Eruption-caused volcaniclastic mass flows were a significant feature of the four-month-long 2023 eruption of Shishaldin Volcano in Alaska. The volcano supports a nearly continuous cover of glacier ice and snow on the flanks of its upper edifice, and the emplacement of pyroclastic density currents over this snow and ice cover led to the generation of meltwater and lahars. Pyroclastic density currents that formed during the eruption were long and narrow in map view and did not develop marginal levees. Although the upper part of the Shishaldin Volcano cone is very steep (> 30 degrees), pyroclastic density currents typically travelled less than 2 km. These limited-runout flows resulted from low-level column collapse on all flanks of the volcano, but primarily on the north flank. A few episodes of lava fountaining in the summit crater resulted in the formation of small, unstable mounds of spatter and agglutinate. The mounds occasionally collapsed, forming hot, granular, incandescent flows. Pyroclastic density currents formed by all mechanisms interacted with snow and ice on the edifice to produce lahars. The pyroclastic density currents and lahars that formed throughout the 2023 eruption were similar to the eruptive products generated by previous historical eruptions of Shishaldin Volcano.
Vulcanian eruptions are among the most common explosive volcanic events, yet their characterization remains limited because associated deposits are poorly preserved, have restricted dispersal, and show high variability linked to the transient nature of explosions. This study presents an integrated volcanological analysis of tephra deposits produced by Vulcanian eruptions at La Fossa volcano, Vulcano (Italy) during the last 1100 years. Field mapping, stratigraphic profiling, grain-size and componentry analyses, density/vesicularity measurements, and geochemical characterization of juvenile clasts allowed us to identify three groups of deposits. Group 1 comprises well-stratified tephra sequences dominated by dense juvenile clasts and abundant recycled material, consistent with repetitive discrete explosions and limited dispersal. The 1888–1890 eruption is representative of this style. Group 2 is defined by pumice-rich deposits associated with both fallout and pyroclastic density currents, the latter being relatively uncommon at La Fossa and linked to higher-intensity events. Group 3, including eruptions from the 10th to the 13th centuries, is instead characterized by vesicular juvenile clasts and scarce lithics, suggesting reduced conduit erosion and efficient fragmentation of more volatile-rich magma. Integration of characteristics of La Fossa deposits and comparison with those of Vulcanian eruptions worldwide identifies three eruptive end-members (Types 1–3). These range from brittle fragmentation of degassed plugs with abundant recycled ejecta to fragmentation of gas-rich magma producing vesicular clast-bearing fallout deposits. The broad spectrum of Vulcanian dynamics commonly overlaps with sub-Plinian, Violent Strombolian, and hybrid activity, highlighting the need for a revised, process-based classification integrating petrological, geophysical, textural and sedimentological criteria.
Lava flows pose a significant hazard for communities living near volcanoes. Usually not life-threatening, they can cause substantial infrastructure damage, resulting in severe socioeconomic consequences. The emplacement distance of a lava flow is often extended by the formation of efficient transport structures, such as lava tubes, which are well-insulated conduits that limit atmospheric heat loss, allowing lava to remain molten over long distances. Understanding the physicochemical conditions during lava tube formation and development is essential to comprehend flow dynamics and improve hazard assessments. Here, we combine synchrotron X-ray computed microtomography, petrological analysis and viscosity modelling to investigate the conditions that controlled the crystallisation and rheological evolution of the 1858 lava flow field at Vesuvius (Italy) and its largest lava tube by examining natural samples. Our results show that variations in groundmass crystallisation were driven by differences in cooling conditions, with crystallisation occurring from 1100 to 855 °C. During lava flow emplacement, crystallisation kinetics are primarily affected by the degree of undercooling and shear rate. The morphology and petrology of the 1858 flow field suggest piling-up of flows. Variation in groundmass crystallinity within wall linings indicates unstable thermo-redox conditions inside the lava tube during its activity. Shear rate and cooling by conduction, together with alternating filling and emptying of the tube, control wall lining formation. The evolution of internal cooling conditions affects lava flowing toward the flow front. Constraining cooling conditions will help improve numerical models simulating lava tubes or lava flows, hazard maps and response strategies during eruptive crises.
The onset and early evolution of submarine volcanic eruptions are rarely observed directly, limiting our understanding of the processes that govern shallow marine volcanism. Here, we reconstruct the first 3 weeks of the May 2026 eruption of Titan Ridge Volcano, Bismarck Sea, Papua New Guinea from a large multi-disciplinary dataset: regional seismic records, a hydroacoustic array at 3159 km range, and multi-sensor satellite imagery. Coherent acoustic radiation began at 08:04 UTC on May 8, 17 min before the first regional seismic detection, 4 h before the largest earthquake, and 17 h before any surface expression was visible from orbit. The combination of hydroacoustic array data with high spatial resolution satellite data enables both precise timing of acoustic onset and precise location of the eruption source. Multi-sensor satellite observations document two upwelling zones located 2.5 km apart atop the volcanic eruption, and track their migration over time. The sea-surface features suggest that the discolored-water and pumice-raft products were sourced from multiple eruptive vents. These vents fed pumice rafts giving a dense-rock-equivalent volume of at least 0.011 to 0.014 km3 and a time-averaged discharge of order 104 kg s−1, from a pre-eruption vent depth of 400 to 700 m. Our study demonstrates the potential of combining seismic, hydroacoustic, and satellite-based observations for the detection and characterization of remote shallow submarine eruptions in tectonically complex and sparsely monitored oceanic environments.
Explosive collapse calderas that form late in the evolution of large central volcanic complexes represent the end point of a mechanical history spanning reservoir construction over 105–106 years, repeated unrest over months to decades, eruptive withdrawal over hours to days, and roof failure over minutes to days. Because researchers commonly investigate these intervals separately, it remains unclear how repeated loading conditions prepare the crust for collapse. Moreover, quantities with identical dimensions need not describe the same deforming component or constitutive regime. Characteristic bulk strain-rate estimates are approximately 10⁻14–10⁻12 s⁻1 during reservoir assembly, 10⁻11–10⁻9 s⁻1 during ordinary unrest, 10⁻7–10⁻5 s⁻1 during Plinian withdrawal, and 10⁻6–10⁻3 s⁻1 during rapid roof-scale collapse increments. Local fault-core rates may be orders of magnitude higher and are not directly comparable with kilometre-scale deformation. In this contribution, we propose the mechanical-memory hypothesis: the response of a caldera system to a new loading episode depends on state changes retained from earlier cycles, including residual stress and strain, damage connectivity, permeability, elastic moduli, thermal structure, and fault state. Memory is not synonymous with progressive weakening; it emerges from competition between accumulation processes (damage growth, structural linkage, and persistent stress heterogeneity) and recovery processes (viscous relaxation, fracture healing, sealing, and stress redistribution). Loading rate matters because it controls which processes can operate during and between cycles. The hypothesis predicts that proximity to withdrawal-driven collapse should be expressed more reliably by persistent localization, cross-signal coupling, and incomplete recovery than by acceleration of any single deformation signal. Restricted to collapse preceded by magma withdrawal and reservoir decompression, this framework defines measurable proxies and testable priorities for monitoring, field analysis, experiments, and coupled reservoir–conduit–fault models.
