Satellites capture spectacular formation of giant iceberg on Antarctica's Brunt Ice Shelf

Updated

It's among the most remote and hostile environments on the face of the Earth.

For months on end, the Brunt Ice Shelf, nestled on the edge of Antarctica's frozen desert near the Weddell Sea, sits in darkness.

Battered by icy winds and heavy snowfalls, it's not uncommon for temperatures on the shelf to drop well below minus 50 degrees Celsius.

Despite its isolation, the giant floating glacier is perhaps one of the most closely watched ice shelves on the planet. That's because it's home to Halley Research Station, a multi-million-dollar scientific base run by the British Antarctic Survey.

The station is well known for its work monitoring the atmosphere, which led to the discovery of the hole in the ozone layer in the 1980s. But in recent years, the station has been forced to turn some of its attention away from the sky above and instead focus on the ice floor below.

In 2013, a rift in the ice shelf, which had been dormant for more than three decades, began cracking within eyeshot of the base.

"It was on the skyline but one could definitely see the shadow of this crack," said Professor David Vaughan, director of science at the British Antarctic Survey.

"So there was a huge sense of urgency about picking up the station and moving it upstream of the crack."

The fracture in the ice, known as Chasm 1, has now grown so large that it's about to slice off a portion of the shelf twice the size of New York City.

It's as spectacular as it is formidable, but it's also giving scientists a rare look inside the mechanics involved in creating a giant iceberg.



This is the Brunt Ice Shelf as seen from NASA's Landsat 5 satellite more than 30 years ago.

From this view, the ice shelf's persistent crawl toward the Weddell Sea becomes evident.

The shelf is in a perpetual state of change, as huge build-ups of ice further inland push the glacier outwards at a rate of around 400 metres a year.

When the ice reaches the sea, two things can happen. "Either they break up immediately as icebergs that float, or in some places they can actually make the transition from what we call grounded to floating ice without breaking up," Professor Vaughan said. "When that happens we have a floating glacier which we call an ice shelf."

For decades, the Brunt Ice Shelf formed in this manner with relative stability.

It wasn't until 2010 when the first visible signs of change began to appear.

In the north-eastern corner of the shelf, a spectacular series of cracks and rifts, known as the McDonald Ice Rumples, appeared. The rumples formed as the moving ice shelf pushed over underwater bedrock.

Then in 2013, the dormant Chasm 1 began tearing.

As the crack grew, the Halley Research team was forced to scramble and move their facility further upstream of the glacier before the station was stranded on an iceberg.

The instability was amplified months later when another fracture, known as the Halloween Crack, opened up to the north.

That crack is now about 60 kilometres long.

Glaciologists say these changes are just part of the natural life cycle of an ice shelf and are not necessarily linked to climate change.

But it's still fascinating scientists around the world, who are keeping a close eye on the state of the shelf.

Even through the perpetual darkness of the winter, they are able to monitor the situation with the use of thermal imagery like this.

When the cracks meet, a 1,600-square-kilometre iceberg is expected to break away from the Brunt glacier.

It's anyone's guess when exactly that will happen; it could be days or it could be years.

"Surprisingly, the crack hasn't accelerated as the piece of remaining ice has grown narrower and narrower, which was our prediction at the beginning, that towards the end things would move much more rapidly," Professor Vaughan said.

"Over the last months, things have, if anything, slowed down a little bit and the crack appears to be progressing rather slowly."

CrackAnimation3 Source: Terra Sar-x

When it does eventually break free it will be about the same size as the D-28 iceberg, which broke away from the Amery Ice Shelf in late September.

It will be enormous, but it will still only be a fraction of the size of the biggest iceberg on record.

The B-15 iceberg, which broke away from the Ross Ice Shelf in 2000, had a whopping surface area of more than 11,000 square kilometres.

B-15 B-15 calved from the Ross Ice Shelf in 2000,

it was about 11,000km² A-68 A-68 calved from the Larsen C ice

shelf in 2017, it was almost 6,000km² Brunt

iceberg The Brunt iceberg is expected to be

around 1,600km² A-68 A-68 calved

from the

Larsen C ice

shelf in 2017,

it was

almost

6,000km² B-15 B-15 calved

from the

Ross ice

shelf in

2000, it

was about

11,000km² Brunt

iceberg The Brunt iceberg is

expected to be

around 1,600km²

Being able to watch the formation of the iceberg in such detail has been a gold mine for researchers. Not only is the imagery spectacular, it's giving scientists the chance to study how ice shelves fracture in Antarctica.

"Iceberg calving is one of those processes we don't know very much about and it's one of the biggest uncertainties that we have in ice-sheet models at the moment," said ice-shelf glaciologist Sue Cook, who's based at the University of Tasmania.

The ice-sheet models predict what happens to continents like Antarctica under different scenarios of climate change. Being able to better understand the breaking up of large ice shelves will help in the development of more accurate models for sea-level rise.

"What we're learning on the Brunt Ice Shelf around Halley, is actually helping inform us around what will happen in west Antarctica as climate changes, as more icebergs are formed and the ice begins to flow more rapidly," Professor Vaughan said.

And it just so happens the Brunt Ice Shelf is an ideal location to study these changes.

Unlike other parts of Antarctica that are feeling the impact of climate change through surface and ocean driven melting, the Brunt is in a more-stable location.

That means what is occurring on the shelf now is as close to the natural life cycle of the shelf that scientists can get.

"It is almost like a natural laboratory," Dr Cook said. "We're getting all of these dramatic stories out of west Antarctica with climate change but the Brunt isn't really affected yet, so when we're studying processes there we're getting a very pure system to study calving, it's not been interfered with by all the climate-change-plagued processes."

Using a GPS network, coupled with the satellite imagery, scientists are getting daily updates on how much the crack tip is widening, the deformation of ice around the crack and what is happening when the crack widens.

It's all valuable data that researchers, up until now, have had very few chances to capture.

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Topics: environment, science-and-technology, astronomy-space, earth-sciences, antarctica, australia

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