Pyroclastic Flows Research Articles

Experimental Measurement of Enhanced and Hindered Particle Settling in Turbulent Gas‐Particle Suspensions, and Geophysical Implications

AbstractThe dynamics of geophysical dilute turbulent gas‐particles mixtures depends to a large extent on particle concentration, which in turn depends predominantly on the particle settling velocity. We experimentally investigate air‐particle mixtures contained in a vertical pipe in which the velocity of an ascending air flux matches the settling velocity of glass particles. To obtain local particle concentrations in these mixtures, we use acoustic probing and air pressure measurements and show that these independent techniques yield similar results for a range of particle sizes and particle concentrations. Moreover, we find that in suspensions of small particles (78 μm) the settling velocity increases with the local particle concentration due to the formation of particle clusters. These clusters settle with a velocity that is four times faster than the terminal settling velocity of single particles, and they double settling speeds of the suspensions. In contrast, in suspensions of larger particles (467 μm) the settling velocity decreases with increasing particle concentration. Although particle clusters are still present in this case, the settling velocity is decreased by 30%, which is captured by a hindered settling model. These results suggest an interplay between hindered settling and cluster‐induced enhanced settling, which in our experiments occur respectively at Stokes number O(100) and O(1). We discuss implications for volcanic plumes and pyroclastic currents. Our study suggests that clustering and related enhanced or hindered particle settling velocities should be considered in models of volcanic phenomena and that drag law corrections are needed for reliable predictions and hazard assessment.

Correlation between the Flow Temperature and Mineral Factor for Coal Ashes Based on FactSage Calculation.

To find a simple method to predict the ash flow temperature (FT) based on FactSage calculation, 69 coal ash samples were selected to explore the correlation between the FT and its mineral factor (MF) at a given temperature. An approximate linear relationship was found between ash FT and its MF: FT = 0.64MF + 1332, with a related coefficient value of 0.94 and a standard deviation of 25.77 °C. Ten ash samples were used to investigate its reliability. The calculated FTs were consistent with experimental FTs in the error range of measurement, and the correlation might be more reliable for low iron and low calcium coal.

Hydrovolcanic eruptions of the Paraná Igneous Province: Insights from mafic volcaniclastic deposits in Sertanópolis, Paraná, Brazil

In many continental flood basalt provinces (CFBPs), primary volcaniclastic deposits formed by explosive hydrovolcanism have been shown to be significant counterparts of better-known effusive facies, a notion that challenged traditional views of CFB evolution. For a long time, the only exception to this was the Paraná Igneous Province in South America. In order to better characterize and understand this setting, detailed geological mapping and petrographic studies were carried out on interflow beds at Sertanópolis, a 250 km2 region in northwest Paraná. Four interflow units were identified at the transition between the high and low TiO2 volcanic sequences. Fine-grained interflow facies include vesiculated clastic rocks, with structures ranging from diffuse to well defined stratification, decimeter-scale dune-bedding with preserved backset and foreset laminations. They are formed mainly by fine accessory (non-juvenile) siliciclastic ash (20–70%) and extremely fine ash or mud (10–50%), followed by fine hydrothermal mica (<5–40%), commonly hydrated (clay-mineral-rich) ash aggregates (<5–20%) and lesser amounts of juvenile and accessory glass and basalt fragments (ash to block-sized, <5–30%). In the eastern portion of the research area, a 4 × 2.5 km region with outcrops of scoriaceous basaltic breccias was mapped. These are mainly matrix to clast-supported breccias with finely laminated matrix similar to the fine-grained units. These rocks are interpreted as accessory-rich mafic pyroclastic beds, and their features suggest that multiple pyroclastic density currents (PDCs) formed each interflow unit, with minor discrete fallout contribution in medial successions. Pyroclastic breccias represent proximal PDC and ballistic deposits that help outline a possible conduit in which magmatic-like fragments are dominant in the framework. Stratified tuff-breccia strata in medial deposits represent progressive dilution of PDCs and continuous reworking of scoriaceous fragments by multiple currents. The local stratigraphy is consistent with repeated explosive hydrovolcanic eruptions in a maar-diatreme-like system similar to hydromagmatic volcanoes of other CFBPs.

