Greenland mega tsunamis: First direct observation of trapped waves shook Earth

Summary

Copernicus Sentinel-2 satellite image of the Dickson Fjord in East Greenland. Credit: Thomas Monahan. In September 2023, a bizarre global seismic signal was observed which appeared every 90 seconds over nine days—and was then repeated a month later. Almost a year later, two scientific studies proposed that the cause of these seismic anomalies were two mega tsunamis which were triggered in a remote East Greenland fjord by two major landslides which occurred due to warming of an unnamed glacier. The waves were thought to have become trapped in the fjord system, forming standing waves (or seiches) that undulated back and forth, causing the mystery signals. However, up to now no observations of these seiches existed to confirm this theory. Even a Danish military vessel which visited the fjord three days into the first seismic event did not observe the wave which was shaking Earth. In a new study, Oxford researchers used novel analysis techniques to interpret satellite altimetry data. This measures the height of the Earth's surface (including the ocean) by recording how long it takes for a radar pulse to travel from a satellite to the surface and back again. The work is published in Nature Communications. Up to now, conventional satellite altimeters were not able to capture evidence of the wave due to long gaps between observations, and the fact that they sample data directly beneath the spacecraft, producing 1D profiles along the sea-surface. This makes them incapable of depicting the differences in water height needed to spot the waves. This study used data captured by the new Surface Water Ocean Topography (SWOT) satellite, launched in December 2022, to map the height of water across 90% of the Earth's surface. At the heart of SWOT is the cutting-edge Ka-band Radar Interferometer (KaRIn) instrument, which uses two antennas mounted on a 10-meter boom on either side of the satellite. These two antennas work together to triangulate the return signals that bounce back fro...