Theories on the Breakup - Underwater Fissures:
Unlike the ice shelves of the lower Antarctic, such as the Ross, the ice shelves on the Antarctic Peninsula owe a substantial portion of their 250 meter thickness to fresh snowfall every season which compacts on top of the glacial ice which descends off the Peninsula. This causes the top 50 meters of the ice shelf to be structurally weak, while the glacial ice underneath is the load-bearing structure that holds the shelf together. British scientists theorize that cracks on the bottom of the ice shelf, about 220 meters below sea level, could be the cause of the massive disintegration of Larsen-B, since water at those depths would be highly pressurized (4). Coupled with unusually warm water temperatures, the sea water could have forced open cracks in the dense glacial ice that holds together the ice shelf, allowing it to fragment vertically.
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Maximum ice extents of Larsen-B since 1995 . (6) |
Theories on the Breakup - Melt Water Ponds:
The other, more widely accepted theory on the disintegration of the Larsen ice shelf has to do with the pools of melt water that have appeared on top of the shelf as the climate in the region has warmed. Research done by scientists from the University of Chicago suggests that melt water seeping into existing crevasses tends to break them further since water is more dense than the surrounding ice. As shown in diagram B, as these cracks extend through the ice they exert pressure on the rest of the sheet horizontally since they tend to tip over. After a critical mass of cracks form the combined force of them all breaks the sheet outward like in diagram C as all the pieces topple over sideways (2). This explains the blue color and rapid outward expansion of the ice debris seen from satellite images after Larsen-B collapsed: the pieces falling on their side would have exposed tons of blue, glacial ice usually covered by snow to the sky as they fell sideways (5). This contrasts normal calving events where the iceberg remains white as seen from above since it does not fall sideways, it merely separates and begins to float.
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Broken ice wedges fall like dominoes. (2) |
Repercussions of the Larsen-B Collapse:
Researchers have measured up to eight times increased flow rates in the glaciers that feed the Larsen-B ice shelf since it collapsed. This has caused the elevation of the glaciers to drop by 38 meters in six months (1).
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