Photograph by Stuart Holroyd, Alamy Stock Photo
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Emperor penguins stand on a patch of sea ice just off the Brunt Ice Shelf in Antarctica.

Photograph by Stuart Holroyd, Alamy Stock Photo

This giant chunk of ice could break off Antarctica any day

Two cracks on the Brunt Ice Shelf are creeping closer to each other. When they intersect, an iceberg twice the size of New York City will slide into the ocean.

A chunk of ice more than twice the size of New York City could break off from Antarctica’s Brunt Ice shelf essentially at any moment.

Two large cracks in the shelf have been inching further open over the past few years. When they finally intersect, a berg about 660 square miles wide and almost 500 feet thick will be released into the ocean—where it will eventually melt, joining its brethren in adding more water to the world’s oceans and pushing global sea levels a tiny bit higher.

McDonald Ice Rumples

Brunt Ice Shelf

FEB 7, 2019

OCT 2018

DEC 2017

Chasm 1

MAR 2017

3 mi

3 km

JOHN KAPPLER, NG STAFF

SOURCE: COPERNICUS SENTINEL DATA, 2019

McDonald

Ice Rumples

Brunt Ice Shelf

February 7, 2019

October 2018

December 2017

March 2017

3 mi

3 km

JOHN KAPPLER, NG STAFF

SOURCE: COPERNICUS SENTINEL DATA, 2019

It’s no surprise that the giant berg would eventually break off: The Brunt Ice Shelf is one of the most carefully monitored ice tongues in the world, because it’s the site of the Halley Research Station, a major center for the British Antarctic Survey’s research activities in the region. But no one knows exactly when the berg will dislodge.

Nor is the berg the biggest to break off Antarctic ice sheets in recent years. That prize goes to a Delaware-sized chunk (something like 2,240 square miles) that peeled off the nearby Larsen-C ice sheet in 2017. But this hunk is nothing to sneeze at.

Unlike the dramatic ice break-ups observed over the past few years on the Antarctic peninsula, though, this calving event is not likely driven by warming air or seas.

“The Brunt ice shelf is relatively far south compared to the ice shelves that have calved dramatically on the Antarctic Peninsula,” says Oliver Marsh, a glaciologist at the British Antarctic Survey in Cambridge, England, and the extra-warm air temperatures that have toasted that region haven’t had such a dramatic effect at Brunt yet. “This calving event is just part of a natural cycle.”

The first fault line on the Brunt Ice Shelf, called Chasm 1, has been in place for over 35 years (glaciologists call breaks in the ice sheet that extend all the way from surface to the ocean below “chasms,” while shallower faults are called “cracks” or “crevasses”). It remained relatively stable until 2012, when surveyors noticed that it starting to grow again, creeping across the wide tongue of ice that protruded out over the ocean. Now, it’s extending outward in fits and starts, growing by a few hundred meters each week, on average.

60°W

50°

40°

Atlantic

Ocean

MAP

AREA

60°S

South

Shetland Is.

ANTARCTICA

ANTARCTIC

PENINSULA

Larsen

Ice

LOCATION OF

CRACKING

Shelf

Neumeyer III

Germany

Weddell

Sea

Riiser-Larsen

Ice Shelf

Brunt

Ice Shelf

Halley

U.K.

SANAE IV

S. Africa

Ronne

Ice Shelf

ELLSWORTH

LAND

COATS LAND

Research Station

Vinson

Massif

500 mi

16,067 ft

500 km

80°

JOHN KAPPLER, NG STAFF

60°

50°

40°

30°

SOUTH

SHETLAND IS.

Atlantic

Ocean

MAP

AREA

20°

ANTARCTICA

70°W

ANTARCTIC

PENINSULA

Larsen

Ice

Shelf

Alexander

Island

LOCATION OF

CRACKING

Neumeyer III

Germany

Riiser-Larsen

Ice Shelf

Weddell

Sea

70°S

70°

Seal Bay

Lyddan

Brunt

Ice Shelf

Island

Aboa

Finland

Halley

U.K.

SANAE IV

S. Africa

Svea

Sweden

Ronne

Ice Shelf

Ellsworth

land

Belgrano II Argentina

COATS LAND

Kohnen

Germany

Filchner

Vinson

Massif

Ice Shelf

16,067 ft

Research Station

250 mi

ANTARCTICA

250 km

JOHN KAPPLER, NG STAFF

80°

80°

The second break point, near the top of the image and first observed in 2016, is known as the Halloween crack. The crack is upstream from a set of crinkles, visible from the satellite photos, called the McDonald Ice Rumples. The rumples form when the bottom of the ice shelf, which flows downhill toward the ocean like very slow putty, runs up against an underwater ridge. That ridge pins the ice in place and slows its flow, forcing ice upstream to pile up, fold, crinkle, and sometimes crack.

The end of Chasm 1 is currently about 2.5 miles away from the ice rumples. Sooner or later, the two cracks are likely to intersect. When they do, a monster berg will begin its slow float away from the continent. Alternatively, says Marsh, the stresses on the ice shelf could force Chasm 1 to take a turn toward the ocean. The overall result would eventually be the same—that a berg breaks off—but the timeline for that break-up would change.