Hundreds of iceberg quakes have been detected at the collapsed end of the Doomsday Glacier in Antarctica

Glacial earthquakes are a special type of earthquake that originate in cold and icy regions. First detected in the Northern Hemisphere more than 20 years ago, these earthquakes occur when huge chunks of ice fall from glaciers into the sea.

So far, only a very few have been found in Antarctica. In a new study soon to be published in Geophysical Research Letters, I present evidence of hundreds of such earthquakes in Antarctica between 2010 and 2023, most of them at the ocean end of Thwaites Glacier — the so-called Doomsday Glacier that could cause sea levels to rise rapidly if it collapsed.

A recent discovery

An ice quake occurs when long, thin icebergs fall from the end of a glacier into the ocean.

When these icebergs tip over, they violently collide with the “parent” glacier. The clash generates strong mechanical ground vibrations, or seismic waves, that spread thousands of kilometers from the point of origin.

What makes icequakes unique is that they do not generate any high-frequency seismic waves. These waves play a vital role in detecting and identifying typical earthquake sources, such as earthquakes, volcanoes and nuclear explosions.

Because of this difference, icequakes have only been discovered relatively recently, although other earthquake sources have been routinely documented for several decades.

Varies with the seasons

Most of the ice quakes detected so far are located near the ends of glaciers in Greenland, the largest ice sheet in the Northern Hemisphere.

Icequakes in Greenland are relatively large in magnitude. The largest are similar in size to those resulting from North Korea's nuclear tests in the past two decades. As such, they were detected by a high-quality seismic monitoring network operating continuously around the world.

Greenland events vary with the seasons, and often occur in late summer. They have also become more common in recent decades. The signs may be associated with a faster rate of global warming in the polar regions.

Elusive evidence

Although Antarctica has the largest ice sheet on Earth, direct evidence of icequakes caused by capsizing icebergs there remains elusive. Most previous attempts to detect ice quakes in Antarctica have used the global network of seismic detectors.

However, if the ice quakes in Antarctica are much smaller than those in Greenland, the global network may not be able to detect them.

In my new study, I used seismic stations in Antarctica itself to look for signs of these quakes. My search turned up more than 360 glacial seismic events, most of which are not yet included in any earthquake catalogue.

The juveniles I detected were in two clusters, near the Thwaites and Pine Island glaciers. These glaciers were the largest sources of sea level rise from Antarctica.

Earthquakes at Doomsday Glacier

Thwaites Glacier is sometimes known as Domesday Glacier. If it collapses completely, it will raise global sea levels by 3 metres, and it has the potential to collapse quickly.

About two-thirds of the events it discovered – 245 out of 362 – were located near the offshore tip of Thwaites. Most of these events are likely icequakes due to overturning of icebergs.

The strongest driver of such events does not appear to be the annual fluctuation in warm air temperatures that drives the seasonal behavior of ice quakes in Greenland.

Instead, the most prolific period of icequakes at Thwaites, between 2018 and 2020, coincides with a period of accelerated flow of the ice tongue of the glacier towards the sea. The acceleration period of the ice tongue has been independently confirmed by satellite observations.

This acceleration could be caused by ocean conditions, the effect of which is not yet well understood.

The results indicate a short-term influence of ocean states on the stability of marine glaciers. This merits further exploration to assess the potential contribution of the glacier to future sea level rise.

The second largest group of finds occurred near Pine Island Glacier. However, they were always located 60-80 km from the waterfront, so they were unlikely to have been caused by capsizing icebergs.

These events remain puzzling and require continued research.

What's next for Antarctic icequake research?

The discovery of icequakes associated with the calving of icebergs at Thwaites Glacier could help answer several important research questions. These questions include a fundamental question about the potential instability of Thwaites Glacier due to the interaction of ocean, ice and solid land near where it meets the sea.

A better understanding may hold the key to resolving the current large uncertainty about projected sea level rise over the next two centuries.

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