This study investigates the mechanisms underlying phreatic explosions within the geothermal system of eastern Milos Island. Field, laboratory and historical data suggest that a long-standing hydrothermal system, characterized by silica-rich crusts over altered rhyolitic lava domes and volcaniclastics, experienced multiple explosive events leading to its eventual disruption. The explosions, occurring at depths of 3-20m, were likely triggered by rapid depressurization, possibly induced by seismic activity. Intermediate to large-magnitude local earthquakes or large-magnitude regional earthquakes, such as the AD 365 Crete event, could have generated dynamic stress sufficient to destabilize the system, leading to cavitation-driven explosions. Overlapping craters and deposits indicate repeated explosive activity over years, ultimately resulting in the exhaustion of the hydrothermal system. Archaeological evidence, including Roman-age pottery beneath phreatic deposits, suggests that the explosions were sudden and unanticipated. The concurrent decline in settlement activity on Milos during the fourth century AD may be linked to these disruptions, in combination with broader regional seismic and socio-economic factors. This study highlights the sensitivity of hydrothermal systems to external stressors and the potential role of seismic events in triggering phreatic explosions.

Entablature jointing in cooling lava domes and small shields at the Michoacán-Guanajuato Volcanic Field: Characterization of the 3.32 Ma Leonera small-shield volcano

ABSTRACT A new geological map of the northern sector of the Southern Main Ethiopian Rift is presented, providing unique insights into the processes driving continental rifting (ca. 45 Ma to the present). The map includes a cross-section through the rift valley and records multiple phases of rift evolution. This region, shaped by ongoing extension between the Nubian and Somalian lithospheric plates, preserves a tectonomagmatic history typical of active continental rifts. Evolution begins with a ‘pre-rift’ phase (Eocene-Oligocene), characterized by extensive flood basalt volcanism dominated by tholeiitic to alkaline basalt and trachybasalt flows, driven by mantle plume upwelling. The ‘early-rift’ phase (Miocene) features fault-controlled bimodal volcanism and the initial development of the rift valley. The current ‘late-rift’ phase (Pliocene-Holocene) is dominated by magma-assisted extension with bimodal volcanism, including alternating alkaline basalts and alkaline to subalkaline rhyolite-trachyte flows. This phase also features lava domes, cinder cones, calderas, and voluminous felsic pyroclastic deposits.

ABSTRACT The Choiyoi Group in the Cordillera Frontal and Precordillera of Mendoza Province, Argentina, rests on an irregular erosional surface due to the Lower Permian San Rafael Diastrophic Phase. These rocks are organized into eight lithostratigraphic units in three main sections. The lower section includes both high-energy sedimentation and basaltic to andesitic volcanism, with a probable age of 291.2 Ma. The geochemical features of these rocks resemble magmas generated in subduction zones. The middle section, dated at 276.4 Ma, includes lava flows and domes of dacitic composition and pyroclastic flow deposits. The geochemical signatures suggest a subduction-related magmatic origin. Transitionally, the upper section continues with lacustrine deposits, high-welded tuff related to rhyolitic subvolcanic bodies dated at 273.1 Ma, with geochemical characteristics typical of magmas emplaced in intraplate settings. A model of the evolution of the Choiyoi Group indicates a transition from subduction-related activity to intraplate-related volcanism in the western margin of the Gondwana Continent.

The Triassic to Early Jurassic fore-arc basin successions of the coastal region of Central Chile (approximately 32°14' South latitude) form a continuous belt of sedimentary and volcanic rocks, younging to the south. This belt includes, from north to south, the El Quereo, Pichidangui, El Puquén, and Los Molles formations. This note addresses: i) the facies associations and tectonic setting of the El Puquén Formation and the uppermost strata of the underlying Pichidangui Formation, and ii) the first two Rhaetian zircon U-Pb laser-ablation dates of approximately 201 to 208 Ma on volcanic samples from the former, which are younger than the currently accepted Norian-Carnian ages. Basaltic-andesitic lava domes, hyaloclastites and peperites in the uppermost facies of the Pichidangui Formation were emplaced in a subaqueous environment (lacustrine or marine?). Currently these are considered a subduction-related, bimodal volcanic succession synchronous with rifting. Seven facies associations are identified in the conformably overlying lacustrine deposits of the El Puquén Formation, including storm deposits accumulated in a synsedimentary graben approximately 15 m wide, slump deposits, turbidites, pyroclastic intercalations, sedimentary dikes, peperites, and hyaloclastites.