GEOCHEMISTRY AND MINERAL CONTENT OF ASH FLOW FROM THE MONTSERRAT SOUFRIERE HILLS VOLCANO

The Soufriere Hills Volcano of Montserrat has ancient origins and roared back to life in 1995 wreaking severe havoc and damage to the inhabitants, geography, and ecosystems 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 35,000 feet, impacting air quality and aircraft navigation. The local health authorities recommended masking and physical protection from any potentially harmful effects from the ash to all residents who remained on Island following the 1995 eruption. Volcanic ash can be an irritant to exposed skin and respiratory surfaces upon contact due in part to the sharp and jagged nature of the microcrystalline particulate matter. In addition, the minute size of the smallest particulate matter can impact deep into the unprotected respiratory tree in humans and animals, potentially causing severe respiratory injury. The composition and physicochemical nature of the ash was largely unknown in 1995 and subsequent years. The current study was designed to determine the geochemical composition of the ash. Samples of ash were collected from 7 locations and water samples from three free flowing creeks in Montserrat and indicated that the creek water was acidic in nature. The mean pH of water was 5.2, while the ash showed abundant levels of Iron, Phosphorus, Calcium, Magnesium, Sodium, Aluminum, and sulfur, in addition to lower concentrations of potassium, boron, copper and zinc and intermediate concentrations of Manganese and was devoid of toxic minerals including lead and mercury. The emergence of acute respiratory issues was not found to exceed similar events in other healthy populations including individuals relocated to the UK. In conclusion, direct human and animal exposure to Montserrat volcanic ash was deemed non-harmful to humans when adequate protective measures including masking and exposure precautions were undertaken, while the rich mineral content of the ash can provide a rich source of micronutrient mineralization to soils and surrounding seawaters and support vigorous revegetation and recovery of affected land and sea zones throughout the island community.

Particle-size segregation in self-channelized granular flows

Geophysical mass flows such as debris flows, dense pyroclastic flows and snow avalanches can self-channelize on shallow slopes. The confinement afforded by formed levees helps to maintain the flow depth, and hence mobility, allowing self-channelized flows to run out significantly farther than unconfined, spreading flows. Levee formation and self-channelization are strongly associated with particle-size segregation, but can also occur in monodisperse flows. This paper uses the monodisperse depth-averaged theory of Rochaet al.(J. Fluid Mech., vol. 876, 2019, pp. 591–641), which incorporates a hysteretic friction law and second-order depth-averaged viscous terms. Both of these are vital for the formation of a travelling wave that progressively deposits a pair of levees just behind the front. The three-dimensional velocity field is reconstructed in a frame moving with the front assuming Bagnold flow. This enables a bidisperse particle-size segregation theory to be used to solve for the large and small particle concentrations and particle paths in three-dimensions, for the first time. The model shows that the large particles tend to segregate to the surface of the flow, forming a carapace that extends over the centre of the channel, as well as along the external sides and base of the levee walls. The small particles segregate downwards, and are concentrated in the main channel and in the inner levee walls. This supports the contention that a low-friction channel lining provides a secondary mechanism for run-out enhancement. It is also shown that the entire theory scales with particle diameter, so experiments with millimetre-sized particles provide important insights into geophysical-scale flows with boulders and smaller rock fragments. The model shows that self-channelization does not need particle-size segregation to occur, but supports the hypothesis that particle-size segregation and the associated frictional feedback can significantly enhance both the flow mobility and the levee strength.

Metallogeny and exploration strategy for volcanic rocks hosting world class Be-U-F mineralization at Spor Mountain, Utah, U.S.A.

