for National Geographic News
Two South American glaciers are displaying strange behavior for the times: They're growing.
Most of the 50 massive glaciers draped over the spine of the Patagonian Andes are shrinking in response to a global warming, said Andrés Rivera, a glaciologist at the Center for Scientific Studies in Valdivia, Chile. (Related: "Mountain Glaciers Melting Faster Than Ever, Expert Says.")
"What is happening is not well understood," Rivera said.
Theories center on the geography and topography of the glaciers; the depth and temperature of the waters where the glaciers end; and how quickly, or slowly, they react to changes in the climate.
Yet overall, "if you account for the gains and losses of all of Patagonia's glaciers, they are [still] losing huge amounts of ice," Rivera pointed out.
One hypothesis for the 3-mile-wide (5 kilometer-wide) Perito Moreno's advance is the glacier's apparent insensitivity to changes in what glaciologists call the equilibrium line on glaciers, Rivera said.
Roughly equivalent to the snow line, the equilibrium line is the elevation above which the glacier is growing, due to snow accumulation, and below which the glacier is melting.
When this line moves higher up a hill or a mountain due to rising temperatures, for example, more of the glacier is situated in the melting zone, and the glacier retreats.
But because Argentina's Perito Moreno glacier is so steep in the area where the equilibrium line falls, climate shifts don't impact the line's movement much, at least as it relates to the height of the mountain, Rivera noted.
As a result, the amount of of ice lost or gained is minimal.
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