Moving earth in the Mediterranean

Sicily is located in a very geodynamically active region. Not only can the volcano Mount Etna erupt, but there is a serious risk of earthquakes or tsunamis. In an interdisciplinary project, Kiel scientists are analysing and evaluating the risks.

Europe's largest volcano, the approximately 3,340-metre-high Mount Etna, erupts regularly and emits black ash, glowing rocks and plumes of smoke into the air. Sometimes lava also flows down the mountain and into inhabited areas. There are also often earthquakes in the wake of the eruptions. The people of Sicily have been living with these dangers for a long time, and have come to terms with them as far as possible. Beyond that, they also benefit from them. The lava flows produce fertile soil, and volcano tourism is a welcome source of income.

However, the fact remains that the region carries incalculable risks. These are not only caused by the volcanic activity of Mount Etna: the giant mountain itself is in motion, or more specifically, a part of it. The eastern flank of Mount Etna is slipping slowly but steadily towards the sea, on average at a rate of one to two centimetres per year. In the affected areas, deep cracks run through streets and houses, and the earth shifts. "The rate of movement of the flank is constantly monitored by local measuring stations and satellite observation. Because if it slipped off completely, it could trigger a tsunami, just like Anak Krakatoa in Indonesia in 2018," said Dr Felix Gross from the Institute of Geosciences and the marine science priority research area Kiel Marine Science (KMS).

The Kiel geophysicist found evidence that the slope is also moving under water, during his doctoral research. To test this assumption, he used data from a new, sound-based measurement network, which had been set up under the direction of the GEOMAR Helmholtz Centre for Ocean Research Kiel on the seabed off the south-east coast of Sicily. This measurement was the first of its kind in the marine sector, and confirmed the hypothesis that the movement continues under water. Gross: "We have observed that the undersea continental slope in front of Mount Etna is completely unstable. Distinctive structures can be found on the seabed and in the sediment, which suggest that there is a lot of movement here in the system. That makes this flank of the volcano an even greater risk."

With seismic and hydro-acoustic measurement techniques, on the one hand a morphological map can be created of the surface of the ocean floor, and on the other hand the geological structures in the deep can be determined, explained Gross. "We have recorded and evaluated data between the Strait of Messina in the north and south of Sicily. The entire seabed exhibits many additional fault zones, which in the past may have been responsible for earthquakes and the resulting tsunamis." Above all, three large earthquakes are known to have occurred in the region in 1693, 1783 and 1908, which resulted in many deaths (1693: around 60,000; 1783: 32,000-50,000; 1908: 75,000-110,000). Such events could also occur again in future. The reason for this is that southern Italy (Sicily and Calabria) is located on the collision zone between the African and Eurasian continental plates. "This collision belt is extremely complex. The continental plates are colliding with each other at different angles, and sliding on top of each other," said Gross. "We have observed vertical displacements between the plates. In these fracture zones, the sediments are entirely shifted against each other. And this is only possible if they are subjected to strong forces. Therefore, we assume that the origin of past earthquakes lies here."

In order to model earlier events, the fault zones on the surface of the ocean floor and the subsurface are being mapped. Gross: "When doing so, we not only examine the seabed, but also what happens on land, in order to develop holistic models." But earthquakes or marine natural hazards can also not be accurately predicted with these models. However, examining the geological past allows determination of which areas will pose dangers in future. And in the opinion of the geophysicist, this also includes the sliding flank of Mount Etna.

In order to investigate the current natural hazards in southern Italy more closely, Kiel scientists from the CAU and GEOMAR have formed a multidisciplinary team with cooperation partners from Italy. They monitor active fracture zones, map the seabed and model scenarios. In addition, they consider social and economic aspects, and include them in the analyses. Felix Gross coordinates and leads the joint activities in the newly-founded Center for Ocean and Society at Kiel University.

Author: Kerstin Nees