The 1970 Huascarán Debris Avalanche occurred on May 31, 1970, when a debris avalanche and mudflow triggered by the Ancash earthquake destroyed the Peruvian town of Yungay and ten nearby villages, leaving up to 30,000 people dead. It is the deadliest avalanche or glacier-related disaster in history, and the third or fourth most deadly landslide-related disaster of the 20th century, after the Haiyuan landslides (China), the Armero tragedy (Colombia) and by some estimates the Khait landslide (Tajikistan). The north peak of Huascarán from which the avalanche originated had been considered unstable since 1962, when a smaller collapse wiped out several villages of the Callejón de Huaylas valley near Yungay. However, the provincial government made efforts to prevent the news from spreading and urged people not to panic. The 1970 earthquake destabilized a glacier and snowmass which surged rapidly downhill, becoming a mudflow as it accumulated large volumes of loose dirt, rock and surface water. The death toll was made worse due to the earthquake having occurred on a Sunday, as thousands more people had congregated in Yungay for market when the mudflow struck and leveled the city. The slide then entered the Río Santa and caused extensive damage as it flowed all the way downstream to the Pacific Ocean, a distance of , mostly through a narrow canyon. Following the disaster, the Peruvian government conducted relief efforts and planned to move the provincial capital from Yungay to a safer location at Tingua. Survivors resisted the resettlement proposal and thousands stayed in a camp just north of the destroyed city known as "Yungay Norte", which would eventually become the present-day town of Yungay. The government has forbidden redevelopment or excavation of the original town site, where a memorial has been established to commemorate the dead. Although most of Yungay was completely leveled by the earthquake and mudflow, some remnants, including the ruined cathedral and cemetery, can still be seen in the area. Although Yungay was located outside of the direct avalanche path, the slide was so large that it overwhelmed the natural geographic barriers protecting the town, whose location had previously been considered safe. The United States Geological Survey stated that "conceivably, such an event may not occur again for thousands of years." Background Geography and geology Due to its rugged terrain, high elevation and location in an active seismic zone, the Callejón de Huaylas, or upper Río Santa valley has