Antarctica is shedding a colossal iceberg that could fill Lake Michigan


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

John
Sonntag/IceBridge/NASA Goddard Space Flight
Center



  • Antarctica is about to lose a very large iceberg that
    could calve “within days” or hours.
  • New satellite data shows that when it breaks off, the
    iceberg will rival the volume of Lake Michigan.
  • Human activity likely isn’t responsible for this event,
    but carbon emissions are driving other worrisome changes to
    Antarctic ice.

A widening, meandering crack in an Antarctic ice shelf is about
to birth a colossal iceberg, and new satellite imagery gives the
best sense yet of the object’s mind-boggling size.

A research group in the UK previously estimated the iceberg’s
area as roughly that of Delaware. However, Europe’s
ice-monitoring satellite CryoSat recently took the most precise
measurements to date of the ice block’s thickness, allowing
scientists to gauge its total volume.

Researchers noticed the distinctive crack in Antarctica’s Larsen
C ice shelf in 2010, but that rift has been growing rapidly since
2016. Now only a few miles of ice is keeping the chunk of ice
connected to Larsen C.

When the crack splits open, the resulting iceberg entering the
Southern Ocean will be about 620 feet (190 meters) thick and
harbor some 277 cubic miles (1,155 cubic kilometers) of ice,
Noel Gourmelen, a
glaciologist at the University of Edinburgh, said in a European
Space Agency press release.

That’s big enough to fill more than 460 million Olympic-size
swimming pools with ice, or nearly all of Lake Michigan — one of
the largest freshwater reservoirs in the world.

Gourmelen and the ESA on Wednesday released this 3D animation
that shows the iceberg’s dimensions:

And here’s Lake Michigan for a size comparison:


lake michigan google maps
The
volume of Lake Michigan and the iceberg that’s about to calve
from Antarctica’s Larsen C ice shelf are roughly
comparable.

Google Maps; Business
Insider


The iceberg could break off of Antarctica “within days,”
researchers previously said. When it does, scientists aren’t sure
what will happen.

“It could, in fact, even calve in pieces or break up shortly
after. Whole or in pieces, ocean currents could drag it north,
even as far as the Falkland Islands,” Anna Hogg, a glaciologist
at the University of Leeds, said in the ESA release. (Those
islands lie more than 1,000 miles away from Larsen C in
Antarctica.)

A block of ice thousands of years in the making


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


Antarctica’s Larsen C ice shelf is one of the largest such
shelves in the southern continent.

According to a
tweet
from the Impact of Melt on Ice Shelf Dynamics and
Stability, known as Project MIDAS, “most of the ice that calves
off fell as snow on the ice shelf in the past few hundred years,
but there’s an inner core that’s a bit older.”

Project MIDAS announced in early June that
satellite images
showed the rift had split, turned north, and
begun moving toward the Southern Ocean.

Adrian
Luckman
of Swansea University in the UK, who has been closely
monitoring Larsen C with his colleagues at Project MIDAS,
released an animation of the rift’s rapid growth (below) that
shows how it “jumps” as it
slices through bands of weak ice.
The ocean is shown in
emerald green (top right), the Larsen C ice shelf is the
light-blue patch, and the glacier behind it is depicted in white.

It’s impossible to say precisely when the rift will snap the ice
off, but recent satellite images have
upped the stakes
for the iceberg’s eventual calving.

“New Sentinel-1 data today continues to show the rift opening
more rapidly. We can’t claim iceberg calving yet, but it won’t be
long now,” Martin O’Leary, another glaciologist with Project
MIDAS, tweeted
from the group’s account
on June 30.

According to the latest
measurements
by the Sentinel-1 satellite, the crack needs to
grow just 3 more miles to cut off the giant iceberg.


berg_acceleration_June2017
Satellite images modified by Project MIDAS to show how
fast the Larsen C ice shelf is moving.

Project Midas

Are humans behind this?

When the iceberg calves, it won’t noticeably raise sea levels,
since it’s already floating in the ocean and displacing that
water. But Luckman and O’Leary said that once Larsen C loses the
iceberg, the rest of the shelf “will be less stable than it was
prior to the rift.”

Put another way: There’s a very slim chance that this break could
cause the entire Larsen C ice shelf, and an ancient glacier
behind it, to slowly disintegrate and fall into the sea.

The chaos wouldn’t be unprecedented. In 2002, a neighboring ice
shelf called Larsen B collapsed and broke up in the Southern
Ocean. This animation captures that event unfolding from January
31 through April 13, 2002:

If Larsen C and its accompanying glacial ice collapse, some
scientists think sea levels may rise by
up to 4 inches
.

However, experts on Antarctic ice say that such a loss is
exceedingly unlikely and would mostly be due to natural
processes.

“Large calving events such as this are normal processes of a
healthy ice sheet, ones that have occurred for decades,
centuries, millennia — on cycles that are much longer than a
human or satellite lifetime,” Helen Amanda Fricker, a glaciologist
who studies Antarctic ice for the Scripps Institution of
Oceanography,
wrote in The Guardian
last month. “What looks like an
enormous loss is just ordinary housekeeping for this part of
Antarctica.”

Buy Fricker warned that we shouldn’t be complacent about
climate change
, which is mostly being driven by human
activity.

“Antarctic ice shelves overall are seeing accelerated thinning,
and the ice sheet is losing mass in key sectors of Antarctica,”
she said. “Continuing losses might soon lead to an irreversible
decline.”


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