Iceberg Almost the Size of Chicago Set to Break Off Antarctic Ice Shelf

An iceberg that is almost as big as Chicago is about to break away from an Antarctic ice shelf. The iceberg, which will be around 500 square kilometers (193 square miles) when it breaks away, is expected to separate from the Larsen D ice shelf, which extends along the Antarctic Peninsula's east coast in the Weddell Sea.

Larsen D sits to the south of the Larsen C ice shelf, which made headlines in 2017 when an enormous iceberg broke away. Ice shelves form from ice flowing off the land that accumulates snow on top. They can be hundreds of meters thick. They help hold back the ice on land—so if an ice shelf disappears, the ice on the land would start flowing faster.

Professor Adrian Luckman, a glaciologist at the U.K.'s Swansea University, monitors the Larsen ice shelf and tweeted about the forthcoming iceberg. He said the new iceberg was "imminent" and that it "will probably take with it a much larger area of very old fast ice."

New iceberg imminent from the Larsen Ice Shelf system. This time from Larsen D, just south of Larsen C. The new iceberg will measure 500 square km, and will probably take with it a much larger area of very old fast ice (attached sea ice). Speed colours for LGBT Pride month!

— Adrian Luckman (@adrian_luckman) June 24, 2020

Fast ice is ice that is attached to the ocean bottom or shore. It is normally found over ocean shelves at the edges of continents and it does not move with winds or currents, as with other types, according to the National Snow and Ice Data Center.

Luckman monitors Antarctic ice using the European Space Agency's Copernicus Programme Sentinel-1 satellites. These use microwaves to produce images even during the Antarctic winter, allowing researchers to find rifts in the ice down to around 30 feet in width. It also lets them monitor surface velocities to identify potential iceberg calving events.

Luckman told Newsweek this latest event was a small, natural calving event and is unlikely to lead to anything significant. He said the iceberg will probably break away within a month. "I only spotted the crack a couple of weeks ago when it had just initiated, and it has already traversed nearly the whole distance to calving," he said.

"The calving of small chunks such as this are a natural part of the calving cycle of ice shelves and there is no available evidence to suggest that this event was precipitated early. On the other hand, ice shelves along the Antarctic Peninsula have been losing area at an increasing rate in recent decades as ocean and atmospheric warming has increased."

The Larsen Ice Shelf is made up of sections. Larsen A and B have both broken up, with the latter starting to disintegrate in 2002 after a Rhode Island-sized iceberg broke away from it. When the large iceberg broke away from Larsen C in 2017, there were concerns it could also be at risk of collapse. Research published in 2019 also suggested Larsen C faces the same fate as Larsen A and B.

Aerial image of the Larsen Ice Shelf in 2004. NASA