In September 2023, a peculiar global seismic signal was detected every 90 seconds over nine days and repeated a month later. Two scientific studies have now suggested that these anomalies were caused by two mega tsunamis in the remote Dickson fjord in East Greenland. These events were triggered by major landslides due to the warming of an unnamed glacier. The resulting waves became trapped in the fjord system, forming standing waves or seiches, which led to the mysterious signals.
Thomas Monahan from the Department of Engineering Science at the University of Oxford noted, "Climate change is giving rise to new, unseen extremes. These extremes are changing the fastest in remote areas, such as the Arctic, where our ability to measure them using physical sensors is limited. This study shows how we can leverage the next generation of satellite earth observation technologies to study these processes."
Despite previous attempts, no observations confirmed this theory until recently. Even a Danish military vessel failed to detect any waves during its visit three days into the first seismic event.
Oxford researchers employed novel analysis techniques using satellite altimetry data to measure Earth's surface height through radar pulses. Conventional satellites could not capture evidence due to long gaps between observations and limited sampling capabilities.
The new Surface Water Ocean Topography (SWOT) satellite launched in December 2022 provided critical data for this study. It uses advanced Ka-band Radar Interferometer (KaRIn) technology with two antennas on a 10-meter boom that measures ocean and surface water levels with high accuracy along a wide swath.
Thomas Monahan credited SWOT as "a game changer for studying oceanic processes in regions such as fjords which previous satellites struggled to see into." The research team created elevation maps showing cross-channel slopes with height differences up to two meters after the tsunamis. These maps indicated water movement across channels.
Professor Thomas Adcock highlighted that "this study is an example of how the next generation of satellite data can resolve phenomena that has remained a mystery in the past." He emphasized innovation and machine learning's role alongside ocean physics knowledge for interpreting new results.
The researchers linked their findings with small movements of Earth's crust measured far away, reconstructing wave characteristics even when unobserved by satellites. They also ruled out weather and tidal influences on their observations.
The study titled 'Observations of the seiche that shook the world' has been published in Nature Communications.