The fall of Etna into the sea could trigger a catastrophic collapse

Gravity causes Etna towards the sea, which could cause a catastrophic collapse of the flank of the active volcano.

Nothing indicates that such a collapse is imminent, but new research shows that the southeast flank of the Italian volcano moves both above ground and under the sea. These movements mean that the The risk of collapse of the slope is higher than previously thought, researchers said today (October 10) in the journal Science Advances.

"We need to better understand how this transition works and the types of triggers needed for its collapse," Morelia Urlaub, co-author of the study and marine geodynamic researcher at the GEOMAR Helmholtz Ocean Research Center, told Live. in Kiel (Germany) Science. [History’s Most Destructive Volcanoes]

Eruptive Etna

Etna is the most hectic volcano in Europe. This mountain has experienced periods of active activity since at least 6000 BC. J.-C. and is currently in an eruptive cycle underway since September 2013, according to the Smithsonian Institution's Global Volcanism Program.

Researchers using satellite data and GPS measurements have also observed that the southeast flank of Etna has been crawling offshore for at least 30 years. In March, scientists from the Open University in the UK reported that the slope was moving an average of about 14 millimeters a year between 2001 and 2012 alone.

The debate, according to Urlaub, consisted in determining whether this creep resulted from the displacement of magma under and inside the volcano or whether it resulted mainly from gravity. Mount Etna constantly spits material on its slopes, she said, and gravity pulls this new material down.

"It's common with these big volcanoes," Urlaub said. "They spread to the base."

Etna also has her feet in the water, said Urlaub. Its slopes extend under the Sicilian coast and in the Mediterranean. Until now, however, no one had measured how the flank was moving below sea level.

Underwater slip

Using a network of seabed sensors, Urlaub and his team measured the transponder sound path to a transponder every 90 minutes between April 2016 and July 2017. The weather That it took for the sound to spread reveals the distance between the transponders so that the researchers could detect any changes in the seabed during the study period.

They found that for a period of eight days in May 2017, a fault on the underwater side of the mountain had shifted up to 1.6 inches (4 centimeters). It was not an earthquake; the movement is produced without fault breakage or seismic waves, but rather as a progressive slip.

The area where researchers measured slippage is far from the magmatic chambers at the center of Etna, Urlaub said. This means that the movement does not result from the rise of magma in the underground chambers of the volcano; Instead, it's the work of inexorable gravity, which pulls the entire slope above and below the water.

This is bad news for Etna's risk for human life, Urlaub said.

"According to the geological data, other volcanoes collapsed catastrophically and caused very large landslides," she said, "and if these landslides come into the sea, they can cause a tsunami. "

The likelihood of this happening in Etna can not be quantified yet, Urlaub said. The scientific observations of the mountain date back only a few decades, she said, and the entire history of Etna extends over 500,000 years. Increased monitoring is needed to detect possible changes in the slope's movement and to estimate its risk of collapse, she said.

"There is a danger," Urlaub said. "We just have to keep an eye on Etna's flank and his movement."

Originally posted on Live Science.