Etna slips into the sea

The researchers found new evidence that the south-east flank of Mount Etna was sliding into the sea. The gradual displacement could lead to the collapse of an entire slope, increasing the risk of a major tsunami.

Etna, the largest and most active volcano in Europe, is located east of the island of Sicily. The volcano shows persistent signs of turmoil and has been the subject of studies for years.

It has been known for some time that the southeast flank of the volcano slowly slides towards the sea while the other slopes are largely stable. However, the exact process that triggers this descent is still unknown. Satellite measurements being impossible under the surface of the ocean, researchers have for the first time used the new GeoSEA geodesic monitoring network of the seabed and have detected the horizontal and vertical movement of a submerged volcanic flank .

The data from the system confirmed that Etna had moved, but this movement is probably caused by gravity and not by rising magma, as previously assumed. The catastrophic collapse of the flank or its major parts would trigger a major tsunami with potentially extreme consequences for the region.

"At Mount Etna, we used for the first time a sound-based underwater geodesic surveillance network called" marine geodesy, "said lead author Dr. Morelia Urlaub of the University. from Kiel. "Overall, our results indicate that the slope is slipping due to gravity and not because of rising magma."

For the study, researchers from the GEOMAR team deployed a total of five acoustic monitoring transponder stations on the fault line in April 2016 and received the signal from each transponder every 90 minutes until In July 2017, the system was based on sound, travel time, and revealed the distance between the transponders, which enabled the researchers to detect any flank changes.

"We noticed that in May 2017, the distances between the transponders located on either side of the fault had clearly changed.The flank had slipped four centimeters to the open sea and had reduced of one centimeter in eight days, "explained Dr. Urlaub.

This movement is apparent in a very slow earthquake, also called a "slow slip event". It was the first time that the horizontal movement of such a slow slip event was recorded under water.

"The whole slope is moving because of gravity," said Professor Heidrun Kopp, coordinator of the GeoSEA network and co-author of the study. "It is therefore quite possible that it could collapse catastrophically, which could trigger a tsunami throughout the Mediterranean."