Landslides in the Andes Mountains Nevados Huascaran Peru 1962 1970

The Andes, a steep mountain range in south America, are affected by frequent earthquakes and volcanic eruptions, are glaciated in places, and experience frequent storms from being close to the Pacific Ocean. All of these factors combine, resulting in many landslides and related mass-wasting disasters in the Andes. some of the most catastrophic land slides in the Andes have emanated from Nevados Huascarán, a tall peak on the slopes of the Cordillera Blanca in the Peruvian province of Ancash. In 1962, a large debris avalanche with an estimated volume of 16,900,000 cubic yards (13,000,000 m3) rushed down the slopes of Nevados Huascarán at an average velocity of 105 miles per hour (170 km/ hr). The debris avalanche buried the village of Ran-rahirca, killing 4,000-5,000 people. This scene of devastation was to be repeated eight years later. On May 31, 1970, a magnitude 7.7 earthquake was centered about 22 miles (35 km) offshore of Chimbote, a major Peruvian fishing port, causing widespread destruction and about 3,000 deaths in Chimbote. The worst destruction, however, was caused by a massive debris avalanche that rushed off Nevados Huascarán at 174 miles per hour (280 km/hr). This debris flow had a volume of 39-65,000,000 cubic yards (30-50,000,000 m3), and rushed through the Callejón de Huaylas, a steep valley that runs parallel to the coast. The debris avalanche covered the town of Yungay under thick masses of boulders, dirt, and regolith. Seventy percent of the buildings in the town were covered with tens of feet of debris. The death toll was enormous—most estimates place the deaths at 18,000, although local officials say that 20,000 died in Yungay alone, and as many as 70,000 people died in the region from the landslides associated with the May 31, 1970, earthquake.

There have been many other landslide disasters in the Andes Mountains. In 1974, a rock slide-debris avalanche in the Peruvian province of Huancavelica buried the village of Mayunmarca, killing 450 people. The debris avalanche raced down the mountain with an average velocity of 140 km/hr and caused the failure of a 150-meter-high older landslide dam, initiating major downstream flooding. Debris with a volume of 16,000,000,000 cubic meters from the 1974 avalanche blocked the Mantaro River, creating a new lake behind the deposit. In 1987, the Reventador landslides in Napo, Ecuador, were triggered by two earthquakes with magnitudes of 6.1 and 6.9. These earthquakes mobilized 98,000,000143,000,000 cubic yards (75-110,000,000 cubic m) of soil that was saturated with water on steep slopes. These slides remobilized into major debris flows along tributary and main drainages, killing 1,000 people and destroying many miles (km) of the TransEcuador oil pipeline, the main economic lifeline for the country. The magnitude 6.4 Paez earthquake in Cauca, Colombia, in 1994 also initiated thousands of thin soil slides that grouped together and were remobilized into catastrophic debris flows in the larger drainages. As these raced downstream, 1,971 people were killed, and more than 12,000 people were displaced from their destroyed homes.

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