Climate change-induced landslide caused the earth to shake for nine days

A landslide in a remote part of Greenland triggered a megatsunami that lapped up a fjord for nine days, sending tremors through the Earth, according to new research involving researchers from UCL.

The study, published in the journalScienceconcluded that this water movement was the cause of a mysterious, global seismic signal that lasted for nine days and puzzled seismologists in September 2023.

The first event, which was invisible to the human eye, was the collapse of a 1.2 km high mountain peak into the remote Dickson Fjord below, creating a 200 m high spray and a 110 m high wave. The researchers calculated that this wave, which extended over 10 km of the fjord, had diminished to seven metres in a matter of minutes and would have been only a few centimetres high in the days that followed.

The team used a detailed mathematical model that simulated the angle of the landslide and the unusually narrow and winding fjord to show how the sloshing could continue for nine days without much energy escaping.

The model predicted that the water mass would move back and forth every 90 seconds, which matches the vibration records in the Earth’s crust around the world.

The landslide, the researchers wrote, was caused by the thinning of the glacier at the base of the mountain, which could no longer support the rock face above it. This was ultimately attributed to climate change. The landslide and tsunami were the first to be observed in eastern Greenland.

Co-author Dr Stephen Hicks from UCL Earth Sciences said: “When I first saw the seismic signal I was completely baffled. Although we know that seismometers can record a variety of sources on the Earth’s surface, such a long-lasting, globally travelling seismic wave with just one oscillation frequency had never been recorded before. This inspired me to co-lead a large team of scientists to solve the puzzle.

“Our study of this event astonishingly highlights the complex interrelationships between climate change in the atmosphere, the destabilization of glacial ice in the cryosphere, movements of water bodies in the hydrosphere, and the solid crust in the lithosphere.

“This is the first time that the sloshing of water has been recorded as vibrations through the Earth’s crust, traveling around the world and lasting for several days.”

The mysterious seismic signal – a vibration through the Earth’s crust – was detected by seismometers around the world, from the Arctic to Antarctica. It looked completely different from the frequency-rich ‘rumbles’ and ‘pings’ of earthquake recordings, because it contained only a single vibration frequency, a monotonous hum.

When the study authors first discovered the signal, they noted it as a “USO”: an unidentified seismic object.

At the same time, reports of a large tsunami in a remote fjord in northeastern Greenland reached authorities and researchers working in the area.

The researchers joined forces in a unique multidisciplinary group of 68 scientists from 40 institutes in 15 countries. They combined seismic and infrasound data, field measurements, ground-based and satellite images, and simulations of tsunami waves.

The team also used images captured by the Danish army, which entered the fjord a few days after the event to inspect the collapsed mountainside and glacier, as well as the dramatic scars left by the tsunami.

This combination of local field data and global observations allowed the team to solve the puzzle and reconstruct the extraordinary sequence of events.

Lead author Dr Kristian Svennevig from the Geological Survey of Denmark and Greenland (GEUS) said: “When we started this scientific adventure, everyone was puzzled and no one had the faintest idea what was causing this signal. We only knew that it was somehow related to the landslide. We have only managed to solve this riddle through a huge interdisciplinary and international effort.”

He added: “As a landslide scientist, an additional interesting aspect of this study is that this is the first ever landslide and tsunami observed in East Greenland, showing how climate change is already having major impacts there.”

The team estimated that 25 million cubic meters of rock and ice were washed into the fjord (enough to fill 10,000 Olympic swimming pools).

They confirmed the size of the tsunami, one of the largest in recent history, using numerical simulations and local data and images.

Seventy kilometres from the landslide, four-metre-high tsunami waves damaged a research base on Ella Ø (island) and destroyed cultural and archaeological heritage throughout the fjord system.

The fjord is on a route often used by tourist cruise ships visiting the Greenland fjords. Fortunately, there were no cruise ships near Dickson Fjord on the day of the landslide and tsunami, but if there had been, the effects of a tsunami wave of that size could have been devastating.

Mathematical models that reproduced the width and depth of the fjord at very high resolution showed how the specific rhythm of a water mass moving back and forth matched the seismic signal.

The study found that, with rapidly accelerating climate change, it is becoming more important than ever to characterize and monitor regions previously considered stable and to provide early warning of such massive landslides and tsunamis.

Co-author Thomas Forbriger of the Karlsruhe Institute of Technology said: “We would not have discovered or been able to analyse this astonishing event without networks of high-fidelity broadband seismic stations around the world, the only sensors that can truly capture such a unique signal.”

Co-author Anne Mangeney from the Université Paris Cité, Institut de Physique du Globe de Paris, said: “This unique tsunami challenged the classical numerical models we previously used to simulate only a few hours of tsunami propagation. We had to use an unprecedentedly high numerical resolution to capture this long-lasting event in Greenland. This opens up new avenues in the development of numerical methods for tsunami modelling.”