA, and Soufriére Hills, Montserrat, West Indies), to our knowledge Ubehebe is the first case where such processes have been identified at a maar volcano. These concentrated flows followed paths that were independent of the pyroclastic surges and represent a potential hazard at similar maar volcanoes in areas with complex terrain.

Hydrovolcanic activity on a continental shelf inferred from the subsurface diatreme- and crater-filling deposits of Jeju Island, Korea

Jeju Island comprises numerous tuff rings and tuff cones and their reworked deposits in the subsurface, which formed on the ca. 120-m-deep Yellow Sea continental shelf under the fluctuating Quaternary sea levels. Tens of meter-thick and massive deposits were found by chance during groundwater drilling at three sites. These deposits are interpreted as either syn-eruptive diatreme-filling deposits or post-eruptive crater-filling deposits, both of hydromagmatic volcanoes. The diatremes were cut into shelf sediment, 70 to 250 m thick, and developed generally within it below the Quaternary sea levels. Abundant external water was therefore available for explosive magma-water interactions at shallow levels. The diatreme deposit in one core shows some features attributable to extreme wetness or water saturation of the diatreme fill, such as the matrix support of larger clasts, meager vertical changes in matrix content, and an absence of features related to particle adhesion. Fluidally shaped clasts with delicate reentrant margins in the core suggest minimal particle abrasion and breakage in a water-saturated and highly fluid slurry of tephra and water that was probably filling a shallow bowl-like diatreme, which is distinguished from both phreatomagmatic and kimberlite diatremes. The diatreme deposits in other cores comprise blocky and angular clasts in a sideromelane ash matrix, suggesting phreatomagmatic explosions at a deeper level. One of the cores contains collapsed deposits of thinly stratified tuff emplaced by pyroclastic surges, indicating that the diatreme is associated with an emergent tuff ring. Both Surtseyan and phreatomagmatic eruptions are therefore interpreted to have occurred on the shelf under the controls of fluctuating Quaternary sea levels. The subsurface diatremes suggest that there can be a variety of diatremes with different sizes, shapes, and material characteristics beneath the craters of hydromagmatic volcanoes, including not only maars but also tuff rings and tuff cones.

Probabilistic Volcanic Hazard Assessment for National Park Infrastructure Proximal to Taranaki Volcano (New Zealand)

Hazard assessment for infrastructure proximal to a volcanic vent raises issues that are often not present, or not as severe in hazard assessments for more distal infrastructure. Proximal regions are subject to a greater number of hazardous phenomena, and variability in impact intensity increases with the hazard magnitude. To probabilistically quantify volcanic hazard to infrastructure, multiple volcanic hazards and their effects on exposed elements need to be considered. Compared to single-hazard assessments, multi-hazard assessments increase the size and complexity of determining hazard occurrence and magnitude, typically introducing additional uncertainties in the quantification of risk. A location-centred approach, focusing on key locations rather than key hazards, can simplify the problem to one requiring identification of hazards with the potential to affect the location, followed by assessment of the probability of these hazards and their triggering eruptions. The location-centred approach is more compatible to multi-source hazards and allows for different hazard estimation methodologies to be applied as appropriate for the infrastructure type. We present a probabilistic quantification of volcanic hazard using this location centred approach for infrastructure within Te Papakura o Taranaki National Park, New Zealand. The impact to proposed park infrastructure from volcanic activity (originating from Mt. Taranaki) is quantified using a probability chain to provide a structured approach to integrate differing hazard estimation methods with eruption probability estimates within asset lifetimes.This location-centered approach provides quantitative estimates for volcanic hazards that significantly improve volcanic hazard estimates for infrastructure proximal to the Taranaki summit vent. Volcanic mass flows, predominantly pyroclastic surges or block and ash flows, are most likely (probability >0.8) to affect walking tracks if an eruption occurs. The probability of one or more eruption(s) in the next 50 years is estimated at 0.35–0.38. This use of probability chains and a location centered assessment demonstrates a technique that can be applied to proximal hazard assessments globally.

