Volcanica

Charles Darwin on Volcanoes

Dennis Geist — 2025-12-03

During the voyage of the H.M.S. Beagle (1831–1836), Charles Darwin had the opportunity to visit and observe volcanoes and volcanic deposits at several archipelagos in the Atlantic, Pacific, and Indian Oceans and also in the Andes. In the Galápagos Archipelago, he described hydrovolcanism and what we now know as pyroclastic surge deposits. Darwin also noted the relation between scoria and lava in Strombolian deposits and the role of effective viscosity on lava surface morphology. He observed volcanic eruptions in the Andes from a distance and speculated on the role of earthquakes in triggering eruptions. Darwin's field work on Ascension, the Cape Verde Islands, Mauritius, and the Azores included detailed work on volcanic bombs and the spatial relationship between basalt and evolved lavas. Much of his focus was on making detailed observations at the outcrop scale to deduce large-scale geologic processes, such as the relation between magmatism and mountain building and the distribution of magma in the deep Earth. While many of Darwin's theories involving volcanism did not stand the test of time, in contrast to his theories on coral reefs and the origin of species, they exemplify his genius at developing novel hypotheses and making observations to test those hypotheses.

Post-glacial melt generation in Southern Chile and the development of the Carrán-Los Venados Volcanic Field (40°20'S)

Lucy McGee — 2026-02-11

The Carrán-Los Venados volcanic field in southern Chile comprises small basaltic eruption centres of Holocene to historical ages. These centres are atop extensive, basaltic flows that erupted during late glacial or early postglacial times (< 14ka), marking a dramatic change in eruption style over a short space of time. Differences in trace element characteristics and U-series isotopes point to a dampened subduction influence in the melting environment of the older Basal Lavas. Th isotopes point to higher melting rates and more dominant decompression melting, which may be related to the deglaciation of southern Chile at this time. Olivine textures and chemistry suggest longer storage times for the Basal Lavas compared to the Holocene tephras. The historic eruptions have relatively homogeneous whole rock compositions, suggesting the development of a storage system in the lower crust. This may be the beginning of a thermal environment more akin to those of nearby stratovolcanoes.

The first seismo-volcanological observatory on Montserrat

David M. Pyle — 2026-02-17

The first seismo-volcanological observatory in the anglophone Caribbean was established on Montserrat in 1936, in response to a volcano-seismic crisis that began with repeated felt events in 1933. Staff at Montserrat's agricultural office began routinely recording earthquake shocks in 1934. In 1936, following a scientific expedition dispatched by the Royal Society, an observatory was established at the Grove Botanical Station, Plymouth. This was run by volcano-seismic observers who managed an instrumental network, and monitored gas and steam emissions and air quality. The observatory functioned until 1946. We reconstruct the decision-making and evolution of the instrument networks as the observatory was established, and highlight the personnel involved, including the first female seismo-volcanic observer on Montserrat, Greta Scotland. Observations from the 1930s crisis emphasise the persistent seismicity and gas emissions associated with this extended episode of unrest, and suggest that there were minor phreatic explosions at the height of the crisis. We draw parallels with long-term observations of the activity of the Soufrière Hills Volcano since the 1990s.

A gas-slug model for basaltic Vulcanian eruptions at open-conduit volcanoes, constrained by textural characteristics and dynamics of the July 3rd, 2019, Stromboli eruption (Italy)

Guido Giordano — 2026-02-11

Stromboli is a unique open-conduit mafic volcano known for persistent Strombolian eruptions of highly porphyritic (HP) basalticshoshonite scoria. Stronger paroxysmal explosions occur once or twice per decade, ejecting low porphyritic (LP) golden pumice from deeper volatile-rich magma. The July 3rd, 2019, paroxysm showed features of a Vulcanian eruption—supersonic blast, ballistic ejection, and pyroclastic flows—despite Stromboli’s open-conduit basaltic nature. Textural analysis suggests that LP pyroclasts formed via rapid decompression, fragmentation, and quenching. This event likely resulted from shallow HP-filled conduit pressurization and failure triggered by a rising large gas slug. This caused top-down decompression, evacuating both HP and deeper LP magma. The proposed “basaltic Vulcanian” model better fits geophysical data than the traditional deep LP magma ascent model.

Evaluating steady-state volcanism in Iceland, La Réunion, Hawaiʻi and western Galápagos: connections with volcanic hazards and future perspectives

Federico Galetto — 2026-03-29

Steady-state volcanoes and magmatic provinces erupt magmas at nearly constant rates over the course of decades. Here, we analyzed the reliability of steady-state volcanism and its relationship with volcanic hazard evaluation in terms of forecasting the erupted volume at four frequently erupting oceanic hotspots: Iceland, La Réunion, Hawai‘i, and western Galápagos. Over decadal timespans, these hotspots show steady-state activity often characterized by shorter-term cycles with an initial decrease in eruption rates, followed by an increase that rebalances the erupted volumes with the expected ones, providing a rough estimation of the maximum expected erupted volume of these paroxysmal periods. Although rarer, we also observe the opposite behaviour, with the eruption of more magma than expected, followed by low-rate periods proportional to the excess erupted volume. Steadystate rates can change over time, and future studies should investigate if these changes are related to longer-term episodes.