1,2,3,4,1,- 1National Observatory of Athens, Institute of Geodynamics, Athens, Greece (aganas@gein.noa.gr)
- 2National and Kapodistrian University of Athens, Department of Geology and Geoenvironment, Greece
- 3Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, Catania
- 4Lab. Geosciences Montpellier, University Montpellier 2-CNRS, 34095 Montpellier, France
- 5UMR 8538 CNRS - École Normale Supérieure - PSL, France
Since late summer of 2024 the Santorini Volcanic Complex (SVC) in South Aegean Sea (Greece) entered another phase of unrest as GNSS data indicated the start of strong deformation onshore Thera Island followed by increased seismic activity, offshore, NE of the island in late January 2025. The seismic events were detected first inside the caldera (September 2024 to early 2025), then spreading with intense activity towards the north-east to Anydros Islet, spanning an overall distance of ~30 km, displaying a NE-SW orientation. The seismicity pattern indicated swarm characteristics that culminated during February 2025, and subsequent seismic activity declined but remained above the unrest levels during the rest of 2025. In terms of ground deformation, cm to dm-size displacements were recorded onshore Thera and in neighbouring islands during the period August 2024 - February 2025. In early 2025 several groups installed new permanent GNSS equipment on Thera and surrounding islands. This GNSS instrumentation in South Cyclades reached 32 sites during April 2025. Those stations provide a wealth of open data that we use to study the evolution of the deformation in the broad South Cyclades Islands.
Overall, the GNSS data showed an inflation of the Thera volcano since August 2024. The modelled magma source was located near the inflation centre of 2011-2012 unrest period. At the end of February 2025, the ground displacements in South Cyclades islands depicted a NE-SW converging pattern between Thera and Anydros, and a NW-SE diverging pattern between Ios-Naxos and Astypalaia Islands. The motion amplitudes were large, exceeding 13 cm at Thera and 3 cm at Naxos. The February 2025 GNSS data fits well with a dislocation model of a south-east dipping fault located between the Kolumbo submarine volcano and the Anydros islet (Briole et al. 2025). Since March 2025, the deformation continues with the positive, 3D baseline rate changes between GNSS stations exceeding the pre-unrest rates thus indicating a nearly-aseismic opening of the Santorini – Amorgos graben. This implies that new magma continues to arrive at shallow crustal depths.
Briole, P., Ganas, A., Serpetsidaki, A., Beauducel, F., Sakkas, V., Tsironi, V., Elias, P. 2025. Volcano-tectonic interaction at Santorini. The crisis of February 2025. Constraints from geodesy, Geophysical Journal International, ggaf262, https://doi.org/10.1093/gji/ggaf262
How to cite: Ganas, A., Sakkas, V., Bonforte, A., Vernant, P., Briole, P., Liadopoulos, E., Consoli, S., Doerflinger, E., Madonis, N., Mintourakis, I., and Goutsos, G.: GNSS data highlight new spatial and temporal dimensions of the Santorini volcano-tectonic unrest during 2025, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15028, https://doi.org/10.5194/egusphere-egu26-15028, 2026.
