Scree slopes. Weathered rock material on slopes in an alpine valley. Weathering of surface rock in alpine regions is caused by successive freeze-thaw cycles that cause it to shatter into fragments. This material accumulates on slopes and gradually moves downwards due to gravity. Normally, upland areas in alpine regions are perennially frozen (permafrost). An increase in temperatures in the region is causing scree slopes to become destabilised. On this slope, material is moving more quickly down the slope and accumulating in the lake below the slope (bottom). Photographed in the Fluela Pass, eastern Switzerland.