Alpaca Malealpacamale@social.cologne

🌊 In September 2023, seismometers around the world detected a mysterious signal repeating every 92 seconds for nine straight days. The source: a standing wave trapped inside a Greenland fjord.

Here is what happened. A glacier in East Greenland had been thinning for years, no longer supporting the mountain slope above it. On September 16, about 25 million cubic meters of rock and ice collapsed into Dickson Fjord, triggering a tsunami with a runup height of 200 meters near the impact.

The fjord is 540 meters deep, 2.7 km wide, with walls taller than 1,800 meters. That geometry trapped the wave energy. The tsunami stabilized into a seiche, a standing wave sloshing back and forth across the fjord every 90 seconds. Each oscillation shifted millions of tons of water, loading and unloading the crust below, generating seismic waves detected globally.

The signal decayed extraordinarily slowly. It was still detectable after 9 days. A second, smaller event happened October 11 from another landslide in the same gully.

In 2025, the SWOT satellite directly observed the seiche, confirming the theory. The study published in Science calls it the first evidence of fluid sloshing persisting for days without an external driver.

The landslide was preconditioned by climate-driven glacial thinning, the first such event recorded in East Greenland.

#geology #seismology #climatechange