Tuesday 19 November 2013

Massive iceberg breaks away from Pine Island Glacier.

NASA's Aqua Satellite has recorded a massive iceberg breaking away from Pine Island Glacier, which flows along the south side of the Hudson Mountains into Pine Island Bay (named for the seaplane USS Pine Island which first explored the area, not for any local flora) drains about 10% of Antarctica's Western Ice Shelf. The iceberg, designated B-31, has an area of about 700 km², about the same size as Anglesey or Singapore, and broke away over the period 9-11 November 2013.

Images of Pine Island Glacier taken by Aqua on 3 November 2013 (top) and 10 November 2013 (bottom). Earth Observatory.

Pine Island Glacier has both accelerated and thinned notably since observations began, increasing in speed by about 73% and losing an average of 46 gigatonnes of mass per year between 1973 and 2007. The loss of icebergs from Pine Island Glacier into the sea is a natural process; all glaciers flow, and eventually either calve into the sea (or sometimes a big lake) or reach an area warm enough to melt, feeding streams and rivers. However the increase in the rate at which Pine Island Glacier is flowing and thinning is reason for concern. 

Glaciers are fed by precipitation, like rivers, but increased precipitation will not necessarily lead to increased flow as it will with a river, as the flow of a glacier is determined by its mass-balance ratio. Effectively this means a glacier's flow is driven by a combination of input and temperature. It the amount of precipitation increases and the temperature drops the glacier will slow and thicken. I the case of Pine Island Glacier it is thought that the increased flow is driven primarily by the warming of the Amundsen Sea, which removes more material at the calving front (warm a glacier and it calves more rapidly) causing the glacier to flow more rapidly, which in the absence of a notable increase in precipitation, has led the glacier to thin.

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