News Picks : Pressure and stress create sandstone arches
Nature: Sandstone arches have long been thought to be formed by erosion. Now Jiri Bruthans of Charles University in Prague, Czech Republic, and his colleagues suggest that the structures form instead as the result of the pressure exerted by the rock's own weight. Prompted by observations of the creation of arches at a sandstone quarry, Bruthans's team sandwiched cubes of sandstone between pressure plates and then artificially weathered the rock. They found that as erosion removed material, which was initially relatively loose, the parts that suffered less erosion had to bear more of the weight and therefore suffered higher stress. In those areas, the grains locked together and became much more resistant to erosion. The result was the formation of arches and other similar structures.