International audience

The Antimilos volcanic field of the Aegean Volcanic Arc is studied, based on an oceanographic survey off the northwestern margin of Milos Island, conducted onboard R/V Meteor, comprising high resolution bathymetric data, AUV operations and seismic parasound profiles. The scope of the paper is to describe the three submarine volcanic cones adjacent to Antimilos Island and the interaction of volcanism and tectonics in the Milos-Antimilos region. The results comprise a bathymetric map and a morphological slope map, utilizing a 5-meter grid interval. A morphotectonic map off Antimilos Island was compiled, comprising the three submarine volcanic domes and a hummocky relief extending to the Myrtoon Basin in the NW up to 800 m depth. NW-SE fault zones delimit the tectonic graben between the Cycladic plateau and the western Ridge, hosting the volcanic features and a 72 km 2 hummocky area with VDA deposits representing some recent sliding hazard events triggered by earthquakes. A prominent ENE-WSW fault delimits the Antimilos volcanic field from the NW Milos structure with disruption of the shelf breakThe shelf area at 130–150 m depth is well developed around Antimilos Island and on top of the two shallow submarine volcanic cones at least during the last three low stand periods, indicating their onshore/offshore evolution. The geological hazard of the studied area comprises earthquakes of magnitude Mw 6.0-6.6, submarine landslides with extended VDA deposits and volcanic activity related to the ongoing intense submarine hydrothermal vents.

Abstract. Venus is also known as Earth’s twin sister, remains one of the least explored planets due to its dense clouds and extreme surface conditions. The dense atmosphere blocks visible light and makes surface observation difficult through optical remote sensing methods. Advanced remote sensing techniques like Synthetic Aperture Radar (SAR) provide a better solution by using microwave signals that can penetrate the cloud cover and explore detailed surface characteristics of Venus. This study aims on the characterization of surface features of Idunn Mons and its surrounding region using SAR data from NASA’s Magellan mission. The analysis identified major surface features like lava flows, fractures, ridges, domes, craters, and other surface features, determined their area extent, and understood their elevation using global topography data. The correlation of SAR imagery with topographic information helps the generation of three-dimensional surface views improving the interpretation of Venusian terrain. The results highlight the effectiveness of radar and topographic datasets in surface feature mapping and their importance for studying the structure and geomorphology of Venus. This work will support future radar based planetary exploration missions to understand Venus’ mysterious geodynamics better.

Abstract The floor of deep summit craters is often obscured, hindering monitoring and limiting understanding of the dynamic processes within it. At Lascar Volcano, a sudden eruption in December 2022 was accompanied by lava emplacement. We employed satellite and drone imagery to generate high-resolution point clouds, optical and thermal orthomosaics through photogrammetry. Quantitative morphological analysis revealed an initial crater floor uplift from lava extrusion, followed by rapid subsidence that reduced nearly half the volume and formed a central funnel-shaped depression. To investigate surface deformation linked to internal structure evolution, we experimentally simulate lava dome extrusion and subsidence in a scaled 3D-printed mold. The analogue experiments reproduced a funnel-shaped structure consistent with satellite observations and demonstrated the extrusion along divergent faults followed by piston-like subsidence accommodated along convergent faults. The structural pattern constrains underlying conduit geometry and provides insights into dome emplacement dynamics and magma withdrawal mechanisms in upper conduits.

Abstract The current volcanic output of Venus is unknown. In the 2030s, the VenSAR (Venus Synthetic Aperture Radar) instrument onboard the European Space Agency's (ESA) EnVision mission will estimate the global volcanic mass flux by looking for new flows with radar imaging at resolutions of 10 or 30 m/pixel, which can be compared with the 1990s‐era Magellan data (100–300 m/pixel). Based on eruptions on Earth and Io, we make suggestions for measuring the Venusian global eruptive flux. We do not need to observe small eruptions with Eruption Magnitude (based on mass) <3 because (at least on Earth) they produce <10% of the aggregate erupted mass. Assuming that the size–frequency distribution of Earth lava flows and domes holds on Venus and is augmented to include flows 75% longer as predicted for the Venus surface, we find that all Eruption Magnitude ≥3 eruptions are detectable by VenSAR–VenSAR imaging and >80% by VenSAR–Magellan. However, only 80% of eruptions may produce a detectable change in radar backscatter based on our examination of 24 basaltic terrestrial lava flows from 2014 to 2023 from the ESA Sentinel‐1a/b satellites. From observed Earth basaltic flows, thickness will rarely be measured on Venus due to low vertical accuracy. If VenSAR images 20%–40% of the most active volcanoes (as planned), it could detect 79%–92% of the flux if the Eruption Magnitude–frequency distribution is similar to Earth and Io. A few eruptions could then be extrapolated to a global flux, but this is dependent on quantifying the largest eruption, so targeting the right volcanoes is critical.

