Holocene Volcanoes Research Articles

Seismic structure beneath Ebeko Volcano and surrounding areas of Paramushir Island (Kuril Arc) inferred from local earthquake tomography

Paramushir is a large northernmost island of the Kuril Arc in the Russian Far East. Here, we study the northern part of Paramushir, which is dominated by the Vernadsky Ridge with an altitude of around 1000 m above sea level. This ridge is composed of a series of Pleistocene and Holocene volcanoes and includes the presently active Ebeko Volcano, which exhibits frequent phreatomagmatic eruptions and ongoing fumarolic activity. Studying the internal structure beneath Northern Paramushir is important to understand the interrelationship of magmatic, hydrothermal, hydrological and geological processes below Ebeko Volcano. We use seismic data of a portable network consisting of 20 broadband stations installed for one year from the summer 2021 to 2022 and one permanent station in the city of Severo-Kurilsk. We performed the local earthquake tomography inversion, which provided the distributions of Vp, Vs, Vp/Vs and local seismicity in an area of northern Paramushir with lateral extent of ∼20 km and depth of a ∼ 15 km. The results of several tests gave the information about the resolution limitations of the computed model, which were taken into account during its interpretation. In the resulting model, the coexistence of low Vp, high Vs, low Vp/Vs and a seismicity cluster down to ∼10 km below Ebeko indicates the presence of a large gas-saturated area that was formed due to the contacts of liquid fluids with hot magmatic intrusions. The western border of this area coincides with the location of Verkhne-Yurievsky hot water sources and possibly highlights the path of fluids traveling around the hot body below Ebeko. Below the upper part of the eastern slope, we observe a shallow anomaly of low Vs and high Vp/Vs indicating the presence of a near-surface aquifer, confirming the previous results of ambient noise tomography. Below the lower part of the eastern slope, a nearly vertical anomaly of low Vs and high Vp/Vs may represent a fault zone, which is also marked on the surface by a series of lineaments.

Deep-sourced CO2 emissions from the Eastern Himalaya Syntaxis and the Tengchong Volcanic Field, southeast Tibet

The India-Asia collision zone is believed to play a central role in Earth's geological carbon budget. The processes controlling soil CO2 flux and mechanism at this continental subduction zone margin remain however poorly constrained. Here, we focus on hydrothermal CO2 emissions from southeast Tibet, specifically from the Eastern Himalaya Syntaxis (EHS) and the Tengchong Volcanic Field (TVF), with the twin goals of informing models of carbon cycling and ascertaining the source of hydrothermal degassing systems. In-situ measurements of soil CO2 flux from the Aqiong, Caquka, Nongchaka, Rongduo, and Woka hydrothermal fields of the EHS yield average soil CO2 fluxes of 72, 5, 13, 66, and 10 g m−2 day−1, respectively. Regional heat flow, tectonic regimes, and CO2 content in the spring gas are plausible controlling factors for soil CO2 flux, which is crucial to quantifying total CO2 output in continental collision zones. The compositions and He-C-N isotopes of hydrothermal volatiles from two study regions are reported here as well. Analysis of the He-C-N isotopes in terms of distances to the Jiali fault and the nearest Holocene volcano confirms that the Jiali fault and Holocene volcanoes have a significant impact on discharging deep-sourced CO2 from the EHS and TVF hydrothermal systems to the surface. The 3He/4He values of EHS hydrothermal volatiles (92 to 98°E), combined with previous data (82 to 92°E), show a clear increasing trend from south to north. Thus, we propose an updated model of enriched mantle wedge source for the EHS hydrothermal volatiles, based on multi-component mixing calculations of the He-CO2 systematics. The EHS hydrothermal volatiles exhibit systematics spatial variations from the core location to the bilateral segments, suggesting the highest 3He/4He ratio and carbonate-rich characteristics at the core location possibly controlled by the asthenosphere upwelling caused by the deep fragmentation structure.

