The Day in History:

The Great Chilean Earthquake

The Great Chilean Earthquake or Valdivian Earthquake (Terremoto de Valdivia in Spanish) of 22 May, 1960 is the most powerful earthquake ever recorded, rating 9.5  on the Moment magnitude scale. It occurred in the early afternoon (19:11 UTC) and its resulting tsunami affected southern Chile, Argentina, Hawaii, Japan, the Philippines, eastern New Zealand and the Aleutian Islands in Alaska.

The epicentre was near Valdivia, Chile some 700 kilometres south of Santiago. It caused localised tsunamis that severely battered the Chilean coast, with waves up to 25 metres. The main tsunami raced across the Pacific Ocean and devastated Hilo, Hawaii. Waves as high as 10.7 metres were recorded 10,000 kilometres from the epicentre, and as far away as Japan and the Philippines.

The death toll and monetary losses arising from such a widespread disaster can never be precisely known. Various estimates of the total number of fatalities from the earthquake and tsunamis have been published, with the USGS citing studies with figures of 2231, 3000, or 5700 killed, and another source uses an estimate of 6000 dead. Different sources have estimated the monetary cost ranged from 400 million to 800 million US dollars (or 2.6 to 5.2 billion in 2005 dollars, adjusted for inflation.) The earthquake in Chile

A Valdivia street after the earthquake of 22 May 1960

The Cordon Caulle in the picture erupted some days after the main earthquake.The Great Chilean Earthquake was preceded by a smaller earthquake in Arauco Province at 06:02 on 23 May 1960. Telecommunications to southern Chile were cut off and President Jorge Alessandri had to cancel the traditional ceremony of the Battle of Iquique memorial holiday to oversee the emergency assistance efforts. The government was just beginning to organize help to the affected region when the second earthquake occurred at 14:55 UTC on 22 May in Valdivia.

The second earthquake affected all of Chile between Talca and Chiloé Island, more than 400,000 square kilometers. Coastal villages, such as Toltén, disappeared. At Corral, the main port of Valdivia, the water level rose 4 meters before it began to recede. At 16:20 UTC, an eight-meter wave struck the Chilean coast, mainly between Concepci?n and Chiloe. Ten minutes later, another wave measuring 10 meters was reported.

Hundreds of people were already reported dead by the time the tsunami struck. Ships, like the Canelo, that were at the mouth of Valdivia River sank after being moved 1.5 km backward and forward in the river. The mast of the Canelo is still visible from the road to Niebla.

A number of Spanish-colonial forts around Valdivia were completely destroyed. Soil subsidence also destroyed buildings, deepened local rivers, and created wetlands in places like the R?o Cruces and Chorocomayo, a new aquatic park north of the city. Extensive areas of the city were flooded. The electricity and water systems of Valdivia were totally destroyed. Witnesses reported underground water flowing up through the soil. Despite the heavy rains of 21 May, the city was without a water supply. The river turned brown with sediment from landslides and was full of floating debris— including entire houses. The lack of potable water became a serious problem in Chile"s most rainy region.

Two days after the earthquake, the Cord?n Caulle erupted. It is possible that other volcanoes also erupted, but none were recorded due to the lack of communication in Chile at that time. The relatively low death toll in Chile (estimated at 6,000) is explained, in part, by the fact that many people were attending church at the time of the temblor. Churches were usually constructed on stronger foundations than most residential buildings. Coastal towns also tended to be located on higher ground, following a pre-Hispanic tradition.

The Ri?ihuazo

Main article: Ri?ihuazo.

During the Great Chilean Earthquake, several landslides near Tralcan Mountain blocked the outflow of Ri?ihue Lake by (). Ri?ihue Lake is the lowest of the Seven Lakes chain and receives a constant inflow from the Enco River. The blocked San Pedro River, which drains the lake, passes through several towns and the city of Valdivia before finally reaching Corral Bay.

Because the San Pedro River was blocked, the water level of Ri?ihue Lake started to rise quickly. Each meter the water level rose was equivalent to 20 million cubic meters, which meant that 4800 million cubic meters of water would release into the San Pedro River (easily overpowering its flow capacity of 400 cubic meters per second) if it rose above the final, 24-meter-high dam. This potential disaster would have destroyed all the settlements along the course of the river in less than five hours, and had more dire consequences if the dam suddenly broke.

About 100,000 people lived in the affected zone. Plans were made to evacuate Valdivia, and many people left.

To avoid the destruction of the city, several military units and hundreds of workers from ENDESA, CORFO, and MOP started an effort, called the Ri?ihuazo, to control the lake. Twenty-seven bulldozers were put into service, but they had severe difficulties moving in the mud near the dams, so dykes had to be constructed with shovels. The work was not restricted to the lake; drainages from other parts of the Seven Lakes were also dammed to minimize the flow into Ri?ihue Lake. These dams were removed later, with the exception of Calafquén Lake, which still retains its dam.

By 23 May, the main dam had been lowered from 24 to 15 meters, allowing 3000 million cubic meters of water to leave the lake gradually, but still with considerable destructive power. The team led by engineer Ra?l S?ez finished two months after beginning the works. Previous earthquakesThere is evidence that a similar landslide and earthquake occurred in 1575.

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