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NASA
IMAGE REVEALS GIANT CHIP OFF THE ANTARCTIC ICE BLOCK
There appears
to be a new crack in the Antarctic's icy armor. The massive
iceberg-to-be was captured by a NASA satellite that's also
tracing hidden continental features that shape the future
of the world's largest ice sheets.
Landsat 7, a
cooperative mission between NASA and the United States Geological
Survey, Reston, VA, completed its second annual continent-wide
mapping of Antarctica last month. With its capability to see
features as small as 15 meters (50 feet) across, Landsat 7
provides the most detailed observations available of the remote
continent, many parts of which have never been mapped at this
resolution before.
"This multi-year
archive of Landsat 7 images is an invaluable investment in
research on Antarctica," says glaciologist Robert Bindschadler
of NASA's Goddard Space Flight Center, Greenbelt, MD, a member
of the Landsat 7 science team. "We only have one chance
to capture today's changes on this dynamic continent, and
with this targeted mapping strategy, we're committed to doing
that." NASA plans to conduct annual Antarctic surveys.
On January 16
Bindschadler, during his daily review of new Landsat 7 images
of Antarctica, noticed a striking feature on the Pine Island
Glacier: a thin crack more than 25 kilometers (15 miles) long,
stretching more than two-thirds of the way across the glacier.
There was no crack in a previous image 10 months earlier.
To get a fix
on when the fracture had formed and how fast it was growing,
Bindschadler contacted colleagues working with other earth-observing
sensors -- two instruments onboard NASA's Terra satellite,
the Canadian Space Agency's Radarsat, and the European Space
Agency's radar imager. By comparing observations from different
dates, the researchers were able to estimate the growth rate
of the crack and when it had formed.
"Most of
this crack formed very rapidly, in less than five weeks,"
says Bindschadler. "Right now it is growing much more
slowly, at about 13 meters (40 feet) a day. My prediction
is that the crack will result in the calving of a major iceberg
in probably less than 18 months."
Landsat 7 was
launched by NASA in April 1999 and began routine scientific
observations in June 1999. Images are archived, processed,
and distributed by the U.S. Geological Survey, which is also
responsible for day-to-day operations of the satellite.
Landsat 7 passes
over the continent 16 times a day in its nearly pole-to-pole
orbit, taking an average of 300 images each week during the
Antarctic summer (November to February) when the surface is
best illuminated with sunlight.
This year's collection
of images promises to reveal a wealth of new surface features
due to a change in the spacecraft's observing schedule. In
previous years, Landsat took images of the surface as it approached
the pole, but this year for the first time images were taken
after the spacecraft passed by the pole. The new viewing angle
changed the patterns of shadows on the uniform, white surface,
exposing subtle differences in surface topography.
When the two
years of Antarctic images taken at different sunlit angles
are combined, researchers will not only have an unprecedented
view of the ice surface, they will also be able to infer the
hidden topography of the continental bed below. Features visible
on the ice are shaped by the contours and roughness of the
underlying surface as the ice slowly moves across it.
This Landsat
7 project is part of NASA's Earth Science Enterprise, an interdisciplinary
research program dedicated to improving our understanding
of the Earth System and how it is changing due to both natural
and human-induced processes.
The formation
of an iceberg is captured by satellite for the first time.
(Under viewable images click on Quicktime movie of ice crack
over time.) Beginning with a wide shot of Antarctica using
the RADARSAT satellite, the image then zooms in and dissolves
to a Landsat 7 sequence of Pine Island Glacier. On March 6,
2000, no crack is present. By January 4, 2001 a crack had
stretched over 25 km (15 miles), more than two-thirds of the
width of Pine Island glacier.
ASTER
instrument captures the crack
Click on image to enlarge
The crack on Pine Island glacier
also as seen by the ASTER instrument, onboard the TERRA satellite.
This Dec. 12, 2000 image pans across the crack as it stretches
across the glacier. The crack is 400-500 meters across at
its widest point. On the left hand side of the image, stress
fractures in the ice are clearly seen.
Side
by side comparison of the area before and after the crack
Click on image to enlarge
Landsat
Before and After Images
Jan.
4, 2001 image
(click
on image to enlarge)
March
6, 2000 image
(click on image to enlarge)
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