Several seafloor depressions have been found on the seafloor around the Western Pontine Archipelago (Palmarola, Ponza and Zannone Islands) located around 30 km away from the Latium coast. By the integration of different geophysical data have been possible to identify specific gas related structures as little pockmarks and large depressions located both on the continental shelf and upper slope. The large depressions are located few kilometers away from the Zannone Island at depths between 105 and 140 m. They have an average surface of 0.25 km2 and are 10 m deep compared to the surrounding seafloor. Other gas related features have been found in the north-western sector of Palmarola Island (depth between 60 and 90 m), in the southern sector of Ponza Island (depth between 130 and 140 m) and in the northern sector of the archipelago (depth between 200 and 400 m).
Video observations (by Remotely Operated Vehicle) acquired across the depressions placed offshore the Zannone Island, were use
