The Amery Ice Shelf is an important dynamic system responsible for
draining about 16 percent of the grounded East Antarctic ice sheet through only
2 percent of its coastline. Most of the mass input to the system occurs from
the Lambert Glacier and several other glaciers. Mass loss from the system occurs
through basal melting and iceberg calving. These images from the
Multi-angle Imaging SpectroRadiometer (MISR) portray the ice shelf front
on October 6, 2001 (top), and September 29, 2002 (bottom), and illustrate
changes that took place over the year elapsed between the two views.
Two longitudinal rifts, oriented roughly parallel to the direction of
ice flow and measuring about 25 and 15 kilometers in length, are
apparent near the seaward edge of the ice shelf. Between them, a
transverse fracture extends eastward from the base of the western rift.
This rift system is colloquially named the Amery “loose tooth.” Over the
course of the one-year interval between these two MISR images, the ice
front has advanced approximately 1.6 - 1.7 kilometers, and the
transverse fracture and a three-way fissure at the juncture of the rifts
have widened. When the transverse fracture eventually reaches the
eastern rift, a large iceberg (25 kilometers x 25 kilometers) will be released.
These false-color multi-angle composites combine red-band data from
MISRs 60-degree forward, nadir, and 60-degree aftward viewing cameras, displayed as
red, green, and blue, respectively. Different colors represent angular reflectance variations. Since generally smooth surfaces predominantly forward-scatter sunlight, these surfaces appear in shades of blue. Rough surfaces tend to backward-scatter sunlight, and these surfaces appear in shades of red or
orange. Low clouds appear bright purple, since they exhibit both forward and backward scattering. Using this technique, textural variations among ice types are revealed, and clouds can be easily distinguished from ice.
Illumination conditions on the two dates are nearly identical.
Understanding the “normal” frequency of calving events from a particular
ice shelf is necessary before it can be determined whether calving rates
are changing. As part of an effort to determine the normal rate of ice
flow and iceberg calving events, the Amery Ice Shelf front has been monitored by various remote-sensing instruments for many years. The
Amery Ice Shelf is currently considered to be about two-thirds of the way through a calving cycle. The last major calving event occurred in
the early 1960s, when a massive iceberg (measuring about 140 kilometers x 70 kilometers) was released.
The Amery “loose tooth” is the subject of a joint field experiment
during the 2002 austral summer, partially funded by NASA and undertaken by the Scripps Institution of Oceanography and the Australian Antarctic Division. The Multi-angle Imaging SpectroRadiometer observes the daylit
Earth continuously from pole to pole, and every nine days views the entire
globe between 82 degrees north and 82 degrees south latitude. The
MISR Browse Image Viewer provides access to low-resolution true-color versions of these images. These data
products were generated from a portion of the imagery acquired during Terra orbits 9579 and 14807. The panels cover an area of about 204 kilometers x 110 kilometers, and utilize data from blocks 146 to 147
within World Reference System-2 paths 127 and 128, respectively. Data
from the two orbital paths have been remapped to identical polar
projections, and were cropped to include the same geographic area.
Image courtesy NASA/GSFC/LaRC/JPL, MISR Team
Text by Clare Averill, David J. Diner (Jet Propulsion Laboratory), and Helen A. Fricker (Scripps Institution of Oceanography).