Gigantic Iceberg Nearly Smashes Into Antarctic Ice Shelf

Gigantic Iceberg Nearly Smashes Into Antarctic Ice Shelf
Iceberg A-74 and the Brunt Ice Shelf as they appeared on August 11, 2021. (Image: ESA/Sentinel-1)

After lying dormant for over half a year, the world’s second largest iceberg has finally sprung to life — and it narrowly avoided a collision that could have resulted in an even larger iceberg.

Iceberg A-74 calved from Antarctica’s Brunt Ice Shelf in late February, but it didn’t do much in the subsequent months, preferring to loiter around its birthplace in the Weddell Sea. At 1,270 square kilometres, it’s currently the second largest free-floating iceberg in existence.

The largest iceberg, A-76, broke off the Ronne Ice Shelf in May and is currently 4,320 square kilometres. Neither of these ‘bergs are to be confused with A68a, which held the title of biggest iceberg until its disintegration early this year.

Animation showing the movements of iceberg A-74 from August 9-18, 2021. (Gif: ESA/Sentinel-1) Animation showing the movements of iceberg A-74 from August 9-18, 2021. (Gif: ESA/Sentinel-1)

But the situation has changed for A-74, as ocean currents and strong winds have compelled the iceberg to broaden its horizons and leave the nest. Radar images taken by the Copernicus Sentinel-1 satellite mission from August 9 to 18 show A-74 moving south and rotating counterclockwise, as the European Space Agency explains in a statement.

As it was moving, however, A-74 nearly smashed into the Brunt Ice Shelf. And in fact, it lightly grazed and impacted the ice shelf from which it formed. The ice shelf is only 150 metres thick, and it features several prominent cracks, or rifts, including Chasm 1 (the long crack that runs vertically from the southernmost point of the ice shelf) and the Halloween crack (a newer crack that appears just above Chasm 1 in the images).

“The nose-shaped piece of the ice shelf, which is even larger than A-74 remains connected to the Brunt Ice Shelf, but barely,” Mark Drinkwater, a researcher from the ESA’s Mission Science Division, explained in the statement. “If the berg had collided more violently with this piece, it could have accelerated the fracture of the remaining ice bridge, causing it to break away.”

It’s possible that a stronger collision could’ve jostled the Brunt Ice Shelf, causing another gigantic iceberg to form. Such an iceberg would have measured 1,700 square kilometres in size, according to the ESA. A “minor impact” was reported, and the “prospective berg remains tenuously attached in the vicinity of McDonald Ice Rumples, where the ice shelf is locally grounded on the seabed,” writes ESA.

As an aside, the annotated map provided by the ESA shows the location of the Halley VI research station. Given the precarious state of the ice shelf, the modular station, which rests on skis, was moved 20 km from Chasm 1.