A model-estimation of gas overpressure in gas saturated layers in a volcanic setting: A case study from the Banco della Montagna (Naples Bay, Italy)

The 5 km wide Banco della Montagna (BdM) morphological high is located on the seafloor of Naples Bay (Tyrrhenian Sea, Italy) and is characterized by a hummocky surface. Oceanographic surveys revealed active fluid vents at BdM. High-resolution mono-channel seismic and multibeam bathymetry allow us to define the detailed morphology and the inner geometry of BdM, which consists of a complex set of dome-like structures (pagodas) affecting the present-day seabed. We suggest that a gas-water-sand sediment mixture upraises from a gas saturated layer pushing up the overlying marine deposits and forming mounds, folds, and faults. According to a thin-plate elastic model, we estimate the fluid (gas) pressure Pdef required to form BdM and obtain Pdef = 0.3 Pa, a value consistent with that for doming processes in gas-hydrate settings. At BdM, the pressure ?P required to break the seabed is in the order of 2-3 MPa, while the gas column height is about 240 m.