A massive landslide last September in an East Greenland fjord has been identified as the ultimate cause of mysterious vibrations that shook the entire Earth every 90 seconds for nine days. It also offers further proof that climate change is causing cascading and calamitous large-system feedback, scientists warn.
The large international team of experts who investigated the mysterious global phenomenon—and recently published their results in the academic journal Science—initially named the cause an “unidentified seismic object”, or USO. Eventually, they determined that it was the final act of a drama that began Sept. 16, 2023, when 25 million cubic metres of rock and ice—“a volume equivalent of 25 Empire State Buildings,” notes the BBC News—crashed into the waters of Greenland’s Dickson Fjord, causing a mega-tsunami some 200 metres (50 storeys) high.
Some of that water made it out of the narrow, winding fjord and into the Greenland Sea. A 60-metre wave eventually reached Ella Island, 70 kilometres offshore, wiping out an abandoned research station, reports Surfer Today.
Most of the wave was trapped inside the narrow fjord, however, and proceeded to slosh back and forth, ultimately settling into a seven-metre-high oscillating wave pattern which then delivered the mysterious “nine-day-long, global 10.88-millihertz (92-second) monochromatic very-long-period seismic signal” to seismometers around the world, writes the 68-member research team in the abstract to their study.
Months of collaborative work between scientists in 40 research institutions across 15 countries, together with the Danish Navy, have now yielded a full answer to what caused the signal, originally labelled a USO because it looked nothing like those produced by the underwater earthquakes that typically cause tsunamis.
The team concluded that the landslide that triggered the mega-tsunami, and in turn produced the USO, occurred when the melting glacier at the foot of a 1,200-metre mountain in the fjord collapsed, taking the mountain with it.
“That glacier was supporting this mountain, and it got so thin that it just stopped holding it up,” co-author and computational seismologist Stephen Hicks of University College London told the BBC.
Lead researcher Kristian Svennevig, senior researcher at the National Geological Surveys for Denmark and Greenland, said the landslide in Dickson Fjord was not an isolated event.
“We are witnessing a rise in giant, tsunami-causing landslides, particularly in Greenland,” he told BBC.
“As climate change continues to melt the Earth’s polar regions, the number of large-scale landslides involving earth, rock, and ice that generate destructive events will multiply,” co-author and seismologist Alice Gabriel from the University of California, San Diego, told Surfer Today.
Dickson Fjord is a popular destination for cruise ships, and it was pure luck that none were in the area when the glacier and mountain collapsed, said the research team.
The global heating-induced landslide occurred six years after a similar but smaller event in western Greenland’s Karrat Fjord triggered a tsunami that smashed the nearby village of Nuugaatsiaq, killing four.
Concerns about the terrifying linkage between glacial retreat and landslide-triggered tsunamis are growing throughout polar regions.
Four years ago this May, researchers were calling for real-time monitoring of a glacier in Prince William Sound, roughly 100 kilometres east of Anchorage, whose undergirding of a 1.6-kilometre-long slab of rock in a fjord grows ever more tenuous as the region warms and the ice melts.
