Before (left) and after pictures of the mountain where a landslide caused by rocks and ice falling into a fjord caused a megatsunami. Photo / Soren Rysgaard, Danish Army
Before (left) and after pictures of the mountain where a landslide caused by rocks and ice falling into a fjord caused a megatsunami. Photo / Soren Rysgaard, Danish Army
A huge landslide last year caused a megatsunami so powerful it made the planet vibrate for nine days, a study has found.
A 1.2km-tall mountain peak in eastern Greenland collapsed and brought 25 million cubic metres of rock and ice – enough to fill 10,000 Olympic swimming pools– crashing into a remote fjord, triggering a tsunami.
The wave travelled back and forth across the Dickson fjord in September 2023, with vibrations detected around the globe from the sloshing water.
It is thought the slab of the mountain collapsed because the rock-face propping up the peak was buttressed by a glacier, which was thinning and weakened by climate change.
Scientists from UCL partnered with academics around the world as well as the Danish military to investigate the source of the mysterious vibrations, which began on September 16, 2023.
Analysis of the signals, which were picked up every 92 seconds for nine days, revealed Greenland as the source, while mathematical models recreated the landslide and its impact.
Data, as well as visible scars in the fjord, indicate the weakened glacier led to an avalanche of material down a ravine, which caused an initial splash measuring 200m high. Tsunami waves of up to 110m tall were then created, which spread rapidly along the 2.7km-wide fjord.
The tsunami reached a top speed of 169km/h and dwindled in size in a matter of minutes, before settling as a 7m tall wave, which flowed back and forth throughout the fjord for several days.
Little energy was lost because the fjord is a constrained body of water, which allowed it to form a standing wave, called a seiche, that sloshed back and forth in a regular rhythm, much like a wave in a bathtub.
Satellite imagery captures the mountain before and after the landslide.
The site is often visited by cruise ships, but was deserted at the time of the avalanche, which meant nobody was harmed.
Dr Stephen Hicks, the study’s co-author said: “When I first saw the seismic signal, I was completely baffled.
“Never before has such a long-lasting, globally travelling seismic wave, containing only a single frequency of oscillation, been recorded. This inspired me to co-lead a large team of scientists to figure out the puzzle.
“Our study of this event amazingly highlights the intricate interconnections between climate change in the atmosphere, destabilisation of glacier ice in the cryosphere, movements of water bodies in the hydrosphere, and Earth’s solid crust in the lithosphere.
“This is the first time that water sloshing has been recorded as vibrations through the Earth’s crust, travelling the world over and lasting several days.”
Dr Kristian Svennevig, the lead author from the Geological Survey of Denmark and Greenland, said: “When we set out on this scientific adventure, everybody was puzzled and no one had the faintest idea what caused this signal.
“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.
“As a landslide scientist, an additional interesting aspect of this study is that this is the first-ever landslide and tsunami observed from eastern Greenland, showing how climate change already has major impacts there.”