Abstract Pumice rafts derived from submarine eruptions can remain afloat for months or even years, traveling thousands of kilometers on ocean currents. These natural phenomena disperse marine organisms and provide important evidence for submarine volcanism yet are not fully understood. Here, we describe pumice clasts from Falkland Islands shorelines and use major‐minor‐trace element analyses to trace their provenance to the 1962 volcanic eruption on Protector Shoal, a large seamount in the South Sandwich Islands, Scotia Sea. Compositional variability between rafted and dredged pumice from Protector Shoal suggests eruptions have varied from explosive to non‐ or mildly explosive (the latter from lava domes and during neptunian events) and the seamount is volcanically diverse. Oceanographic modeling simulations and historical observations show that clasts from the 1962 eruption reached the Falkland Islands via the Antarctic Circumpolar Current, a journey of ∼20,000 km that took approximately three years. Although oceanographic variability strongly affects modeled transport pathways, in all simulations particles consistently reach the Falkland Islands from Protector Shoal seamount, suggesting a persistent long‐distance connection. The results highlight the potential for pumice rafting to disperse non‐native, potentially invasive, marine organisms throughout the Southern Ocean as climate warms.

Abstract Volcanic eruptions cause large‐scale topographic changes, through the emplacement of lava flows and lava domes, the formation of craters and calderas, and thick ash and pyroclastic deposits. Here we analyze the TanDEM‐X Digital Change Map (DCM), which compares the DEM produced during 2010–2015 with satellite acquisitions collected in 2016–2022. The DCM covers 159 eruptions at 103 volcanoes; the data was good quality at 44 of these but not useable at 28. Topographic changes associated with volcanic activity was visible at 58 volcanoes including lava flows, domes, intrusions, pyroclastic flows, lahars, tephra fall, crater formation and landslides. We analyze five case studies in detail: Sierra Negra, Galápagos; Erta Ale, Ethiopia; Sangay, Ecuador; Ebeko, Russia; and Nabro, Eritrea. Our measurements of the lava flows at Sierra Negra and Nabro and crater formation at Ebeko agree to within 15% of previous measurements, confirming the accuracy of the TanDEM‐X DCM in volcanic areas. At Erta Ale, we find maximum lava thickness of >40 m, greatly exceeding previous field‐based estimates (<2.5 m); consequently, our total volume estimate is an order of magnitude higher. At Sangay, the patterns of height change are consistent with local reports, but our measurements have high uncertainties due to the prevalence of vegetative noise and steep topography. Overall, we demonstrate that the TanDEM‐X DCM can measure topographic changes at volcanoes, and in many cases allows us to make new measurements. Finally, we discuss the lessons learned from the TanDEM‐X DCM for planning future satellite missions, including the upcoming European Space Agency Harmony Mission.

Abstract The Great Bear deposit is a new world-class gold deposit (~6.6 Moz Au) in the Red Lake greenstone belt of the Archean Superior craton in Canada. The deposit is defined by three key zones of mineralization that are located adjacent to an interpreted upper crustal fault (known as the Lithoprobe fault): (1) quartz veining in mafic volcanic rocks in the hinge zone; (2) quartz veining in sulfide-rich argillite horizons in the limb zone; and (3) disseminated and vein-hosted gold within a high-strain zone in the hanging wall of the Lithoprobe fault. The stratigraphy in the hanging wall of the Lithoprobe fault, known colloquially as the Felsic domain, consists of sedimentary rocks (MS1, MS2, and MS3), felsic volcaniclastic rocks (F1), and felsic porphyries (E31 and E32), which were metamorphosed to lower amphibolite facies conditions. We interpret the felsic porphyries, which host a significant fraction of the established gold mineralization, as synsedimentary, emplaced as subvolcanic intrusions and lava domes within an interpreted structural basin. Uranium-lead dating by chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) of magmatic zircons from the synsedimentary quartz-feldspar (QF) porphyry (E31) constrains the age of magmatism to 2710.2 ± 1.2 Ma, which is inconsistent with existing interpretations of the stratigraphy as part of the 2748 to 2742 Ma McNeely sequence of the Confederation assemblage. The E31 porphyry is instead temporally equivalent with a suite of younger syntectonic porphyries and tonalite-trondhjemite-granodiorite intrusions in the Red Lake gold camp. This age also constrains the maximum age of mineralization to <2710 Ma, which is younger than other established gold deposits in the Red Lake greenstone belt, including the giant 2723 to 2712 Ma Campbell-Red Lake deposit, suggesting a second major mineralization event succeeded regional D2 shortening and mineralization in the Red Lake greenstone belt. High-strain zones and structural basins associated with major faults, somewhat akin to the fault-related orogenic gold deposits of the Abitibi subprovince, may therefore represent important first-order targets for exploration in the Red Lake greenstone belt and the adjacent greenstone belts of the Uchi subprovince.

