A wall of water taller than most skyscrapers roared through a remote Greenland fjord, yet the strangest part of the story unfolded after the splash. A NASA satellite watched the tsunami’s energy get trapped and recycled inside the landscape, while seismometers around the world listened to Earth itself hum for more than a week. What looked like a single landslide turned into a planetary experiment in how a “mega-tsunami” can behave in ways that defy intuition.
Scientists now say that this event, driven by a collapsing mountain and amplified by a warming climate, created a standing wave that bounced inside Greenland’s icy inlets and then echoed through the entire planet. I want to walk through how researchers pieced that together, what the satellites actually saw, and why this bizarre wave is forcing a rethink of tsunami risk in a hotter world.
The day a Greenland fjord exploded
The chain of events began when a huge section of rock on a peak known simply as Mountain collapsed into Greenland’s Dickson Fjord, hurling millions of tons of debris into the water in a single violent motion. That impact displaced so much seawater that it produced a 650-foot wave inside the narrow fjord, a height that rivals downtown office towers in cities like Seattle or Frankfurt. Instead of radiating cleanly out to sea, much of that energy slammed into the steep walls and side inlets of Dickson Fjord, turning the basin into a natural wave tank where the water surface heaved up and down long after the initial crest had passed.
That violent rearrangement of mass did not stay local. The sudden movement of rock and water shook the crust hard enough to send seismic waves racing through the planet, registering on instruments thousands of kilometers away. Researchers later traced those vibrations back to the same Greenland landslide, confirming that the collapse in Dickson Fjord was powerful enough to act like a moderate earthquake in its own right and to seed the strange global signal that would puzzle seismologists for days.
A global hum that lasted nine days
In September, seismologists began comparing notes about an odd pattern that had appeared on their instruments, a repeating signal that did not match the sharp spikes of a typical quake. In September, the waveforms showed a slow, rhythmic oscillation that persisted far longer than any normal aftershock sequence, as if the planet had been struck once and then left to ring like a bell. According to one detailed account, In September 2023, seismologists around the world were puzzled by this strange signal, which appeared simultaneously on stations spread across continents.
Follow up analysis showed that the Earth’s free oscillations, excited by the Greenland event, persisted for roughly nine days before finally fading into background noise. Instead of a single burst of energy, the data looked like a sustained forcing mechanism, as if something in the source region kept pumping the crust at just the right rhythm to maintain the vibrations. That mystery, why the signal lasted so long, is what pushed scientists to look beyond the initial landslide and focus on what the water itself was doing in the fjord.
The “trapped wave” that refused to die
When researchers dug deeper into the seismic records and combined them with satellite observations, they realized they were not dealing with a conventional tsunami that simply raced outward and dispersed. Instead, the geometry of the fjord and surrounding basins had created what one team described as a massive “standing wave” that became locked in place and kept oscillating for over a week. A synthesis of the work notes that the The Mystery Solved moment came when scientists identified this trapped wave as the driver of the nine day global seismic signal.
In practical terms, that meant the water in and around Dickson Fjord was sloshing back and forth at a resonant frequency, much like water in a bathtub that keeps rocking after you push it. Each cycle of that slosh shifted enough mass to tug on the solid Earth, reinforcing the planet’s own natural modes of vibration. The result was a feedback loop: the standing wave kept the ground moving, and the ground motion in turn helped sustain the oscillation, a coupled system that blurred the line between oceanography and seismology.
How NASA’s SWOT satellite caught the wave in the act
To confirm that such a standing wave really existed, scientists turned to a new generation of space based instruments designed to map the height of the ocean surface with exquisite precision. NASA’s Surface Water and Ocean Topography mission, better known as SWOT, happened to pass over Greenland shortly after the landslide and recorded a detailed snapshot of the water surface inside and around the fjord. One analysis describes how NASA used SWOT to show the shape of a wave as water piled up and dipped in a pattern that matched the expected standing oscillation.
Crucially, the SWOT data were not interpreted in isolation. Teams compared the satellite’s measurements of water height with independent readings taken under normal conditions, looking for anomalies that could only be explained by a large, coherent wave pattern. A separate technical summary notes that on Oct 17, 2023, the day after the initial rockslide and tsunami, researchers used SWOT measurement data and compared them with baseline conditions to confirm that the tsunami’s energy was effectively locked in place within the fjord system.
From fjord to planet: why the Earth “rang”
Once the standing wave was mapped, the link to the global seismic hum became easier to understand. Each time the water in Dickson Fjord surged toward one end of the basin and then retreated, it shifted billions of tons of mass over distances of several kilometers, a motion that slightly flexed the underlying crust. Repeated over many cycles, that flexing acted like a slow, rhythmic hammer, exciting the Earth’s normal modes and sending low frequency waves propagating around the globe, the same waves that seismologists had first noticed in their records.