Analysis of the 2020 Taal Volcano tephra fall deposits from crowdsourced information and field data

After 43 years of dormancy, Taal Volcano violently erupted in January 2020 forming a towering eruption plume. The fall deposits covered an area of 8605 km2, which includes Metro Manila of the National Capital Region of the Philippines. The tephra fall caused damage to crops, traffic congestion, roof collapse, and changes in air quality in the affected areas. In a tropical region where heavy rains are frequent, immediate collection of data is crucial in order to preserve the tephra fall deposit record, which is readily washed away by surface water runoff and prevailing winds. Crowdsourcing, field surveys, and laboratory analysis of the tephra fall deposits were conducted to document and characterize the tephra fall deposits of the 2020 Taal Volcano eruption and their impacts. Results show that the tephra fall deposit thins downwind exponentially with a thickness half distance of about 1.40 km and 9.49 km for the proximal and distal exponential segments, respectively. The total calculated volume of erupted fallout deposit is 0.057 km3, 0.042 km3, or 0.090 km3 using the exponential, power-law, and Weibull models, respectively, and all translate to a VEI of 3. However, using a probabilistic approach (Weibull method) with 90% confidence interval, the volume estimate is as high as 0.097 km3. With the addition of the base surge deposits amounting to 0.019 km3, the volume translates to a VEI of 4, consistent with the classification for the observed height and umbrella radius of the 2020 main eruption plume. VEI 4 is also consistent with the calculated median eruption plume height of 17.8 km and sub-plinian classification based on combined analysis of isopleth and isopach data. Phreatomagmatic activity originated from a vent located in Taal Volcano’s Main Crater Lake (MCL), which contained 42 million m3 of water. This eruptive style is further supported by the characteristics of the ash grain components of the distal 12 January 2020 tephra fall deposits, consisting dominantly of andesitic vitric fragments (83–90%). Other components of the fall deposits are lithic (7–11%) and crystal (less than 6%) grains. Further textural and geochemical analysis of these tephra fall deposits contributes to better understand the volcanic processes that occurred at Taal Volcano, one of the 16 Decade Volcanoes identified by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) because of its destructive nature and proximity to densely populated areas. The crowdsourcing initiative provided a significant portion of the data used for this study while at the same time educating and empowering the community to build resilience.

A Unifying Model for Pyroclastic Surge Genesis and Pyroclastic Flow Fluidization

AbstractPyroclastic density currents (PDCs) are hot and fast ground‐hugging mixtures of volcanic fragments and gases, which represent a major threat to people living near explosive volcanoes. Mechanisms causing the separation into the concentrated (the pyroclastic flow) and dilute (the pyroclastic surge) layers, as well as the mechanism causing their remarkably high mobility are still unclear. Here, we present a conceptual model based on field observations of lava dome collapses, laboratory experiments, and numerical modeling that unifies these mechanisms. Our model shows that they are caused by the fall of fine volcanic particles onto steep, irregular topography. The ambient air entrapped during the fall both creates the pyroclastic surge through elutriation and induces high fluidity in the pyroclastic flow by increasing its pore pressure. Our conclusion reveals the importance of topography in the destructive capacity of PDCs.

Transmission of Zoonotic Diseases in the Daily Life of Ancient Pompeii and Herculaneum (79 CE, Italy): A Review of Animal-Human-Environment Interactions through Biological, Historical and Archaeological Sources.

Simple SummaryThere is a wide range of historical, archaeological and biological sources to help understand the nature of health and disease in the ancient Roman world. In this study, we examine various predisposing elements typical of the urban environment in relation to zoonotic diseases in the ancient Roman cities of Pompeii and Herculaneum, both devastated by pyroclastic surges as a consequence of the eruption of Mount Somma–Vesuvius in 79 CE. We analyse the meaning and value of the sources to develop an understanding of the many features of everyday life in these cities. We make judgements about issues relevant to the reconstruction of the past, and finally, we synthesize evidence from different sources to construct historical explanations and arguments in relation to the transmission of zoonotic diseases in these ancient Roman populations.There is no doubt that the cultural and urban environments contributed to the animal–human interaction in the daily life of the ancient Roman world. The singularity of the circumstances of the burial of Pompeii and Herculaneum, together with literary sources and the extraordinary state of preservation of the archaeological and biological material found, has provided researchers with an opportunity, unique in its kind, to reconstruct the life and ways of living of its inhabitants. This study illustrates the main drivers and mechanisms for the distribution and transmission of zoonotic diseases in these ancient Roman populations, such as (i) the large number and role that different animal species played in the ancient Roman world; (ii) the environmental conditions for the survival of parasites, pathogens and vectors; (iii) the great variety and intensity of commercial activities and occupations that presented certain risks of infections; (iv) the absence of adequate safety controls during processing, distribution and preservation of foodstuffs in unsuitable environments and some culinary habits; (v) the inadequate mechanisms of the disposal of human waste and the biotic contamination of watercourses and reservoirs; and finally (vi) the use of animals related to religious and cultural practices.

