Early last month, the iceberg cracked

A huge crack that grew across an Antarctic glacier for more than a year has spawned a gargantuan iceberg much earlier than expected.

Scientists first reported the 25-kilometer-long fissure in the Pine Island Glacier in satellite photos in January 2001 (SN: 5/12/01, p. 298: Big Bergs Ahoy!). Since then, they’ve been able to detect the crack in images collected as far back as September 2000.

After an adolescent growth spurt, the crevasse slowed its midlife advance to about 15 meters per day.

In May, researchers predicted that the crack would traverse the 40-km-wide glacier and calve a new berg in 12 to 18 months. However, images taken Nov. 11 reveal that the 600-square-kilometer, 400-m-thick slab of ice broke free ahead of that schedule and is now drifting northwest.

Satellite measurements show that Pine Island Glacier, already the fastest flowing ice stream on the continent, is thinning and speeding up (SN: 2/3/01, p. 70: Antarctic glacier thins and speeds up). The new iceberg represents about 7 years’ worth of ice flow from the glacier, says Eric Rignot, a glaciologist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Because the ice was already floating before it calved from the continent, the new berg will have no effect on global sea levels.

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