Greenland landslide-induced tsunami produced global seismic signal that lasted 9 days
In 2023, a massive rockslide in East Greenland, driven by glacial melt, triggered a towering tsunami and a rare global seismic signal that resonated for nine days, according to a new study. The study provides insights into how climate change-induced events like glacial thinning can lead to significant geophysical phenomena with impacts extending throughout the Earth system. Due to climate change, steep slopes are increasingly vulnerable to landslides. In Arctic regions – which are undergoing the most rapid warming globally – landslides can be driven by glacial debuttressing, permafrost degradation, and altered precipitation patterns. These landslides can trigger large and destructive tsunamis, particularly when they occur in confined water bodies like fjords. Such events have been recorded around the globe, including recently in West Greenland. Large tsunamigenic landslides produce long-period seismic waves, which can be detected remotely, and their tsunamis may create standing waves known as seiches, in which water sloshes back and forth at a specific resonant frequency. Seiches create long-period, monochromatic signals useful for studying energy transfer between the hydrosphere and the solid Earth. However, current observations of seiches have been limited to short-duration effects recorded by local seismometers. What’s more, numerical modeling of tsunami-induced seiches is limited, leaving a gap in understanding of how climate change can cause cascading, hazardous feedbacks between the cryosphere, hydrosphere, and lithosphere. Here, Kristian Svnnevig and colleagues report data from a significant landslide event in East Greenland that occurred in September 2023, which produced a very-long-period seismic signal that was detected globally for nine days. The event, which was triggered by glacial thinning, led to a massive rock-ice avalanche into Dickson Fjord, generating a 200-meter-high tsunami. This tsunami stabilized into a 7-meter-high long-duration seiche with a 90-second period, which produced a 10.88 millihertz (mHz) global seismic signal that resonated for nine days. Using a variety of geophysical techniques, Svennevig et al. show that the observed seismic signal was driven by the seiche. The findings further reveal that seiches in narrow fjords can produce long-duration seismic signals without persistent external driving forces, like strong winds or storm events.
Journal
Science
Article Title
A rockslide-generated tsunami in a Greenland fjord rang the Earth for 9 days
Article Publication Date
13-Sep-2024
Climate-change-triggered landslide caused Earth to vibrate for nine days
A landslide in a remote part of Greenland caused a mega-tsunami that sloshed back and forth across a fjord for nine days, generating vibrations throughout Earth, according to a new study involving UCL (University College London) researchers
University College London
image:
From left: before (August 2023) and after (September 2023) photos of the mountain peak and glacier, taken from the fjord.
view moreCredit: Søren Rysgaard / Danish Army
A landslide in a remote part of Greenland caused a mega-tsunami that sloshed back and forth across a fjord for nine days, generating vibrations throughout Earth, according to a new study involving UCL researchers.
The study, published in the journal Science, concluded that this movement of water was the cause of a mysterious, global seismic signal that lasted for nine days and puzzled seismologists in September 2023.
The initial event, not observed by human eye, was the collapse of a 1.2km-high mountain peak into the remote Dickson Fjord beneath, causing a backsplash of water 200 metres in the air, with a wave up to 110 metres high. This wave, extending across 10km of fjord, reduced to seven metres within a few minutes, the researchers calculated, and would have fallen to a few centimetres in the days after.
The team used a detailed mathematical model, recreating the angle of the landslide and the uniquely narrow and bendy fjord, to demonstrate how the sloshing of water would have continued for nine days, with little energy able to escape.
The model predicted that the mass of water would have moved back and forth every 90 seconds, matching the recordings of vibrations travelling in the Earth’s crust all around the globe.
The landslide, the researchers wrote, was a result of the glacier at the foot of the mountain thinning, becoming unable to hold up the rock-face above it. This was ultimately due to climate change. The landslide and tsunami were the first observed in eastern Greenland.
Co-author Dr Stephen Hicks, of UCL Earth Sciences, said: “When I first saw the seismic signal, I was completely baffled. Even though we know seismometers can record a variety of sources happening on Earth’s surface, 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.”
The mysterious seismic signal – coming from a vibration through the Earth’s crust – was detected by seismometers all over the globe, from the Arctic to Antarctica. It looked completely different to frequency-rich ‘rumbles’ and ‘pings’ from earthquake recordings, as it contained only a single vibration frequency, like a monotonous-sounding hum.
When the study’s authors first discovered the signal, they made a note of it as a “USO”: unidentified seismic object.
At the same time, news of a large tsunami in a remote northeast Greenland fjord reached authorities and researchers working in the area.
