The Seiche That Shook the World: How a Greenland Landslide Triggered a Global Mystery

Greenland fjord - a setting for unprecedented seismic events

Introduction: When the Earth Hums, We Listen

On September 16, 2023, nothing seemed out of the ordinary. The Arctic remained still, its vast fjords silent beneath early autumn skies. But beneath this calm surface, something extraordinary was brewing. Deep within a remote fjord in East Greenland, a massive landslide triggered a 650 ft megatsunami unlike anything seen before – one that would go on to hum for days.

Seismometers (a device used to measure and record ground vibrations caused by earthquakes, volcanic eruptions, tsunamis and other seismic waves) around the whole world, from Antarctica to the equator, picked up a low consistent vibration every 90 seconds – lasting nine whole days. Scientists were puzzled. It wasn't an earthquake, nor a typical tsunami. It was something the world had never recorded at this scale before. And it signaled not just a new geophysical event, but a new warning about our changing climate.

How It All Started

At the heart of this event was a dramatic collapse: a massive landslide that sent approximately twenty-five million cubes of rocks and ice running down a 1200 meter high mountain into the Dickson fjord in East Greenland. The impact of the landslide generated a 200 meter high tsunami, roughly twice the height of the Statue of Liberty.

Massive landslides in arctic regions are becoming more common due to climate change

What Caused the Landslide?

The evidence points clearly to climate change. The mountain didn't just fall in one day. Over recent decades, satellite and field data derived from the study show that the glacier beneath the mountain top had been thinning by up to 30 meters. The steady loss of ice weakened the support structure of the mountain top until it could no longer hold, triggering the landslide. This is just one example of how warming temperatures are destabilizing frozen regions across the globe, turning once-frozen landscapes into active geohazard zones.

What It Wasn't: Earthquakes, A Normal Tsunami and Other Suspects

At first, scientists were unsure what they were seeing. Was it an earthquake? Not quite.

"If we were to hear the vibrations of an earthquake," Dr. Stephen Hicks, a co-author of the study, explained, "it would sound like a rich orchestra of rumbles and pings. Instead, the signal from Greenland was a completely monotonous hum."

That is to say, it sounded like a piano stuck playing the same note. And crucially, no earthquakes were reported anywhere nearby.

Was it a normal tsunami? Not really.

Tsunamis typically lose energy within hours as their waves disperse across the open sea. But this one was different. After the initial impact, the wave didn't just stop. Instead, it persisted for days and even re-emerged a month later.

It was quite literally a USO (Unidentified Seismic Object) - a term adopted by the scientists in the early stages of the mystery.

It took 68 researchers, nearly a year of analysis, and a breakthrough in satellite technology to understand what had happened.

A Tsunami That Wouldn't Die

We've established that it wasn't just a normal tsunami because tsunamis disperse within hours. Well, this event continued to rage on for days, leading the scientists to believe that maybe it was maybe an unending tsunami.

Unlike traditional tsunamis that occur in the open ocean (usually caused by earthquakes or undersea volcanic eruptions), this one happened 200 km inland, in a glacially carved fjord system surrounded by unstable terrain. The complex topography of the fjord was what prevented the energy of the wave from dispersing quickly thereby trapping the energy and turning it into a seiche.

What Is A Seiche?

A seiche is a standing wave in an enclosed or partially enclosed body of water. It can be comparable to water sloshing back and forth in a bathtub. The enclosed geography of the fjord acted like a bathtub, trapping the energy of the tsunami and bouncing it back and forth.

Seiches aren't new, but they're rare and usually short lived - lasting an hour and affecting only local areas. What made this seiche exceptional was its duration, scale, and reach. It generated a monotone seismic signal every 90 seconds for 9 days and was detected as far as 5000 kilometers away.

Seiche waves trapped in enclosed water bodies can persist for extended periods

How They Figured It Out

To unravel the mystery, scientists used a combination of analytical models, numerical simulations, and satellite observations.

Initial data came from a water-level gauge in the fjord, which measured ocean tides twice a day. On September 16, it picked up an unusual spike from the tsunami. But since it recorded water height only once every 15 minutes, it missed the finer details of the wave's behavior.

Traditional satellite altimeters were also limited. These instruments don't provide continuous coverage over small areas and can only measure water elevation directly beneath their flight path, making them ineffective for observing short-lived or complex wave systems in rugged terrains like fjords.

Even a Danish military vessel, which visited the fjord three days (September 19) into the first seismic event, could not physically observe the wave.

All these could hypothesize that a seiche occurred in Greenland but, none of them could prove that a seiche occurred in Greenland.

And that's where KaRIn comes in.

Enter KaRIn: The Game Changer

The breakthrough came when Oxford researchers used a brand-new satellite launched in December 2022 by the Surface Water and Ocean Topography (SWOT) mission — KaRIn (Ka-band Radar Interferometer).

It measures the height of the Earth's surface (including the ocean) by recording how long it takes for a radar pulse to travel from a satellite to the surface of the earth and back again. KaRIn will transmit radar pulses to Earth's surface and use its two antennas to triangulate the return signals that bounce back.

KaRIn is the most advanced spaceborne radar altimeter to date. With a 10-meter-long boom and the largest antenna of its kind ever sent into space, it can detect changes in water height with unmatched precision and resolution. Crucially, it scans a 50-kilometer swath on each side of its orbit, solving the blind spot issue that plagued previous satellites. It uses high-frequency Ka-band radar waves and onboard processing to create real-time radar maps of surface water. This allowed researchers to directly observe the trapped standing waves in the fjord — confirming the presence of a long-lived seiche for the first time.

Advanced satellite radar technology like KaRIn enables unprecedented Earth observation

What caused the landslide - top view analysis

What caused the landslide - bottom view analysis

Why This Matters: Science, Safety, and Society

This was more than a curious anomaly. It's a wake-up call.

Practically, it reveals gaps in our early warning systems and natural hazard models. Arctic cruise ships often traverse these fjords, and while none were present at the time of the event, the destruction of an unoccupied military base on Ella Island — 70 kilometers from the landslide — shows how far the energy can travel. Similar events in more populated regions could be devastating.

Societally, it's a story about climate change in action. The Arctic is warming four times faster than the rest of the planet. As glaciers retreat and ice melts, more mountain slopes become unstable. These aren't isolated events — they're symptoms of a rapidly changing planet.

Works Cited