We report new geochemical data (major-elements, trace-elements, and Nd-Pb isotopes) for the Spor Mountain Formation (SMF), a volcanic sequence that hosts the largest deposit of beryllium in the world. Understanding the genesis of the deposit is critical for improved recognition of regional exploration targets containing additional volcanic-hosted beryllium resources. The deposit occurs in an area of extensive alkalic rhyolitic ash flow tuffs and calderas underlain by Paleozoic and older limestone, dolomite, shale, and quartzite. The lower fluorite and bertrandite-rich tuff and upper topaz-rich rhyolite of the SMF have overlapping zircon crystallization ages (25.59 + 0.29/−0.45 Ma). Enrichment of Be, U, and F is a key attribute of the SMF inherited from melting heterogeneous source materials and magma hybridization in the continental lithosphere. Two mineralization stages are implicated: magmatic, and hydrothermal/metasomatic. The magmatic stage occurred early, as indicated by the high beryllium content in early-crystallizing zircon. The post-magmatic/hydrothermal stage involved F-rich fluids that reacted with glass and carbonate nodules in the tuff to form bertrandite (and U-rich fluorite and opal) and high-grade mineralization. The rhyolite best displays the magmatic stage of enrichment. The SMF is alkaline. Chondrite-normalized REE patterns for tuff and rhyolite are regular, stacked subparallel, and imply a shared source derivation and evolution. The tuff and rhyolite plot along a sub-vertical array for Pb isotopes and suggest they are cogenetic; both have negative values of εNd. Pb isotopic ratios for SMF do not match the slopes, initial isotopic values, or estimated basement ages of precious and base metal mining districts in Utah; thus, they do not share a source region or evolution. Crustal ages from Nd isotopes (average TDM ~ 2.29 Ga) are older than basement ages obtained by Pb isotopes. The deposit occurs in a transitional area of thinned crust near the boundary between two basement domains, the eastern Great Basin and Colorado Plateau, which have contrasting ages. Many geochemical attributes are shared between SMF and the Ermakovka deposit in Russia: they represent the world's major commercial Be deposits. Rare-metal indices of granite-related mineralization show that SMF resembles other global beryllium-bearing granitic deposits. Despite this coincidence, none of these examples matches the mineralogy, geologic setting, or type of rare metal mineralization at Spor Mountain.

KOMATIITE LAVAS FROM THE QUEBRA OSSO GROUP (RIO DAS VELHAS GREENSTONE BELT, SOUTHEAST BRAZIL): A FIELD GUIDE TO AN ARCHEAN FLOW FIELD

The Quebra Osso Group encompasses one of the best preserved Archean komatiite flows in the Quadrilátero Ferrífero region, southern São Francisco craton (Brazil). It is commonly associated with the base of the Rio das Velhas greenstone belt within the Santa Bárbara tectonostratigraphic block. The Quebra Osso rocks are well exposed along the valley of the homonymous river, near the Catas Altas city (Minas Gerais state), and in inactive serpentine quarries. In this field guide, we provide the descriptions of the key outcrops in this area, including a variety of komatiite flows, sedimentary rocks and pyroclastic rocks. Despite the pervasive alteration of primary mineral assemblages due to greenschist to amphibolite facies metamorphism, the ultramafic rocks exhibit diverse igneous textures and structures. Volcanic textures are recognizable due to the morphology of the original igneous olivine and pyroxene, which underwent pseudomorphosis by hydrous minerals – serpentine and chlorite. These features include distinctive spinifex and cumulate textures that provide clues of the conditions operating during emplacement and crystallization of the ultrabasic liquids. The predominance of thick-packages of massive flows suggests channelized lava flows, with subordinate thin marginal layered (spinifex-textured), pillowed, brecciated and pyroclastic flows. Volcanic breccias, pillow lavas and chemical sedimentary rocks indicate that these rocks erupted underwater. These multiple volcanic products characterize a unique komatiite flow field and their remarkable preservation distinguishes the Quebra Osso Group from the other ultramafic associations within the São Francisco Craton.

