Greenland's unprecedented megatsunami caused the Earth to shake for 9 days in a row

Last September, an unprecedented event took place off the coast of Greenland. A landslide caused a 200-meter-high wall of water to rush down the Greenland fjord. Fortunately, no one was hurt, and besides scientists, almost no one noticed it, but this event caused the Earth to "shake" for another 9 days.

Seismologists around the world were baffled by signals they had never seen before. Fortunately, the research station at the mouth of Dixon Fjord, abandoned for the winter, had automatic recording devices that provided a wealth of information.

Normally, you would expect a tsunami the height of a skyscraper to get a lot of attention, but it happened near a deserted fjord in Greenland, so it didn't get the attention it deserved. Many people outside the region first heard about the event last month, almost a year after it happened, when waves were shown bouncing back and forth across the fjord for a week. These waves were perpendicular to the direction of the initial tsunami, which flowed along the fjord.

Although the wave was confined by the fjord, the Earth is a single connected system, and the energy that dissipated against the walls of the fjord caused the Earth's crust to shake so violently that it was recorded by seismometers on other continents. Dr. Christian Svennevig from the Geological Survey of Denmark and Greenland noted:

When we set out on this scientific adventure, everyone was baffled and no one had the faintest idea what was causing the signal. We only knew that it was somehow related to the landslide. We managed to solve this mystery only thanks to a huge interdisciplinary and international effort.

Earthquake movies usually show seismometers swinging wildly during a major earthquake, followed by subsidence and sometimes aftershocks an unpredictable amount of time later. The signals recorded in September 2023 looked very different, with a peak every 92 seconds that repeated over days with little loss of strength.

At first, seismologists around the world had no idea what was causing this, but they soon realized that the timing was too close to the reports of the Greenland landslide to be considered a coincidence. Then they started using satellite images and conducting research directly on the ground.

Seismic effects of similar standing waves, also known as seiches, have been observed before, but they lasted less than an hour and were only detected within 30 kilometers of the event.

Researchers believe that the landslide that caused the unprecedented tsunami was caused by climate change. Extreme temperature swings between summer and winter in Greenland used to lead to spring landslides, but global warming is making the situation worse.

Scientists estimate that 25 million cubic meters of rock and ice fell from the 600-900-meter 45-degree slope into the side channel of the fjord. The volume is almost twice the volume of the largest building in the world - the Boeing Everett factory.

It was extremely lucky that there were no ships nearby when the landslide occurred, as cruise ships often pass near this fjord.