Katherine L.C. Bell

Tsunami hazard risk of a future volcanic eruption of Kolumbo submarine volcano, NE of Santorini Caldera, Greece

Kolumbo submarine volcano, located NE of Santorini caldera in the Aegean Sea, has only had one recorded eruption during historic times (1650 AD). Tsunamis from this event severely impacted the east coast of Santorini with extensive flooding and loss of buildings. Recent seismic studies in the area indicate a highly active region beneath Kolumbo suggesting the potential for future eruptive activity. Multibeam mapping and remotely operated vehicle explorations of Kolumbo have led to new insights into the eruptive processes of the 1650 AD eruption and improved assessments of the mechanisms by which tsunamis were generated and how they may be produced in future events. Principal mechanisms for tsunami generation at Kolumbo include shallow submarine explosions, entrance of pyroclastic flows into the sea, collapse of rapidly accumulated pyroclastic material, and intense eruption-related seismicity that may trigger submarine slope collapse. Compared with Santorini, the magnitude of explosive eruptions from Kolumbo is likely to be much smaller but the proximity of the volcano to the eastern coast of Santorini presents significant risks even for lower magnitude events.

The Detection of Volcanic Debris Avalanches (VDAs) Along the Hellenic Volcanic Arc, Through Marine Geophysical Techniques

Recent marine oceanographic surveys using geophysical techniques have revealed a number of volcanic debris avalanche deposits (VDAs) on the external flanks of Antimilos, Santorini and Nisyros volcanoes in the South Aegean Sea. Swath bathymetry and side-scan sonar surveys led to the recognition of characteristic hummocky topography on all of these deposits. On seismic profiles the VDAs are identified by chaotic facies, with incoherent areas bordered by continuous undisturbed seismic reflectors. High-resolution examination of the morphological characteristics of the VDAs was accomplished by using Remotely Operated Vehicles (ROVs), in order to distinguish them from other clastic deposits. In some cases the VDAs can be traced upslope to horseshoe-shaped collapse depressions and represent the expression of the complex evolution of these volcanic edifices. Recognition of VDAs at these volcanic centers has important implications for geohazard assessments as flank collapses have the potential for triggering of large-scale tsunamis. The relationship between the distribution/emplacement mechanisms of the VDA deposits and the source flank collapses remains an area of ongoing research.