In September 2023, a globally detected seismic signal sparked curiosity among scientists when it persisted for up to nine days. This signal, unlike typical earthquake waves, was traced back to a massive rockslide in Greenland’s Dickson Fjord. A multinational team of researchers, including those from the Karlsruhe Institute of Technology (KIT), set out to uncover what caused the prolonged vibrations. Their investigation revealed that the seismic signal was generated by the continuous movement of water sloshing back and forth in the fjord, following the rockslide. The study linked the rockslide to glacier thinning, a consequence of climate change.
Seismometers, which are sensitive instruments used to record ground vibrations, typically capture seismic waves from earthquakes. However, in this instance, the seismic signal detected was markedly different. It was characterized by a dominant frequency and resembled a monotonous hum that decayed slowly. According to Dr. Thomas Forbriger from KIT, this signal was detectable across the globe, and its unusual nature prompted a detailed investigation. A collaborative effort of 68 researchers from 40 institutions in 15 countries ensued. The team used seismometer data, infrasound measurements, field observations, satellite imagery, and even photos from the Danish Army to reconstruct the event. The combination of global data and local field measurements played a key role in uncovering the sequence of events that produced the signal.
The researchers’ analysis showed that a “seiche,” or standing wave, formed in the fjord after the rockslide. A seiche is a phenomenon where water oscillates in a confined basin, similar to how water moves back and forth in a bathtub. This oscillation caused the prolonged vibrations that were detected around the world. The rockslide itself occurred when a mountain peak, which had stood 1,200 meters above the fjord, collapsed into the narrow waterway. The volume of the falling debris was immense—more than 25 million cubic meters, enough to fill 10,000 Olympic-sized swimming pools. This falling mass displaced a huge amount of water, resulting in a mega-tsunami with an initial height of 200 meters. Though the massive waves lasted only a few minutes, the water continued to slosh back and forth in the fjord for days, generating the persistent seismic signal.
Calculations by the research team showed that the water in the fjord oscillated every 90 seconds, which aligned with the observed seismic waves. The special geography of Dickson Fjord allowed this oscillation to decay very slowly, making it a unique case in scientific literature. The seismic waves generated by the water’s movement were so strong that they continued to be detected at seismometers nine days later. The waves even traveled across the globe, reaching as far as Antarctica, nearly 20,000 kilometers away. Outside the fjord, four-meter-high waves caused damage to a research station and destroyed archaeological heritage sites.
The rockslide was tied to the thinning of a glacier at the foot of the mountain, a process linked to climate change. Satellite images revealed that the glacier had thinned significantly in recent decades, contributing to the mountain’s instability. This event marked the first observed rockslide and tsunami in northeastern Greenland, highlighting the increasing vulnerability of the region to the effects of climate change.
In response to this discovery, researchers plan to install more seismic instruments in Dickson Fjord to gain further insights and potentially predict future events. Given the accelerating pace of climate change, monitoring previously stable regions has become more crucial than ever. By doing so, scientists hope to provide early warnings for future landslides and tsunamis, minimizing the risks posed to both local and global communities. The unique nature of this seismic signal and its connection to climate change underscores the growing need for enhanced geological monitoring in sensitive regions.