A giant crack in Antarctic ice is ‘days or weeks’ from breaking off a Delaware-size iceberg


antarctica larsen c ice shelf rift crack nov 2016 john sonntag nasa gsfc.JPG
The
Larsen C ice shelf rift snaking into the
distance.

John Sonntag/IceBridge/NASA
Goddard Space Flight Center



  • A giant crack in one of Antarctica’s largest ice
    shelves is about to break off a Delaware-size block of
    ice.
  • The crack in the ice shelf, called Larsen C, has forked
    toward the Southern Ocean and is growing rapidly.
  • Scientists think a glacier behind the ice block could
    destabilize after the calving event.

An Antarctic ice shelf that has existed for thousands of years is
about to shed a 1,000-foot-thick block of ice that’s roughly the
size of Delaware.

New satellite images show that an enormous crack or rift in the
Larsen C ice shelf has suddenly forked and accelerated toward the
Southern Ocean. Scientists can’t say exactly when the rift will
snap off the block, which makes up about 10% of Larsen C’s total
area. However, Dan McGrath, a scientist with the US Geological
Survey, says it won’t be long.

“I would expect it to occur quite rapidly, within days or weeks,”
McGrath, who researches Larsen C,
told Reuters
on Thursday.

Adrian
Luckman
and Martin O’Leary, both scientists with Swansea
University in the UK, say the crack lengthened 11 miles from May
25 to May 31, and that less than that — 8 miles of ice — is all
that stands between the birth of an enormous iceberg.

“The rift tip appears also to have turned significantly towards
the ice front, indicating that the time of calving is probably
very close,” Luckman and O’Leary wrote on Wednesday in a blog post for the Impact
of Melt on Ice Shelf Dynamics and Stability project, or MIDAS.
“There appears to be very little to prevent the iceberg from
breaking away completely.”

What’s more, Luckman and O’Leary say, the larger swath of the
Larsen C ice shelf that sits behind the soon-to-calve iceberg
“will be less stable than it was prior to the rift” and may
rapidly disintegrate like a neighboring ice shelf did in 2002.
Such an event could quickly raise sea levels by several inches.

The scientists’ latest update came one day before President
Donald Trump announced his intention to
withdraw the US
from the Paris Agreement on climate change.

A growing rift


larsen c ice shelf diagram antarctica
Diti
Torterat/Wikipedia (CC BY 2.0)


Larsen C ice is the leading edge of one of the world’s largest
glacier systems. A single large crack in the ice shelf has grown
in spurts since 2010, lengthening to about 120 miles.

But sometime between January 1 and May 1, the crack
forked in two directions
. One fork continued traveling
parallel to the Southern Ocean, while the other turned northward
toward the water.

That 6-mile fork has increased by another 11 miles, leaving
precious little ice holding back a catastrophic calving event.

“When it calves, the Larsen C ice shelf will lose more than 10%
of its area to leave the ice front at its most retreated position
ever recorded,” Luckman and O’Leary wrote in a blog post
on May 1. They say that the slab’s breaking off “will
fundamentally change the landscape of the Antarctic Peninsula.”

The Larsen C ice shelf is located off of Antarctica’s prominent
peninsula and is called a shelf because it floats on the ocean.
It’s normal for ice shelves to calve big icebergs as snow
accumulation pushes old glacier ice out to sea.

However, the size of the pending Larsen C iceberg and the speed
at which it has developed has alarmed some researchers, who
suggest that the consequences of it splitting off could be huge.

An iceberg for the record books


antarctica larsen c ice shelf rift nov 2016 john sonntag nasa gsfc
A
300-foot-wide, 70-mile-long rift in Antarctica’s Larsen C ice
shelf, as seen in November 2016.

John
Sonntag/IceBridge/NASA Goddard Space Flight
Center


The piece of floating ice in question is colossal. It’s at least
1,100 feet thick at the edge — it thickens inland — and roughly
2,000 square miles. It’s destabilizing quickly, a process
accelerated by
human-caused climate change
.

Previous satellite images suggest that the crack in Larsen C
opened around 2010 and had lengthened by dozens of miles by June
2016. In November, a team of scientists in NASA’s
Operation IceBridge survey
flew over the rift and confirmed
it was at least 80
miles long
and 300 feet wide.

