The hidden volcanic hazard: the low-water submarine volcanoes of th e Sicily Channel

The Sicily Channel (central-western Mediterranean) represents a Pliocene-Pleistocene rift system bordered by NW-SE-striking normal faults, cutting the accretionary prism of the Maghrebide-

Sicilian-Apennine orogen. This sector, floored by a variably thinned and faulted continental crust, was the site of intense magmatic activity. Geophysical data suggest that tectonic deformation along

the rift is still active but the processes that generated rifting in this zone are not fully understood

although this sector is crucial for the comprehension of the magmatism of the northern African

plate. Magmatism (Miocene to Present in age), both subaerial and submarine, has generated a wide

spectrum of volcanic rocks with different affinities, and originated the Linosa and Pantelleria

islands and several seamounts (e.g. Cimotoe, Tetide,Graham, Foerstner, Terribile), mainly located

along extensional NW-SE-striking faults. On the seafloor of theSicily Channel several recent

submarine volcanoes of various dimensions occur. Some of these volcanoes have erupted during

historical times; others are covered by undisturbed Pliocene-Quaternary sediments and have been

detected by seismic profiles and magnetic survey. Unfortunately, studies of volcanism in the Sicily

Channel have been limited almost exclusively tothe subaerial portions ofthe volcanoes. The best

known eruption of Sicily Channel occurred incorrespondence of the Graham Bank in 1831 AD.

This bank is located about 50 km south of the Sicily coast, shows a N-S-elongated shape and rises

from a sedimentary basement sited about 350 m below sea level. The eruption produced the

ephemeral Isola Ferdinandea that was rapidly dismantled by marine erosion. In 1891, a likely

submarine eruption from a centre 5 km NW of Pantelleria was documented and in 1941, above the

SE portion of the Graham Bank, gaseous emissions were observed. During the 2002-03 volcano-

seismic crisis, an increase in submarine degassing at the summit of the Graham Bank stirred worries

about a possible renewal of volcanic activity. Although submarine volcanism at the general level, a

nd particularly in the Mediterranean, is a very widespread phenomenon, it hasn't been intensely

studied due to the difficulties in reaching and analysing the submarine centres. This represents an

important gap to fill even considering that very recently (May 2006), on the northern slope of the Graham Bank, intense fumarolic emissions, which could suggest the presence of a shallo

w-depth magmatic body, have been documented. According to recent marine geological surveys, th

e Graham Bank belongs to a much wider volcanic complex that rises about 350 m from the sea floor, has a base diameter of 30x25 km and is constituted by numerous small volcanic edifices, some of them unknown. In particular, on the Graham Bank, the Ferdinandea volcano is associat

ed to several cones of similar dimensions. Although the described volcanic complex has to be regarded as active and critical in terms of hazard, the knowledge of its volcanological characteris

tics is limited to the scanty accounts of the 1831 eruption and to a few petrological, geochemical and isotopic data carried out on rocks dredged from the Graham Bank during the surveys of the '70-.80. These data possibly indicate the presence in the Sicily Channel of a HIMU-FOZO mantle source and the existence of a fossil plume that variably contributed to magmatogenesis, in response to variab

le lithospheric stretching. 

[A.P.Santo Dipartimento di Scienze della Terra, Università di Firenze, Italy;

C.Corselli, C.Tessarolo, A.Tibaldi, Dipartimento di Scienze Geologiche e Geotecnologie,

Università di Milano-Bicocca, Ital]

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