CRACKS
IN THE ICE - NEW INSIGHTS INTO ANTARCTIC ICE SHEET FAILURES
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Introduction:
Most
people regard the desolate expanses of polar ice as practically
unchanging and imperturbable, poetically bookending the rest
of our vibrant, blue-green world. Not so, says a new study.
According to a paper released in the latest issue of the Journal
of Glaciology, major stretches of ice shelves along Antarctic
peninsulas literally collapsed into floating splinters as
several recent warmer than normal summers took their toll.
The research adds strong evidence to the case that climate
change can have a significant impact on the condition of the
Earth’s polar caps, which in turn can play a major role in
changes to wider planetary climate and environmental conditions.
IMAGES
OF THE LARSEN ICE SHELF AND THE MECHANISMS OF CHANGE
Zooming
in for a Closer Look
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here for animation
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The
Larsen Ice Shelf is one of a number of shelves on the southernmost
continent. Looking at it from above, the region lies on the
eastern side of the northernmost peninsula, a stretch of land
pointing towards South America.
In
1995 alone, a region of ice on the Larsen Ice Shelf more than
two-thirds the size of Rhode Island disintegrated in a fierce
storm. Additional ice broke away from the rest of the shelf
in 1998. This dramatic change to so much ice is the product
of several forces acting in concert. In this visualization
we start with an overall picture of the continent and zoom
in to the specific area of study.
These
images are the product of the Landsat 7 satellite. They
are provided courtesy of NASA/USGS.
Surface
Water
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This
image shows a section of the remaining Larsen Ice Shelf. The
dark patches scattered around the white background are regions
of surface melt water, formed during the summer season. It’s
from these pools that water drained into cracks in the shelf
to form the wedges that ultimately shattered the ice. NASA’s
Landsat 7 spacecraft took this picture on February 21, 2000.
Images
courtesy: NASA/USGS
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Before
and After
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here for animation
Large
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image from 1993
Large
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image from 2000
The Larsen Ice
Shelf is one of several so-called ice shelves in Antarctica.
Although not the largest, experts consider it to be most in
jeopardy of further recession due to its comparatively northern
position. In this sequence, we see how the ice there has changed
through time, starting in December 1993 and ending in March
2000.
These images
are the product of NOAA’s AVHRR instrument, (Advanced Very
High Resolution Radiometer), flying aboard that agency’s POES
(Polar Orbiting Environmental Spacecraft) satellite.
The POES spacecraft
took the images used to create this sequence on the following
dates:
December 26,
1993, February 13, 1995, March 21, 1998, November 21, 1998,
March 2, 2000.
Images courtesy:
NOAA/NASA
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A
Process of Change: What Happened to Shatter the Ice
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here for animation
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The
mechanism that rends vast stretches of Antarctic ice from
its moorings is similar to what causes roads to crack in late
winter.
Cracks
form in the ice shelf for a number of reasons. But crevasses
often appear along the landward side of the shelf as ice moving
in glaciers grinds past features on the coast and plows into
the ice on the shelf.
As
melting water on the surface of the shelf fills in those fissures
and crevasses, pressure builds in the structure of the sheet.
That process can either increase gradually, or it can be repeated
seasonally. What happens is a gradual splintering of
a wide section of shelf, which is then ultimately rent asunder
by tides or storms.
The
process is believed to be more a function of mean summertime
temperatures, as opposed to overall annual temperatures.
Antarctica’s
ice shelves account for about two percent of all ice found
there. Experts say that advance and retreat of those shelves
usually happen in terms of decades, not individual years.
These
images are the product of the Landsat 7 satellite. They
are provided courtesy of NASA/USGS.
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A
Look at the Retreating Ice Sheet
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here for animation
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We
start this animation with a look at Antarctica’s ice pack
as it appears today. Then the scene changes to describe how
the continent likely looked at the peak of the last ice age,
nearly 20,000 years ago. As the years roll backwards in a
matter of seconds, we see just how significantly the area
can be altered as planetary conditions change.
As
the animation cycles back to the present, consider that since
the last ice age, the west Antarctic ice sheet has lost nearly
two thirds of its mass during this period, a volume of ice
sufficient to raise sea levels approximately 33 feet around
the globe.
Images
courtesy: NASA
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A
TOUR OF SEVERAL ANTARCTIC ICE SHEETS
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The
largest of the ice shelves in Antarctica is the Ross. Its
thickness varies from six hundred feet to as much as three
thousand in places; it covers an area approximately as large
as France. The Ross catches the outflow of major glaciers
and ice streams, draining ice from the continent’s interior.
Experts caution that a massive collapse of the Ross Ice Shelf
could have measurable effects on global sea levels.
This
image is the product of the Canadian Space Agency's RADARSAT
satellite. They are provided courtesy of NASA, the Canadian
Space Agency, and Ohio State University.