Selected Crater and Small Caldera Lakes in Alaska: Characteristics and Hazards

This study addresses the characteristics, potential hazards, and both eruptive and non-eruptive role of water at selected volcanic crater lakes in Alaska. Crater lakes are an important feature of some stratovolcanoes in Alaska. Of the volcanoes in the state with known Holocene eruptive activity, about one third have summit crater lakes. Also included are two volcanoes with small caldera lakes (Katmai, Kaguyak). The lakes play an important but not well studied role in influencing eruptive behavior and pose some significant hydrologic hazards. Floods from crater lakes in Alaska are evaluated by estimating maximum potential crater lake water volumes and peak outflow discharge with a dam-break model. Some recent eruptions and hydrologic events that involved crater lakes also are reviewed. The large volumes of water potentially hosted by crater lakes in Alaska indicate that significant flowage hazards resulting from catastrophic breaching of crater rims are possible. Estimates of maximum peak flood discharge associated with breaching of lake-filled craters derived from dam-break modeling indicate that flood magnitudes could be as large as 103–106 m3/s if summit crater lakes drain rapidly when at maximum volume. Many of the Alaska crater lakes discussed are situated in hydrothermally altered craters characterized by complex assemblages of stratified unconsolidated volcaniclastic deposits, in a region known for large magnitude (>M7) earthquakes. Although there are only a few historical examples of eruptions involving crater lakes in Alaska, these provide noteworthy examples of the role of external water in cooling pyroclastic deposits, acidic crater-lake drainage, and water-related hazards such as lahars and base surge.

Destructiveness of pyroclastic surges controlled by turbulent fluctuations (Data set)

Destructiveness of pyroclastic surges controlled by turbulent fluctuations (Data set)

Destructiveness of pyroclastic surges controlled by turbulent fluctuations

Pyroclastic surges are lethal hazards from volcanoes that exhibit enormous destructiveness through dynamic pressures of 100–102 kPa inside flows capable of obliterating reinforced buildings. However, to date, there are no measurements inside these currents to quantify the dynamics of this important hazard process. Here we show, through large-scale experiments and the first field measurement of pressure inside pyroclastic surges, that dynamic pressure energy is mostly carried by large-scale coherent turbulent structures and gravity waves. These perpetuate as low-frequency high-pressure pulses downcurrent, form maxima in the flow energy spectra and drive a turbulent energy cascade. The pressure maxima exceed mean values, which are traditionally estimated for hazard assessments, manifold. The frequency of the most energetic coherent turbulent structures is bounded by a critical Strouhal number of ~0.3, allowing quantitative predictions. This explains the destructiveness of real-world flows through the development of c. 1–20 successive high-pressure pulses per minute. This discovery, which is also applicable to powder snow avalanches, necessitates a re-evaluation of hazard models that aim to forecast and mitigate volcanic hazard impacts globally.

