“Grossgufer” is the local name of the cone of debris from the rockslide. In the local dialect, “Gufer” means scree, rocks, or a heap of rubble. In total, three rockslides occurred on the Längenfluhberg.
- Rockslide of 18 April 1991: 15 million cubic metres of rock thundered down to the valley. The result: railway line buried, the Vispa river blocked. A lake formed behind the cone of debris, but since the water was able to continue flowing through the rubble, the level of the lake remained constant.
- Rockslide of 21 April 1991: 100,000 cubic metres of rock. No further consequences.
- Rockslide of 9 May 1991: 33 million cubic metres of rock. This event had major consequences for the valley. The railway line was buried again; this time, the road was also covered with rock debris. The river, further blocked, now formed a lake 1.3 km long that presented a great danger for the valley: the water was no longer able to escape.
As if by a miracle, no one was hurt. However, 35 sheep and seven horses perished. Large areas of the hamlet of Lerch, with 33 agricultural buildings and holiday homes, disappeared for ever. A layer of dust several centimetres thick covered the valley.
The Swiss army helped lay a new railway track for the Matterhorn Gotthard Bahn within ten weeks. A detour road was also built. Finally, engineers excavated a 20-metre-deep channel through the rock debris allowing the water in the reservoir to escape and the Vispa river to flow freely once again. Nonetheless, parts of the village of Randa flooded during storms in July and August 1991.
- Photo subject: cone of debris and bare cliffs exposed by the rockslide
- Photo subject: green larches among the white-grey rocks of the cone of rock debris