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.