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Wild satellite view shows near-collision of giant A-74 iceberg in Antarctica

A series of images shows iceberg A-74 between Aug. 9 and Aug. 18, 2021.
A series of images shows iceberg A-74 between Aug. 9 and Aug. 18, 2021. (Image credit: modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)

An iceberg 20 times the size of Manhattan careened dangerously close to its parent ice shelf in Antarctica, a series of satellite photos show.

The iceberg, called A-74, calved from Antarctica's Brunt Ice Shelf earlier this year and has been sticking close to the shelf for six months due to ocean currents, according to a statement from the European Space Agency (ESA). A strong east wind in early August then pushed A-74 into a near-collision that came close to spawning a still-more-massive iceberg.

ESA tracked the iceberg using radar aboard the Copernicus Sentinel-1 spacecraft. The new images showed the berg swinging near the ice shelf, which already is weakened by severe cracks and rifts, between Aug. 9 and 18. 

Related: Watch this giant iceberg break off from Antarctica

"Had the drifting iceberg hit the unstable ice shelf with severe force, it may have triggered the release of a new 1,700 square kilometer [656 square mile]-sized iceberg," ESA officials wrote in the statement. For perspective, A-74 is roughly 490 square miles (1,270 square kilometers) in size.

Radar images are a requirement to monitor ice shelves in Antarctica, ESA added, because the region is plunged into 24-hour darkness during local winter and it can also be quite stormy or cloudy.

But the danger to the Brunt Ice Shelf continues. ESA said the glacial region threatened by A-74 is only "tenuously attached" to the seabed. Glaciologists continue to watch the formation and extension of rifts and chasms in the ice shelf, because already its unstable situation is causing problems for scientific researchers in the region.

"With the ice shelf deemed unsafe due to the encroaching cracks in 2017, the British Antarctic Survey closed their Halley VI Research Station and re-positioned it to a more secure location," ESA said, noting the researchers moved 20 miles (32 km) inland. "Halley is made up of eight interlinked pods built on skis, which allows the pods to be easily moved in case of unstable ice or new chasms forming on the ice shelf," the agency added.

For the past half-decade, the researchers have only come to Halley in the Antarctic summer due to the difficulty of predicting accelerating iceberg calving, and the difficulty of leaving the region suddenly during the frigid winter. From Halley, more than a dozen GPS monitors measure and relay information about ice deformation of the shelf. 

A-74 isn't the only major iceberg event in Antarctica in 2021. In February, another satellite photo north of Antarctica showed an "alphabet soup" of broken icebergs. The 11 pieces being tracked at that time used to belong to the world's largest iceberg, called A-68a.

The entire Antarctic region is under threat from global warming, as temperatures are up to 5 degrees Fahrenheit (3 degrees Celsius) higher in the region since the 1950s and continue to rise. That said, scientists don't think that human-induced climate change caused the calving of A-74 or another large iceberg that recently broke away from Antarctica, called A-76.

"A76 and A74 are both just part of natural cycles on ice shelves that hadn't calved anything big for decades," Laura Gerrish, a researcher at the British Antarctic Survey, wrote on Twitter. "It's important to monitor the frequency of all iceberg calving, but these are all expected for now."

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Elizabeth Howell

Elizabeth Howell is a contributing writer for Space.com who is one of the few Canadian journalists to report regularly on space exploration. She is the author or co-author of several books on space exploration. Elizabeth holds a Ph.D. from the University of North Dakota in Space Studies, and an M.Sc. from the same department. She also holds a bachelor of journalism degree from Carleton University in Canada, where she began her space-writing career in 2004. Besides writing, Elizabeth teaches communications at the university and community college level, and for government training schools. To see her latest projects, follow Elizabeth on Twitter at @howellspace.