A large tabular iceberg (42 kilometers x 17 kilometers) broke off
Pine Island Glacier, West Antarctica (75°S latitude, 102°W longitude)
sometime between November 4 and 12, 2001. Images of the glacier were
acquired by the Multi-angle Imaging SpectroRadiometer (MISR) instrument
aboard NASA's Terra spacecraft. This event was preceded by the
formation of a large crack across the glacier in mid 2000. Data
gathered by other imaging instruments revealed the crack to be
propagating through the shelf ice at a rate averaging 15 meters per
day, accompanied by a slight rotation of about one percent per year
at the seaward margin of the rift.
The image set shows three views of Pine Island Glacier acquired by
MISR's vertical-viewing (nadir) camera. The first was captured in
late 2000, early in the development of the crack. The second and
third views were acquired in November 2001, just before and just
after the new iceberg broke off. The existence of the crack took
the glaciological community by surprise, and the rapid rate at
which the crack propagated was also not anticipated. Glaciologists
predicted that the rift would reach the other side of the glacier
sometime in 2002. However, the iceberg detached much sooner than
anticipated, and the last 10-kilometer segment that was still attached
to the ice shelf snapped off in a matter of days.
The animated sequence consists of 11 snapshots acquired by MISR's nadir
camera between September 16, 2000 and November 12, 2001. Due to frequent
cloud cover, the time interval between successive frames is not uniform.
The flow of the glacier, widening of the rift, and subsequent break-off
of the iceberg are evident. A "jump" in the position of the rift near
the middle of the sequence is due to a gap in image acquisition during
Antarctic winter, when the glacier was in continuous darkness.
Pine Island Glacier is the largest discharger of ice in Antarctica
and the continent's fastest moving glacier. This area of the West
Antarctic Ice Sheet is also believed to be the most susceptible to
collapse. The evolution of this glacier is therefore of great interest
to the scientific community. "The climatic significance of this calving
event is not yet clear, but is taking place in an area of Antarctica
which is experiencing rapid changes", said glaciologist Eric Rignot
of the Jet Propulsion Laboratory. Rignot points out that the grounding
line of Pine Island Glacier is retreating, the glacier is thinning
rapidly, and its ice flow is accelerating. Additionally, the sea ice
cover in front of the glacier has been decreasing steadily for several
decades. The newly hatched berg represents nearly seven years of ice
outflow from Pine Island Glacier released to the ocean in a single
event. Although this has no effect on sea level (the ice is already
afloat), it is an exceptional event for this glacier, and provides
additional evidence that this area is undergoing rapid change.
MISR was built and is managed by NASA's Jet Propulsion Laboratory,
Pasadena, CA, for NASA's Office of Earth Science, Washington, DC.
The Terra satellite is managed by NASA's Goddard Space Flight Center,
Greenbelt, MD. JPL is a division of the California Institute of
Technology.
Image credit: NASA/GSFC/LaRC/JPL, MISR Team.
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