Ancash earthquake

Earthquake

Date: May 31, 1970

Place: Northern Peru

Magnitude: 7.7

Result: Approximately 70,000 dead, 140,000 injured, 500,000 homeless, 160,000 buildings destroyed or damaged

The scene of this disaster is known for its rugged beauty. Towering, snow-capped mountains with steep, rocky slopes overlook the valley of the Santa River, which flows to the north through the Department of Ancash and then turns west until it empties into the Pacific Ocean. This narrow valley—about 5 miles at its widest point—runs for 125 miles parallel to Peru’s Pacific shore and is dotted by a series of towns and small cities. For example, Yungay, an old town with roots in the colonial era, was by the 1960’s a forward-looking community with an interest in tourism.

One of the region’s greatest assets is its physical environment. Looming 14,000 feet above the valley floor are the twin peaks of Mount Huascarán, which measure 22,190 and 21,860 feet above sea level. The peaks are prominent in a section of the Andes Mountains that also includes glaciers and, at lower altitudes, cold lakes drained by streams that feed the Santa River. The monumental Huascarán attracts mountain climbers from around the world because of the extraordinarily steep slopes that rise at angles of 45 to 90 degrees. At the base of these mountains are large boulders, evidence of the area’s geological instability.

The Santa River Valley, also known as the Callejón de Huaylas, has a long record of human settlement. Archaeologists have found remains of the Chavin culture that date back as far as 800 b.c.e. The Inca Empire reached into the area in the 1460’s, only to be superseded by the Spanish conquistadors in the 1530’s. The Spanish controlled most of the agriculture in the valley during the colonial period (1530’s-1820’s), but the population became heavily mestizo—a mixture of Native Americans and Europeans.

The independence of Peru from Spain brought few changes in the society and the economy, with much of the best land in the valley in the hands of a few landowners well into the twentieth century. Yungay, an important political center, was also a leading market for the peasant farmers who bought and sold foodstuffs and textiles. By the 1960’s, however, a new dynamism took hold in Yungay. A paved highway provided easy access to people and goods outside the region. Yungay had a dependable source of electricity, and plans were in place for the construction of a large hotel for visiting mountain climbers and tourists.

In spite of its location in the Andes, a mountain chain well known for earthquakes, the Callejón de Huaylas had experienced relatively few cataclysmic events before 1970. The three most serious events, however, did furnish forebodings of geological conditions that harbored the potential for a major disaster. The large avalanche of 1725 that destroyed the colonial city of Ancash was caused by the breaking of a high mountain glacier that sent tons of ice hurtling downward, picking up rocks and debris as it crashed into the unsuspecting city in the valley below. Another city, Huaraz, was inundated by the bitterly cold waters of a mountain lake that spilled into the valley in 1941. In 1962 another large avalanche overran the community of Ranrahirca. These events all involved loss of life, injuries, and property damage, but, in comparison with the earthquake of 1970, they also served as warnings of a disaster of much greater magnitude.

Earthquake and Avalanche. The Sunday afternoon of May 31, 1970, was a time of relaxation for the people of the valley, with extended family visits, casual strolls through town plazas, and leisurely meals at local restaurants. This pleasant scene ended abruptly at 3:23 p.m. with the first rumblings in the ground. The Callejón de Huaylas and, indeed, all of Peru rests on or near the place in the earth’s crust where two major tectonic plates come together. The Nazca Plate, gradually moving beneath the Pacific Ocean, tends to push under the South American Plate, causing the latter to rise. On May 31, the Nazca Plate’s movement become sudden and intense, pushing the edge of the South American Plate upward. This extraordinary tectonic shift broke off a large section of Huascarán overlooking the Callejón de Huaylas—probably 0.5 mile wide and 0.75 mile long. The huge mass crashed down upon a glacier, adding large chunks of ice to the avalanche that, because of the steep slope, accelerated as it moved downward, reaching a speed of approximately 200 miles per hour. The rock and ice collided and shattered into smaller segments that, in spite of the fragmentation, weighed tons when they reached the valley floor.

Yungay was in the path of the avalanche. Within four minutes a great mass of rock, ice, soil, and water covered the 10 miles from Huascarán to the town. Eyewitnesses described the mass as being as high as a ten-story building as it roared across the valley floor to bury Yungay and nearby villages beneath a sea of mud and rock that, after settling for several days, was over 15 feet deep. Approximately 3,500 of Yungay’s population perished beneath the huge avalanche. Only an estimated 200 survived.

A portion of the avalanche veered to the north along the Santa River, crushing virtually everything in its path. Included in the debris of this mass were bodies and houses from Yungay. Another section, or lobe, of the avalanche crossed the river bed and rolled about 200 feet up the mountain slope on the western side of the valley. As these lobes of the avalanche moved to the north and west, they carried boulders the size of automobiles and deposited them considerable distances from Huascarán, some reportedly as far north as the Canón de Pato, approximately 25 miles from Yungay.

The earthquake that caused the avalanche also produced devastating results in areas not reached by the mass of rock, ice, and debris. For example, the city of Huaraz, about 35 miles south of Yungay, experienced the collapse of many of its structures, including portions of the cathedral on the main plaza and the homes of both rich and poor. All through the valley, walls made of adobe crumbled and roofs caved in. In Huaraz and other communities, some cemeteries were so severely shaken that monuments collapsed and tombs broke open. Recently built highways and bridges that linked towns and cities in the Santa River Valley were destroyed. The violent shaking of the earth also destroyed the region’s electric-power grid, as well as water and sewer lines. Within a few minutes most of the human-made structures in the Callejón de Huaylas were in ruins or covered by thick layers of rock and mud. Surveys after the earthquake indicate that more than 160,000 buildings were destroyed or damaged—approximately 80 percent of the structures in the area. Although the impact of the earthquake was most intense in the Callejón de Huaylas, buildings collapsed throughout the Department of Ancash, including those in cities and villages along the Pacific coast.

