Earth was shaking. In September and October 2023, a strange seismic signal rippled across the globe, repeating every 90 seconds for nine days straight. Now, scientists have used cutting-edge satellite data to confirm the likely culprit: a massive, trapped wave called a seiche sloshing back and forth in a remote Greenland fjord. This first-ever direct observation of such a phenomenon from space opens new doors for studying extreme ocean events in hard-to-reach places.
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The Mystery of the Global Tremors
Imagine dropping a pebble in a bathtub; the water sloshes back and forth. Now, imagine a wave so big it makes the whole tub vibrate slightly. That’s a bit like what happened when seismic sensors worldwide picked up that persistent, rhythmic signal. It was like a steady pulse from the planet, and scientists were eager to understand its origin.
Initial analysis pointed towards a powerful megatsunami occurring in a remote fjord in East Greenland. Such an enclosed space could trap the wave, causing it to rebound repeatedly off the steep sides, creating a sustained seiche – essentially a standing wave in a confined body of water. The question remained: if this seiche formed in a distant fjord with no one watching, how could we be sure it was the source of the global tremors?
When a Glacier Breaks: The Trigger
The suspected cause of the Greenland megatsunami was intense glacier melt. This melt led to two massive landslides plummeting into the remote Dickson Fjord. These colossal splashes generated powerful tsunami waves. With the fjord acting like a natural basin, these waves had nowhere to dissipate into the open ocean. Instead, they bounced back and forth, potentially reaching towering heights of nearly 9 meters (about 29 feet).
Because the location was so isolated, no one was there to witness this dramatic event firsthand, not even a passing ship days later. The mystery lingered, supported only by the distant seismic echoes.
Video thumbnail showing potential visuals of a massive seiche wave in a narrow fjord.
Eyes in the Sky Confirm the Story
To solve this puzzle, scientists turned to space. A technique called altimetry uses radar from satellites to measure the precise height of the Earth’s surface, including water bodies. Most altimetry satellites don’t have the resolution or speed needed to capture the detailed movement of waves within a narrow fjord.
However, NASA’s Surface Water Ocean Topography (SWOT) satellite, launched in 2022, is different. It carries an instrument capable of measuring water height with unprecedented precision. By chance, SWOT passed over the Dickson Fjord several times during the days following the suspected tsunami events.
Using data from SWOT’s Ka-band Radar Interferometer, the researchers created elevation maps of the fjord’s water surface. The results were stunning: clear, significant variations in water height were visible, consistent with a wave around 2 meters high sloshing back and forth across the fjord.
Satellite image overlay showing measured water height changes in Greenland's Dickson Fjord during a seiche event.
Connecting the Satellite Dots to Seismic Signals
Seeing the seiche with the satellite was the crucial missing piece. The team could now compare the satellite’s direct observations of the water movement with the distant seismic data. This comparison allowed them to reconstruct the characteristics and evolution of the wave events, even for times the satellite didn’t observe.
By linking the two distinct datasets – physical measurements from space and vibration data from the ground – the scientists could confirm that the seiches observed by SWOT were indeed powerful enough and sustained enough to generate the strange, rhythmic global seismic signals. They could rule out other explanations and confidently attribute the planet’s rumbling to the trapped waves in the remote Greenland fjord.
SWOT satellite observation visualizing the water surface height in a Greenland fjord after a tsunami.
Why This Discovery Matters
This study is more than just solving a seismic mystery. It’s a powerful demonstration of how next-generation satellite technology can help us understand phenomena that were previously impossible to observe directly, especially in remote or dangerous environments.
“This study is an example of how the next generation of satellite data can resolve phenomena that has remained a mystery in the past,” notes ocean engineer Thomas Adcock. This is particularly important as climate change increases the likelihood of extreme events like glacial melting and landslides, especially in the Arctic.
engineer Thomas Monahan adds, “These extremes are changing the fastest in remote areas, such as the Arctic, where our ability to measure them using physical sensors is limited.” SWOT is proving to be a “game changer” for studying oceanic processes in complex regions like fjords. By combining satellite observations with other data, potentially using methods like machine learning, scientists can gain new insights into tsunamis, storm surges, and other powerful ocean events.
The research has been published in the journal Nature Communications. It highlights the incredible potential of space-based observation to help us understand our dynamic planet, even when the most dramatic events happen far from human eyes.
