Mega tsunami triggered by falling mountain created a 9-day-long earthquake

Something incredible happened in Greenland in 2023, when a mountaintop collapsed into the sea, triggering a mega-tsunami about 200 metres (650 feet) tall. The giant wave was so strong that it rocked inside the narrow Dickson Fjord for nine days.

The event generated seismic waves that cut through the Earth's crust and also lasted for a whopping nine straight days.

When scientists recorded a mysterious seismic signal in 2023, they were unsure of what was happening. Instead of the frequency-rich rumble typical of earthquakes, they noticed only a monotonous hum, with only a single vibration frequency.

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An international team of scientists decided to solve the mystery. They traced the origin of the seismic signal back to the tsunami waves in Greenland. The study has been published in the journal Science.

"When we set out on this scientific adventure, everybody was puzzled and no one had the faintest idea what caused this signal," said Kristian Svennevig, a geologist at the Geological Survey of Denmark and Greenland (GEUS) and the study's lead author.

"All we knew was that it was somehow associated with the landslide. We only managed to solve this enigma through a huge interdisciplinary and international effort."

Rock and ice that could fill 10,000 Olympic-sized swimming pools had plunged into the fjord. A 200-metre-high mega-tsunami was triggered, along with a phenomenon known as a seiche.

Siche is when a wave continues to slosh around in an icy fjord back and forth. This one rocked some 10,000 times over nine days. It was 200 metres tall, the tallest wave recorded anywhere on Earth since 1980.

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It was many times higher than the tsunami waves triggered by an undersea earthquake in Indonesia in 2004, and in Japan in 2011, the authors wrote in the paper.

Stephen Hicks, Research Fellow in Computational Seismology, UCL and Kristian Svennevig, Senior Researcher, Department of Mapping and Mineral Resources, Geological Survey of Denmark and Greenland, informed that 66 other scientists from 40 institutions across 15 countries worked together to find the source of the mysterious signal.

What caused the fall?

Climate change. Study authors say that global heating had "thinned the glacier by several tens of metres, meaning that the mountain towering above it could no longer be held up."

"The landslide travelled down a very steep glacier in a narrow gully before plunging into a narrow, confined fjord," they wrote.

Scientists say that this is not the last time something like this has happened. "As permafrost on steep slopes continues to warm and glaciers continue to thin we can expect these events to happen more often and on an even bigger scale across the world's polar and mountainous regions," they said.