Magma and hydrothermal sources below the northern part of Paramushir Island (Kuril Arc) inferred from ambient noise tomography

Paramushir is the northernmost island of the Kuril Arc comprising several Holocene volcanoes, of which two are presently active: Ebeko and Chikurachki. We present the first crustal-scale three-dimensional seismic shear-wave velocity model of the northern part of Paramushir derived with the use of data of 20 temporary stations operated in 2021–2022 and one permanent station. The continuous seismic data were used to obtain the Rayleigh wave dispersion curves for periods ranging from 0.5 s to 12 s through computing ambient seismic noise cross-correlation functions. Then the 3D shear wave velocity distribution was constructed by seismic tomography. The synthetic tests demonstrate that the model has sufficient resolution down to 7–10 km depth. We observe a series of low-velocity anomalies at the depths of 4–6 km below the volcano-origin Vernadsky Ridge. They may likely represent magma reservoirs that are responsible for Holocene eruptions along the ridge. These anomalies are overlain by the high-velocity anomalies associated with the rigid cover consisting of an upper-crustal granite-granodiorite body and consolidated magma intrusions. Along the eastern flank of Ebeko we reveal a thin low-velocity anomaly at a depth of ∼1 km that can be interpreted as a water-saturated layer. The contact of this layer with hot magma intrusions leads to the formation of a large amount of steam that is ejected during the frequent phreatic eruptions of Ebeko and from numerous fumaroles in the summit area. On the other hand, this layer, which is following down to the Pacific Coast, might be promising for the geothermal energy exploitation.

Conductivity distribution beneath Socompa volcano, northwestern Argentina, from 3-D magnetotelluric characterization

The Socompa volcano is one of the Holocene volcanoes of the Central Volcanic Zone of the Andes. Given that it records effusive activity after 5910 YBP and that recent studies reveal unrest associated with the uplift of its edifice, it is considered an active volcano. With the aim of explaining new features that provide information about the nature of its state, here we present a geoelectric structures model of the subsurface of Socompa volcano obtained with the magnetotelluric method. One of the main features defined by the 3-D model is a body with an electrical resistivity value lower than 10 Ωm between 2 and 7 km depth and located below the volcanic edifice. This body, interpreted as the magmatic heat source of the volcano, is connected to a shallow and thick high conductive layer that covers the surrounding area. Our results highlight a possible shallow magma reservoir below the Socompa volcano and an associated -active or not- hydrothermal system.

Pleistocene to Holocene volcanism in the Canadian Cordillera

The Canadian Cordillera hosts numerous Pleistocene and Holocene volcanoes and volcanic deposits, including a number of volcanoes that have erupted within the last several hundred years. The nature and composition of volcanic edifices and deposits are diverse and dictated by the complex configuration of tectonic plates along the western margin of British Columbia and the thermal structure of the underlying mantle. Our modern knowledge of these is built upon more than a century of field- and increasingly, laboratory-based studies. We recognize five distinct volcanic domains within the Cordillera that are distributed across British Columbia, the Yukon Territory, and easternmost Alaska. These include the Wrangell Volcanic Belt, the Northern Cordilleran Volcanic Province, the Anahim Volcanic Belt, the Wells Grey-Clearwater Volcanic Field, and the Garibaldi Volcanic Belt representing the northern extension of the Cascade Volcanic Arc. Volcanism in the Canadian Cordillera spans the full range of explosive to effusive behaviours, encompasses the suite of common volcanic chemical compositions (alkaline to calc-alkaline and nephelinite to peralkaline rhyolite), and is expressed by long-lived stratovolcanoes, shield volcanoes, and calderas, as well as shorter-lived tephra cones and associated lava flows. The range in tectonic settings (subduction to extension), eruption environments (subaerial–subaqueous–cryospheric), and topographic variability make volcanism within the Canadian Cordillera as diverse as anywhere on Earth, yet it is also the least studied. Here, we summarize the current state of knowledge concerning volcanism within the Canadian Cordillera and conclude with thoughts on research areas that merit further effort, namely glaciovolcanism and volcanic hazards.