The researchers joined forces in a unique multidisciplinary group involving 68 scientists from 40 institutions in 15 countries, combining seismometer and infrasound data, field measurements, on-the-ground and satellite imagery, and simulations of tsunami waves.
The team also used imagery captured by the Danish military who sailed into the fjord just days after the event to inspect the collapsed mountain-face and glacier front along with the dramatic scars left by the tsunami.
It was this combination of local field data and remote, global-scale observations that allowed the team to solve the puzzle and reconstruct the extraordinary cascading sequence of events.
Lead author Dr Kristian Svennevig, from the Geological Survey of Denmark and Greenland (GEUS), 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.”
He added: “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.”
The team estimated that 25 million cubic metres of rock and ice crashed into the fjord (enough to fill 10,000 Olympic-sized swimming pools).
They confirmed the size of the tsunami, one of the largest seen in recent history, using numerical simulations as well as local data and imagery.
Seventy kilometres away from the landslide, four-metre-high tsunami waves damaged a research base at Ella Ø (island) and destroyed cultural and archaeological heritage sites across the fjord system.
The fjord is on a route commonly used by tourist cruise ships visiting the Greenland fjords. Fortunately, no cruise ships were close to Dickson Fjord on the day of the landslide and tsunami, but if they had been, the consequences of a tsunami wave of that magnitude could have been devastating.
Mathematical models recreating the width and depth of the fjord at very high resolution demonstrated how the distinct rhythm of a mass of water moving back and forth matched the seismic signal.
The study concluded that with rapidly accelerating climate change, it will become more important than ever to characterise and monitor regions previously considered stable and provide early warning of these massive landslide and tsunami events.
Co-author Thomas Forbriger, from Karlsruhe Institute of Technology, said: “We wouldn’t have discovered or been able to analyse this amazing event without networks of high-fidelity broadband seismic stations around the world, which are the only sensors that can truly capture such a unique signal.”
Co-author Anne Mangeney, from Université Paris Cité, Institut de Physique du Globe de Paris, said: “This unique tsunami challenged the classical numerical models that we previously used to simulate just a few hours of tsunami propagation. We had to go to an unprecedentedly high numerical resolution to capture this long-duration event in Greenland. This opens up new avenues in the development of numerical methods for tsunami modelling.”
Before and after the landslide: annotated image
before (August 2023) and after (September 2023) photos of the mountain peak and glacier, taken from the fjord.
Credit
Søren Rysgaard, Danish Army
Pre- (30 minutes before) and post-landslide (7 minutes after) Planet Labs satellite image
Credit
Planet Labs
ground motion visualisation animation and simulation of tsunami and seiche
Ground motion visualisation animations showing the very long-period seismic wave propagating around the globe. The left panel shows a ground motion visualisation, showing the seismic wave from the Greenland seiche spreading out around the planet. Each circle shows the data from an individual seismic monitoring station. The right panel shows a numerical simulation of the 16 September 2023 tsunami and seiche in Dickson fjord.
Ground motion visualisation animations showing the very long-period seismic wave propagating around the globe. The left panel shows a ground motion visualisation, showing the seismic wave from the Greenland seiche spreading out around the planet. Each circle shows the data from an individual seismic monitoring station. The right panel shows a numerical simulation of the 16 September 2023 tsunami and seiche in Dickson fjord.
Credit
Music credit: Isabelle Ryder https://isabellerydermusic.weebly.com/; animation credit: Stephen Hicks; Kristian Svennevig; Alexis Marbeouf.
Music credit: Isabelle Ryder https://isabellerydermusic.weebly.com/; animation credit: Stephen Hicks; Kristian Svennevig; Alexis Marbeouf.
Drone footage following landslide showing destroyed mountain peak
Drone footage taken high above the fjord after the 16 September 2023 event showing the destroyed mountain peak and glacier.
Credit
Credit: Wieter Boone, Flanders Marine Institute.
Journal
Science
Method of Research
Computational simulation/modeling
Subject of Research
Not applicable
Article Title
A rockslide-generated tsunami in a Greenland fjord rang the Earth for 9 days
Article Publication Date
12-Sep-2024
Climate change-triggered landslide unleashes a 650-foot mega-tsunami
Wave created a seismic signal that lasted for nine days
image:
'Before' image of landslide site taken on Aug. 12, 2023
view moreCredit: Søren Rysgaard
In September 2023, scientists around the world detected a mysterious seismic signal that lasted for nine straight days. An international team of scientists, including seismologists Alice Gabriel and Carl Ebeling of UC San Diego’s Scripps Institution of Oceanography came together to solve the mystery.