Then in January, MIDAS revealed that the entire block of ice had
just
12 miles of unfractured ice
. Luckman began sounding the
alarms.

“If it doesn’t go in the next few months, I’ll be amazed,” he
said in
a January 6 press release
. “It’s so close to calving that I
think it’s inevitable.”

This graphic shows the crack’s progression to May 31 using data
from the USGS’s Landsat-1 satellite and the European Space
Agency’s Sentinel-1 InSAR satellite.


larsen c ice hslef lenght may 31 2017 a luckman swansea university midas
The
state of the Larsen C ice shelf’s rift through May 31,
2017.


Courtesy
MIDAS Project/A. Luckman, Swansea
University



Other satellite images show just how quickly the ice is moving
relative to land.

In the two Sentinel-1 satellite pictures below, from February and
April and May 2017, the white, hot pink, and magenta areas show
where the ice’s surface is moving the fastest — and where the ice
block is threatening to break off.

Red and orange show relatively quick speeds, while the slowest
speeds are shown in yellow, green, and blue.


antarctica larsen c ice shelf crack midas sar rift map february april may 2017 luckman midas swansea labeled
Adrian
Luckman/MIDAS/Swansea University; Business
Insider


Luckman and O’Leary say it’s difficult to get an exact read on
the crack’s progress because it’s winter in Antarctica, making it
tough to see.

NASA’s Ice, Cloud, and Land Elevation Satellite, or ICESat, was
used to provide more current, year-round views of Antarctic ice.
But that mission ended in 2009, so researchers now have to fly
over the region to confirm estimates of the crack.

The next similar satellite, ICESat-2, isn’t
scheduled for launch until 2018. Trump’s transition team
suggested in December that the administration might
strip NASA of funding
for such earth science missions, which
date back to the formation of the space agency 59 years ago.

“Rifting of this magnitude doesn’t happen so often, so we don’t
often get a chance to study it up close,” Joe
MacGregor
, a glaciologist and geophysicist at NASA’s Goddard
Space Flight Center, previously told Business Insider in an
email. “The more we study these rifts, the better we’ll be able
to predict their evolution and influence upon the ice sheets and
oceans at large.”

NASA’s program to fly over the ice with airplanes is funded
through 2019 and (poetically) called
IceBridge
.

The big breakup

When it breaks off, the block could be the third-largest in
recorded history.

MacGregor said it would then “drift out into the Weddell Sea and
then the Southern Ocean and be caught up in the broader clockwise
… ocean circulation and then melt, which will take at least
several months, given its size.”

Computer modeling by some researchers suggests that the calving
of Larsen C’s big ice block might destabilize
the entire ice shelf, which is about 19,300
square miles
— roughly two times as large as Massachusetts —

via a kind of ripple effect
.

However, while MacGregor and Luckman acknowledge the possibility,
they haven’t expressed confidence that this will happen.

“We would expect in the ensuing months to years further calving
events, and maybe an eventual collapse — but it’s a very hard
thing to predict, and our models say it will be less stable,”
Luckman said in the January 6 release, adding that it wouldn’t
“immediately collapse or anything like that.”

However, a rapid ice-shelf collapse would not be unprecedented.

“Larsen C may eventually follow the example of its neighbor
Larsen B,” Luckman and O’Leary wrote in their blog post on
Wednesday.

In 2002, a large piece of the nearby Larsen B ice shelf snapped
off, but within a month — and quite unexpectedly — an even larger
swath of the 10,000-year-old feature behind it
rapidly disintegrated
. The rest of Larsen B may splinter off

by 2020
.

If there’s any good news about the rift in Larsen C, it’s that
the ice shelf “is already floating in the ocean, so it has
already displaced an equivalent water mass and minutely raised
sea level as a result,” MacGregor had said. In other words, when
the iceberg melts, it won’t cause the sea level to rise any
further.

The bad news is that if all of Larsen C were to collapse, the ice
it holds back could
add about 4 inches to sea levels
over the years — and it’s
just one of many major ice systems around the world
affected by climate change
.


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