Quaternary basaltic volcanic fields of the American Southwest

AbstractThe southwestern United States contains numerous monogenetic basaltic volcanoes distributed in intraplate volcanic fields. We review, on a regional scale, our current understanding of the Quaternary basalts with a focus on aspects pertinent to hazard assessment, such as physical volcanology and geochronology, while also summarizing the several petrogenetic conceptual models that have been proposed for the range of local tectonic settings in the region. We count 2229 volcanoes in 37 volcanic fields (including the Pinacate volcanic field, which is mostly in northern Sonora, Mexico). Volcanic landforms are dominantly scoria cones and ramparts with attendant lava fields that have a spectrum of ‘a'ā and blocky to pāhoehoe morphologies, while a small percentage of the volcanoes are maars and tuff cones. Explosive eruption styles that were driven mainly by magmatic volatiles, where they have been studied in detail, included Hawaiian, Strombolian, violent Strombolian, and sub-Plinian activity. The latter two have resulted in substantial fallout deposits that can be traced tens of kilometers from source vents. Phreatomagmatic styles have produced pyroclastic current (mainly pyroclastic surges), ballistic, and fallout deposits. These eruption styles pose hazards to humans when they occur in populated areas and to air travel and regional infrastructure even in sparsely populated areas. All but one of the major volcanic fields (fields that contain ∼100 or more Quaternary volcanoes) together form a northwest-southeast–trending band, which we suggest may reflect an influence of plate-boundary-related shearing on melt segregation in the upper mantle along with other factors; this view is consistent with recent global positioning system (GPS) and structural geologic data indicating the influence of dextral motion along the North America-Pacific plate boundary deep inside the Southwest. Of the 2229 Quaternary volcanoes identified, ∼548 (25%) have been dated, and only ∼15% have been dated with methods such as 40Ar/39Ar and cosmogenic surface exposure methods that are considered optimal for young basalts. Acknowledging the large uncertainty due to the poor geochronological data coverage, we use a simple Poisson model to provide a first-order estimate of recurrence rates of monogenetic volcanoes on the scale of the region as a whole; recurrence rates using our compiled age data set range from 3.74 × 10−4 yr−1 to 8.63 × 10−4 yr−1. These values are only based on dated and mapped volcanoes, respectively, and do not account for undated and buried volcanoes or other uncertainties in the volcano count. The time between monogenetic eruptions in the Southwest is similar to the repose times of some polygenetic volcanoes, which suggests that the regional hazard is potentially commensurate with the hazard from a reawakening stratovolcano such as those in the Cascade Range. Notable in our review is that only a few volcanoes have been the subject of physical volcanological characterization, interpretation, and detailed petrologic study that may elucidate factors such as magma generation, ascent (including time scales), and controls on eruption style.

Hazardous base surges of Taal\u2019s 2020 eruption

After 43 years of repose, Taal Volcano erupted on 12 January 2020 forming hazardous base surges. Using field, remote sensing (i.e. UAV and LiDAR), and numerical methods, we gathered primary data to generate well-constrained observed information on dune bedform characteristics, impact dynamic pressures and velocities of base surges. This is to advance our knowledge on this type of hazard to understand and evaluate its consequences and risks. The dilute and wet surges traveled at 50-60 ms−1 near the crater rim and decelerated before making impact on coastal communities with dynamic pressures of at least 1.7 kPa. The base surges killed more than a thousand livestock in the southeast of Taal Volcano Island, and then traveled another ~ 600 m offshore. This work is a rare document of a complete, fresh, and practically undisturbed base surge deposit, important in the study of dune deposits formed by volcanic and other processes on Earth and other planets.

Microtextural evidence for vesiculated tuff formation in Songaksan tuff ring, Jeju Island, Korea

Vesiculated tuff, containing submillimeter-size vesicles, is commonly found in Surtseyan and phreatomagmatic deposits. However, the processes and conditions of vesicle formation and preservation in granular substances have been poorly explored so far in spite of their potential importance in understanding the eruptive and depositional processes of these deposits. This study provides a detailed account of a vesiculated tuff in Songaksan tuff ring, Jeju Island, Korea, together with comparison with non-vesiculated tuffs. The vesiculated tuff, which is interpreted to have been emplaced by a wet pyroclastic surge, is poorer-sorted, poorer in fines, richer in coarser particles, and has lower porosity than the non-vesiculated tuffs. The pores are closed and have round margins surrounded by a fine-grained matrix. On the other hand, non-vesiculated tuffs, emplaced by either pyroclastic surges or fall, are composed of loosely packed ash aggregates and have large interconnected pores. We interpret that the vesicle formation in granular substances is possible only when the pores are water-saturated and airtight. Expansion of trapped gases is also necessary to produce the generally round shape of the vesicles. The gas expansion is possible only when the heat is transferred from the surrounding hotter pyroclasts into the gas bubbles. Vaporization of liquid water and gas exsolution from pyroclasts can be ignored. In order for the heat transfer to take place, the pyroclastic surge needs to be non-isothermal, having different temperatures of the solid and gas phases. The thermal disequilibrium of the surge can be maintained by continual mixing of cold ambient air and thermal expansion of the surge. The pyroclasts deposited from the surge need to increase the temperature of the trapped air/gases by only 3 K. Then, the trapped air/gases can overcome the yield strength of the surrounding wet ash matrix and expand. The essential conditions for vesiculated tuff formation, such as water saturation of pyroclasts and thermal disequilibrium of surge, are closely related with the properties of the diatreme-filling materials and the behavior of pyroclastic surges. Therefore, vesiculated tuffs can provide useful information on the eruptive and transport processes of Surtseyan and phreatomagmatic deposits in addition to the wet nature of tephra.

