Greenland's Silent Shaker Unlocking the Mystery of the 90-Second Tsunamis

Greenland's Mega Tsunamis: First Direct Observation of the Trapped Waves That Shook the World

In a remarkable scientific breakthrough, researchers have achieved the first direct observation of the "trapped waves" or seiches that resulted from mega tsunamis in Greenland. These waves, triggered by significant landslides due to glacier warming, caused a bizarre global seismic signal observed in September 2023. The findings, recently published in Nature Communications, shed light on a previously unseen phenomenon and highlight the power of advanced satellite technology in monitoring remote and rapidly changing environments.

The Mystery of the Global Seismic Signal

In September 2023, a peculiar global seismic signal was detected, repeating every 90 seconds for nine consecutive days, with a recurrence a month later. Two scientific studies proposed that these anomalies were caused by mega tsunamis originating from landslides in an East Greenland fjord, induced by the warming of an unnamed glacier.

These tsunamis were theorized to have become trapped within the fjord system, creating standing waves (seiches) that oscillated back and forth, producing the mysterious seismic signals. However, until now, no direct observations of these seiches existed to validate this theory. Even a Danish military vessel that visited the fjord shortly after the first seismic event failed to detect the wave.

Breakthrough Using Advanced Satellite Technology

Researchers from the University of Oxford have now successfully observed these elusive waves using innovative analysis techniques on satellite altimetry data. This data measures the Earth's surface height, including the ocean, by timing the travel of radar pulses from a satellite.

Conventional satellite altimeters have limitations due to observational gaps and 1D data profiles, hindering the detection of water height variations needed to spot the waves. The key to this breakthrough was the use of data from the Surface Water Ocean Topography (SWOT) satellite, launched in December 2022, which maps water height across 90% of the Earth's surface.

SWOT's Game-Changing Capabilities

At the heart of SWOT is the cutting-edge Ka-band Radar Interferometer (KaRIn) instrument. This instrument utilizes two antennas on a 10-meter boom to triangulate return signals from radar pulses, enabling highly accurate measurements of ocean and surface water levels (up to 2.5 meters resolution) along a 50-kilometer wide swath.

Key Findings and Observations:

• The KaRIn data allowed researchers to create elevation maps of the Greenland Fjord at various times after the tsunamis.
• These maps revealed clear, cross-channel slopes with height differences of up to two meters.
• The slopes occurred in opposite directions, demonstrating water movement back and forth across the channel, confirming the presence of seiches.

The researchers correlated these observations with subtle movements in Earth's crust thousands of kilometers away, allowing them to reconstruct the wave's characteristics even during periods without satellite observation. Weather and tidal conditions were also analyzed to rule out wind or tides as potential causes.

Impact and Implications

According to lead author Thomas Monahan (DPhil student, University of Oxford), "Climate change is giving rise to new, unseen extremes. These extremes are changing the fastest in remote areas, such as the Arctic, where our ability to measure them using physical sensors is limited. This study shows how we can leverage the next generation of satellite earth observation technologies to study these processes."

Co-author Professor Thomas Adcock added, "This study is an example of how the next generation of satellite data can resolve phenomena that has remained a mystery in the past. We will be able to get new insights into ocean extremes such as tsunamis, storm surges, and freak waves. However, to get the most out of these data we will need to innovate and use both machine learning and our knowledge of ocean physics to interpret our new results."

This research underscores the importance of continued investment in advanced satellite technology for monitoring and understanding our planet's changing environment, particularly in remote and vulnerable regions like Greenland. The ability to directly observe and analyze these mega tsunamis and their resulting seiches provides crucial insights into the impacts of climate change and the potential for similar events in the future.

Tags: Greenland, Dickson Fjord, Tsunami, Seismic signal, Landslide, Glacier warming, Seiches, Sentinel-2, East Greenland, Climate change

Source: https://phys.org/news/2025-06-greenland-mega-tsunamis-shook-world.html