Marsili undersea volcano - tsunami risk for Naples, and coastal areas of South West italy and northern Sicily

Marsili is a large undersea volcano in the Tyrrhenian Sea, about 175 km south of Naples. It has evidence of a magma chamber 2.5 km below the summit, and of hydrothermal systems. It has a steep flank made up of weak and low density rocks with a total volume of 100 km3 some of which may collapse in a single event. There are no signs of it erupting at present but it had previous eruptions 3,000 and 5,000 years ago (by carbon dating of fossil shells).

If this happens then it could cause a tsunami of between 30-40 cm and 3-4 meters in height that could affect Naples (population over a million) and other low lying coastal regions of south-west Italy and northern Sicily.

A computer simulation by Steve Ward suggests a potential for a larger tsunami of 10-20 meters if 20 km3 of the flank were to collapse in a single event (see ).

The tsunami would take 20-25 minutes to reach the coast, so there may be a case for installing a warning system in case this event happens, for affected areas. At over 100 km from the nearest land, studying it is a challenge, but two GEOSTAR remotely operated observatories have been set up on the flanks of the mountain to help with monitoring.

Tsunami studies
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 it has a steep flank 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 steep flanks of the Marsili seamount might experience an undersea landslide that could trigger destructive tsunamis on the Italian coast. They came to this conclusion after studying the collapse of 50 km3 of material from the Vavilov Seamount which seems to have taken place in a single event. Marsili's steep flank contains around 100 km3 of weak rock.

Dr Enzo Boschi, in an interview in 2010 said

"It could happen tomorrow. The latest research says that the volcanic edifice is not strong and its walls are fragile. Furthermore we have measured the magma chamber that has formed in recent years and it is of large dimensions. All this tells us that the volcano is active and could erupt unexpectedly."

However there are no signs of it erupting and Aldo Piombino put it like this :

"It is statistically very unlikely that in our lifetimes we will see an explosion of Marsili, and even less likely that we will see a tsunami caused by a landslide on its flanks, but it is to be hoped that it will be placed under close seismic and geochemical surveillance, as with other active Italian volcanoes. I believe that it is necessary for civil protection and for science that one of the largest volcanoes in Europe is better understood."

A 2018 analysis by Alberico et al for the Naples region estimated the size of tsunami that could be generated and found that there is a risk of

"a tsunami amplitude varying from a few centimetres (30–40 cm) to some metres (3–4 m)"

It would take 20 - 25 minutes to get to the coast so another study by Nicola et al recommends

"the installation of an alert system need along the tyrrhenian coast of Calabria, with an alert advise of around 10 minutes and an evacuation plan of 10 minutes."

Steve Ward simulation
Steve Ward of UC Santa Cruz seismology laboratory has a simulation that predicts tsunamis of 10-20 meters from collapse of 20 cubic kilometers of rock.

U_WIyCs0XTI

Geomorphology
Mt. Marsili belongs to the Aeolian Islands Volcanic arc, being 70 kilometers long and 30 kilometer wide (covering a 2100 square km area) it is the largest active volcano of the chain, larger than Mount Etna. It was discovered during the 1920s and named after Italian geologist Luigi Ferdinando Marsili. Extensive studies have been carried on only since 2005 as the Italian National Research Council started a vulcanology research program on the site.

The volcano rises from a plateau of thin oceanic (or pseudo-oceanic) crust with a thickness of only 10 km, which forms its own sea basin. The basin crust is made of tholeiitic basalt which is most typical of inflated basins at the back of oceanic volcanic arcs. The Marsili basin appears to have formed very recently (2 million years) as a consequence of the growth of the volcanic arc, and Mt. Marsili could be the result of the thermal inflation of the thin crust at the center of the basin. The start of the volcano activity could date back as recently as 200,000 years ago.

There is evidence of hydrothermal activity from Helium 3 / Helium 4 isotope ratios in several sites, and from analysis of the basalt, then a magma chamber is proposed 2.5 kkm below the sumit. It is difficult to study because of the remote location both beneath the sea and far from land, more than 100 km from the nearest land. This remote sensing essential. Two remotely operated GEOSTAR observatories were set up at the base of the NW flank to permit long term monitoring.

On Google Maps
 Marsili volcano~Marsili Seamount~100 km from the nearest land ~ Marsili Seamount 


 * This map is resizeable, you can also show it full screen, click on the marker for brief summary informatio and you can right click anywhere on the map to copy the click point co-ordinates to the clipboard.