Merapi Volcano, situated at the boundary between Central Java Province and the Special Region of Yogyakarta, is regarded as one of the most active volcanoes in the world. Its high volcanic activity indicates the episodic movement and accumulation of magma within the volcano’s shallow system. Surface deformation associated with such activity is monitored using the Electronic Distance Measurement (EDM) method, which records changes of slope distance (CSD) between benchmarks on flanks and summit reflectors. This study analyzes 17 EDM baselines from June 1, 2022, to December 31, 2024, to determine the influence of block movement and pressure source inflation on surface deformation. Block movement correction was applied to the northwestern sector, particularly for the 1888 lava dome block, which experienced a northwestward shift of approximately 4.24 meters, including 2.49 meters of vertical uplift. A grid search method was used to estimate the displacement vector and to model a spherical pressure source beneath the summit. The pressure increased fluctuated 0.9 and 35 MPa, with a cumulative increase of approximately 211 MPa. The total magma supply volume during the observation period was calculated at 9.31 ± 0.39 × 106 m 3 , with a fluctuating supply rate between 0.8 and 115 × 103 m 3 /day. The relationship between CSD, block movement, with a lesser but significant contribution from pressure-induced inflation. These findings provide insights into Merapi’s shallow magmatic dynamics and may support future volcanic hazard assessments.

The mostly submarine Kikai caldera in SW Japan underwent a caldera-forming eruption at 7.3 ka. Its subsequent post-caldera volcanic activity has included subaerial eruptions whose onland deposits have been well studied, and a historical island-forming eruption from a submarine vent. Marine surveys have also documented a giant, 32 km 3 submarine dome that has been emplaced on the caldera floor during the post-caldera period, but the timing and style of its eruption is not known. Here we investigate this giant submarine dome using seafloor observations and rock samples collected during dredging surveys. The dome is covered by large blocks; based on porosity, matrix glass volatile contents and thermal demagnetisation data we infer that these are giant pumice that floated hot at the sea surface prior to sinking. Without suitable radiocarbon material we instead use the extent of secondary hydration of giant pumice matrix glasses to estimate eruption age, yielding an age of 13th Century CE or younger. We infer that the dome grew both endogenously under a thin sediment covering and also via exogenous seafloor lava flow, and that the giant pumice formed from a pumiceous carapace on this lava. We also find preliminary textural evidence that this shallow submarine dome was formed by cryptic fragmentation and pyroclast sintering as is proposed for subaerial silicic lavas. Together our findings suggest that the Kikai caldera has a high average eruption rate in its current post-caldera volcanic stage, and that eruptions, potentially explosive, from submarine vents comprise a significant portion of this activity. • Giant silicic submarine lava dome in Kikai caldera is covered by giant pumice blocks. • Glass secondary hydration implies giant pumice erupted sometime after 13th Century CE. • Giant pumice formed by buoyant detachment from pumiceous carapace of exogenous lava. • Cryptic fragmentation may produce shallow submarine silicic domes and lavas. • Current Young Iwo-dake Stage volcanism at Kikai has high average eruption rate.

