The September 16, 2023 a huge landslide broke away from Dickson Fjord, in a remote area of the Greenland north-easterncaused a megatsunamithat is, a very violent tsunami. A recent study by German researchers from the GFZ German Research Centre for Geosciences and the Institute for Geosciences at the University of Potsdam has clarified the dynamics of the phenomenon by analyzing satellite images And seismic dataThe megatsunami, whose seismic signals were detected around the world for days, generated two types of waves: an initial 200 m high and then one sexthat is, a stationary oscillating wave in a semi-confined mass of water (in this case that of the fjord), which has continued for about 9 days. The study by the German researchers was joined a few days later by that of an international team of 68 scientists from 40 institutions in 15 different countries.
The dynamics of the Greenland megatsunami triggered by a landslide
The German researchers first analyzed the satellite images of the area to locate the landslide. The missing portion of rock along the cliff of the Dickson Fjord.
The analysis of the seismic data collected during the event around the world has then revealed a high energy signal (0.02-0.06 Hz) different from the seismic ones recorded in the event of an earthquake. This signal is compatible with the fall into the water of an enormous mass of rock that during its journey also incorporated ice: it would be more than 25 million cubic meters of materialan amount sufficient to fill 10,000 Olympic swimming pools. Seismic signals contain information on the type of source that generates the signal and how the energy is radiated. In this case it was therefore possible to trace the direction of movement of the landslide (also thanks to satellite images) and estimate the height of the wave that rose near the point of impact of the landslide, above 200 m (the wave then propagated with an average height of 60 m for 10 km in the fjord). It is believed that the collapse was caused by the progressive ice meltingwhich occurred over the course of decades, at the foot of the rock mass.
Seismic data also showed another very long-term signal (VLP) (0.0109 Hz) which lasted about nine days and it spread up to 5000 km away. Analysis of the VLP signal indicates the formation of a sex. Other signals of this type have been observed in the past in Greenland, usually generated by the collapse of large portions of ice into the sea, but of shorter duration.
The usefulness of the results
The type of analysis carried out by researchers on the Greenland landslide could be useful for examining other similar events in the past and future, which are becoming more frequent due to global warming that increases the instability of glaciers and rocky slopes. In this case, since it was a remote and uninhabited area, the tsunami only hit a military installation on a nearby island. However, there have been other less fortunate cases: also in Greenland, in the Karrat Fjord, in 2017 an avalanche caused a tsunami that devastated a village, causing several deaths.