Introduction and characterization of Neogene volcanic eruptions in the Parizarea (Kerman province) and their petrological features using pyroclastic deposits

In the Pariz area, (Kerman province), there are special deposits and in the geological maps, they have introduced as detrital unconsolidated Neogene Conglomerates (Ng). Detailed field observations of these deposits in this study showed that they are pyroclastic deposits from the post Eocene unknown explosive eruptions. Stratigraphically, these units overlie the Eocene basaltic rocks, and their clasts are dacitic and rhyolitic in compositions, which means that they are completely different from the Eocene rocks. Genetically, these deposits are pyroclastic surges and flow deposits in association with the laharic units. Lithological features of these pyroclastics along with the absence of ducite or rhyolite lava flows and the relatively large dispersion of these deposits indicate that they have been formed by water bearing explosive eruptions. The clasts of these pyroclastic deposits contain plagioclase, amphibole, biotite and quartz and they are geochemically belong to the calcalkaline magmatic series. The geochemical characteristics of these rocks show that they formed in a post-collision environment and their geochemical nature are similar to the continental magmatic arc associations. These results are consistent with other studies on the post Eocene magmatic rocks of the Dehaj-Sardouieh belt.

A window on mantle-derived magmas within the Central Andes: eruption style transitions at Cerro Overo maar and La Albóndiga lava dome, northern Chile

Cerro Overo maar and La Albondiga lava dome are two independent monogenetic volcanoes located in the Central Volcanic Zone of the Andes in northern Chile, close to the active Lascar and Chiliques volcanoes. Cerro Overo maar was formed <77 ka ago by explosive-effusive eruptions, including phreatomagmatic activity, while La Albondiga lava dome (Pleistocene) is the result of magmatic explosive-effusive activity alone. Cerro Overo and La Albondiga are characterized by deposits composed of pyroclastic rocks and dense coherent lava blocks. At Cerro Overo, these deposits are located around the crater rim, while at La Albondiga, they form coherent in situ lava dome features. Cerro Overo also displays thin ash- and lapilli-dominated deposit layers presumed to be pyroclastic surge deposits, which include juvenile pyroclasts exhibiting cauliflower textures, numerous exotic accidental lithics, and ballistically transported lapilli, bombs, blocks, and bomb sags. These fragments include recycled, juvenile pyroclasts, as well as material from older volcanic and intrusive rocks from the stratigraphic units immediately below. These small-volume volcanoes represent two of the less silicic volcanoes (~54 wt.% SiO2) in the northern Chilean Pleistocene to Holocene volcanic provinces. They are characterized by a fine grain size (mainly fine lapilli), olivine phenocrysts with skeletal textures, ignimbritic, dioritic, and granitic xenoliths, and quartz xenocrysts, with high concentrations of incompatible trace elements and light rare earth elements. The general magmatic evolution of the Cerro Overo and La Albondiga systems has been controlled by fast ascent (e.g., skeletal olivine phenocrysts) of mantle-derived magma associated with mixing, fractional crystallization, and a low degree of crustal assimilation during turbulent ascent processes. Such eruptions provide evidence that various factors play an essential role in the transition from explosive-effusive magmatic (Cerro Overo and La Albondiga) to phreatomagmatic (Cerro Overo) volcanic eruption styles.