Dickson Fjord’s 650-foot mega-tsunami: How a giant wave sent shockwaves worldwide

In September 2023, seismic stations worldwide began picking up an unusual, rhythmic signal repeating every 90 seconds. This steady pulse continued for nine days and returned briefly a month later. It was faint, unlike a typical earthquake, but strong enough to register across continents—from Alaska to Australia. Scientists were baffled. No known earthquake, volcanic eruption, or explosion had caused it.

The source was traced to the remote Dickson Fjord in East Greenland, a narrow inlet bordered by towering cliffs. But what exactly had triggered this steady, global beat?

Mega-tsunamis rock Greenland’s Fjord

The answer lay in a massive natural disaster: on 16 September 2023, more than 25 million cubic metres of rock and ice—a volume large enough to fill 10,000 Olympic swimming pools—collapsed from the mountainside into Dickson Fjord. This triggered a mega-tsunami with waves reaching 650 feet high, about half the height of the Empire State Building.

The waves surged along the two-mile-long fjord, smashing against cliffs and bouncing back, creating a prolonged sloshing motion known as a seiche. Unlike tsunamis, which travel outward as single giant waves, seiches occur when water oscillates repeatedly in an enclosed space. This ongoing motion produced rhythmic seismic pulses detectable around the world.

Seiches vs. Tsunamis: The science behind the waves

Tsunamis are caused by sudden, large displacements of water—usually due to earthquakes, landslides, or volcanic eruptions—and travel as single massive waves. Seiches, however, are standing waves formed in enclosed or semi-enclosed bodies of water, like lakes or fjords. They can be triggered by landslides or strong winds, causing the water to rock back and forth in a steady rhythm.

In Dickson Fjord, the narrow, enclosed shape trapped the tsunami energy. The waves couldn’t escape, so they kept bouncing, sending low-frequency seismic energy through the Earth’s crust for days.

How advanced satellites and machine learning solved the puzzle

The mystery was unraveled thanks to the Surface Water and Ocean Topography (SWOT) satellite, a joint NASA and French space agency mission launched in December 2022. Unlike traditional satellites that scan narrow lines, SWOT uses Ka-band Radar Interferometer (KaRIn) technology to map wide swaths of ocean surface in high detail.

Using SWOT data, researchers observed subtle water elevation changes—slopes of up to two metres—sloshing across the fjord. These shifts matched the oscillations expected from seiches.

To fill gaps, scientists employed machine learning to simulate wave behaviour over time. They also analysed crustal deformation data from sensors thousands of kilometres away, plus weather and tidal records, ruling out other causes like wind.

Lead researcher Thomas Monahan, a University of Oxford engineering student, said, “Climate change is giving rise to new, unseen extremes. These changes are happening fastest in remote areas like the Arctic, where our ability to monitor them has historically been limited.”

Climate Change: The silent driver

The underlying cause of the landslide was the rapid melting of Greenland’s glaciers. As glacier ice shrinks, it removes the natural support holding mountainsides in place. This weakening triggers massive rock and ice avalanches.

Monahan explained, “Climate change is shifting what is typical on Earth, and it can set unusual events into motion.” Past disasters, like a deadly tsunami in Karrat Fjord in 2017, show how these events can devastate local communities.

Dickson Fjord lies near popular cruise routes, raising concerns about future risks as Arctic tourism grows. Authorities are now exploring early-warning systems combining satellite data and real-time seismic monitoring to protect people in vulnerable areas.

A breakthrough in Earth monitoring

This event represents a turning point in how we observe and understand Earth’s dynamic processes. Professor Thomas Adcock of Oxford said, “This study is an example of how the next generation of satellite data can resolve phenomena that have remained a mystery in the past.”

He added, “We will be able to get new insights into ocean extremes such as tsunamis, storm surges, and freak waves. To fully harness these data, we need to innovate using both machine learning and ocean physics.”

A Danish military vessel patrolled the fjord three days after the first pulse but observed nothing unusual. This shows how even massive natural events can leave little trace without sophisticated monitoring tools.

Researchers are now searching through historical seismic data for similar slow, rhythmic pulses. Carl Ebeling from UC San Diego said, “This shows there is stuff out there that we still don’t understand and haven’t seen before.”

Every new discovery will improve forecasts of how landslides, fjord shapes, and water depth interact. The hope is to provide early warnings that could save lives in remote, high-latitude regions.

The silent, powerful waves in Greenland’s fjord prove one thing: the most isolated places on Earth are changing fast—and we must listen carefully to what they tell us.