Watching a Glacier Move
February 28, 2001
Antarctica may appear to be a land frozen in time, but it certainly is not still. Glaciers plow down the continent's center to the sea, icebergs snap off and crash into the ocean, and great rivers of ice snake through the ice sheet, evidence of a dynamic relationship between this remote continent and global climate. A joint NASA and Canadian Space Agency mission now provides a more comprehensive view of how the Antarctic ice sheet moves and changes and may help answer some fundamental questions about this mysterious place at the end of the world, including whether the ice sheet is advancing or retreating.
This image shows the movement of the Lambert Glacier in Antarctica. The ice velocity vectors were obtained by using RADARSAT synthetic aperture radar imagery from the 2000 Antarctic Mapping Mission. Yellow represents the areas of no motion, which are either exposed land or stationary ice. The smaller confluent glaciers have generally low velocities, shown in green, of 100-300 meters (330-980 feet) per year, which gradually increase as they flow down the rapidly changing continental slope into the upper reaches of the faster flowing Lambert Glacier.
Most of the Lambert Glacier itself has velocities between 400-800 meters (1,310-2,620 feet) per year, with a slight slowing in the middle section. As the glacier extends across Amery Ice Shelf, velocities increase to 1000-1200 meters (3,280-3,937 feet) per year as the ice sheet spreads out and thins. The ice velocities are obtained from pairs of images obtained 24 days apart, using a technique called radar interferometry. This technique enables a highly precise alignment of image pairs that provides accurate measurements of topography as well as surfaces that have changed or moved over the short time interval, including glaciers.