COULD ETNA CAUSE A TSUNAMI?

The volcanic activity of Mount Etna in the run-up to Christmas has generated a lot of publicity in the media, with talk of the possibility of a major tsunami resulting from the volcano’s landslide that would be catastrophic for the entire Mediterranean.

The news is generated by an article published in Science Advances where a group of scientists from the University of Kiel report a decrease in the southeast flank of Etna, through a new sound-based geodetic monitoring network, the results indicate movements underwater. The research showed that over a period of eight days the flank slipped by about four centimetres, resulting from a comparison with satellite data. See the original article here.

Scientists warn that a sudden and rapid descent of the entire slope could trigger a tsunami with disastrous effects for the entire region, which may be too frightening considering that Etna’s descent has been rather gradual, but we should not panic until we have certified news from experts.

The Science Advances results indicate that the slope is sliding because of gravity and not because of rising magma.

This is a novel result as studies of Etna have shown for years, through satellite measurements, that Etna was progressively “sinking”. Scientists believed that this descent was due to rising magma and was due to the size of the volcano, which covers an area of more than 1600km2 and is certainly as heavy as it is large.

However, thanks to GEOMAR’s team of marine geologists, we now know that the reason Etna is continually sliding into the sea is gravitational instability.

Satellite measurements can measure movements above the water, while sound measurements can measure movements within the seabed where Etna is rooted.

To make the underwater measurements, the Kiel geologists used transponders, devices that emit and receive acoustic signals, on the seabed off the east coast of Catania, where Etna is located and the displacement is visible. Between April 2016 and July 2017, they installed a network of five transponders equipped with pressure sensors to monitor seabed displacements on both sides of the fault into which Etna dives.

The transponders send out acoustic signals, these movements are recorded, when the wave comes and when it goes. By knowing the speed at which sound travels underwater, researchers know how long it takes to get from one transponder to another and can calculate the distance between them. When that distance changes, it is because there has been movement of the seabed.

For 15 months, the acoustic measurements remained stable, except for a change of a few centimetres between 12 and 20 May. In those eight days a very clear pattern phenomenon occurred, the unstable east side of Etna moved daily, dropping a total of 4cm corresponding to an aseismic fault movement in the region.

The result not only shows that Etna is descending because of gravity but also reveals a very important fact, that the descent is episodic and is out of tsunami risk.

COULD ETNA CAUSE A TSUNAMI?

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