In a groundbreaking discovery, scientists have solved the enigma behind two extraordinary events that caused tremors across the globe for nine consecutive days. Their research concludes a protracted investigation aimed at tracing the seismic signals back to their origins. In September 2023, global seismometers detected unusual activity, with the Earth experiencing minor tremors every 90 seconds—a phenomenon that persisted for nine days. Remarkably, a month later, a similar occurrence unfolded, leaving scientists puzzled as conventional tectonic processes could not elucidate these anomalies.
After approximately a year of meticulous research, two independent studies published in 2024 proposed that these tremors resulted from two massive landslides in the Dickson Fjord of East Greenland. These landslides triggered colossal mega-tsunamis, creating enormous standing waves, or seiches, that oscillated within the fjord, prompting minor movements in the Earth's crust. While both studies presented compelling evidence supporting this hypothesis, some uncertainties lingered, complicating the confirmation of their findings. As Thomas Monahan, a Schmidt AI in Science fellow at the University of Oxford, noted, “there were some big uncertainties that made it difficult to fully corroborate that this was actually the root cause.”
Determined to verify these hypotheses, Monahan and his team embarked on a new study, recently published in the journal Nature Communications. They unveiled the first direct satellite observations of the seiches, establishing a definitive connection between these waves and the seismic anomalies. Utilizing data from NASA’s Surface Water Ocean Topography (SWOT) satellite, which launched in December 2022, the team was able to map water heights across 90% of Earth's surface. This satellite employs a method known as satellite altimetry, which transmits radar pulses to the Earth and measures the time it takes for the signals to bounce back.
Traditional altimeters often struggled to capture evidence of the seiches due to gaps in their observational data, especially in complex fjord regions. However, SWOT's advanced altimeter features two antennas that triangulate return signals, enabling it to capture high-resolution measurements of surface water levels. Monahan remarked, “What we’re able to get is essentially an incredibly high-resolution snapshot of what the elevation of the sea surface is doing in these complex regions.” These snapshots facilitated a clearer understanding of the fjord’s sea surface height changes during the seismic events of 2023, allowing the team to calculate the slopes of the massive waves formed.
Despite identifying the timing of the seiches with the seismic signals, the researchers needed more direct evidence to establish a definitive link. They correlated the SWOT snapshots with minor movements in the Earth's crust detected at seismic stations located thousands of miles away from the fjord. By coupling continuous seismic data with intermittent satellite observations, they successfully reconstructed the characteristics of the waves, even during periods when SWOT was inactive. This comprehensive analysis ruled out weather or tidal conditions as potential causes, ultimately concluding that the seiches were indeed the sources of the tremors.
These waves formed as a result of a glacier collapsing inward, which produced substantial landslides that, upon striking the fjord, generated massive mega-tsunamis reaching heights of approximately 200 meters, or 600 feet. Monahan noted, “This was the first time that a mega-tsunami of that nature had occurred in Eastern Greenland.” He expressed concern over this phenomenon spreading to other parts of the ice sheet, highlighting the accelerating impact of climate change in this region.
Monahan emphasized the broader implications of their findings, stating, “Climate change is a global phenomenon.” He pointed out that some of the most rapid changes are happening in the Arctic and in remote areas that may not be immediately visible. “It’s crucial to understand and quantify these changes, as they will eventually affect us where we live,” he added. The seismic waves that resonated globally serve as a stark reminder of the profound consequences of rising global temperatures.