Late Holocene volcanic stratigraphy and eruption chronology of the dacitic Young Doña Juana volcano, Colombia

We present the late Holocene eruption history of the poorly known Doña Juana volcanic complex, in SW Colombia, which last erupted in the twentieth century. This represents a case study for potentially active volcanism in the rural Northern Andes, where tropical climate conditions and a fragmented social memory blur the record of dormant volcanoes. We reconstructed the volcanic stratigraphy of the central-summit vent area by integrating new mapping at 1:5000 scale with radiocarbon ages, sedimentology analysis, and historical chronicles. Our results revealed cyclic transitions from lava-dome growth phases and collapse to explosive Vulcanian and possibly subplinian phases. Pyroclastic density currents were generated by dome collapse producing block-and-ash flows or by pyroclastic fountain/column collapse and were rapidly channelized into the deeply incised fluvial valleys around the volcano summit. The pyroclastic density currents were ∼4−10 × 106 m3 in volume and deposited under granular flow− or fluid escape−dominated depositional regimes at high clast concentrations. In places, more dilute upper portions reached a wider areal distribution that affected the inhabited areas on high depositional terraces. The coefficient of friction (ΔH/L) is higher for block-and-ash flows and dense lava−bearing fountain/low-column-collapse pyroclastic density currents compared to pumice-bearing, column-collapse pyroclastic density currents. Associated mass-wasting processes included syneruptive and intereruptive debris flows, with the last one documented in 1936 CE.

Petrogenesis of late Ediacaran volcanic rocks of the Kerdous and Tagragra d’Akka inliers (Anti-Atlas Morocco): Involvement of slab-failure

Late Ediacaran rocks of the Ouarzazate Group define a thin pile of sediments and pyroclastic deposits between the Paleoproterozoic basement and the Cambrian sedimentary cover in the southern Kerdous and Tagragra d’Akka inliers. In the Tafeltast area, terrigenous sediments with volcano-sedimentary and pyroclastic rocks are located in grabens controlled by syn-sedimentary normal faults. The sedimentation is characterized by a maximum flooding outlined by the Agoujgal carbonates. In the Tagragra-n-Daouizid area, the Ouarzazate Group represents the surficial emission of rhyolitic pyroclastic flows. This pyroclastic activity was associated with continental coarse-grained sedimentary deposits. In the Tagragra Ouahallal area, the volcanic sequence is comparable to that observed in subglacial volcanoes. Massive ash layers, intrusive pillow lavas in waterlogged deposits, stacking of lava flows, alternation of emerged and submerged periods under shallow water, are characteristics described in sub-glacial mafic volcanoes.According to geochemical data, volcanic rocks of the Ouarzazate Group are: (i) mafic rocks with continental flood basalt and calc-alkaline basalt affinity; (ii) high-K calc-alkaline felsic rocks, generated by partial melting of crustal lithologies, or by an enriched mantle with involvement of crustal component; and (iii) intermediate to felsic slab failure rocks derived through mantle processes including melting of mafic upper portion of the subducted slab.

A geophysical insight of the lithostratigraphic subsurface of Rodafnidia area (Lesbos Isl., Greece)

&lt;abstract&gt; &lt;p&gt;The study area of Rodafnidia on the island of Lesbos (Greece) is considered of archaeological interest, as Paleolithic stone tools have been recovered through excavation and collected from the ground surface in recent years. Geologically, the area is mostly covered by Quaternary post-alpine deposits and volcanic rocks. This paper presents the application of a local geophysical survey to determine the volume of the upper Quaternary deposits in which the Paleolithic artefacts can be found and the identification of their ignimbrite substrates. For this reason, the geoelectrical method was selected as the most appropriate for determining the lithostratigraphic subsurface layers. More specifically, a grid of twenty-one (21) Vertical Electrical Soundings (VES) along with an Electrical Resistivity Tomography (ERT) was carried out. The interpretation of the results of these surveys, in conjunction with the results of older excavation trenches, revealed that the Quaternary deposits have been investigated at depths ranging from 0.5 up to 28.5 meters. Furthermore, the lithological boundary of these post-alpine deposits and their underlying pyroclastic ignimbrite flow (with resistivity 24.0–58.0 Ohm.m) seem to dip to the north. The volume of the Quaternary layer is proposed as the maximum depth for archaeological investigation with high chances to recover more Paleolithic material.&lt;/p&gt; &lt;/abstract&gt;

