Reassessing the volume of the Cape Riva eruption (Santorini) using integrated seismic imaging and marine sediment cores

Explosive caldera-forming eruptions discharge large volumes of silicic magma and pose one of the greatest hazards to human population. Effective risk evaluation depends on detailed records of past events, however, accurately quantifying the volume of ejected material and therefore the magnitude of eruptions remains a challenge. This is particularly the case in marine settings, where much of the eruptive record is obscured or poorly preserved. Santorini in the Aegean Sea is one of the world’s most prominent calderas and the result of at least four caldera-forming eruptions. The 1600 BCE Minoan eruption represents the most recent caldera-forming event, and is among the most extensively studied eruptions worldwide. While recent marine geological and geophysical analyses enabled reconstruction of the 1600 BCE eruption volume and temporal evolution in greater detail, little is known about its predecessor, the caldera-forming Cape Riva eruption, which occurred at ~22 ka. Recent investigations of marine sediment cores suggest that the Cape Riva eruption produced a tephra volume comparable to or exceeding that of the Minoan eruption. In this study, we integrate for the first time high-resolution 2D and 3D seismic reflection data with sedimentological constraints from marine sediment cores to assess the volume of the Cape Riva eruption with high precision and compare it to the Minoan eruption. Our results reveal that the Cape Riva eruption emplaced, at least in near offshore areas, substantially thicker ignimbrite deposits than the Minoan eruption. These results imply that the Cape Riva eruption may have been larger than previously recognized and that previous offshore ignimbrite volumes attributed to the Minoan eruption may have been overestimated. Our study emphasizes the challenges of reconstructing large explosive eruptions in submarine environments, and highlights the importance of integrating high-resolution seismic imaging with marine sedimentological analyses to improve volume estimates.