Hatching An Iceberg: Satellite Views Large Crack In Glacier
These two images of Pine Island Glacier in Antarctica show the recently discovered 25-kilometer (15-mile) long crack that scientists expect will turn into a large iceberg within the next 18 months. The views from NASA's Multi-angle Imaging SpectroRadiometer (MISR) on the Terra satellite also reveal differences in the ice sheet's surface texture, highlighting surface fractures and enabling distinction of rough crevasses from smooth blue ice.
The image data shown was acquired on December 12, 2000, during Terra orbit 5246. At left is a conventional, true-color image from the downward-looking (nadir) camera. The false-color image at right is a composite of red-band data taken by the MISR forward 60-degree, nadir, and aftward 60-degree cameras, displayed in red, green and blue, respectively.
Color variations in the true-color image at left highlight spectral differences. In the multi-angle composite, on the other hand, color variations act as a proxy for differences in the angular reflectance properties of the scene. In this representation, clouds show up as light purple. Blue to orange gradations on the surface indicate a transition in ice texture from smooth to rough.
For example, the bright orange carrot-like features are rough crevasses on the glacier's tongue. In the conventional nadir view, the blue ice labeled "rough crevasses"' and "smooth blue ice" are similarly colored, but the multi-angle composite reveals their different textures, with the smoother ice appearing dark purple instead of orange.
This could be an indicator of different mechanisms by which this ice is exposed. The multi-angle view also reveals subtle roughness variations on the frozen sea ice between the glacier and the open water in Pine Island Bay.
To the left of the 'icebergs' label are chunks of floating ice. Smaller icebergs embedded in the frozen sea ice are visible below and to the right of the label. These small icebergs are associated with dark streaks. Analysis of the illumination geometry suggests that these streaks are surface features, not shadows. Wind-driven motion and thinning of the sea ice in the vicinity of the icebergs are a possible explanation.
Recently, Robert Bindschadler, a glaciologist at the NASA Goddard Space Flight Center discovered in Landsat 7 imagery a newly-formed crack traversing the Pine Island Glacier.
This crack is visible as an off-vertical dark line in the MISR nadir view. In the multi-angle composite, the crack and other stress fractures show up very clearly in bright orange. Radar observations of Pine Island Glacier in the 1990's showed the glacier to be shrinking, and the newly discovered crack is expected to eventually lead to the calving of a major iceberg.
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Ross Ice Shelf Carves B-20
Suitland - October 8, 2000
A new iceberg, 345 square miles in area, has splintered away from Antarctic's Ross Ice Shelf in the Ross Sea, the National Ice Center in Suitland, Md., reports. Iceberg B-20 was detected on September 27 using the Defense Meteorological Satellite Program's Optical Linescan Sensor infrared imagery.