Effects on Sedimentary Processes via Upper Triassic Climate Forcing Caused by Multiple Impacting and Large Igneous Provinces (LIP)-Rifting/Degassing: Jordanian Platform/Arabian Plate and Germanic Basin/Central Europe

Upper Triassic sedimentary systems of both the Arabian Plate and the Germanic Basin reveal climate- and plate tectonic-forced effects through certain time-intervals experienced by architectural elements, lithofacies types, unconformities, flash flood deposits, maximum flooding surfaces/sequence boundary (MFS/SB), mineralogy, and isotope anomalies. Further, Moon recession and changes of Earth’s rotation velocity (core/mantle boundary) are associated with multiple impacting and large igneous provinces/Mid Oceanic Ridge Basalt, LIP/MORB-rifting/degassing. While acidification (by degassing, sturz-rain) does influence tectosilicates and carbonates, montmorillonite represents a key mineral as transformation of volcanic/impact glass (Tephra) to be found as co-components in and in certain pelite units as “boundary clay-suspicions” (mixture of eolian paleoloess, pelite, paleosol, and tephra → tuffite). Obviously, unconformities and sequence boundaries of both study areas separate and dislocate interrupted ∂13C and 87Sr/86Sr-data groups along the isotope curves. Both Proto-Arctic Ocean rifting/degassing comprising kimberlitic pyroclastic eruptions and Neotethys rifting/degassing as well as multiple impacting played the most important role during the Norian, followed by the incipient Central Atlantic Magmatic Provinces rifting since the Rhaetian. The following associations are encountered and dealt with in this study: Sequence boundaries-∂13C, maximum flooding surfaces-(FUCs)-∂13C, unconformities-plate motion, tephra-pelite-tuffite-montmorillonite. Norian: maximum flooding surfaces (MFSs)-“paleosol”/boundary clay?-rifting-volcanism, Moon/Earth data change. So the Norian (~221 - 206 Ma) hosts anomalous “amalgamated maximum flooding surfaces (MFSs)”, amalgamated paleosol (Jordanian Platform), multiple impacting (~219 - 214 Ma), the maximum opening of the Proto-Arctic Ocean (PAO) (~230 - 200 Ma), Neo-Tethys (NT)-subvolcanic (sills, dikes) in the NE Dead Sea area prior the Rhaetian, and a significant change of Earth/Moon relation data. The study concludes that rare and extreme events are very strongly shaping the geologic constellations in the Earth System.

Seismic tremor location of 10 large paroxysmal eruptions of Tungurahua volcano, Ecuador

SUMMARYThe most recent eruptive period of Tungurahua volcano lasted 17 yr (1999–2016), generating strong eruptive phases with the release of large amounts of seismic and acoustic energies. We have selected 10 large eruptions and located their seismic sources. The location method involves applying a new method for correcting for site effects in the seismic records and identifying, in the frequency domain, the signals from the ground-coupled airwaves and pyroclastic flows. The locations are computed by minimizing the differences of the source energy rates in the [0.4, 2.5] Hz range. The results suggest that the first three eruptions have locations mainly concentrated at the [−1, 2] km depth range (asl), and the locations of the fourth eruption are mainly coincident with depths of a possible reservoir estimated from petrological studies. This fact strongly suggests that this eruption was responsible of changes in the dynamics of Tungurahua, making the volcano prone to produce Vulcanian eruptions.

