Ancash earthquake caused a substantial part of the north side of the mountain to collapse. 66,000 killed
The avalanche mass, an estimated 80 million cubic feet of ice, mud and rock, was about half a mile wide and a mile long. It advanced about 11 miles (18 km) at an average speed of 280 to 335 km per hour 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