A USO – or ‘unidentified seismic event’ – baffled scientists, sparking a global hunt for its source
Across the world in September 2023, for more than a week, tiny ground vibrations echoed beneath our feet. Although imperceptible to humans, seismic stations detected the unusual signal, which resonated from the Arctic to Antarctica.
“When I first saw the seismic signal, I was completely baffled,” says Dr Stephen Hicks from UCL Earth Sciences, who co-led a global team of 68 scientists to solve the puzzle.
The team discovered the source of this mysterious nine-day-long tremor was not an earthquake but a mega-tsunami in a remote, uninhabited part of Greenland. A massive landslide had sent waves crashing through Dickson Fjord, generating a strange, monotonous hum that resonated through the Earth’s crust.
“Even though we know seismometers can record a variety of sources happening on Earth’s surface, never before has such a long-lasting, globally travelling seismic wave, containing only a single frequency of oscillation, been recorded,” says Hicks.
The landslide, triggered by climate change, occurred when the glacier thinned significantly due to rising temperatures. As the ice melted, it could no longer support the mountain peak, causing it to collapse into the fjord.
The impact caused a backsplash of water 200 metres into the air, creating a wave up to 110 metres tall. Although not witnessed by any humans, instruments recorded the wave as it sloshed back and forth in the fjord, producing the unique vibrations that travelled through the Earth.
Although the consequences for Greenland’s ecosystems remain uncertain, Hicks points out that drone footage showed soil and vegetation had been swept away, leaving the fjord filled with sediment, which may affect marine life.
The team hopes the study will inspire other scientists to further investigate how events like these might affect wildlife, particularly as larger collapses may occur.
“It was a relatively small glacier, but it’s had such big impacts, which means that larger systems could have even more significant consequences,” Hicks notes.
Dr Kristian Svennevig from the Geological Survey of Denmark and Greenland (GEUS), and lead author of the study into the event, adds that as climate change accelerates, monitoring regions previously considered stable will become increasingly important to mitigate the risks of such massive events.
“This is the first-ever landslide and tsunami observed from eastern Greenland, showing how climate change already has major impacts there,” he says.
Read more about the study: A rockslide-generated tsunami in a Greenland fjord rang Earth for 9 days