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article imageGiant crack in Antarctica's Brunt ice shelf frees massive iceberg

By Karen Graham     Feb 27, 2021 in Environment
A giant iceberg, more than 20 times the size of Manhattan, split off from Antarctica's Brunt Ice Shelf on Friday, almost a decade after scientists with the British Antarctic Survey (BAS) first detected growth of vast cracks in the ice.
The BAS has had a presence on the Brunt ice shelf since 1956 when they set up the Halley Research Station.
The Halley station has been moved several times recently due to the threat posed by chasms and cracks in the ice, and BAS glaciologists have been expecting a big calving event for at least a decade. The 12-person team working at the station left mid-February, and the station is now closed for the Antarctic winter.
The first indication that this particular calving event would likely happen came in November 2020, when a new chasm, called the North Rift, headed towards another large chasm near the Stancomb-Wills Glacier Tongue 35 km (22 miles) away. The North Rift is the third crack in the ice shelf to become active in the last 10 years.
Image taken January 23  2019.
Image taken January 23, 2019.
NASA Earth Observatory
In February 2019, NASA Earth Observatory images showed a crack along the top of a January 23 image of the Brunt ice shelf—the so-called Halloween crack—which first appeared in late October 2016 - was continuing to grow.
At the same time, a second crack that had been stable for nearly 35 years, as seen in the center of the above image, had also started spreading northward at an accelerated rate of about 4 kilometers (2.5 miles) a year. So BAS researchers had those two cracks to keep an eye on.
A massive iceberg
But during January, the North rift pushed to the northeast at up to 1 km (0.6 miles) per day, cutting through the 150-meter (492 feet) thick floating ice shelf. The iceberg was formed when the crack widened several hundred meters in a few hours on the morning of February 26, releasing it from the rest of the floating ice shelf.
Map of Brunt ice shelf and Halley Research Station
Map of Brunt ice shelf and Halley Research Station
British Antarctic Survey
The resulting iceberg is massive - with an estimated size of about 490 square miles (1,270 square km). And depending on whether or not you live in the UK or the U.S., the iceberg is the size of the county of Bedfordshire, UK, or more than 20 times the size of Manhattan in New York.
"Although the breaking off of large parts of Antarctic ice shelves is an entirely normal part of how they work, large calving events such as the one detected at the Brunt Ice Shelf on Friday remain quite rare and exciting," Adrian Luckman, a professor at Swansea University in Wales who was tracking the shelf through satellite images in the last few weeks, told the BBC, per Live Science.
The Brunt Ice Shelf is probably the most closely monitored ice shelf on Earth. A network of 16 GPS instruments measure the deformation of the ice and report this back on a daily basis.
European Space Agency satellite imagery (Sentinel 2), TerraSAR-X, NASA Worldview satellite images, US Landsat 8 images, ground-penetrating radar, and on-site drone footage have all played critical roles in providing the basis for early warning of changes to the Brunt Ice Shelf.
More about Antarctica, Iceberg, brunt ice shelf, "North Rift" crack, Halley research station
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