Numerical investigation of Bi-model slurry transportation in a straight pipe

Slurry transportation through a pipeline system is a conventional mode of conveying solid material, which several industries have adopted across the globe. However, this mode of transportation is a complex phenomenon that requires high suspension stability of the particulates and high-energy requirements to deliver the solid materials continuously. Further, the researchers have adopted various techniques to make the continuous flow of solid materials through pipeline systems, such as additive addition and increasing the percentage of fine particles in the mixture. However, the accurate bi-model for the transportation of solid materials is not yet established. Therefore, in the present work, different mixture ratios (65:35, 75:25, 85:15 and 95:05) of silica sand and fly ash are considered to investigate the slurry flow characteristics. A numerical investigation is carried out for a bi-model slurry flow of silica sand (2650 kg/m3) and fly ash (2100 kg/m3) particulates having a mean diameter of 450 and 75 μm through a horizontal pipeline of 0.0549 m diameter. The accuracy of the numerical model and the procedure adopted for the current simulation is also validated by the available results in the literature. The work's outcomes reveal a significant drop in pressure with the increase in the percentage of fly ash in silica sand slurry. Further, the contours of the solid concentration, velocity distribution, granular pressure, granular temperature and wall shear stress are also envisaged and discussed in detail to analyze the effects of fly ash in silica sand slurry. Furthermore, Specific energy consumption is also calculated from the empirical relation for the different silica sand and fly ash ratios. The calculations show that the slurry mixture of 35% of fly ash in 65% of silica sand requires the least energy for transportation.

PyroCLAST: a new experimental framework to investigate overspilling of channelized, concentrated pyroclastic currents

PyroCLAST: a new experimental framework to investigate overspilling of channelized, concentrated pyroclastic currents

Outgassing and in-gassing of Na, K and Cu in lunar 74220 orange glass beads

Formed in a fire-fountain eruption, lunar 74220 orange glass beads are excellent recorders of the volcanic plume associated with the gas-driven eruption on the Moon. The bead surface is often coated with a thin (about 20 nm thick) and volatile-rich layer, with scattered euhedral vapor-condensates (the largest dimension is of a few μm). Hence, bulk analyses of glass beads show high concentrations of volatiles and moderately volatile elements, without the characteristic depletion of these elements in lunar basalts. The bead interiors contain lower concentrations of volatiles than olivine-hosted melt inclusions in the same sample, indicating loss of volatiles. These observations are commonly explained as outgassing from the melt during eruption and subsequent re-condensation of some of the gas species onto the surface of the quenched beads. Here, we report the first discovery of pervasive “U-shaped” Na, K and Cu concentration profiles across lunar 74220 orange beads with Na, K and Cu enrichment near bead surfaces and Na, K and Cu loss in the bead interiors. We propose that such U-shaped Na, K and Cu profiles were formed by initial outgassing and subsequent in-gassing of Na, K and Cu when the beads were flying from the vent onto the surface through the cooling volcanic gas plume. Hence, in-gassing and the formation of surface coatings are two processes that are genetically linked during the pyroclastic eruption and evolution of the gas cloud. The condensation of grains on bead surfaces is due to oversaturation of solid phases in the cooling volcanic plume.To quantify the processes that formed the U-shaped profiles, we developed a diffusion and surface-equilibrium model using available literature data on Na and Cu diffusivity in basaltic melts. The model assumed an asymptotic cooling history for spherical glass beads, a homogeneous initial composition, and surface equilibrium with the ambient atmosphere. The model reproduced U-shaped Na and Cu concentration profiles with outgassing at high temperature and subsequent in-gassing as beads cooled. By fitting the measured Na and Cu profiles, we found that the cooling time scales of individual orange glass beads range from 48 to 179 s. This is the first time that both outgassing and in-gassing were modeled and the cooling time scales of individual 74220 volcanic orange glass beads were estimated. The discovery of the U-shaped profiles of moderately volatile elements inside volcanic beads provides significant constraints on partial pressures of relevant volcanic gas species in the eruption plume.