Abstract Gas escape from volcanic systems is regulated by permeable pathways. When gas escape is hindered, pressure within the edifice can increase, possibly resulting in explosive eruptions. We present a study on enclave bearing dome lavas from Chaos Crags and Lassen Peak, California, to understand the impact of mechanical and textural heterogeneities on the permeability fabric of dome lavas. We combine field and laboratory measurements of permeability and porosity. The data show that in the presence of mechanical heterogeneities, shear deformation induces permeability anisotropy and heterogeneity with higher permeability parallel to the shear fabric and varying on decimeter scale around mechanical heterogeneities. Based on these insights we discuss implications for the accumulation of gas pockets in the conduit margin, which may contribute to cyclic explosive gas venting commonly observed at dome forming volcanoes.

Abstract. Multiple magma storage levels are commonly recognized beneath magmatic systems and may play an important role in the processes leading to the build-up of large silicic magma chambers in the crust, with possible critical implications for the occurrence of explosive eruptions. Within such reservoirs, interactions between different magmas due to new recharge events are common processes, as demonstrated by the presence of mafic enclaves, which also reveal the occurrence of magma immiscibility conditions. In Nisyros (Greece), the two most recent eruptive events are the caldera-forming explosive eruption of the Upper Pumice (UP) and the following effusive activity of the Post Caldera Domes (PCD), which emplaced a thick pyroclastic deposit and six main lava domes, both hosting mafic components as crystal-rich clasts (CRCs) and enclaves, respectively. These two eruptions show differences in the abundance, petrographic characteristics, mineral chemistry, and geochemical and isotopic signatures of their mafic components, as well as in the extent of their mingling processes, indicating that the magma interaction conditions were different, possibly related to a change in the magma chamber dynamics and/or in the deeper feeding system structure. In this work, we investigated the textural characteristics and mineral chemistry of the products erupted by these two eruptive episodes, exploring their crystallization histories and the possible variations in physical conditions to reconstruct the structure of the plumbing system throughout the two phases of activities. Our results revealed the occurrence of evident mineral disequilibria within CRCs and enclaves related to their rapid crystallization due to the undercooling within the host. In the PCD systems, mineral disequilibria are also related to the extensive crystal transfer from the host to the enclaves and vice versa, generating mingling at the microscale, which increases with time. The application of geothermobarometers records progressively higher pressure from the UP to the PCD under similar temperature conditions. This indicates a deepening of the main eruptible reservoir, sampled by the PCD activity, after the UP–caldera collapse. Between the two periods, an interconnected evolved magma-rich system developed through new inputs of mafic melts that refilled and reheated the system, progressively mingling with the host and generating new conditions for the eruption.

Colima volcano, Mexico, deformation from GNSS and InSAR time series

Abstract Ignimbrites, with their relatively massive and poorly-sorted characteristics, are commonly underlain by finer-grained, stratified and cross-stratified deposits (basal deposits). The former are often inferred to reflect emplacement from high particle concentration pyroclastic flows, while the stratified and cross-stratified deposit are interpreted to have been deposited by low-concentration, dilute pyroclastic surges. We document basal deposits from the upper (Tshirege) member of the large-volume Bandelier Tuff, which erupted from the Valles caldera (New Mexico, USA). Two paleotopographic settings are characterized: (1) plateau settings that contained approximately-radial shallow canyons, valleys and interfluves, and (2) settings associated with rugged topography of pre-Bandelier Tuff lava domes. We find that the stratified and cross-stratified basal deposits consist of the same components as the overlying ignimbrite matrix but are selectively finer grained. In plateau settings the basal deposits thicken somewhat with distance from the caldera and on paleo-interfluves relative to locations near paleovalley bottoms. Basal deposits are thickest, and have the best developed cross-stratification, in topographic lows in the lava dome settings. We infer that the basal deposits were deposited by ash-cloud surges that consisted of fine particles entrained from underlying pyroclastic flows. The ash-cloud surges either (1) ran ahead of the more sluggish flows and onto interfluves in the relatively low-relief plateau settings, followed by burial by aggrading ignimbrite as pyroclastic flows reached a location; or (2) overtopped topographic highs that temporarily blocked pyroclastic flows in the lava dome setting, until ignimbrite aggradation allowed the flows to spill over and cover the basal deposits. Larger thicknesses of basal deposits reflect longer times of deposition from ash-cloud surges before ignimbrite inundation. The result is a sort of inverted stratigraphy, where ash-cloud surge deposits, originating atop the moving pyroclastic flows, ran ahead or over the surrounding terrain and deposited first.

Seismic activity that accompanied the lava dome eruptions at andesitic Volcán de Colima (2016–2017) and dacitic Mount St. Helens (2004–2008)