A string of large and deep gas-induced depressions (pockmarks) offshore Killini peninsula, western Greece

A string of five large depressions (pockmarks) has been discovered offshore Killini peninsula in western Greece. They can be considered as some of the deepest (61-m maximum detected depth), if not the deepest observed on the seafloor world-wide. The pockmarks erode deeply buried compacted sediments and are modified by sliding. Their formation is attributed to gases which were detected in the subbottom sedimentary layers. Gas origin is considered to be both biogenic and thermogenic as gas was detected geochemically in exploratory wells in the neighbouring Katakolon area. Although uncertainties concerning their mode of formation, age and activity still remain, it is believed that the high seismicity and salt tectonics of the region contributed to the violent eruption and escape of large quantities of gases through small faults or joints which enabled erosion deep into the seafloor.