Global volcanic rock classification of Holocene volcanoes

This data descriptor assigns the major and minor rock names from worldwide Holocene volcanoes of the Global Volcanism Program (GVP) using the Total Alkali-Silica diagram (TAS) for the chemical classification of volcanic rocks using the Geochemistry of Rocks of the Oceans and Continents (GEOROC) database. The precompiled files of the GEOROC database provide the chemical composition of volcanic rock samples, from which we computed major and minor rocks for global Holocene volcanoes reported in GVP. The combined dataset associates each volcano with the relative abundance of each volcanic sample type (whole rock, glass, melt inclusion) and provides the five major (more than 10% abundance) and minor rock names. In total, over 138,000 GEOROC volcanic rock samples were considered, for ~1000 Holocene volcanoes. The resulting major rock compositions are in general consistent with those given in GVP. The dataset provides a global panorama of rock composition for Holocene volcanoes.

Investigation of hot spring gas components and soil gas fluxes in Arxan Holocene volcanic field, Inner Mongolia, NE China

The latest research results show that there is a unified magma system and heating channel beneath the Arxan volcanic field, indicating a potential risk of eruption. The Arxan volcanic field features multiple gas emission sites (e.g., Jinjianggou hot springs and Yinjianggou hot springs) and exhibits strong hydrothermal activity. In this study, measurements of the hot spring gas composition and soil CO2 flux in the Arxan Holocene volcanic field were conducted, and the results were combined with previous research results to analyze the degassing characteristics of this region. The results show that the volcanic gases in the Arxan volcanic field are composed of 0.07%–1.09% CO2, 0.33–12 ppm CH4, 1.57–53 ppm H2, 800–30,241 ppm He, and 1.14%–1.86% Ar. The He content in this area is notably higher than that in other dormant volcanoes in China. This difference is possibly caused by U–Th decay in the Mesozoic granodiorite and acidic volcanic rocks in the study area, which can produce substantial radiogenic He. The soil gas concentrations near the Jinjianggou and Yinjianggou hot springs are higher than those of two Holocene volcanoes. The peak CO2 concentration in the soil near the Jinjianggou hot spring can reach 35,161 ppm. The single-site soil microseepage CO2 flux in the Arxan volcanic field is 4.66–107.18 g m−2 d−1, and the estimated annual CO2 emission flux from the volcanic field to the atmosphere is 0.63 × 105 t, which also demonstrates that soil CO2 flux of Arxan volcano is comparable to the soil CO2 emission level of the Iwojima volcano.

Repeated seismic swarms near Paricutin volcano: precursors to the birth of a new monogenetic volcano in the Michoacán-Guanajuato volcanic field, México?

The birth of a new monogenetic volcano is difficult to forecast with precision, both in space and time. Nevertheless, seismic activity can alert of the imminence of such an eruption because it usually occurs as small-magnitude earthquake swarms that can last for a few weeks to months prior to an eruption. These swarms are usually related to magma that becomes stalled in the Earth’s crust for variable periods of time before its eventual eruption at the surface. For several reasons, volcanic seismic swarms have rarely been recorded with seismometers before the birth of a new monogenetic volcano. Over the past 25 years, six distinct seismic swarms (in 1997, 1999, 2000, 2006, 2020, and 2021) were detected between Tancítaro and Paricutin volcanoes, in the southwestern part of México’s Michoacán-Guanajuato volcanic field. They are believed to represent repeated attempts of magma to reach the surface hinting that in this region magma might become stalled for some time, so as to not reach the surface in a single ascent event from its source in the mantle. To better understand the magma’s migration path through the crust, we re-located with greater precision some of these seismic swarms by using the same methodology and velocity model to the entire data set. Our results show that these swarms originated within a small area beneath the NE flank of Tancítaro at depths of between 15 and 8 km below sea level (bsl). Apparently, magma is trying to reach the surface within the same conduit network at these crustal depths, but stalls when reaching a depth of ~ 8 km bsl. It is crucial to study these swarms because they might be precursors to a new eruption in this part of the Michoacán-Guanajuato volcanic field. This monogenetic field has been very active, producing several dozen eruptions during the Holocene, the last two Jorullo (1759–1774) and Paricutin (1943–1952). Furthermore, the Tancítaro area displays one of the highest densities of Holocene volcanoes within the entire field, making it a probable candidate location for the birth of a future monogenetic volcano. For these reasons, a permanent seismic network should be installed as soon as possible.