Aftermath. Seismographic records made clear to the outside world that a powerful earthquake had struck the Callejón de Huaylas, but the survivors in the devastated valley had to struggle without external aid for four days. Airplanes and helicopters dispatched by the Peruvian government encountered billowing clouds of dust that extended as high as 18,000 feet, blocking visual observation of most of the valley. The destruction of telephone lines and highways prevented communication and the movement of people. Meanwhile, the survivors attempted to care for themselves. The only hospital in the valley was in the city of Huaraz, and it quickly became the gathering place for the injured. The hospital structure was damaged but remained standing as five doctors attended to a steady stream of hundreds of patients over the four-day period between the earthquake and the arrival of outside aid.

Finally, on June 5, the atmosphere cleared enough for pilots to find relatively clear drop zones and landing strips. The Peruvian air force dropped 70 tons of food and other supplies by parachute and transported over 400 injured residents to outside medical facilities by helicopter. Later on the same day, a landing field near Huaraz was sufficiently repaired to accommodate small transport planes. By June 9, Peruvian engineers had repaired highways into the valley, opening the way for emergency vehicles. On the same day, Peruvian president Juan Velasco Alvarado established the Committee for the Reconstruction and Rehabilitation of the Affected Zone (CRYRZA), a government agency that was responsible for supervision of efforts to supply material aid and the implementation of long-term plans for the rebuilding of communities. Soon military and other emergency aircraft from Argentina, Brazil, the United States, Canada, France, and the Soviet Union arrived not only with much-needed supplies but also with experienced crews who soon joined with the Peruvian air force to provide a continuous flow of relief and evacuation missions. Medical personnel, engineers, government officials, and volunteers worked with the survivors on the necessary tasks: the burial of the dead, the erection of shelters for the living, and the distribution of food and medicine throughout the valley.

Recovery. The reconstruction of communities began within weeks after the earthquake, but the complicated processes of reestablishing the physical infrastructure, such as roads, public buildings, private homes, and commercial establishments, as well as the institutions of local government and private businesses, required many months and, in some cases, years. For example, Yungay had virtually disappeared, buried beneath the avalanche, but, within a year, approximately 1,800 people had moved into its vicinity to build a new community with the same name. By the middle of 1971, Yungay had a functioning local government, primary and secondary schools, and a revived commercial sector. Huaraz also rebuilt quickly, highlighted by the construction of a modern airport with the capacity to handle small jet aircraft. By 1980, all the valley’s cities were linked to a modern electric power grid and the new highway system that ran down the Santa River Valley to the Pacific coast.

This recovery, although impressive in many ways, was not free of acrimony and accusations. The distribution of aid was more prompt in some areas than in others, causing angry complaints from those who felt neglected. Some of the materials to be used in home construction were not suitable for the mountain environment. Finally, frustrated locals accused government officials of incompetence and corruption as some reconstruction projects dragged on for months and, in a few cases, years.

Much uncertainty remained about the future safety of the inhabitants of the valley. The geological conditions that had caused the disaster remained: an unstable land prone to earthquakes surrounded by steep-sided mountains with high-altitude glaciers and lakes. A key to the safety of the region was the Santa Corporation, a government agency charged with the responsibility of monitoring the buildup of ice and snow on the mountain summits and changes in the conditions of glaciers and lakes. The Santa Corporation was primarily responsible for avoiding another disaster soon after the events of May 31, 1970. The earthquake had thrust a large boulder into the stream that customarily drained Lake Orkococha, located on the flank on Mount Huascarán. As a result, the level of that lake was much higher than normal and threatened to spill over its banks, causing a flood on the valley floor. Working furiously, an international team of mountain climbers cut a new drainage channel for the lake by June 7, thereby averting a second disaster for the people of the valley. The Santa Corporation’s duties were taken over by a new government agency called Ingeomin in 1977.

Bibliography

Bode, Barbara. No Bells to Toll: Destruction and Creation in the Andes. New York: Scribner, 1989.

“Death by Glacier.” Scientific American 223, no. 2 (August, 1970): 46.

Dorbath, L., A. Cisternas, and C. Dorbath. “Assessment of the Size of Large and Great Historical Earthquakes in Peru.” Bulletin of the Seismological Society of America 80, no. 3 (June 1, 1990): 551-576.

Levy, Matthys, and Mario Salvador. Why the Earth Quakes: The Story of Earthquakes and Volcanoes. New York: W. W. Norton, 1995.

Lomnitz, C. “The Peru Earthquake of May 31, 1970: Some Preliminary Seismological Results.” Bulletin of the Seismological Society of America 61, no. 3 (June, 1971): 535-542.

Machado, Jesús Ángel Chávez. “Remembering the Worst Earthquake in Latin America: The Day the Apus Turned Their Backs on Peru.” ISDR Informs—Latin America and the Caribbean, no. 1 (2000).

Oliver-Smith, Anthony. The Martyred City: Death and Rebirth in the Andes. Albuquerque: University of New Mexico Press, 1986.