Revealing Initial Explosive Eruptions in the Southern Pausanias Volcanic Field (Southern Aegean Volcanic Arc) from Seismic Reflection Data

The Pausanias volcanic field forms part of the South Aegean Volcanic Arc and is located within the Epidavros Basin west of Methana Island in the Saronic Gulf. Volcanic activity initiated around 450 ka, with the most recent eruption dated to approximately 14 ka. Given the close proximity of the volcanic field to the Greek mainland, eruption recurrence rates and eruptive styles—explosive versus effusive—are critical parameters for regional geohazard assessment. Previous studies were largely based on bathymetric data, unmigrated legacy seismic profiles, and petrochemical analyses of seafloor sediments and rock samples.

Seismic reflection data calibrated with results from IODP Expedition 398 now allow, for the first time, a systematic discrimination between effusive and explosive submarine volcanic products. This approach was applied to the Pausanias volcanic field using new high-resolution multichannel seismic data acquired during the MULTI-MAREX-2 expedition (MSM135) aboard RV MARIA S. MERIAN in spring 2025. MULTI-MAREX is a research initiative of the German Marine Research Alliance (DAM) aimed at improving the assessment of geomarine extreme events and supporting the development of mitigation strategies through a living-lab approach.

Our analysis focuses on five of the six previously identified volcanic edifices. The seismic sections resolve the internal architecture of the volcanic cones, enabling the identification of distinct constructional styles and eruptive phases. The two northern most volcanoes are characterized by complex channelized and ridge-like morphologies composed of multiple lava flows. Their internal reflection patterns are typical of effusive eruptions of low-viscosity lava which explains the ridge-dominated seafloor morphology. Vertically stacked edifices indicate a polygenetic evolutionary history.

In contrast, three of the southern volcanoes exhibit predominantly conical morphologies. Their lower edifices are characterized by outward-prograding, evenly stratified seismic reflections. Core–seismic integration of IODP Expedition 398 sediment data and seismic imagery from the Kolumbo volcanic chain indicates that such reflection patterns are typical of volcaniclastic deposits formed during explosive eruptions. The uppermost parts of the cones, however, display more chaotic, high-amplitude reflections, interpreted as coherent volcanic material such as lava flows or coarse tephra. This stratigraphic transition documents a temporal shift from predominantly explosive activity toward weakly explosive or effusive eruptions during the final constructional stages. The documented occurrence of explosive submarine eruptions significantly increases the geohazard potential of this densely populated region.