The 1970 Ancash earthquake was an undersea earthquake that occurred on May 31 of that year. Combined with a resultant landslide, it was the worst catastrophic natural disaster ever recorded in the history of Peru.

The earthquake affected the Peruvian regions of Ancash and La Libertad. The epicenter of the earthquake was located 30 km off the coast of Casma and Chimbote on the Pacific Ocean, where the Nazca Plate is being subducted by the South American Plate. It had a magnitude of 7.9 on the Richter scale and an intensity of up to 8 on the Mercalli scale.

The earthquake struck on a Sunday afternoon at 15:23:31 local time (20:23:31 UTC) and lasted 45 seconds. The quake destabilized the northern wall of Mount Huascarán, causing a rock, ice and snow avalanche and burying the towns of Yungay and Ranrahirca. The avalanche started as a sliding mass of glacial ice and rock about 3,000 feet wide and one mile long. It advanced about 11 miles to the village of Yungay at an average speed of more than 100 miles per hour. The fast-moving mass picked up glacial deposits and by the time it reached Yungay, it is estimated to have consisted of about 80 million cubic meters (61,000,000 m³) of water, mud, and rocks.