What made this event so unusual was not just the size of the initial wave but the efficiency with which the fjord geometry trapped and recycled its energy. Instead of dissipating within hours, the oscillation persisted for nine days, long enough for the signal to be detected on instruments that usually only respond to major earthquakes. In effect, the Greenland mega-tsunami turned a remote Arctic inlet into a planetary loudspeaker, broadcasting a low, steady note that wrapped around the Earth multiple times before finally fading.
Climate change, melting ice, and the risk of repeat events
As striking as the physics are, the broader context is even more sobering. The landslide that triggered the Greenland tsunami did not happen in a vacuum, it occurred in a landscape where glaciers are retreating and permafrost is thawing, conditions that can destabilize steep slopes and make catastrophic collapses more likely. One synthesis of the research argues that climate driven changes in ice cover and ground stability helped set the stage for the Dickson Fjord failure, a point underscored in a report that ties the event to Greenland glacier melting and the resulting seiches in nearby basins.
That same report notes that the tsunami in Greenland’s Dickson Fjord reached a 200-metre-high wall of water at its peak, a figure that aligns with the 650-foot estimate from other analyses and underscores just how extreme the event was. If warming continues to undercut slopes around other glaciated fjords in places like Alaska or Patagonia, the same combination of landslide, confined basin, and resonant sloshing could repeat elsewhere, potentially closer to populated coasts and critical infrastructure.
What a tsunami really looks like from space
One of the most counterintuitive lessons from the Greenland event is that even a mega-tsunami can be almost invisible to the naked eye when viewed from orbit. Instead of a towering crest, satellites like SWOT see subtle changes in sea surface height, often less than a meter, spread over hundreds of kilometers. A recent visualization project used SWOT data to show that a tsunami’s signature in space is a broad, gently undulating pattern rather than a sharp ridge, a point highlighted in a feature explaining what a tsunami looks like from orbit, where the wave height can be less than 1.5 feet even when it is devastating onshore.
That subtlety is exactly why high resolution radar altimeters and interferometric techniques are so important. By measuring tiny differences in the time it takes radar pulses to bounce off the water surface, missions like SWOT can reconstruct the shape of a tsunami in both space and time, even when the wave is still far from land. This capability was demonstrated not only in Greenland but also in a separate case where a Satellite captured unprecedented detail of a massive Pacific tsunami that followed a magnitude 8.8 earthquake, mapping the wave’s evolution as it crossed the open ocean.
From rare coincidence to new warning tool
In Greenland, the alignment of events bordered on improbable: a massive landslide, a confined fjord that favored resonance, and a cutting edge satellite passing overhead at just the right moment. Yet that apparent coincidence is exactly what has given scientists a template for how to use space based observations in future disasters. One detailed account describes how, for the first time ever, For the Greenland event, SWOT caught the tsunami live as it was passing overhead, providing a real world test of models that had previously only been run in simulations.
That success is already feeding into efforts to integrate satellite data into operational tsunami warning systems. If missions like SWOT, Sentinel-2, and their successors can routinely detect the shape and speed of tsunami waves in the open ocean, forecasters will have a powerful cross check on seafloor pressure sensors and coastal tide gauges. In the longer term, the Greenland mega-tsunami may be remembered less for its freakish trapped wave and more for how it accelerated the use of orbital measurements as a standard part of global hazard monitoring.
A new way of listening to a restless planet
For me, the most striking aspect of the Greenland story is how it blurs the boundaries between disciplines that usually operate in separate silos. Oceanographers, seismologists, climate scientists, and satellite engineers all had to pool their tools and perspectives to understand why a single landslide could make the Earth ring for nine days. The event showed that the solid planet and its oceans are not separate systems but parts of a single, coupled machine, where a disturbance in one can reverberate through the other in unexpected ways, a point that was underscored when Jun and colleagues framed the episode as Jun identifying the cause behind the mysterious trapped wave.
It also reframes how I think about the phrase “natural disaster.” The Greenland mega-tsunami was natural in the sense that no one pushed the rock off Mountain by hand, yet the conditions that primed that slope, from glacier retreat to permafrost thaw, are tightly linked to human driven climate change. As satellites continue to sharpen our view of these events, from the Arctic to the Pacific, they are not just giving us prettier pictures of waves, they are forcing a reckoning with the ways our warming world is reshaping the physics of extreme hazards, sometimes in ways as bizarre as a tsunami that refuses to fade.
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