Rock characteristics of post-caldera volcanoes in Dieng volcanic complex (DVC), Central Java, Indonesia

The Dieng volcanic complex (DVC) has one of the densest post-caldera volcanisms activity presents in Indonesia, yet its population density is considerably high. Therefore, it is important to identify the rock characteristics produced by the DVC post-caldera volcanoes to understand the risks and future hazards (i.e., eruption style). Based on lithology, we have classified DVC post-caldera volcanoes as (1) pyroclastic domain (PD; including Pagerkandang, Merdada, and Pangonan), and (2) lava domain (LD; including Prambanan, Kendil, Pakuwaja, Sikunir, Sikarim, and Seroja). PD is characterized by the domination of pyroclastic materials (mostly ash and lapilli) with oxidized scoria and volcanic lithics (fresh and/or altered) as the main components. The oxidized scoria clasts are moderately vesicular (27–41 % vesicularity; ) and phenocryst poor (&lt;5 % phenocryst crystallinity, ), with plagioclase, pyroxene, and oxides as the main phenocryst phases. The LD is composed predominantly of lava. The observed lavas are typically dense (mostly &lt;1 % , phenocryst rich (21–47 % ), and include plagioclase, pyroxene, biotite, amphibole, and oxides as the main phenocryst phases. Such differences in mineralogy and textures (i.e., vesicularity and crystallinity) suggest that PD and LD were likely sourced from different magmatic sources with different eruption styles (explosive and effusive styles, respectively). We have suggested that civilization settlements near PD are facing major threats from explosive magmatic, phreatomagmatic, and phreatic eruptions that could produce significant fallouts, ballistic materials, and highly destructive pyroclastic density currents. LDs pose a threat in the form of effusive magmatic eruptions such as lava flows and/or domes.

Evolution Magmatism of Nagasari Volcano Dieng, Central Java, Indonesia

Nagasari Volcano, part of the Dieng volcanic complex, is one of the unique volcanoes in Central Java. Around this volcano grow eruption craters, volcanic cones, and pyroclastic flow ridges. There were several 14 eruption centers around Mount Nagasari, so it is necessary to know the development of magmatism evolution. The aims of the research to determine the evolutionary development of magmatism. The methodology used is geological mapping and petrographic analysis. The observations of rocks found in the study area include andesite lava, lapilli-tuff, fallen pyroclastic breccias, and flow pyroclastic breccias. Meanwhile, geological mapping and petrographic observations of volcanic rock samples show that the evolution of magmatism in the study area from the oldest to the youngest is basaltic magma that formed Prau Volcano in the pre-caldera period. On the other hand, magmatism in the post-caldera I period was of the type of pyroxene andesite forming the Gembol to Jimat Volcano group. In contrast, in the post-caldera II period, the hornblende-biotite andesite group formed the Dieng Kulon to Kendil group.

Explosive multiples preceding the growth of a new lava dome: Volcán de Colima, México, January–February 2016

Explosive multiples (EM) represent the continuous sequencies of small-amplitude explosive events (members of multiples), which are characterized by low-height emissions of gas and ash. In this article, the seismic signatures of EMs, recorded in January–February 2016 at Volcán de Colima, México, by broadband seismic station at 4 km from the crater before the new lava dome growth, are discussed. The EM signals were recorded during the vent-clearing period; they practically disappeared with appearance of a new lava dome. Video images, recorded simultaneously with EMs, demonstrated that the EM signals were associated with the venting of low-height ash plumes. The durations of 24 selected EM seismic signatures varied from 1.5 to 8 min. The sequences of EM consisted of 3 to 7 explosive impulses, members of the EMs. Comparison with Vulcanian explosions, which were recorded simultaneously with EMs during vent-clearing period before the lava dome growth and were followed with pyroclastic flows and igneous rockfalls (PFIRs), demonstrates that the energy of the first members of EMs sequences was lower than the energy of Vulcanian explosions. The EMs were originated at more shallow depths comparing with Vulcanian explosions. Our study allows to see a feedback type relationship between the process of the vent-clearing by Vulcanian explosions, followed with PFIRs, and simultaneous explosive ash-venting by EMs with exit of gas and ash. As was noted by Zobin et al. (2021), the volume of PFIRs, following the Vulcanian explosions during vent-clearing period, decreased in time before the exit of a new lava dome. At the same time, there was recorded a simultaneous contrary tendency of increasing in durations of the EM seismic signatures in time (coefficient of correlation 0.55). Therefore, while the Vulcanian explosions worked digging large masses of rocks, which formed then PFIRs, the sequences of more shallow EMs, generated along the purified faults of crack system of the lava cap, blowed out clogged cavities clearing a way for lava exit with ash-venting. When the volume of explosive generated PFIRs became smaller, indicating the appearance of well-purified faults in the crater, the sequences of EMs became longer, increasing in the number of their explosive members occurring along these faults. They began intensive ash-venting of the fault cavities clearing way for lava exit. This feedback collaboration of two processes during vent-clearing period gives us an option for modelling of the preparation of the way for exit of the lava body into the crater.

