Measuring Mount Etna – an underwater monitoring first

A network of Sonardyne instruments deployed by scientists from GEOMAR Helmholtz Centre for Ocean Research in Kiel for 15 months has measured underwater slippage of the southeast flank of Europe’s most active volcano, Mount Etna.

The challenge

While satellite observations have previously shown that the flank of the volcano is slowly sliding towards the sea, until the establishment of this network, it had been impossible to confirm if and how the submerged segment was moving beneath the ocean.

Results published in the international journal Science Advances confirm that the entire flank of the volcano is in gravity-driven motion and in one event the slope slipped about four centimetres in just eight days. The risk is that sudden and rapid failure of the entire slope could result in a catastrophic tsunami in the Mediterranean.

The solution

A network of five Sonardyne Autonomous Monitoring Transponders (AMTs) were deployed in April 2016 by scientists at GEOMAR and Kiel University. The placement of the transponders covered the fault line that represents the boundary between the sliding flank and the stable slope. Three AMTs were situated on the sliding sector and the final two on the side of the fault line that was presumed to be stable.

The AMTs acoustically measure the distances between each other with a millimetric precision. This sound based underwater geodetic monitoring network, so-called marine geodesy, was a first for monitoring a volcano’s movement underwater.

Geraint West, Global Business Manager – Ocean Science told us “The AMT is a highly flexible instrument that has been used by research institutes around the world to measure seabed movements as diverse as rapid canyon turbidity flows to plate motion at deep subduction zones. This project is the first time that it has been used to measure the slippage of a volcano’s submerged flank.”

“The AMT was originally developed to measure deformation of the seabed caused by the extraction of hydrocarbons over several years.” Tom Bennetts, Sonardyne Projects Manager added.

“Sonardyne first deployed AMTs on a large project over the Ormen Lange field in the Norwegian sector of the North Sea. For that project, some 220 individual instruments were deployed. The precision and endurance required for the Ormen Lange project showed us – and others – that our AMTs are also ideally suited for scientific studies of the seabed.” Bennetts clarified.

The results

The results published in the international journal Science Advances confirm that the entire flank of the volcano is in gravity-driven motion rather than the ascent of magma. One event saw the slope slip about four centimetres in just eight days. There is a very real risk that a sudden and rapid failure of the entire slope could result in a catastrophic tsunami in the Mediterranean.

Chris Hammersley, Project Engineer – Navigation Systems for Sonardyne said “Through several projects with major AMT deployments, we’ve built up a close relationship with the scientists and engineers at GEOMAR. We’re on standby to support them remotely through AMT deployment and routine data recovery missions. From our head office in the UK, we’re able to support these projects remotely, 24/7. For the Mount Etna Measurement project, we’ve been able to advise on optimal configurations for the instruments as well as troubleshoot any issues that arise, ensuring that GEOMAR have been able to use valuable ship time on site to best effect.”

The results of the study do not allow a prediction of whether and when a rapid failure of the slope might occur. For this reason, further research into the geological processes at and around Etna and other coastal volcanoes will continue. The success of our AMT deployments at Etna has secured the future use of sound-based geodetic monitoring networks for further studies.

Read more about GEOMAR’s project here.