Marsili is a large
undersea volcano in the
Tyrrhenian Sea, about south of
Naples. The
seamount is about 3,000 m (9,800 feet) tall; its peak and
crater are about 450 m below the sea surface. Though it has not erupted in recorded history,
volcanologists believe that Marsili is a relatively fragile-walled structure, made of low-density and unstable rocks, fed by the underlying shallow
magma chamber. Volcanologists with the Italian National Institute of Geophysics and Volcanology (INGV) announced on March 29, 2010 that Marsili could erupt at any time, and might experience a catastrophic collapse that would suddenly release vast amounts of magma in an undersea eruption and landslide that could trigger destructive
tsunamis on the Italian coast and nearby Mediterranean coastlines.