New insights on explosive volcanism at Santorini (South Aegean Volcanic Arc) based on marine sediments drilled during IODP Expedition 398.

The establishment of continuous volcanic time series is a key to understanding the volcanic evolution and behaviour of arc systems and volcanic complexes. Yet the establishment of continuous records is often hindered by incomplete volcanic archives on land due to erosion or inaccessibility of volcanic deposits. Growing steadily over the past decades, the field of marine tephra studies has shown great potential in overcoming these issues. As marine drilling techniques advance, they now enable the recovery of continuous and undisturbed marine sediment records, often even extending the volcanic onland records significantly further back in time. Drilling close to volcanically active environments, like volcanic arcs, provides the most complete eruptive archive possible and therefore allows us to unravel the volcanic and magmatic behaviour of volcanic systems over geologically long periods of time. Furthermore these long and continuous records enable multi-disciplinary studies, such as the establishment of volcano-tectonic or volcano-climate relationships.

IODP Expedition 398 drilled the marine sediments in the basins of the Christiana-Santorini-Kolumbo Volcanic Field (CSKVF) with the aim of expanding our knowledge of its volcanic evolution, and its interaction with tectonics and climate. The CSKVF belongs to the South Aegean Volcanic Arc (Greece), and particularly Santorini has been known for its highly explosive volcanism and caldera-forming eruptions since c. 250 ka that laid down the Thera Pyroclastic Formation (TPF). Before that, Santorini’s volcanic activity has been described as mainly effusive to weakly explosive forming the Peristeria stratocone (c. 530-430 ka) and the Early Centres of Akrotiri (c. 650-550 ka). However, IODP Expedition 398 identified a large submarine rhyolite deposit, the Archaeos Tuff (AT), interpreted as the product of a highly explosive submarine eruption of Santorini occurring at c. 765 ka, clearly pushing the boundaries of the unkown.

Here, we present the revised <765 ka tephrochronostratigraphy using the marine basin sediments drilled during IODP Expedition 398. Geochemical fingerprinting of tephras has enabled the identification of all known Plinian TPF eruptions, as well as numerous “new” explosive volcanic events within the TPF but also beyond. We have identified a total of 298 eruptions derived from Santorini and Kolumbo, and the established volcanic time series shows multiple tempos of arc volcanism, each about 250-300 kyr long. The eruptions range between magnitudes M2 to M6 throughout the record. However, the period <250 ka clearly stands out in terms of volcanic productivity and has produced about 3x more cumulative magma mass compared to the period 765-250 ka.

Our record fills the currently existing gap between Santorinis AT eruption at c. 765 ka and the onset of the TPF, and shows that Santorini was continuosly producing (highly) explosive eruptions. Furthermore, our findings highlight the importance of complementary and multi-disciplinary studies to reveal the most complete picture of arc volcanism.