Mountaintop falling into sea caused mega-tsunami, shook Earth for 9 days

A new study, involving researchers from UCL, reveals that a landslide in a secluded region of Greenland triggered a massive tsunami that oscillated within a fjord for nine days, sending vibrations through the Earth.

The research determined that this prolonged water movement was responsible for a puzzling global seismic signal detected by seismologists in September 2023.

“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,” said study co-author Stephen Hick.

9-day-long disturbance

The study revealed that the initial event, unseen by humans, occurred when a 1.2km-high mountain peak collapsed into the remote Dickson Fjord in Greenland. This caused a massive backsplash of water, shooting 200 meters into the air, with a wave reaching up to 110 meters in height.

The wave, stretching across 10 kilometers of the fjord, quickly diminished to seven meters within minutes and was reduced to just a few centimeters over the following days, according to the researchers.

Using a detailed mathematical model, the team simulated the angle of the landslide and the distinct shape of the narrow, winding fjord. Their model showed how water continued sloshing for nine days, with little energy able to escape. The water’s back-and-forth movement every 90 seconds aligned with global seismic recordings of vibrations traveling through Earth’s crust.

The researchers noted that the landslide was caused by glacier thinning at the mountain’s base, which could no longer support the rock above it—a consequence of climate change. This event marked the first recorded landslide and tsunami in eastern Greenland.

USO: Unidentified seismic object

The unusual seismic signal, a vibration traveling through Earth’s crust, was detected by seismometers across the globe, from the Arctic to Antarctica. Unlike the typical “rumbles” and “pings” from earthquakes, this signal featured only a single vibration frequency, resembling a continuous, low-pitched hum.

The study’s authors initially classified it as a “USO,” or unidentified seismic object, according to the press release .

Around the same time, reports of a massive tsunami in a remote fjord in northeast Greenland reached local authorities and researchers. This prompted the formation of a unique multidisciplinary team of 68 scientists from 40 institutions across 15 countries.

They unraveled the mystery behind the seismic signal by combining data from seismometers, infrasound sensors, field studies, satellite imagery , and tsunami simulations.

One of the largest tsunamis in recent history

The research team estimated that approximately 25 million cubic meters of rock and ice—enough to fill 10,000 Olympic-sized swimming pools—plunged into the fjord, triggering the massive tsunami.

Using numerical simulations alongside local data and imagery, they confirmed that the tsunami was one of the largest recorded in recent history.

The study emphasized that as climate change accelerates, it is increasingly critical to monitor and assess regions once thought to be stable. This will help provide early warnings for potential large-scale landslides and tsunami events in the future.

The study was published in the journal Science .