Integrating global geochemical volcano rock composition with eruption history datasets

The major element composition of volcanic rocks carries important information about the source and differentiation processes affecting the magma, the physical properties that allow it to erupt, and its eruptive style. Although global rock geochemical databases exist, these are not linked to volcanic eruption history which hampers our global understanding of the relationship between magma composition and eruption dynamics. Here, we integrate two global databases, the Geochemistry of Rocks of the Oceans and Continents (GEOROC) and the Holocene volcanoes of the world of the Global Volcanism Program (VOTW-GVP). The integration is based on matching the location name, geographic position and eruption time, which is automated by a tool called DashVolcano. The tool is open-source, accessible at https://github.com/feog/DashVolcano, and gives access to the integrated datasets via an interactive dashboard. DashVolcano is based on more than 138,000 volcanic rock samples and provides the basis for the identification of global relationships between eruption styles, volcano types, and rock composition for more than 700 volcanoes and their eruptions for the last 10,000 years. The combined record of the eruptive history and its corresponding geochemical rock composition that DashVolcano provides can be used for characterizing global geochemical differences between volcanoes, and should also prove useful for improved long-term hazard and risk evaluations.

Mantle thermochemical variations beneath the continental United States through petrologic interpretation of seismic tomography

The continental lithospheric mantle plays an essential role in stabilizing continents over long geological time scales. Quantifying spatial variations in thermal and compositional properties of the mantle lithosphere is crucial to understanding its formation and its impact on continental stability; however, our understanding of these variations remains limited. Here we apply the Whole-rock Interpretive Seismic Toolbox For Ultramafic Lithologies (WISTFUL) to estimate thermal, compositional, and density variations in the continental mantle beneath the contiguous United States from MITPS_20, a joint body and surface wave tomographic inversion for Vp and Vs with high resolution in the shallow mantle (60–100 km). Our analysis shows lateral variations in temperature beneath the continental United States of up to 800–900°C at 60, 80, and 100 km depth. East of the Rocky Mountains, the mantle lithosphere is generally cold (350–850°C at 60 km), with higher temperatures (up to 1000°C at 60 km) along the Atlantic coastal margin. By contrast, the mantle lithosphere west of the Rocky Mountains is hot (typically >1000°C at 60 km, >1200°C at 80–100 km), with the highest temperatures beneath Holocene volcanoes. In agreement with previous work, we find that the chemical depletion predicted by WISTFUL does not fully offset the density difference due to temperature. Extending our results using Rayleigh-Taylor instability analysis, implies the lithosphere below the United States could be undergoing oscillatory convection, in which cooling, densification, and sinking of a chemically buoyant layer alternates with reheating and rising of that layer.

