Toppling icebergs sped breakup of Larsen B ice shelf

From San Francisco, at a meeting of the American Geophysical Union

Early this year, most of Antarctica’s Larsen B ice shelf fell apart during the region’s warmest summer on record (SN: 3/30/02, p. 197: Available to subscribers at All Cracked Up from the Heat? Major hunk of an Antarctic ice shelf shatters and drifts away). Now, scientists think they know what accelerated that rapid disintegration.

In just 5 weeks, a 3,200-square-kilometer, Rhode Island–size section of the ice shelf collapsed and spread into a 6,750-square-kilometer mélange of icebergs, says Douglas R. MacAyeal of the University of Chicago. However, only about 1,600 square kilometers of that area appeared white and covered with snow, as the ice shelf had. The rest of the exposed ice was riddled with rocks and showed the distinct blue color of ice that’s been compressed in glaciers. On satellite images, the sea “looked like a big blue Slurpee,” says MacAyeal.

That exposed glacial ice provides a big clue about why the ice shelf disintegrated so quickly. MacAyeal and his colleagues speculate that much of the shelf had been fractured into tall, thin bits that resembled dominos standing on end–a configuration that would become unstable if the fragments weren’t tightly packed. Once the outer edge of the ice shelf gave way, individual domino-bergs began to wedge each other apart as they fell over.


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