On 31 May 1970 , the Ancash earthquake caused a substantial part of the north side of the mountain to collapse . The avalanche mass , an estimated of ice , mud and rock , was about half a mile wide and a mile long ( ) . It advanced about at an average speed of , burying the towns of Yungay and Ranrahirca under ice and rock , killing more than 20,000 people . At least 20,000 people were also killed in Huaraz , site of a 1941 avalanche which killed over 6000 ( see Palcacocha Lake ) . Estimates suggest that the earthquake killed over 66,000 people
Ancash earthquake
1970 Ancash earthquake
Huascarán