NSF PR 00-16 - March 31, 2000
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Motion of Massive Antarctic Ice Berg Causes Another
Immense Berg to "Calve"
The gyrations of an enormous iceberg that broke free
of the Ross Ice Shelf in Antarctica last week appear
to have loosened another large iceberg, and the "calving"
of additional bergs may continue in coming weeks due
to the ebb and flow of ocean tides.
Satellite images of the new berg indicate dimensions
of about 130 kilometers (80 miles) by 20 kilometers
(12 miles). The new berg is considerably smaller at
2480 square kilometers (960 square miles) than the
piece of ice -- now designated as iceberg B-15 --
which broke off the Ross Ice Shelf earlier in March.
Satellite images also indicate that the newest berg
appears already to be breaking into several smaller
B-15 broke off the Ross Ice Shelf roughly 200 miles
east of McMurdo Station, the largest of the National
Science's Foundation's Antarctic Research Stations,
and measured about 273 kilometers (170 miles) long
by 40 kilometers (25 miles) wide. Its area of approximately
11,007 square kilometers (4,250 square miles) is roughly
equivalent to the state of Connecticut's.
NSF-supported researcher Douglas MacAyeal, of the
University of Chicago, said that his models of iceberg
behavior, based on the calving of previous large icebergs
in other areas of Antarctica, led him to conclude
correctly that B-15 was likely to collide repeatedly
with the Ross Ice Shelf and cause other large bergs
to split off.
"The tides are constantly trying to move a new iceberg
in a circular orbit," said MacAyeal. "The effect of
that motion is that the iceberg that has just calved
is like a bull in a china shop and that causes anything
else that is ready to calve to come off too."
MacAyeal said that tides and currents around Antarctica
aren't well understood, making it difficult to predict
the fate of B-15 and the newer berg that it has spawned.
But, he added, tidal motion may cause collisions that
will calve other large bergs over the next several
weeks before these two big icebergs begin to drift
away from the Ross Ice Shelf.
"The appearance of this new iceberg confirms this
dynamic," he said, "The fact is that we could be in
for more calving."
Large icebergs, similar in size to B-15 have calved
from the Ross Ice Shelf before, notably in 1956. But
MacAyeal noted that today's ability to watch the calving
of these icebergs almost as it happens through satellite
imagery is very exciting to scientists.
Matthew Lazarra, a researcher at the NSF-funded Antarctic
Meteorological Center at the University of Wisconsin,
first noticed the calving of the new iceberg while
scanning satellite photographs of B-15 and a smaller
fragment of that berg, dubbed B-16. Both B-15 and
B-16 had been obscured by cloud cover for a period
of several hours.
Lazarra said that the latest satellite images indicate
that the newest berg already appears to have broken
into as many as four smaller pieces.
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