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In this July 19, 2011 photo, a cloud drifts past the ever-collapsing calving 6-kilometer-wide (4-mile-wide) front of Jakobshavn Glacier, situated at the edge of the vast Greenland ice sheet, near Ilulissat, Greenland. Greenland is the focus of many researchers trying to determine how much its melting ice may raise sea levels. (AP Photo/Brennan Linsley)

Huge crack discovered in Antarctic glacier

A major glacier in Antarctica is melting unusually quickly because ocean currents are undermining it from below, researchers find. Scientists are gathering meaningful and accurate data of how ice sheets and glaciers are changing over time, and what this means for our planet.