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[Stockbild] Eroded canyons. Aerial photograph showing rock formations in the Needles district of the Canyonlands National Park, Utah, USA. Erosion of the soft sedimentary rocks has widened an existing network of fractures in the rock. These fractures of solid rock are caused by tectonic forces acting on and within the Earth's crust. Erosional forces such as water, ice and wind act on these fractures to produce the structures seen. (KEYSTONE/SCIENCE PHOTO LIBRARY/BERNHARD EDMAIER) === ===