Temporal linkages of explosive activity on the South Aegean Volcanic Arc related to changing lithospheric stresses

Extensional tectonic regimes often host volcanoes that produce highly hazardous, caldera-forming explosive eruptions. An example is the Santorini-Kolumbo volcanic centre on the continental South Aegean Volcanic Arc. The volcanic centre includes Santorini caldera, the submarine polygenetic Kolumbo Volcano to the northeast of Santorini,  and the linear zone of more than 20 smaller volcanic cones making up the Kolumbo Volcanic Chain. It is one of the most active eruptive centres on the South Aegean Volcanic Arc and experienced a period of unrest in 2024-2025. IODP Expedition 398 deep-drilled the volcano-sedimentary infills of submarine half-grabens around Santorini and on the western flank of Kolumbo in order to produce a high-resolution eruptive chronostratigraphy for the volcanic field, ground-truth seismic stratigraphy, and to extract an integrated timeline of interactions between the neighbouring volcanoes and volcano-tectonic couplings. In the new, more complete volcanic record, we: (1) recognise a transition of Santorini from moderately explosive, arc stratovolcano behaviour (~570 – 250 ka) to repeated caldera-forming behaviour (<250 ka), (2) identify 19 explosive eruptions of the KVC beginning at 265 ka with a lifespan-averaged recurrence time of explosive activity of ~6 k.y. (but as low as ~1 k.y. in certain time periods), (3) observe that the three main phases of edifice construction at Kolumbo (ca. 265–193 ka, 24 ka, and 0.4 ka) broadly correspond to the periods of caldera-forming eruptions at Santorini (186 ka – 177 ka and 22 ka – 3.6 ka). By ground-truthing seismic stratigraphy through core-seismic integration, we also produce a unique high-resolution record of volcanic activity and lithospheric extension for the volcanic field. This allows us to show that Santorini’s caldera-forming eruptions all lie above a seismic reflection onlap surface that records a phase of rapid rifting.  This phase of rapid rifting may have amplified the normal internal dynamics of the magmatic system driving the transition of Santorini from a prolonged state of arc stratovolcano behaviour to a state of repeated caldera-forming eruptions. In addition, the birth of Kolumbo coincided with the transition of Santorini to highly explosive activity, possibly due to joint interactions with the regional lithospheric stresses. Through our new integrated record, we show a possible example of rift modulation of an arc magmatic system on the 10⁴-10⁵ yr timescales typical of caldera cycles and the coupling of neighbouring volcanoes on 10⁴  yr timescales.