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LARSEN
ICE SHELF – Another comparison
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here for animation
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In
1978, scientists predicted that global warming would lead
to a disintegration of Antarctic Peninsula ice shelves. Spaceborne
data indicate that this prediction may be coming true. In
these before and after images, note the dramatic change in
the apparent shoreline. Scientists captured the first image
in using the ERS-1 satellite in 1992. As seen in the second
image, collected by RADARSAT in 1997, huge changes have come
to the coastline. Notice how the once attached expanse of
ice that was Larsen became thousands of floating shards and
icebergs, drifting out to sea.
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FIMBUL
ICE SHELF
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here for animation
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Icebergs
form when hunks of ice break away from glaciers pushing into
the ocean. Ice shelves are the edges of those glaciers, extending
out into the ocean faster than ice bergs can break off from
the edge. The Fimbul Ice Shelf has remained relatively consistent
in its appearance for the last thirty years, but researchers
are paying close attention to changes. Ice shelves are considered
to be particularly sensitive to climatic changes and scientists
have detected a marked retreat along the Antarctic Peninsula.
Note the fascinating formations along the Fimbul, believed
to be the product of glacial ice flowing over rocky outcroppings
and islands.
These
images are the product of the Canadian Space Agency's RADARSAT
satellite. They are provided courtesy of NASA, the Canadian
Space Agency, and Ohio State University.
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AMERY
ICE SHELF
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At
the mouth of the Lambert Glacier spreads the Amery Ice Shelf.
For the most part, ice shelves grow from glaciers pushing
down into the sea. They also grow from precipitation. Ice
Shelves respond to climate change faster than sheets of ice
on the ground or continental glaciers. Scientists hope that
continued study of ice shelves like Amery will help them better
understand what sorts of changes are happening to the world’s
climate in general. Of particular interest is whether observed
changes in various ice shelves are the result of natural processes
or are anthropogenic, that is, the result of actions taken
by humans.
These
images are the product of the Canadian Space Agency's RADARSAT
satellite. They are provided courtesy of NASA,
the Canadian Space Agency, and Ohio State University.
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RONNE
ICE SHELF
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The
Ronne Ice Shelf grows primarily due to a constant flow from
inland ice sheets. Where shearing stresses are greater than
the strength of the ice itself, cracks form. These cracks
ultimately widen and spread like varicose veins in the frozen
skin of the coast, only to break loose and become icebergs.
Early in the 1990’s a slab of ice the size of Delaware broke
free from this area. A recent iceberg more than 40 miles wide
now floating in the South Atlantic originated from the Ronne
Ice Shelf.
Interestingly,
as ice shelves break up into icebergs, the sea level generally
doesn’t rise. That’s because ice shelves are ostensibly floating
in the water already. That floating ice, connected to the
shore by ice sheets and glaciers, displaces a volume of water
equal to the volume of water contained in the shelf. When
a berg breaks off, or calves, there is no new water to displace.
It simply separates from shore...and goes on its way.
These
images are the product of the Canadian Space Agency's RADARSAT
satellite. They are provided courtesy of NASA, Canadian
Space Agency, and Ohio State University.
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LANDSAT
7 - KEEPING AN EYE ON EARTH'S CHANGING FACE
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here for animation
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From
an altitude of 438 miles (730 kilometers), Landsat 7 can see
surface features as small as 15 meters, providing world-wide
land resource information for a diverse range of uses. The
satellite is part of a global research effort NASA calls the
Earth Science Enterprise, which seeks to acquire a long term
understanding of the changes to our planet. Landsat 7 is the
latest in a series of satellites. It roared into orbit aboard
a Boeing Delta II rocket on April 15, 1999 from Vandenberg
Air Force Base in California. NASA officially called the first
Landsat satellite the Earth Resources Technology Satellite,
or ERTS-1, on July 23, 1972. Since then the program has continued
to pave the way in research and data acquisition techniques
about the surface of our planet.
Images
courtesy: NASA/USGS
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THE
RADARSAT SATELLITE
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here for animation
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NASA
launched the RADARSAT satellite for the Canadian Space Agency
in exchange for certain operational executions. Unlike mapping
satellites that rely on reflected sunlight or infrared readings,
RADARSAT’s Synthetic Aperture Radar (SAR) is able to penetrate
cloud cover or work in the dark of night.
Courtesy:
NASA/Canadian Space Agency
This multimedia
project is the work of a dedicated team of researchers, animators,
and media specialists. A detailed companion video to this
web site is available from NASA-TV. Below are a list of agencies,
departments, and researchers who provided expertise and data
for this production:
NASA - Goddard Space Flight Center
Scientific Visualization Studio
Television Production NASA-TV/GSFC
GSFC Studio 13
Content Preparation & Project
Production: Michael Starobin
GSFC Public Affairs Contact:
Wade Sisler
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