Cévennes National Park, FranceThese are the headwaters of a river in the south of France, the Chasse

Cévennes National Park, FranceThese are the headwaters of a river in the south of France, the Chassezac. The river originates near here, in the area of Cévennes National Park and Mont Lozère.These rocks are the last remnants of what was once a large mountain range, the Variscan (or Hercynian) Mountains, which stretched from the Appalachians in the U.S. all the way to Eastern Europe. This area in south-central France is known as the Massif Central; made up generally of uplands left over from those mountains.These are igneous rocks. They’re granites; the weathering pattern of large, rounded boulders is a distinct characteristic of that rock type. They formed during the Carboniferous period, over 300 million years ago, underneath those mountains.The surrounding rocks are metamorphosed sedimentary rocks which testify to the origin of the granites. As a mountain range was built, the sedimentary rocks in the area were pushed to greater and greater depths, where their temperatures increased as a consequence of the heat within the Earth. Eventually, some of those rocks reached their melting points, leading to the formation of the magmas that would one day be these granites.The granites were somewhat able to migrate upwards into the heart of the mountains, but erosion is the process that really does the job of getting them to the surface. Similar processes are observed in actively eroding areas of the Himalayas today. After the forces building the mountains went away, erosion took over, bringing the cores of the old mountains up to the surface. As the rocks above the granites eroded, the weight above them decreased, and they began to expand and crack as a consequence.Granites are difficult for water to erode and so erosion tends to focus along areas where cracks already exist. That’s what forms the rounded-bouldery texture you see here.The area of Cévennes National Park has been declared a UNESCO world heritage site as an area where the types of villages and agriculture which dominated pre-industrial Europe are well represented and preserved. It contains in-tact villages built of the type of stone you see here and regular migrations of livestock herds between summer and winter pastures, as has happened in the area for over a thousand years.-JBBImage credit: Alain Bachellier (Creative commons license share):http://www.flickr.com/photos/alainbachellier/3476011274/Geology of the area: http://www.virtual-geology.info/lozere/lozere.htmlUNESCO: http://whc.unesco.org/en/list/1153Official park website: http://www.cevennes-parcnational.fr/See Translation -- source link

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