The majority of the Aletsch area consists of skewed schists and gneisses of old crystalline which is 1,2 - 2 billion years old. Since the end of the Little Ice Age around 1860, the Aletsch glacier has been melting very quickly. In the tongue area it lost more than 300 m in thickness during the last 150 years and along the valley sides the ice lost its function as an abutment. At the steep valley sides gravitational movements resulted in slope instability as well as small and large-scale sagging. The rock formations once covered by the glacier are also disrupted by cracks and fissures due to the penetration of freezing water (frost wedging). A small scale sagging occurred in the Tälli: around 1966, a demolished plate opened a crack of approximately 350 meters on the steep slope between Driest and Oberaletsch rivers. First occurred cut offs and smaller rock breakouts at the rock wall freed from snow. Finally, the entire rock body sank noticeably and was penetrated with cracks and crevices. The complete disintegration of the once massive rock body ended in 1975 and mazy pile of rubble remained. Since the 1970s, on the right side of the valley an approximately 450.000 m2 large slope section moves a few centimeters per year downhill. By the moving, massive un-weathered rock was exposed, which is well visible from the Aletsch forest and stretches as a bright band over about 250 m. Also below the Silbersand exists a larger sagging, but its age is not known.