Investigation of Undulating Seafloor Features on the Slopes of Large Subduction Zone Volcanoes

Abstract:

Multibeam bathymetric mapping and seismic airgun surveys of the submarine region around Santorini, Greece, reveal three regions of undulating or step-like topography. The undulating features extend 30 km to the west in the Christiana basin, 20 km southwest into the Cretan Basin, and 10 km in a channel oriented from northeast to southwest, south of Santorini into the Cretan Basin. They are located on slopes of 0.1 to 3.3 and in water depths ranging from 80 to 1,000 m. The features are wave-like, having amplitudes from 0.5 to 16 m, and wavelengths on the order of 0.4 to 0.9 km. Similar seabed features have been described in other submarine environments, but the interpretation of their origin as either deformational (e.g. slumping) or depositional (e.g. sediment gravity flows) remains controversial. Features found on the slopes of Santorini are most similar to those found on other submarine calderas from the western Pacific and Aeolian archipelago, suggesting a common origin. Bathymetric mapping reveals that the features look like steps that are parallel to or concentric around the flanks of each volcano. They have regular periodicity that remains constant or decreases in magnitude with distance from the upper slope. A comparison of the Santorini features with those from other submarine volcanic centers has been carried out in an attempt to discriminate between deformational and depositional mechanisms based on criteria such as slope angle, wave amplitude, wavelength, and sub-bottom structure. We hypothesize that the features owe their origin to simultaneous catastrophic influx of unconsolidated volcaniclastic sediment and intense seismic activity associated with large-volume eruptions in subduction zone environments.