The 1970 Peru earthquake and avalanche constitutes the most destructive natural disaster in the history of the Western Hemisphere and one of the world’s worst ever. In less than five minutes, more than sixty thousand people perished.
On May 31, 1970, at 3:23
The earthquake that led to the massive devastation in Peru was actually a series of earthquakes (also called aftershocks) that lasted approximately 45 seconds. The epicenter of the earthquake was 15 miles west of the coastal city of Chimbote, where the Nazca oceanic tectonic plate is being subducted by the South American continental tectonic plate. The earthquake was triggered by subsea faulting extending about 100 miles along a well-defined fault zone near the point where the two plates abut. The first earthquake occurred at a depth of about 35 miles below the ocean floor. Subsequent shocks were located at depths ranging from 27 to 40 miles. The aftershocks were strong; several registered in excess of 7 on the Richter scale.
The quakes’ devastation extended over an area of approximately 40,000 square miles. The heaviest destruction occurred in an area located between 50 and 75 miles east of the epicenter of the earthquake, although some areas 100 miles distant from the epicenter did not escape damage. The area of greatest destruction, especially in terms of the loss of human life, was in the Andes Mountains. Situated within this vast mountain region is the Callejón de Huaylas, an extensive valley lodged between the Cordillera Negra (black range) to the west and the Cordillera Blanca (white range) to the east.
The characteristics of the Cordillera Negra and the Cordillera Blanca are quite dissimilar. Several peaks in the Cordillera Blanca exceed 20,000 feet in elevation. The highest mountain in the range is Huascarán, with a south peak of 22,190 feet and a north peak of 21,850 feet. The range is exceedingly rugged and has extensive areas of near-vertical slopes. Numerous glaciers and extensive snow fields are found at the higher elevations. Throughout the range, vast areas of unstable rock lead to frequent landslides and to rock and ice avalanches. In contrast, the topography of the Cordillera Negra is much more subdued, with maximum elevations of about 14,000 feet. Moreover, the glaciers and extensive snow fields found in the Cordillera Blanca are absent from the Cordillera Negra.
The Callejón de Huaylas is drained by the Río Santa, which runs in a northerly direction for about 125 miles before it turns west and cuts through the Cordillera Blanca and descends to the Pacific Ocean. From its origin in the south to the point where the Río Santa leaves the Callejón de Huaylas in the north, the elevation falls from about 13,000 to 6,500 feet.
The prolonged series of earthquakes off the west coast of Peru triggered thousands of landslides,
As the rock, ice, and snow mass fell, it gained velocity, slid over Glacier 511, and disintegrated on impact at the base of the mountain. The debris avalanche then roared down the narrow gorge of the Río Shacsha and Llanganuco Valley toward the Callejón de Huaylas. Evidence shows that at one point the avalanche became airborne as it accelerated through the gorge on a cushion of compressed air. The composition of the debris avalanche changed as frictional heating melted much of the glacial ice and snow, creating a highly fluid debris mass. In addition, as the avalanche moved, it picked up surface water from streams and water-saturated soils, which added to its liquidity. Other evidence indicates that the avalanche ricocheted from side-to-side as it made its violent descent from the mountain, which may have accelerated its velocity.
On reaching the eastern margin of the Callejón de Huaylas, the debris avalanche surged toward the provincial capital of Yungay
Elsewhere in the Callejón de Huaylas, thousands perished as adobe and masonry buildings collapsed from the violent vibration of the earthquake. Hardest hit was Huaraz
Another devastated area was Peru’s north-central coastal region, extending from north of Trujillo to Pativilca in the south, a distance of about 250 miles. About 120 towns and villages were totally or partially destroyed, compared to seventy in the mountains. Fatalities in the coastal districts, which extend from the coast to the foothills, were substantially less than in the mountains. One exception was Casma, where about three thousand died. Few other cities and towns recorded more than a few hundred deaths in coastal areas, although property damage was extensive and severe. It has been suggested that coastal communities with a relatively low number of fatalities were spared major loss of life because of the broad streets, which enabled residents to avoid falling debris from collapsing buildings. In many of the coastal cities and towns, however, 75 to 90 percent of the adobe and masonry structures were destroyed. In many areas, better-constructed buildings withstood the earthquakes.
The 1970 Peruvian earthquake, landslides, and cataclysmic avalanche remains the greatest natural disaster recorded in the Western Hemisphere. It would be impossible to measure the extent of human suffering that accompanied the massive loss of life. The destruction was so widespread and complete that it was virtually incomprehensible. Nearly two hundred towns and villages were obliterated. The infrastructure in the affected area lay in ruin. Communication and transportation systems essential to reconstruction and recovery were destroyed. Water, electrical, and sanitation systems were annihilated. Public buildings, industries, schools, and homes throughout the affected region were destroyed.
Furthermore, the catastrophe made clear the danger faced by residents of mountain regions. Nevertheless, the indigenous peoples of the mountains in Peru are stoic in the face of ever-present danger. Their attachment to their land and fatalistic view of life enable them to survive. This resolve became evident when the few survivors of Yungay strongly resisted a proposal to rebuild the town in a safer location. A compromise was eventually reached, and it was rebuilt a short distance from its original site. It was little solace to the surviving residents of Yungay when Peruvian president Juan Velasco Alvarado declared the destroyed town a national cemetery.
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Cluff, Lloyd S. “Peru Earthquake of May 31, 1970: Engineering Geology Observations.” Bulletin of the Seismological Society of America 61 (June, 1971): 511-533. A comprehensive overview of the earthquake, landslides, and avalanche. -
Funnell, Don, and Romola Parish. Mountain Environments and Communities. New York: Routledge, 2001. Explores the environmental and social dimensions of mountain regions around the world. -
Kovach, Robert L. Early Earthquakes of the Americas. New York: Cambridge University Press, 2004. This study brings together recent research concerning earthquakes in the Americas. -
Plafker, George, et al. “Geological Aspects of the May 31, 1970, Peru Earthquake.” Bulletin of the Seismological Society of America 61 (June, 1971): 543-578. A detailed account of the earthquake based on field research.
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