The Graham Bank (Sicily Channel, Central Mediterranean Sea) : seafloor signatures of volcanic and tectonic controls

Abstract

Graham Bank is a dominant physiographic element of the NW Sicily Channel (central Mediterranean Sea), affected in the last 100 years by numerous well-documented volcanic eruptions. We present the first results of a geomorphological study where the Graham Bank region in the depth interval 7–350 m was mapped for the first time with multi-beam echosounder and high-resolution seismic and multi-channel seismic reflection profiles. We describe in high resolution the detailed geomorphological features of Graham Bank, and how the superficial expression of different process and dynamics occurring in the sub-seafloor evidence volcanic and tectonic controls on seafloor morphology across a relatively small area. The north-eastern part of the study area is dominated by seamounts with heights ranging from 97 to 152 m and auxiliary small cones, reaching heights of 2–10 m, on the whole forming a hummocky surface. In this region, fluid seepages are an important expression of the volcanic processes affecting the study area. The western region com- prises a flat seafloor covered by Upper Pleistocene-Holocene outer shelf sedimentary deposits; here aligned mounds and pockmarks are predominantly oriented NW–SE or NNW-SSE, running parallel to the main structural trend of the Sicily Channel. The pockmarks have sub-circular planform shapes and U-shaped cross-section and different depths and mean axis lengths. Numerous Mass Transport Deposits (MTDs) are distributed across the study area. Graham Bank is 45 km from the coast of Sicily and is intersected by submarine cables. Consequently, the mapped volcanic seamounts, pockmarks and MTDs could pose a significant economic risk to the submarine cables.