Massive Greenland landslide sent seismic waves around earth for nine days Premium

On September 16, 2023, roughly 25 million cubic metres of ice and rock, enough to fill 10,000 Olympic-sized swimming pools, splashed into Greenland’s Dickson Fjord, displacing the water enough to give rise to a 200-metre-high mega-tsunami and send seismic waves around the earth for nine days, a new study in Science has reported.

On September 16, 2023, several seismic stations worldwide detected a bizarre signal. Earthquakes are not rare. In 2023 alone, 1,712 earthquakes of magnitude 5 or more were registered worldwide. But these seismic waves were puzzling; the signatures clearly indicated that earthquakes had not caused them, and the reverberations lasted for a staggering nine days.

“We saw it on sensors everywhere, from the Arctic to Antarctica,” Stephen Hicks, a computational seismology research fellow at University College London, and Kristian Svennevig, senior researcher at the Geological Survey of Denmark and Greenland, wrote in a recent article. They are coauthors of the study reporting their findings, published in Science on September 12.

When you play the violin, you yank multiple strings together, which emit sounds at a mix of frequencies. Seismic waves from earthquakes behave the same way. However, the hum the seismologists recorded had only one frequency — like only one string of the violin had been plucked. That isn’t characteristic of tremors.

At first, the seismologists classified this wave as a “USO”, an unidentified seismic object. “Even more puzzling was that the signal kept going for nine days,” Hicks and Svennevig wrote. Earthquake vibrations also produce aftershocks. But in this case, the reverberations faded more slowly than one might anticipate from an earthquake.

What set off the tremble? Only powerful events like volcano eruptions or clandestine nuclear weapons tests could unleash this much energy. Seismologists were intrigued. 

To resolve the enigma, more than 68 researchers from 40 universities in 15 countries teamed up across disciplines. After piecing together numerous datasets and using computer simulations, the team realised the waves were caused by a massive landslide on the banks of the Dickson Fjord in Greenland.

According to Hicks and Svennevig, “solving this mystery required putting many diverse pieces of evidence together, from a treasure trove of seismic data to satellite imagery, in-fjord water level monitors, and detailed simulations” of how the water reacted.