Temperature and Hf-O isotope correlations of young erupted zircons from Tengchong (SE Tibet): Assimilation fractional crystallization during monotonic cooling

Young zircons from crystal-poor volcanic rocks provide the best samples for the investigations of pre-eruption magmatic processes and for testing a possible relationship between zircon Eu anomalies and crustal thickness. We report trace element chemistry and Hf-O isotope compositions of young zircons from 3 Holocene volcanoes in the Tengchong volcanic field, SE Tibet, in order to provide insights into magma evolution processes and conditions for high-K calc-alkaline volcanic rocks in a post-collisional setting. As decreasing zircon Ti content and falling temperature, zircon Hf content and Yb/Sm increase whereas zircon Eu anomaly and Th/U decrease, indicating fractional crystallization of plagioclase and zircon during magma cooling. More importantly, zircon Hf isotope ratio (εHf values) increases with decreasing zircon Ti content and falling temperature (T), suggesting gradually increasing incorporation of relatively high εHf juvenile materials in the crystallizing zircons during magma evolution. Negative correlations between zircon εHf and zircon δ18O also support open-system magma evolution. Our data suggest fractional crystallization of a magma with simultaneous contamination by high εHf and low δ 18O juvenile (immature) crustal materials during monotonic cooling after zircon saturation. The low-T, high-εHf and low- δ 18O zircons may indicate the involvement of the early Cretaceous juvenile granitic country rocks during shallow magma evolution. Average Eu anomalies in zircons from young Tengchong lavas yield crustal thickness of 40.7 ± 6.8 km, consistent with present crustal thickness (42.5 km) determined by geophysical methods.

Seismic Full‐Waveform Inversion of the Crust‐Mantle Structure Beneath China and Adjacent Regions

AbstractWe present the first‐generation full‐waveform tomographic model (SinoScope 1.0) for the crust‐mantle structure beneath China and adjacent regions. The three‐component seismograms from 410 earthquakes recorded at 2,427 stations are employed in iterative gradient‐based inversions for three successively broadened period bands of 70–120 s, 50–120 s, and 30–120 s. Synthetic seismograms were computed using GPU‐accelerated spectral‐element simulations of seismic wave propagation in 3‐D anelastic models, and Fréchet derivatives were calculated based on an adjoint‐state method facilitated by a checkpointing algorithm. The inversion involved 352 iterations, which required 18,600 wavefield simulations. SinoScope 1.0 is described in terms of isotropic P‐wave (VP), horizontally and vertically polarized S‐wave velocities (VSH and VSV), and mass density (ρ), which are independently constrained with the same data set coupled with a stochastic L‐BFGS quasi‐Newton optimization scheme. It systematically reduced differences between observed and synthetic full‐length seismograms. We performed a detailed resolution analysis by repairing input random parametric perturbations, indicating that resolution lengths can approach the half propagated wavelength within the well‐covered areas. SinoScope 1.0 reveals strong lateral heterogeneities in the lithosphere, and features correlate well with geological observations, such as sedimentary basins, Holocene volcanoes, Tibetan Plateau, Philippine Sea Plate, and various tectonic units. The asthenosphere lies below the lithosphere beneath East and Southeast Asia, bounded by subduction trenches and cratonic blocks. Furthermore, we observe an enhanced image of well‐known slabs along strongly curved subduction zones, which do not exist in the initial model.

Assessing the Use of Optical Satellite Images to Detect Volcanic Impacts on Glacier Surface Morphology

Globally, about 250 Holocene volcanoes are either glacier-clad or have glaciers in close proximity. Interactions between volcanoes and glaciers are therefore common, and some of the most deadly (e.g., Nevado del Ruiz, 1985) and most costly (e.g., Eyjafjallajökull, 2010) eruptions of recent years were associated with glaciovolcanism. An improved understanding of volcano-glacier interactions is therefore of both global scientific and societal importance. This study investigates the potential of using optical satellite images to detect volcanic impacts on glaciers, with a view to utilise detected changes in glacier surface morphology to improve glacier-clad volcano monitoring and eruption forecasting. Roughly 1400 optical satellite images are investigated from key, well-documented eruptions around the globe during the satellite remote sensing era (i.e., 1972 to present). The most common observable volcanic impact on glacier morphology (for both thick and thin ice-masses) is the formation of ice cauldrons and openings, often associated with concentric crevassing. Other observable volcanic impacts include ice bulging and fracturing due to subglacial dome growth; localized crevassing adjacent to supraglacial lava flows; widespread glacier crevassing, presumably, due to meltwater-triggered glacier acceleration and advance. The main limitation of using optical satellite images to investigate changes in glacier morphology is the availability of cloud- and eruption-plume-free scenes of sufficient spatial- and temporal resolution. Therefore, for optimal monitoring and eruption prediction at glacier-clad volcanoes, optical satellite images are best used in combination with other sources, including SAR satellite data, aerial images, ground-based observations and satellite-derived products (e.g., DEMs).

