The Graham volcanic field offshore southwestern Sicily (Italy) revealed by high-resolution seafloor mapping and ROV images

The understanding of submarine monogenetic volcanic fields, especially if located near
to coastal areas, is fundamental for volcanic risk assessment. Using high-resolution
bathymetric data and ROV images, the submarine Graham volcanic field, located
40–50 km offshore southwestern Sicily (Italy), has been described in detail. The field
comprises a ten of monogenetic volcanic seamounts aligned along a N-S trending belt at
150–250 m water depths and includes the relict of the short-lived “Ferdinandea Island”
produced during the well-documented 1831 “Surtseyan-type” eruption. The presentday
morphology of the cones is the result of the interplay between volcanic activity, wave
and current erosion, mass-wasting and depositional processes, in relationship with sealevel
change, acting in both subaerial and submarine environments. The analysis of the
morphometric parameters allowed a detailed morphological classification of the cones.
The seamounts are composed of poorly consolidated tephra and show steep slopes
and pointy or flat tops, often characterized by sub-vertical knolls. Taking into account
analogies with other volcanic seamounts worldwide, the analysis of some morphological
characteristics, such as presence and depth of terraces on top and along the slope
of the cones in relationship with sea-level fluctuations, allowed us to hypothesize a
Late Pleistocene-Holocene age for the volcanism forming the field. The probably older
Terribile volcanic field was also identified on the adjacent Terribile Bank and analyzed.
Numerous mass-transport deposits and pockmarks were identified in the surroundings
of the volcanic fields, suggesting the occurrence of diffuse slope failures and fluid
releases, respectively. The distribution and shape of the cones within the volcanic fields
provided important insights into the interaction between volcanism and tectonics. The
alignment of the cones and the main axis of the clusters in which they are grouped
revealed two preferred directions, N-S and NW-SE, respectively, which are consistent
with those of the main tectonic structures of the Sicily Channel. The detailed bathymorphological
analysis of the cones proved the monogenetic nature of this volcanism,
which represents a peculiarity since it took place outside the typical geodynamic settings
of other volcanic fields worldwide such as subduction or oceanic rift zones, and far from
long-lived volcanic systems.