The Alps form a crescent stretching from the Mediterranean coasts of Italy and France to Vienna, Austria. On January 17, 2011, clear skies afforded the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite an uninterrupted view of the mountain range.


This natural-color image shows snow-capped mountains interspersed with vegetated valleys. Clouds snake through valleys in the north and west, and a nearly continuous cloud bank fills the Po Valley in the south, but skies over the mountains are clear.

The Alps’s began forming tens of millions of years ago, when the African tectonic plate slowly collided with the European plate. The plate collision helped close the western part of the ancient Tethys Sea and lifted up the massive European mountain chain that persists today.
Across the Earth, some mountain ranges are gaining elevation through tectonic uplift, while others are losing elevation through erosion. A study published in Tectonophysics in 2009 found that the Alps are doing both. The actions of glaciers and rivers scrape away fine sediment, which is carried away by water and wind. As this happens, the mountain range loses weight, lightening the load for the Earth’s crust. So just as ice and water scrape off the top, deeper rock layers push up from below. In the Alps, these processes appear to be in equilibrium, keeping the mountain range at a near-constant elevation.

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