A massive landslide triggered by climate change unleashed a 650-foot “mega-tsunami” that caused Earth to vibrate for nine days.
The seismic event in a remote part of Greenland last September saw the giant wave repeatedly slosh back and forth across a fjord – generating vibrations around the world, say scientists.
A new study, involving University College London (UCL) researchers, concluded that the movement of water was the cause of a mysterious, global seismic signal that lasted for nine days and puzzled seismologists.
The trigger, not observed by human eye, was the collapse of a 1.2km-high (nearly 4,000ft) mountain peak into the remote Dickson Fjord beneath, causing a backsplash of water 200 metres (656ft) in the air, with a wave up to 110 metres (360 ft) high.
Researchers estimated that 25 million cubic metres (882 million cubic feet) of rock and ice crashed into the fjord – enough to fill 10,000 Olympic-sized swimming pools.
They calculated that the wave, extending across six miles (10 km) of fjord, reduced to 23ft (seven metres) within a few minutes, and would have fallen to just a few centimetres in the days after.
Four-meter-high tsunami waves damaged a research base on Ella Island more than 40 miles from the landslide.
The fjord is on a route used by tourist cruise ships visiting the Greenland fjords.
But no cruise ships were close to Dickson Fjord on the day of the landslide and tsunami.
Scientists say the consequences of a tsunami wave of that magnitude could have been “devastating” if a passenger liner had been in the area.
The research team used a detailed mathematical model, recreating the angle of the landslide and the uniquely narrow and bendy fjord, to show 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 through the Earth’s crust all around the globe.
The researchers say that the landslide was a result of the glacier at the foot of the mountain thinning, becoming unable to hold up the rock-face above it.
It was ultimately due to climate change, according to the findings published in the journal Science.
Study 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 vibrations were detected by seismometers all over the world, from the Arctic to Antarctica.
Scientists say 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 research team 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 scientists working in the area.
A team of 68 scientists from 40 institutions in 15 countries teamed up to investigate.
They used images 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.
The combination of local field data and remote, global-scale observations allowed the team to solve the puzzle and reconstruct the “extraordinary” cascading sequence of events.
Study 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.”
Seismologist Professor Alice Gabriel, of University of California San Diego’s Scripps Institution of Oceanography, added: “Climate change is shifting what is typical on Earth, and it can set unusual events into motion.
“It was a big challenge to do an accurate computer simulation of such a long-lasting, sloshing tsunami.”
