![]() For 21 years-since the last time an iceberg calved from the Ronne Ice Shelf-melting has taken a toll on the exposed front edge. Notice that the seaward edge appears lower. The green and purple beams reveal the more typical profile of a tabular iceberg. As “fast” flowing ice pushed past the rocky ice-covered peninsula, powerful stresses caused the ice to crumple. The irregular shape was created when the berg was still attached to the ice shelf and flowing through a zone known as a shear margin. Notice the jagged texture of the ice where the blue beam clips the berg’s western edge. The beams first pass over relatively flat open water before reaching the leading edge of the iceberg, where the elevation profiles begin to differ. The radar image was acquired on May 18, 2021, just 20 hours after ICESat-2 passed over. The data have been overlaid on an image of the iceberg acquired with the synthetic aperture radar (SAR) on the Copernicus Sentinel-1A satellite (operated by the European Space Agency). The laser light is actually bright green, but the beams are represented here in blue, green, and purple to better differentiate the elevation data derived from each one. The image shows the elevation data acquired by three different ATLAS laser beams as the satellite passed over the new iceberg on May 17, 2021. From this information scientists can derive the height of the surface hit by the photon. ATLAS is a photon-counting lidar that sends pulses of laser light toward Earth and precisely times each photon’s round-trip journey as it bounces off a surface and returns to the sensor. The profile above was acquired with the Advanced Topographic Laser Altimeter System (ATLAS) on NASA’s Ice, Cloud, and land Elevation Satellite 2 (ICESat-2). “We’re not used to its particular combination of strength, brittleness, and bendy-ness.” “Ice is a somewhat strange material,” said Ted Scambos, a research glaciologist at the University of Colorado. Iceberg A-76 represents a classic tabular iceberg, but as the elevation profile above shows, even this picture-perfect berg is not perfectly flat. The largest are usually tabular icebergs, named for their table-like shape with steep sides and large, flat tops. When the berg calved from Antarctica’s Ronne Ice Shelf in May 2021, it became the largest iceberg floating anywhere in the world.Īntarctica’s ice shelves are famous for cutting loose some mammoth icebergs. In terms of size, only one iceberg can reign supreme at a time-a position recently held by Iceberg A-76 in the Weddell Sea.
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