In mid-September 2023, a mysterious event set off earthquake sensors worldwide. However, unlike typical earthquake readings, which are quick and sharp, this data showed a slow, constant wave. What surprised scientists even more was that the rumbling continued for nine consecutive days before finally subsiding.
“No one had ever seen this. We have nothing to compare it with,” said Dr. Kristian Svennevig, a geologist at the Geological Survey of Denmark and Greenland.
After a year-long investigation, an international team of 68 scientists led by Dr. Svennevig has finally traced the rumble to a landslide and tsunami in a fjord in East Greenland.
The researchers’ first lead came when they tracked down the seismic signal to the Dickson Fjord. Photographs and satellite images revealed that part of a nearby mountain and glacier had collapsed on September 16, 2023. It dumped about 33 million cubic yards of rock and ice — enough to fill 10,000 Olympic-sized swimming pools — into the fjord. This triggered a 650-foot-tall (198 m) tsunami — one of the highest in recent history. However, the massive wave alone did not fully explain why the Earth shook for so long.
"We knew there was a landslide and a tsunami... but then there was this other seismic signal that continued for nine days, and they were taken from roughly the same area, so they must be associated somehow," said Dr. Svennevig.
The missing piece of the puzzle came from a high-resolution sonar survey of the fjord conducted by the Danish Navy. The footage showed that the confined space in the narrow fjord caused the mega-tsunami wave to travel back and forth, creating a standing wave known as a seiche. With so much energy concentrated in one place, the rolling wave shook the entire Earth for nine days! This phenomenon is similar to water sloshing back and forth in a bathtub or swimming pool, but on a much larger scale.
Søren Rysgaard, Danish Army/ CC-BY-SA-2.0)
"This landslide happened about 200 km inland from the open ocean," explained Dr. Stephen Hicks, a seismologist at UCL. "And these fjord systems are really complex, so the wave couldn't dissipate its energy."
The scientists published their findings in the September 2024 issue of the journal, Science. They assert that the landslide is the result of rising temperatures in Greenland, which have melted the glacier at the base of the mountain.
“That glacier was supporting this mountain, and it got so thin that it just stopped holding it up,” said Dr. Hicks. “It shows how climate change is now impacting these areas.”
He added, "[This] is perhaps the first time a climate change event has impacted the crust beneath our feet all the world over."
Resources: Smithsonianmag.com, BBCnews.com, ScientificAmerican.com
