In 1941, glacial Lake Palcacocha in the Peruvian Andes burst its moraine dam of earth and stones, sending a torrent of water through the city of Huaraz and killing an estimated 5,000 people. Between 1941 and 1950, two more glacial lake outburst floods, or GLOFs, which can occur after enough water fills in behind a glacier’s end moraine, killed another 5,000 people in the Cordillera Blanca. In response, the government set up one of the most effective glaciological units in the world with the goal of preventing future outburst floods. Using drain pipes, reinforced terminal moraine dams, sophisticated tunnels, and valve systems, they drained or contained 34 lakes in the region. As a result, thousands of lives were saved.