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Giant Iceberg Drifts out to Sea
This page contains archived content and is no longer being updated. At the time of publication, it represented the best available science. However, more recent observations and studies may have rendered some content obsolete.
Over the past two and a half years, several unusually large icebergs
have calved off of the Ross Ice Shelf in Antarctica. While some have
made their way out into the Pacific Ocean to melt, others continue to
shift and float slowly through the Ross Sea. Three of these icebergs
can be seen in the above image, taken on November 17, 2002, by the
Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s
Mainland Antarctica lies across the left side of the image. A broad
mountain range extends along its coast. The Ross Ice Shelf is the solid,
uniform white mass on the lower righthand corner of the image. The
icebergs, which broke off from the shelf, can be seen clustered together
at the southern edge of the gray, mottled Ross Sea north of the ice
Iceberg B-15A is in the center of the image about a third of the way
up into the image and resembles a tall bottle resting on the Ross Ice
Shelf. B-15A was part of the larger B-15 iceberg that was the size of
Connecticut when it calved from the Ross Ice Shelf in March 2000. Since
then, the iceberg split into several sections. B-15A is now trapped by
water currents against Ross Islandthe small, L-shaped mountainous
outcropping near the edge of the Ross Ice Shelf. Nestled between B-15A
and the island is iceberg C-16, which also calved from the ice sheet in
March 2000. Both icebergs could become dislodged when the weather
Iceberg C-19 formed most recently, breaking free of the shelf in May
of this year. The iceberg resembles a solid white finger pointing toward
Antarctica, parallel to the edge of the ice sheet and about two thirds
of the way up in the image. Two months ago C-19 sat right next to B-15A.
C-19 has been moving north away from the ice shelf slowly since. Should
the iceberg continue its trek, it may reach the Pacific, splinter, and
become a hazard for shipping in the southernmost Pacific.
Though all three of the icebergs are larger than normal, the calving
of icebergs is a natural process. Ice shelves form when slow moving
glaciers on land flow into the sea. The stiff ice stretches out on the
sea as a thick sheet. The more rapidly ice is fed to the shelves, the
larger they become. The ice shelf gradually grows thinner farther from
shore until cracks within the ice and tidal forces succeed in breaking
off pieces, creating icebergs.
The calving of these icebergs does not cause the seas to rise since
the ice shelf already floats on the sea. Scientists are concerned,
however, if the Ross Ice Shelf becomes unstable, it could disintegrate
in much the same way as the Larson B Ice Shelf did last spring. There is
evidence to suggest that ice shelves act as a brake for the glaciers
that pour into them. Without the Ross Ice Shelf in place, the glaciers
that feed it may begin pumping ice into the sea at a faster rate, which
could raise sea levels. Scientists will be watching the Ross Ice Shelf
and the loose icebergs as summer approaches in the Antarctic.