Spatially and Geochemically Anomalous Arc Magmatism: Insights From the Andean Arc

AbstractWhile most volcanic arcs show a distinctive spatial relationship to subducting plates, there are many examples where volcanoes occur in anomalous locations. These are commonly also geochemically anomalous relative to the composition of more typical subduction‐related rocks. Using Holocene volcanoes in South America as a case study, we document the spatial and geochemical patterns along the Andean volcanic belt. To determine whether spatial variations are also geochemically anomalous, we assess a series of geochemical indices that provide information on the depth and degree of melting, and the role of metasomatic subduction inputs in melt generation. We use these parameters to develop a scoring system, with the lowest and highest scores indicating “typical” and “anomalous” arc melting processes, respectively. Typical arc magmatism is defined as melts generated in the sub‐arc mantle wedge through slab‐derived fluid metasomatism, with or without contributions from subducted sediments. In contrast, we show that anomalous volcanism in South America appears to relate to geometric anomalies in the subducting Nazca plate (e.g., beneath Sumaco, Laguna Blanca and Payun Matru), or to areas affected by variations in mantle flow due to the proximity to the slab edge (Crater Basalt Volcanic Field). By establishing relationships between anomalous magmatism and slab structure, we propose that similar geochemical fingerprints could be used to explore the magmatic response to slab deformation and/or tearing in older arc systems, particularly in cases where the three‐dimensional slab structure is no longer detectable.

Magmatic Processes in the East African Rift System: Insights From a 2015–2020 Sentinel‐1 InSAR Survey

AbstractThe East African Rift System (EARS) is composed of around 78 Holocene volcanoes, but relatively little is known about their past and present activity. This lack of information makes it difficult to understand their eruptive cycles, their roles in continental rifting and the threat they pose to the population. Although previous InSAR surveys (1990–2010) showed sign of unrest, the information about the dynamics of the magmatic systems remained limited by low temporal resolution and gaps in the data set. The Sentinel‐1 SAR mission provides open‐access acquisitions every 12 days in Africa and has the potential to produce long‐duration time series for studying volcanic ground deformation at regional scale. Here, we use Sentinel‐1 data to provide InSAR time series along the EARS for the period 2015–2020. We detect 18 ground deformation signals on 14 volcanoes, of which six are located in Afar, six in the Main Ethiopian Rift, and two in the Kenya‐Tanzanian Rift. We detected new episodes of uplift at Tullu Moje (2016) and Suswa (mid‐2018), and enigmatic long‐lived subsidence signals at Gada Ale and Kone. Subsidence signals are related to a variety of mechanisms including the posteruptive evolution of magma reservoirs (e.g., Alu‐Dallafila), the compaction of lava flows (e.g., Nabro), and pore‐pressure changes related to geothermal or hydrothermal activity (e.g., Olkaria). Our results show that ∼20% of the Holocene volcanoes in the EARS deformed during this 5‐years snapshot and demonstrate the diversity of processes occurring.

