In April and May 1991, two consecutive rockslides occurred from a cliff above the town of Randa in the Matter valley of Switzerland. The rockslides released a cumulative volume of approximately 30 million cubic meters of debris, with each of the rockslide stages occurring over several hours. Slide debris buried key regional transportation lines including the road and railway leading to Zermatt, and dammed the Mattervispa river which eventually flooded a portion of the town of Randa upstream.