Alps Grow and Shrink at Same Time

Posted 11 8 2009 9:50PM

The European Alps are both growing and shrinking, with two dynamic processes acting against each other for a net effect of ... nothing.

The Alps were formed from the collision of the African and European tectonic plates, which began about 55 million years ago.

While the Alps are now thought to be "dead" in a tectonic sense, they continue to rise. Swiss scientists have measured rising at the Alp summits of up to 1 millimeter (0.04 inches) a year, as compared to lower ground.

This rise is attributed to the melting of Alpine glaciers. The process is something like a melting iceberg (or icecube): when part of the exposed ice melts away, some of the ice below the water's surface will bounce up, said Friedhelm von Blanckenburg of the GFZ German Research Centre for Geosciences. For a mountain, when the weight of the glacier bearing down on the Earth is gone, the mountain can rise up in response.
But this slow yearly rise puzzlingly hadn't seem to add any height to the mountain range over the millennia.

Blanckenburg and his colleagues were able to calculate that the mountain height hadn't increased because they were eroding - by the action of glaciers and rivers - at about the same rate that they were rising.

To calculate the erosion rate, "we use the rare isotope Beryllium-10, which develops in the land surface via cosmic radiation. The quicker a surface erodes, the fewer isotopes of this type are present therein," Blanckenburg explained.

The team's findings are detailed in the journal Tectonophysics.

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• Original Story: Alps Grow and Shrink at Same Time

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