A 200-meter mega-tsunami sparks a global seismic mystery

A Mysterious Signal from Greenland

The east coast of Greenland rarely takes center stage. Yet one day, without any warning, seismic instruments around the world began to vibrate in unison. They recorded a slow, steady rhythm that lasted for nine full days—a pulse that rose and fell every ninety-two seconds.

This rumbling was far too faint to be felt by people, but powerful enough to shake the bedrock from Alaska all the way to Australia. This behavior was unlike that of any conventional earthquake. Scientists were quick to link this signal to Dickson Fjord in Greenland, a narrow strip of sea enclosed by cliffs 3,000 feet (about 900 meters) high on either side.

New satellite images revealed the gaping scar left by the disappearance of an entire section of the mountain. Something colossal had struck the water, setting the entire fjord in motion.

The day the mountain collapsed into the fjord

On September 16, 2023, a mass of more than 25 million cubic meters of rock and ice broke away. That’s enough to fill 10,000 Olympic-sized swimming pools. The mass plunged into the waters of Dickson Fjord, causing an impact of unprecedented violence. A gigantic wave—a mega-tsunami—formed, reaching a height of about 650 feet, or nearly 200 meters.

This wave traveled the two-mile-long corridor, bounced off the cape at the other end, and then headed back in the opposite direction. In its path, it caused about $200,000 in damage to equipment at an unoccupied research station on Ella Island. But the water did not subside after this initial assault. It began to swing from one side of the fjord to the other, a phenomenon known as a seiche.

Computer simulations later showed that the water’s surface rose as high as 30 feet (9 meters) and then fell by the same amount, at a steady rhythm. This movement exerted pressure on the seafloor, acting like a giant piston.

A Never-Before-Observed Seismic “Heartbeat”

Usually, during an earthquake, seismographs record frantic squiggles. This time, the trace was different: smooth, regular peaks, spaced one and a half minutes apart, whose intensity decreased only very slightly over nearly two weeks. Never before had a seiche produced such a persistent global signature.

This anomaly has sparked a scientific debate. A first group of modelers estimated the amplitude of the sway at about 8.5 feet (2.6 meters). A second group proposed a much higher estimate, ranging from 23 to 30 feet (7 to 9 meters). This disagreement stemmed from differing assumptions about the exact geometry of Dickson Fjord. However, both simulations agreed on one fundamental point: the phenomenon was indeed caused by the wave generated by the landslide.

Alice Gabriel, of the Scripps Institution of Oceanography at UC San Diego, highlighted the complexity of the work: “It was a major challenge to produce an accurate computer simulation of a tsunami with such a long duration.”

A Mystery Solved Through Global Collaboration

The mystery mobilized an impressive scientific task force: more than seventy researchers from forty-one different institutions. Kristian Svennevig, of the Geological Survey of Denmark and Greenland, explains: “When we embarked on this scientific adventure, everyone was baffled, and no one had the slightest idea what was causing this signal.”

“All we knew was that it was somehow associated with the landslide. We were only able to solve this mystery thanks to a massive interdisciplinary and international effort,” he added. While field teams measured the fresh gouges left by the impact on the cliffs, supercomputers recreated the avalanche’s trajectory and the fjord’s response.

Robert Anthony of the U.S. Geological Survey shared this enthusiasm: “It was exciting to work on such a puzzling problem with an interdisciplinary and international team of scientists. Ultimately, it took a wealth of geophysical observations and numerical models from researchers in many countries to piece together the puzzle and get a complete picture of what had happened.”

Climate Change: An Accelerator of Risks

How could such a disaster have occurred? Glacial ice once acted as a natural buttress, supporting the unstable slope. But warming air and ocean waters have gradually eroded this barrier. “Climate change alters what is typical on Earth, and it can trigger unusual events,” notes Alice Gabriel.

This is not an isolated incident. A similar instability triggered a deadly tsunami in Karrat Fjord in 2017, destroying eleven homes and claiming the lives of four people. Dickson Fjord, meanwhile, is located near a popular cruise route. Although no passengers were present last year, the incident highlights the growing risks associated with the rise in Arctic tourism.

In light of this new reality, authorities are now exploring options for early-warning systems. The idea is to combine satellite data streams with real-time seismic information to anticipate the danger.

SWOT: The Game-Changing Satellite

Technology is ushering in a new era for observing these remote phenomena. Conventional radar altimeters see only a thin line beneath each satellite. The SWOT (Surface Water and Ocean Topography) mission, launched in December 2022, radically changes this perspective. It maps a 30-mile-wide (approximately 48 km) swath with a resolution of 8 feet (2.4 meters).

Thomas Monahan of the University of Oxford explains: “Climate change is leading to unprecedented extremes, particularly in remote regions like the Arctic, where our ability to monitor conditions using traditional physical sensors is limited.” He continues: “SWOT represents a breakthrough in our ability to study ocean processes in areas such as fjords—places that have long posed challenges for previous satellite technologies.”

This study demonstrates how the new generation of Earth-observing satellites can transform our scientific understanding of these dynamic environments. Professor Thomas Adcock, also of Oxford, notes: “This study demonstrates how advanced satellite data can finally shed light on phenomena that have eluded us for years.” He concludes: “We are now gaining new insights into oceanic extremes such as tsunamis, storm surges, and rogue waves. To fully harness the potential of these new datasets, we will need to push the boundaries of machine learning and our understanding of ocean physics.”

Listening to the Earth to Better Anticipate Tomorrow

Building on this discovery, researchers are now combing through seismic archives in search of similar slow pulses. The goal is to uncover other natural disasters from the past that may have gone unnoticed. “This shows that there are things we still don’t understand and that we’ve never seen before,” says Carl Ebeling of the Scripps Institution.

“The essence of science is trying to answer a question we don’t know the answer to—that’s why it was so exciting to work on this,” he adds. Each new discovery will help refine the models that simulate the interaction between slope failures, fjord geometry, and water depth. The full study was published in the journals Science and Nature Communications.

Ultimately, improved forecasts could one day provide valuable minutes of warning to ships and communities in high-latitude waters. Proof that even the quietest corners of the planet deserve a close listen.

Source: earth.com

A 200-meter mega-tsunami sparks a global seismic mystery