Differences in microbial communities from Quaternary volcanic soils at different stages of development: Evidence from Late Pleistocene and Holocene volcanoes

Volcanic eruptions are a universal cause of ecological and geological disturbance; however, the differences in microbial communities from Quaternary volcanic soils at different stages of development in Inner Mongolia are little known. Microbial communities were investigated in Quaternary volcanic soils from Late Pleistocene volcano and Holocene volcano with the objective of elucidating their differences. The composition and potential functionality of soil microbial communities was significantly diverse between Late Pleistocene volcanic soils and Holocene volcanic soils. Although the richness, diversity and evenness of microbial communities at older volcanic soils were significantly greater than at younger volcanic soils, younger volcanic soils possessed a more complex microbial community network than older volcanic soils. The soil bacterial community was more sensitive to Quaternary volcanic soils than the fungal community, exhibiting significant differences at the phylum level and possessing more biomarkers. Quaternary volcanic soils may have enriched some specific microorganisms, i.e., biomarkers and generalists, closely related to the metabolism of soil carbon, nitrogen and phosphorus. Quaternary volcanic soils first directly mediated soil carbon, nitrogen and phosphorus, and then guided microbial multifunctionality. These results clarify the difference patterns of soil microbial communities in support of better ecological management of volcanic area in Inner Mongolia.

The Tefroid Deposits on an Active Stratovolkano Bezymianny (Kamchatka)

The article highlights the results of a study of volcanic processes on the large active stratovolcano Bezymyanny, located on the Eastern mountain range of Kamchatka, in the Klyuchevskoy group of Holocene volcanoes. It is one of the most active volcanoes in the world, characterized by continuous short-term explosive eruptions with powerful outbursts of ash material, accompanied by lava flows and the formation of extrusions. Among Russian and foreign volcanologists, this volcano became world famous on March 30, 1956, when a catastrophic eruption occurred, which in geological literature was called a "directed explosion" or "an eruption of the Bezymyanny type." In addition to volcanic structures, peculiar volcanic-sedimentary deposits of the volcano were also investigated, represented by the so-called tefroids, which are the product of the movement and washing of volcanic-clastic material of eruptions. Modern volcanological expeditions in Kamchatka and the Kuril Islands have made it possible to prove not only the synchronicity of the forming tefroid accumulations with volcanism, but also the extensive distribution of these rocks, which often prevail over volcanoterrigenous sediments. In all the modern volcanic regions studied in detail, a wide development of tefroid formations has been established. By age, tefroids develop from the early Precambrian to the present day. On the slopes of the volcano and in the area of development of dry streams, there is a constant movement of fine-grained material to the foot of the volcano. These freely moving material in the process of movement are sorted by size, roundness and form well-sustained thick tefroid layers. The volcano stands half submerged in these geologically instantaneously deposited tefroid strata.

Global mapping of future glaciovolcanism

We created a global database of glacierized volcanoes, using a projection optimized for each volcano, to identify locations where land ice (glaciers and ice sheets) and volcanoes co-exist on Earth. Our spatial database melds the Smithsonian Global Volcanism Database (SGVD) and the Randolph Glacier Inventory 6.0 (RGI). We identified all Holocene volcanoes within the SGVD that have glacier ice within radii of 1 km, 2.5 km, and 5 km, and thus have the potential to impact or be impacted by surrounding ice. Our analysis shows that 245 Holocene volcanoes have glacier ice within the specified radii, which are covered partly or fully by 2584 unique glaciers or the Antarctic Ice Sheet. The volcanoes are located in all major volcano-tectonic settings, although the majority (72%) are in subduction zones built on continental crust (greater than 25 km thick). They also cover the majority of the typical compositional ranges for igneous rocks (basalt to rhyolite). Twenty-nine volcanoes, or 12%, have at least 90% ice cover within 5 km, which together comprise 36% of global glacier area on volcanoes. About 20,000 people live within 5 km of a glacierized volcano, while 160 million people live within 100 km of a glacierized volcano and could be impacted by lahars and/or disruption of their water sources during future eruptions. By merging our database with existing ice thickness model estimates we find 850 ± 290 km 3 of ice within 5 km of volcanic vents globally. We compare the eruption history, ice volume, and nearby population estimates to identify the most dangerous volcanoes on Earth. The combination of volcano locations and ice thickness estimates allows us to identify 20 (out of 245) glacierized volcanoes that are most likely to experience ‘thick’ ice eruptions, while the vast majority are more likely to experience ‘thin’ ice eruptions. • 245 Holocene volcanoes have glaciers (2584 total) with a 5 km radius. • Glacierized volcanoes occur predominantly (74%) in subduction zone settings. • 20,000 people live within 5 km of a glacierized volcano, 160 million within 100 km. • 850 ± 290 km 3 of glacier ice is within 5 km of volcanic vents globally.

