Glacial earthquakes are a special type of earthquake that occur in cold, icy regions. First discovered in the Northern Hemisphere more than 20 years ago, these earthquakes occur when huge chunks of ice fall from glaciers into the ocean.
Only a few have been discovered in Antarctica so far. In a new study published in Geophysical Research Letters, I present evidence of hundreds of earthquakes that occurred in Antarctica between 2010 and 2023. Most of it is the seaward edge of Thwaites Glacier, the so-called terminal glacier, which could cause sea levels to rise rapidly if it were to collapse.
recent discoveries
Glacial earthquakes occur when tall, thin icebergs fall off the edge of a glacier and into the ocean.
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When these icebergs capsize, they violently collide with their “mother” glaciers. This impact generates powerful mechanical ground vibrations, or seismic waves, that propagate thousands of kilometers from the epicenter.
What makes glacier earthquakes unique is that they do not generate high-frequency seismic waves. These waves play an important role in the detection and localization of typical seismic sources such as earthquakes, volcanoes, and nuclear explosions.
Because of this difference, glacial earthquakes have only been discovered relatively recently, even though other earthquake sources have been regularly recorded for decades.
Depends on the season
Most of the glacier earthquakes detected so far occur near the edges of glaciers in Greenland, the largest ice sheet in the Northern Hemisphere.
Glacier earthquakes in Greenland are relatively large. The largest would be similar to those caused by North Korea’s nuclear tests over the past two decades. As such, they are detected by high-quality seismic monitoring networks that operate continuously around the world.
Events in Greenland vary by season, with most occurring in late summer. It has also become more common in recent decades. This sign may be related to the faster rate of global warming in the polar regions.
elusive evidence
Antarctica is the largest ice sheet on Earth, but direct evidence of glacial earthquakes caused by capsizing icebergs there has been elusive. Most previous attempts to detect Antarctic glacier earthquakes used a worldwide network of earthquake detectors.
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However, if the magnitude of Antarctic glacier earthquakes is much smaller than the Greenland earthquake, the global network may not be able to detect them.
My new research used seismic stations in Antarctica itself to look for signs of these earthquakes. My search turned up over 360 glacier earthquake events, most of which are not yet listed in any earthquake catalogue.
The phenomena I detected were in two clusters near Thwaites Glacier and Pine Island Glacier. These glaciers are the largest contributor to sea level rise from Antarctica.
Terminus Glacier Earthquake
Thwaites Glacier is also known as Terminal Glacier. If it were to completely collapse, global sea levels could rise by 3 meters (10 feet) and collapse rapidly.
About two-thirds of the events I detected (245 of 362) occurred near the ocean edge of Thwaites. Most of these phenomena can be glacial earthquakes caused by overturning icebergs.
The strongest driver of such phenomena does not seem to be the annual fluctuations in warm temperatures that cause the seasonal behavior of Greenland glacier earthquakes.
Rather, the peak period for glacial earthquakes at Thwaites from 2018 to 2020 coincided with the period when the glacier’s ice tongue accelerated its flow toward the ocean. The acceleration period of the ice tongue was independently confirmed by satellite observations.
This increased velocity may be caused by ocean conditions, but the effects are still poorly understood.
This finding suggests that maritime states influence the stability of oceanic terminal glaciers on short-term scales. This merits further investigation to assess the potential contribution of glaciers to future sea level rise.
The second largest cluster detection occurred near Pine Island Glacier. However, these were consistently located 60 to 80 kilometers apart. [37 to 50 miles] Since it was from the water, it is unlikely to have been caused by an iceberg capsizing.
These events remain puzzling and require follow-up investigation.
The next challenge in Antarctic glacier earthquake research
Detection of glacial earthquakes associated with iceberg calving at Thwaites Glacier could help answer several important research questions. These include fundamental questions about the potential instability of Thwaites Glacier due to interactions between ocean, ice, and hard ground near the ocean-ice interface.
Better understanding may be key to resolving the current large uncertainties about projected sea level rise in the coming centuries.
This edited article is republished from The Conversation under a Creative Commons license. Read the original article.
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