Ancash Earthquake and Yungay Avalanche
On 31 May 1970, a powerful undersea earthquake off the coast of Peru shook the country's northern Andes and set off one of the deadliest natural disasters in the history of the Americas. The shock, with a magnitude of about 7.9, devastated towns across the Ancash region, and a huge avalanche of ice, rock and mud then buried the town of Yungay. Around 70,000 people died in total, making it the worst disaster in Peru's recorded history.
The region's vulnerability had deep roots. Peru lies along the boundary where the Nazca Plate slides beneath the South American Plate, a collision that has built the Andes and produces frequent large earthquakes. The Callejón de Huaylas, the valley running below the Cordillera Blanca, is home to the highest tropical mountains in the world. Its towns, including Yungay and the regional capital Huaraz, sat beneath glaciated peaks, most notably Huascarán, which rises above 6,700 meters. Many buildings were made of adobe, a material that performs poorly in strong shaking. Earlier disasters, such as a glacial flood that struck Huaraz in 1941, had already shown the dangers of living below the ice.
The earthquake struck in the afternoon, and its effects were immediate. Adobe homes collapsed in Huaraz and many smaller communities, killing thousands. The shaking also dislodged an enormous mass of ice and rock from the north face of Huascarán. As it plunged down the mountainside, it picked up meltwater, soil and debris, and it traveled several kilometers in a matter of minutes at very high speed. Part of the flow overtopped a ridge that many residents had assumed would protect Yungay, and it swept over the town. Most of Yungay's inhabitants were killed. Survivors were chiefly those who managed to reach higher ground, including the town cemetery hill, and a number of children who had been taken to a stadium on higher ground to see a circus. Estimates of the death toll in Yungay itself vary, but many thousands were lost.
Relief was slow and difficult because roads and communications were cut and the terrain was rugged. Peru's government, along with many foreign countries and aid organizations, sent assistance. Hundreds of thousands of people were left homeless across the region.
Yungay was not rebuilt on its original site. The buried area was declared a camposanto, or sacred burial ground, and a new town was established nearby. Visitors can still see the tops of palm trees and fragments of the old cathedral that mark the former plaza. The disaster led Peru to strengthen its monitoring of glaciers and its approach to hazard planning, and it remains a central reference point in the study of earthquake-triggered avalanches.