Surface-wave phase-velocity maps of the Anatolia region (Turkey) from ambient noise tomography

The Anatolian region is an area with very heterogeneous crustal structure accompanied by large velocity contrasts. Despite the complexity of the region, the detailed crustal structure remains to be unraveled. In this study, we first measure the dispersion curves of Rayleigh waves between 1,721 pairs of station and then invert these dispersion curves to obtain high-resolution isotropic and azimuthally anisotropic phase-velocity maps in the period range of 5–25 s. The resulting isotropic phase-velocity patterns display strong correlation with the geological features, while the anisotropic patterns are highly consistent with the GPS-measured surface velocity field in the region. Variations of the isotropic as well as anisotropic patterns indicate the presence of active faulting, especially beneath the East and North Anatolian Faults. Beneath the locations of Holocene volcanoes and crystalline massifs in Cappadocia, high velocities (up to 2.5%) are present, whereas negative velocity anomalies (up to −2%) are found beneath the Menderes Massif in southwestern Anatolia (at periods of 5–20 s), suggesting different origins and tectonic regimes of those massifs. On either side of an active fault, two terranes with different stress patterns are generally found. Active fault can thus be identified by different anisotropy patterns on either sides of the fault. The Central Anatolian Fault do not display strong isotropic velocity contrasts, as well as no noticeable variation in the anisotropic pattern across the fault, suggesting that this fault may not be active in recent times.

Imaging crustal melt beneath northeast Japan with Ps receiver functions

To investigate crustal structures related to melt storage, Ps converted waves were used to image crustal velocity discontinuities across the Tohoku region of northeast Japan. Ps receiver functions from 127 permanent seismic stations were migrated to depth, accounting for variations in crustal velocity structure. In the 5-15 km depth range, negative Ps phases indicative of velocity decreases with depth are prevalent in central and western Tohoku, where Holocene volcanoes occur and surface wave tomography indicates low crustal velocities. Large negative Ps phases are largely absent in the crust of the old mountain terranes in eastern Tohoku where crustal velocities are higher. In central and western Tohoku, velocity gradients inferred from Ps phases and shear velocity anomalies are consistent with models for crustal melt storage that involve trans-crustal zones of crystal-melt mush where the highest concentrations of melt are localized at the top of the mush column. Negative Ps phases are concentrated at depths of 5-10 km, and many correlate with the upper margins of localized low velocity zones beneath volcanoes. These correlated features are consistent with the roofs of high melt fraction layers. At depths of 10-30 km, positive Ps phases are consistent with gradual velocity positive gradients that correspond to decreasing melt fraction with depth in the mush column, although some groups of deeper negative Ps phases at depths of 10-20 km may reflect local maxima in melt fraction. The amplitudes of the negative Ps phases at 5-10 km depth vary significantly. In a higher amplitude example, waveform modeling of Ps receiver functions from a station near Hijori volcano indicates a 16% ± 5% Vs drop at 10 km depth, implying melt fractions of 10% ± 3% if Gassmann's equations are assumed, above a velocity increase from 10 to 20 km that indicates decreasing melt fractions with depth. However, modeling of lower amplitude Ps phases in the 5-10 km depth range indicates a 7% ± 3% velocity drop and a maximum melt fraction of 5% ± 2%. The geographic distribution of apparent melt fraction at 5-10 km depth suggests that in some cases the same upper crustal source can supply multiple volcanoes, and in others high melt fraction zones are significantly laterally offset from the nearest volcano.