This iceberg is perfectly rectangular—here’s why

Though it doesn't fit our typical image of icebergs, experts say the common shape has a simple explanation.

By Sarah Gibbens
Published 23 Oct 2018, 21:17 BST
Ice Bridge flight: a tabular iceberg can be seen on the right, floating among sea ice ...
Ice Bridge flight: a tabular iceberg can be seen on the right, floating among sea ice just off of the Larsen C ice shelf. The iceberg's sharp angles and flat surface indicate that it probably recently calved from the ice shelf.
Photograph by NASA Ice

In a world besieged by climate change-induced chaos and disruption, one satisfying image of order has emerged.

It's an iceberg, shared online by NASA, that appears to be in the shape of a perfect rectangle with smooth, even walls, and 90-degree angles. The iceberg sits like a giant floating traybake near the east coast of the Antarctic peninsula.

NASA's IceBridge aircraft spotted the iceberg during a routine aerial survey. Operation IceBridge is a research initiative created to better understand how the poles influence Earth's climate, and it uses a fleet of research planes to regularly collect information.

“The iceberg's sharp angles and flat surface indicate that it probably recently calved from the ice shelf,” NASA tweeted, referring to the Larsen C ice shelf.

Senior research scientist Ted Scambos with the University of Colorado at Boulder says the iceberg is in the ballpark of 40 metres (130 feet tall) and anywhere from a mile or two long.

“If you total the tons of ice [it contains], it would fill every swimming pool in California several times over,” he says, noting that it's only a small piece compared to the ice floating around Antarctica.

A slice of ice

Ice shelfs are full of fractures and fissures, explains geophysicist Kristin Poinar from the University at Buffalo. Tabular icebergs are more common than people realise.

“[Icebergs] look like these beautiful pristine white things from a distance, but if you look a little closer, they're really mangled and full of cracks,” she says.

“The Larsen C is a large ice shelf. The ice has time to spread out and become perfectly flat,” Poinar adds, so when an iceberg breaks off from a large ice shelf along an existing fissure, it looks like a large, flat rectangle. Typically, only 10 percent of an iceberg is visible above the water. As it calved, the iceberg may have been smooth and flat underneath, but ocean currents would have quickly changed it.

(The Antarctic Peninsula is heating up. Read about how the rules of life are being ripped apart.)

Eric Rignot, a research scientist at NASA's Jet Propulsion Lab and a professor at UC Irvine, agrees that Larsen C's massive size created the rectangular shape.

“The 'bergs detaching from Larsen C are so big, they look perfectly rectangular or with linear features because they were created from rifts that run across the ice shelf for hundreds of kilometres straight,” he notes. “In Greenland, you would not find these rectangular bergs so much because it is warmer, icebergs break into smaller pieces and the glaciers are smaller as well.”

Melting Antarctica

An ice shelf is a large, floating chunk of ice attached to a nearby land mass, and Larsen C is just the latest on the frontline. Larsen A collapsed in 1995, and Larsen B collapsed in 2002.

In 2017, an iceberg the size of Delaware broke off from Larsen C. The trillion-ton chunk was one of the largest ever recorded. As more ice calves from Larsen C, it makes the ice shelf less stable, and scientists fear this could cause another collapse like those seen with Larsen A and B.

The Larsen C ice shelf is just one of many climate scientists are monitoring. As climate change continues to warm temperatures at the poles, scientists are increasingly concerned that Antarctica is melting.

Poinar notes that one iceberg doesn't necessarily indicate how stable an ice shelf is.

“You can think of the shelf like a bank account,” she says. Though icebergs often calve off, a portion of that ice is replaced by snowfall.

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