A SUDDEN and rapid descent of one of Mount Etna’s slopes in Sicily could “lead to a tsunami with disastrous effects for the entire Mediterranean”, warn researchers.

Scientists using new, sound-based marine monitoring gear found that the southeastern side of the volcano slipped about four centimetres underwater – in just eight days.

As a result of their findings, published yesterday in the international journal Science Advances, the experts confirmed that Mount Etna’s “entire southeastern flank is in motion”.

“Catastrophic collapse involving the entire flank or large parts of it cannot be excluded and would trigger a tsunami with extreme effects in the region," they added.

As Europe’s most active volcano, Mount Etna is intensively monitored by scientists and Italian authorities.

Research based on satellite-based measurements has previously shown that the southeastern slope is slowly sliding towards the Mediterranean Sea, while the other flanks are largely stable.

However, until now it was not known whether – and how – movement continues underwater, as satellite-based measurements are impossible below the ocean surface.

So, a team of scientists from GEOMAR, Kiel University and the National Institute of Geophysics and Volcanology used new, sound-based underwater surveying and monitoring equipment to better gauge any shift.

Dr Morelia Urlaub, the study's lead author, said it was the “first time” this type of marine monitoring network had been used on a volcano.

The GEOMAR team placed five acoustic monitoring devices across the fault line.

Mount Etna sits on an active fault between the African tectonic plate and the Ionian microplate, both of which are being pushed under the Eurasian plate.

Three monitoring devices were placed on the sliding flank, and two were put on the stable side of the fault line.

Acoustic signals showed “the flank slipped by four centimetres seawards and subsided by one centimetre within a period of eight days,” said Dr Urlaub.

GEOMAR explained that “this movement can be compared to a very slow earthquake, a so-called ‘slow slip event’," and it was the first time that the horizontal movement of such a slow slip was recorded underwater.

Dr Urlaub added: “The entire southeast flank changed its position.”

However, the driving force of the slope’s movement “is most likely gravity, and not the rise of magma,” she said.

If magma had been the cause, the slope’s displacement would be expected to be larger onshore than below water.

Professor Heidrun Kopp, co-author of the study, added: “The entire slope is in motion due to gravity. It is therefore quite possible that it could collapse catastrophically, which could trigger a tsunami in the entire Mediterranean.”

Unfortunately the findings did not help researchers determine when – and whether – such a sudden collapse would happen.