Risk scenarios for a future eruption in the Chichinautzin monogenetic volcanic field, South México City

The Chichinautzin Monogenetic Volcanic Field creates volcanic risks for México City. To evaluate the possible effects and economic impacts of a future eruption, three scenarios based-on the spatial distribution of the most recent eruptions and the study of their characteristic are proposed. Scenario A, a Violent Strombolian eruption at the northwestern edge of the volcanic field, with eruptive columns 6–8 km high and emission of low-viscosity lava flows. Scenario B, Santiaguito-type eruption, a thick, high-viscosity lava flow that generates rock falls and short Merapi-type pyroclastic flows in the central northern area. Scenario C, a Hawaiian to Strombolian eruption with eruptive columns <6 km high and the emission of low viscosity lavas in the central part of the field. From these scenarios, numerical simulations of lava and tephra were carried out to obtain conditional hazard maps. The risk evaluation integrates the analysis of hazard, exposure, vulnerabilities, resilience, and the estimation of the costs of possible damages with physical and sociodemographic indicators available at the city block level, including rural areas. Two vulnerability curves were integrated for housing, the first for lava flows, which considers that a thickness ≥ 2 m of lava causes total loss (considering the loss of the function and accessibility); and a second curve for tephra that considers that an accumulated thickness in dry conditions of 20 cm of tephra produces generalized damage to all type of houses. By combining the vulnerability and hazard maps, two risk maps were constructed, one for lava flows and the other for tephra. The total direct cost of the expected damages was calculated for each scenario considering the cadastral value of the land and buildings for each property at risk. The costs for the most probable and the most catastrophic scenario amount to >14 billion US dollars, equivalent to 1.2% of the national GDP. Mitigation measures, mainly of the non-structural type are proposed.

Origin, transport, and diagenesis of tuffs in organic-rich lacustrine mudstone: An example from the lower part of the Middle–Late Triassic Chang7 Member, Ordos Basin (NW China)

Tuffs, produced by explosive volcanic eruptions, are widely deposited throughout the Precambrian to Cenozoic stratigraphic record. Due to rapid compaction and erosion, preservation and identification of tuffs in distal environments are challenging. However, in deep lacustrine environments, tuffs may be found well-preserved as interlayers in the organic-rich mudstone. This in turn provides valuable insights into the origin, transport, and diagenesis of volcanic material. In this study, we performed an integrated sedimentological, mineralogical, and geochemical analysis of seven tuff samples collected from the lower part of the Chang7 member of the Maquan section to infer on their provenance, transport mechanisms and post-depositional alterations. Immobile element ratios, tectonic discrimination diagrams, trace element distribution patterns, and negative whole-rock εNd(t) reveal an intermediate to felsic continental arc source of the studied tuff. Supported frameworks and ash aggregates in the tuff are in favor of the transport from pyroclastic density currents and ash plumes during multiple volcanic eruptions with various degrees of eruption volume and water content. Tuff diagenesis is characterized by dissolution of plagioclase, illitization of smectite, cementation of carbonate minerals, and presence of buddingtonite. Relatively ordered illite-smectite and low vitrinite reflectance from the adjacent organic-rich mudstone indicate diagenetic evolution of studied tuff have reached mesogenetic stage.