Calvings cause important underwater tsunamis in polar regions | Polarjournal
Glacial calvings and collapses of entire ice walls are common in Antarctica and in polar regions in general. The resulting underwater tunamis are likely to have correspondingly more important roles than previously thought. Image: Dr Michael Wenger

On the one hand, glacier calvings are spectacular events in polar regions, but on the other hand also warning signs of the climate changes there. Especially because of the thousands of glaciers along the Antarctic coast, this tremendous natural spectacle is likely to take place there every day in many places. But to observe them, despite the quantities, one also needs a large portion of luck. That’s exactly what a British-Scottish expedition team had in 2020 when they observed a huge break-off on a glacier wall in Antarctica. But this event was also of great importance scientifically.

Between three and twenty million cubic meters of ice likely broke loose from the Williams Glacier ice wall on Anvers Island on January 21, 2020, resulting in a tsunami that caused complete mixing of the water masses in front of it. This resulted in a matching of water temperatures at different depths, which in turn led to a temporary warming of the deeper water masses. Due to the fact that such events are widespread and frequent along the Antarctic coast, they are likely to have a much more important role in the mixing of water layers, the associated release of nutrients, and also the melting events at glacier edges throughout the polar regions. This is the result of the scientific study of the calving event, published yesterday in the journal Science Advances by Professor Michael Meredith of the British Antarctic Survey and a team of British and Scottish scientists.

The video shows the massive calving (or disintegration) at Williams Glacier on Anver Island, an island off the Antarctic Peninsula. More 78,000 square meters of the glacier wall broke off in the event, causing a huge underwater tsunami that yielded important scientific findings. Video: BAS

A wide section of the glacier wall at Williams Glacier on Antarctica’s Anvers Island broke off within minutes in fornt of the crew of the former BAS research icebreaker James Clark Ross (now the Ukrainian icebreaker Noosfera) on January 21, 2020. More than 78,000 square meters of the up to 40 meter high and 4.5 kilometer long ice wall came down with a tremendous roar into the approximately 300 meter deep water and caused an underwater tsunami, which nearly completely mixed the water layers in front of it, so that in the end the water temperatures were practically the same down to a depth of 100 meters. This was shown by measurements that the team had taken before and after the event by chance. “This was remarkable to see, and we were lucky to be in the right place at the right time,” says Professor Meredith, head of the Polar Ocean Division at BAS. The study, which has now been published, was the result of the power of the tsunami that was created and the consideration that such events must frequently take place in polar regions. “Lots of glaciers end in the sea, and their ends regularly split off into icebergs. This can cause big waves at the surface but we know now it also creates waves inside the ocean.”

To investigate the frequency of such events and their importance to the polar regions as a whole, the team looked more closely at calving events at Williams Glacier. It showed that it has retreated an average of 55 meters per year over the past 70 years. Satellite data on the frequency of such large abort events also showed that in the past seven years alone, ten calving events had occurred that were equal to or greater than the one on January 21, 2020. Another 30 events were about half that size. This clearly shows that such events are frequent and will likely be more frequent, and thus underwater tsunamis will increase. “Lots of glaciers end in the sea, and their ends regularly split off into icebergs. This can cause big waves at the surface but we know now it also creates waves inside the ocean,” says Professor Meredith. “When they break, these internal waves cause the sea to mix and this affects life in the sea, how warm it is at different depths and how much ice it can melt.” With glaciers in retreat around the world, such events are likely to become even more common, as is mixing. However, since this has not even been incorporated into the impact models, the consequences are not yet foreseeable.

Dr Michael Wenger, PolarJournal

Link to study: Meredith et al (2022) Sci Adv 8 (47) : Internal tsunamigenesis and ocean mixing driven by glacier calving in Antarctica; DOI: 10.1126/sciadv.add072

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