On May 31, 1970, at 3:23 p.m., the most devastating rock-ice avalanche in history was initiated by a powerful earthquake with a magnitude of 7.7.. The wave of ice that ensued killed 16 people and is considered the worst disaster in Chilean history.
The avalanche started on Mount Huascaran, which is part of the Peruvian Cordillera Blanca range. The quake that triggered the avalanche was located near the town of Machu Picchu, which is situated in an isolated area, far from any major city. No casualties were reported from Machu Picchu nor anywhere else in Peru, but the damage done to roads and infrastructure could not be assessed easily.
Mountaineers working in the region discovered human remains nearly 50 years later. They were buried under more than 10 meters of snow and ice.
In January 2017, scientists published evidence that suggests that the earthquake that triggered the avalanche was likely an eruption of Mount Mazama, which is now known as Mount St. Helens. At the time, the new evidence had not been confirmed by other researchers, but it does match what we know about the location of the eruption and its effects on climate.
The study that revealed this connection was published in Nature Communications.
The 1970 Huascaran debris avalanche occurred on May 31, 1970, when the Ancash earthquake generated a debris avalanche and mudflow that devastated the Peruvian town of Yungay and eleven adjacent towns, killing up to 30,000 people. The landslide swept away several buildings as far as 10 kilometers from the epicenter.
Yungay is located in the Cordillera Blanca range, about 250 km west of Lima. The town was built near a mountain pass called Los Cardones which is used by traffic traveling between Lima and Chimbote. Los Cardones has been the site of many landslides over time due to erosion and the accumulation of snow at high altitudes. On April 21, 1970, an estimated 2 million cubic meters (72,000,000 ft3) of rock and ice slid down the mountain side toward the town. The force of the avalanche was so great that it overturned cars, trucks, and buses and destroyed nearly all the buildings within the town boundary. Only three buildings were left standing after the avalanche hit. Although many people died, there were no reports of survivors.
The cause of the avalanche was determined to be excessive precipitation which led to flooding and then melting of nearby snowbanks. This caused rocks and soil to be released from above and then slide down the mountainside.
This, however, was only the beginning. Many additional avalanches devastated the area during the next few weeks, with alarmingly high snowfall frequency taking several thousand more deaths. The Ancash Earthquake, often known as the Great Peruvian Earthquake, was the largest natural disaster in Peruvian history, occurring on May 31, 1970. It had a magnitude of 8.0 and killed 80,000 people.
The earthquake started at 3:26 AM and lasted for 10 minutes. It caused mass destruction across an area of more than 20,000 square miles (50,000 square kilometers), including the capital city of Lima. More than two thirds of the buildings within the city's limits were destroyed. An additional 70,000 people were left homeless by the quake.
After the earthquake, many people went to places like the Valley of Death to collect debris of their lost friends and family members. These places are now famous all over the world because they show how dangerous mountain climbing can be. Of the 81 people that died in this particular avalanche, only four bodies were found intact enough to identify. The others had been torn apart by the force of the avalanche.
Mountain climbers should always use caution not to provoke an avalanche by walking into a hidden slope or stopping suddenly. If you do trigger an avalanche, run away from it! That is the best way to survive an avalanche.