As the Pine Island Glacier retreats and flows out to sea, it develops and drops icebergs as part of a natural and cyclical process, Humbert said. But, the way the ice breaks, or "calves," is still somewhat mysterious.
"Glaciers are constantly in motion," she said. "They have their very own flow dynamics. Their ice is exposed to permanent tensions and the calving of icebergs is still largely unresearched."
The Pine Island Glacier ice shelf, the part of the glacier that extends out into the water, last produced large icebergs in 2001 and 2007.
The glacier is the longest and fastest-changing on the West Antarctic Ice Sheet. While Humbert and her colleagues did not draw direct connections between this week's calving event and climate change, other scientists, including marine geologists at the British Antarctic Survey, are investigating whether global warming is thinning Antarctica's ice sheets and speeding up the glacier's retreat.
Yet, the flow of the Pine Island Glacier may be driven by other factors, Humbert said. The glacier flows to the Amundsen Sea at a rate of about 2.5 miles (4 km) per year. She says whether the flow speeds up or slows down is based more on changing wind directions in the Amundsen Sea, and less by rising air temperatures.
"The wind now brings warm sea water beneath the shelf ice," Humbert said. "Over time, this process means that the shelf ice melts from below, primarily at the so-called grounding line, the critical transition to the land ice."
Still, if the glacier's flow speeds up, it could have serious consequences, the researchers said. The Pine Island Glacier currently acts as a plug, holding back part of the immense West Antarctic Ice Sheet whose melting ice contributes to rising sea levels.
Follow Denise Chow on Twitter @denisechow. Follow OurAmazingPlanet @OAPlanet, Facebook and Google+. Original article at LiveScience's OurAmazingPlanet.
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