Wave Led to Earth Vibrating for 9 Days in 2023

A geologic mystery that has lingered for the past year has finally been solved: What caused an odd cascade of vibrations to ripple across the globe for nine days? Using classified seafloor maps from the Danish military, a global network of seismic sensors used to detect earth[1]quakes, drone video of debris washed high up on a remote rock face in eastern Greenland and other evidence, researchers finally pieced together the strange sequence of events. It started when seismic sensors at monitoring stations around the world detected a signal in September 2023 that looked nothing like the squiggles made by earthquakes. This signal oscillated at 90- second intervals and continued for days. “Some of our U.S. col[1]leagues put it down to faulty instruments,” said Kristian Svennevig, senior research scientist at the Geological Survey of Denmark and Greenland, and lead author of a study on the findings published Thursday in the journal Science. “They had never heard anything like it before.” A few days after the signal began, Svennevig got a call from authorities in Greenland who reported damage to an unoccupied research base. Svennevig assembled an earth-science detective squad of 68 experts who reconstructed what happened. The evidence revealed that 33 million cubic yards of rock and ice—the volume of 10,000 Olympic-size swimming pools— had plunged into the Dickson Fjord in eastern Greenland, triggering a tsunami. The massive wave crested at 650 feet above the water’s surface, throwing debris onto a nearby rock face. It settled down to 25 feet, but over the next nine days, it sloshed from one side of the fjord to the other, striking the sides with enough force to move the walls, creating the seismic signal that propagated around the planet, Svennevig said. The landslide was caused by a melting glacier below the mountaintop, according to the study, and Svennevig said scientists are reconsidering the kinds of natural disasters that are now possible in a warming Arctic environment. In 2017, a glacial landslide in western Greenland’s Karrat Fjord flooded a village, destroying 11 homes and killing four residents. In Alaska, U.S. officials are closely watching the Barry Arm glacier for a potential landslide that could trigger a tsunami there and threaten nearby communities. “Had you suggested just a year ago that a nine-day wave could exist on a Greenland seafloor, or anywhere, people would shake their heads,” he said. “Now we’ve seen it, we have to deal with it, and know that these things exist.”

Source: WSJ