Over a matter of days in late September, Stef Lhermitte watched via satellite as a new, massive crack formed along the edge of Antarctica’s Pine Island Glacier.
Just last year that glacier shed a Manhattan-sized slab of ice. But that particular iceberg was relatively small.
Lhermitte, a geoscientist specializing in remote sensing at the Netherlands’ Delft University of Technology, expects this latest rift, when it eventually breaks, to produce an iceberg roughly 30 kilometers wide by 10 kilometers across (19 miles by 6 miles).
That would be Pine Island’s sixth-largest calving event since 2001 — producing an iceberg five times the size of Manhattan.
“They’re like the cork in a bottle,” Josh Willis, a NASA oceanographer who researches glaciers from aboard aircraft, said in an interview. “If you break off a shelf, they [glaciers] can speed up very quickly.”
Pine Island is already breaking off more ice than it can replenish.

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