A new study published today in Science provides the stunning solution: In an East Greenland fjord, a mountaintop collapsed into the sea and triggered a mega-tsunami about 200 meters (650 feet) tall. The giant wave rocked back and forth inside the narrow fjord for nine days, generating the seismic waves that reverberated through Earth’s crust, baffling scientists around the world. This rhythmic sloshing is a phenomenon known as a seiche. Fortunately, no people were hurt, but the waves destroyed some $200,000 in infrastructure at an unoccupied research station on Ella Island.
“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.”
Climate change set the stage for the landslide by melting the glacier at the base of the mountain, destabilizing the more than 25 million cubic meters (33 million cubic yards) of rock and ice – enough to fill 10,000 Olympic-sized swimming pools – that ultimately crashed into the sea. As climate change continues to melt Earth’s polar regions it could lead to an increase in large, destructive landslides such as this one.
“Climate change is shifting what is typical on Earth, and it can set unusual events into motion,” said Gabriel, whose work on this study was supported by the European Research Council, Horizon Europe, the National Science Foundation (NSF) and NASA.
When seismic monitoring networks first detected this signal in September 2023, it was puzzling for two main reasons. First, the signal looked nothing like the busy squiggle that earthquakes produce on seismographs. Instead, it oscillated with a 92-second-interval between its peaks, too slow for humans to perceive. Second, the signal stayed strong for days on end, where more common seismic events weaken more rapidly.
The global community of Earth scientists started buzzing with online discussion of what could be causing the strange seismic waves. The discussion turned up reports of a huge landslide in a remote Greenland fjord that occurred on Sept. 16, around the time the seismic signal was first detected.
To figure out if and how these two phenomena might be connected, the team, led by Kristian Svennevig of the Geological Survey of Denmark and Greenland, combined seismic recordings from around the world, field measurements, satellite imagery and computer simulations to reconstruct the extraordinary events.
The team, comprised of 68 scientists from 41 research institutions, analyzed satellite and on-the-ground imagery to document the enormous volume of rock and ice in the landslide that triggered the tsunami. They also analyzed the seismic waves to model the dynamics and trajectory of the rock-ice avalanche as it moved down the glacial gully and into the fjord.
To understand the tsunami and resulting seiche, the researchers used supercomputers to create high-resolution simulations of the events.
“It was a big challenge to do an accurate computer simulation of such a long-lasting, sloshing tsunami,” said Gabriel.
Ultimately, these simulations were able to closely match the real-world tsunami’s height as well as the long-lasting seiche’s slow oscillations.
By integrating these diverse data sources, the researchers determined that the nine-day seismic signal was caused by the massive landslide and resulting seiche within Greenland’s Dickson Fjord.
“It was exciting to be working on such a puzzling problem with an interdisciplinary and international team of scientists,” said Robert Anthony, a geophysicist with the United States Geological Survey’s Earthquake Hazards program and co-author of the study. “Ultimately, it took a plethora of geophysical observations and numerical modeling from researchers across many countries to put the puzzle together and get a complete picture of what had occurred.”
The study’s findings demonstrate the complex, cascading hazards posed by climate change in polar regions. While no people were in the area when the landslide and mega-tsunami occurred, the fjord is close to a route commonly used by cruise ships, highlighting the need to monitor polar regions as climate change accelerates. For example, a landslide in western Greenland’s Karrat Fjord in 2017 triggered a tsunami that flooded the village of Nuugaatsiaq, destroying 11 houses and killing four people.
Gabriel said the results could also inspire researchers to comb back through the seismic record to look for similar events now that scientists know what to look for. Finding more seiches could help more clearly define the conditions that give rise to the phenomenon.
“This shows there is stuff out there that we still don’t understand and haven’t seen before,” said Ebeling, who co-authored the study with support from NSF and helped manage a network of seismic sensors that detected the seiche’s vibrations. “The essence of science is trying to answer a question we don’t know the answer to – that’s why this was so exciting to work on.”
'After' image of landslide site
Image of landslide site taken on Sept. 19, 2023 following Sept. 16, 2023 event.
Credit
Danish Army
Credit
Danish Army, Joint Arctic Command
Journal
Science
Method of Research
Data/statistical analysis
Subject of Research
People
Article Title
A rockslide-generated tsunami in a Greenland fjord rang the Earth for 9 days
Article Publication Date
12-Sep-2024
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