Interacting Volcanic, Tectonic, and Submarine Geohazards in the Hellenic Volcanic Arc

The Hellenic Volcanic Arc (HVA) is one of the most geodynamically active regions in the Mediterranean, where crustal extension, magma migration, and active faulting interact to generate interconnected and cascading geohazards. These include earthquakes, explosive volcanic eruptions, caldera and flank collapses, submarine landslides, tsunamis, and intense hydrothermal activity. Extending from Methana to Kos and Nisyros, the arc hosts major volcanic centers that display variable levels of deformation, seismicity, and hydrothermal discharge, reflecting ongoing magmatic and tectonic processes.

Explosive eruptions have repeatedly reshaped both island landscapes and the surrounding seafloor. Santorini remains the most hazardous volcanic center, having produced multiple caldera-forming eruptions. Similarly, the Kos Plateau Tuff eruption (~161 ka) demonstrated that pyroclastic flows entering the sea can transform into turbidity currents, depositing widespread ash layers across the southern Aegean and extending the hazard footprint far beyond the eruptive source. These coupled subaerial–submarine processes directly influence coastal stability, sediment redistribution, and tsunami generation.

Recent unrest highlights the arc’s potential for rapid escalation. The 2011–2012 Santorini unrest marked the first major magmatic recharge since 1950, while the 2024–2025 Santorini–Kolumbo volcano-tectonic crisis revealed strong dynamic coupling between adjacent systems, underscoring the vulnerability of nearby coastal communities. In parallel, large-scale flank collapses and submarine debris avalanches represent a major hazard class. During the 1650 AD eruption of Kolumbo, approximately 1.2 km³ of material detached from the volcanic flank, generating a destructive tsunami. Comparable mass-wasting features have been identified off Antimilos, Santorini, Methana, and Nisyros.

Extensive hydrothermal activity across the arc, from low-temperature venting within the Santorini caldera to the high-temperature hydrothermal field of Kolumbo and widespread venting around Milos, reflects sustained magmatic heat flow and affects slope stability and seawater chemistry. Integrating high-resolution morpho-bathymetric data with seismic, geodetic, and remote-sensing observations is therefore essential for improving hazard assessment, early-warning capabilities, and resilient coastal-zone management along the Hellenic Volcanic Arc.