Exploring the submarine Graham Bank in the Sicily Channel

Mauro Coltelli Mauro Coltelli,Stefano Gresta Stefano Gresta,Domenico Patanè Domenico Patanè,Danilo Cavallaro Danilo Cavallaro,Giorgio Mangano Giorgio Mangano,Antonino D’alessandro Antonino D’Alessandro,Giuseppe D’anna Giuseppe D’Anna,Fausto Grassa Fausto Grassa

doi:10.4401/ag-6929

Abstract

<p>In the Sicily Channel, volcanic activity has been concentrated mainly on the Pantelleria and Linosa islands, while minor submarine volcanism took place in the Adventure, Graham and Nameless banks. The volcanic activity spanned mostly during Plio-Pleistocene, however, historical submarine eruptions occurred in 1831 on the Graham Bank and in 1891 offshore Pantelleria Island. On the Graham Bank, 25 miles SW of Sciacca, the 1831 eruption formed the short-lived Ferdinandea Island that represents the only Italian volcano active in historical times currently almost completely unknown and not yet monitored. Moreover, most of the Sicily Channel seismicity is concentrated along a broad NS belt extending from the Graham Bank to Lampedusa Island. In 2012, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) carried out a multidisciplinary oceanographic cruise, named “Ferdinandea 2012”, the preliminary results of which represent the aim of this paper. The cruise goal was the mapping of the morpho-structural features of some submarine volcanic centres located in the northwestern side of the Sicily Channel and the temporary recording of their seismic and degassing activity. During the cruise, three OBS/Hs (ocean bottom seismometer with hydrophone) were deployed near the Graham, Nerita and Terribile submarine banks. During the following 9 months they have recorded several seismo-acoustic signals produced by both tectonic and volcanic sources. A high-resolution bathymetric survey was achieved on the Graham Bank and on the surrounding submarine volcanic centres. A widespread and voluminous gas bubbles emission was observed by both multibeam sonar echoes and a ROV (remotely operated vehicle) along the NW side of the Graham Bank, where gas and seafloor samples were also collected.</p>

Highlights

Introduction and geodynamic framework of theSicily ChannelWithin the geodynamic framework of the central Mediterranean area, the Sicily Channel belongs to the central portion of the northern margin of the African continental plate, called Pelagian Block [Burollet et al 1978]
It corresponds to the foreland area of the Sicilian sector of the Neogene Apenninian-Maghrebian fold-andthrust belt, the outermost and youngest thrust sheet of which is represented by the Gela Nappe [Ogniben 1969] (Figure 1)
The tectonic setting of the Sicily Channel is the product of the Neogene continental collision between the African and European plates and of the NeogeneQuaternary NW-trending rift [Jongsma et al 1985, Boccaletti et al 1987, Reuther et al 1993]

Summary

Introduction and geodynamic framework of the Sicily Channel

Within the geodynamic framework of the central Mediterranean area, the Sicily Channel belongs to the central portion of the northern margin of the African continental plate, called Pelagian Block [Burollet et al 1978]. Most earthquakes of the Sicily Channel are focused along a broad NS oriented belt extending from Lampedusa Island to southwestern Sicily coast passing through the Graham Bank [Cello 1987, Argnani 1990, Rotolo et al 2006, Civile et al 2010, Calò and Parisi 2014] (Figure 1). Inside this belt the alkaline volcanic centres of Linosa Island, and the Nameless and Graham banks are located. In order to control in real time the correct deployment on the sea bottom of the seismometer from the arm of the OBS/H, two ROV dives were performed (Figure 5)

Morphological analysis of the new bathymetric map

Preliminary gas composition

Conclusions and future work