Nevado del Ruiz

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Nevado del Ruiz
Steam eruption in September, 1985
Elevation	5,321 metres (17,457 feet)
Location	Colombia
Range	Cordillera Central
Coordinates	4°53′33″N, 75°19′25″W
Type	Stratovolcano
Last eruption	1991
First ascent	1936 by M. Rapp and party

Space radar image of Nevado del Ruiz

Nevado del Ruiz 2006

Nevado del Ruiz is an Andean stratovolcano in Caldas Department, Colombia. It lies about 50 miles west of Bogotá, with the town of Armero in the valley below. It is also the northernmost and highest Colombian volcano with historical activity.

The Nevado del Ruiz was produced by the subduction of the Nazca oceanic plate beneath the South American continental plate. Stratovolcanoes in the Andes are for the most part Plinian, as is Nevado del Ruiz, and contain pyroclastic flows. As a typical Plinian volcano, the Nevado del Ruiz consists of andesitic and dacitic magma.

On November 13, 1985, Nevado del Ruiz erupted. Pyroclastic flows melted ice and snow at the summit which formed lahars that rushed down several river valleys. The lahars were up to 50 metres thick and travelled more than 100 kilometres.^[1]

Many houses and towns were devastated by the lahars. The town of Armero was completely covered by debris, killing approximately 21,000 people (out of 28,700). The eruption caused an estimated 23,000 deaths, 5,000 injuries, and destroyed more than 5,000 homes. This was the second-deadliest volcanic disaster in the 20th century (the 1902 eruption of Mount Pelée was the worst).

Survivors who fled to other towns in the area were gradually housed in new government schemes, but problems for the displaced population occurred for many years after. The villagers were warned about the possibility of the disaster but because of past false information about it happening and the false statements of the Tolima Department Governor, among other officials, saying that the volcano was not going to erupt, many people did not believe these warnings.

There were hundreds of cases where people a few feet apart were either killed by the massive mud and stone wave or survived the disaster. Among the terrible consequences for survivors was that the temperature of the mud and rock avalanche served as a gigantic culture media for all kinds of pathogenic fungus and bacteria. Some survivors who had minor cuts were killed by the infections, which could not be treated with known antibiotics.

Several years later the scarred sides of the creeks along which the lahar flowed were clearly visible from commercial airplanes.

Even in the mid 1990s the town was covered with up to 20 feet of ash and debris. Local villagers harvested stones for building work and often, still found human bones that they placed on the shrines that dot the area. A few small trees were trying to grow, protected from wandering animals by makeshift fences.

A lack of preparation contributed to the high death toll. Armero had been built directly on old mudflows and authorities ignored a hazard-zone map which showed the potential damage to the town if lahars were to avalanche down the mountain. Habitants were also told to stay inside and avoid the falling ash, not thinking the mudflows would bury them.

The eruption cost Colombia 7.7 billion dollars; about 20% of the country’s GNP for the year in question.

Nevado del Ruiz has been called "the Sleeping Lion" by the local towns around it.

Now a new system can detect lahars, giving people more warning to evacuate before they happen. The system involves the use of acoustic flow monitors (AFM) which analyze ground shaking that could potentially result in a lahar. These AFMs are placed in the volcano and warn officials if there is an exceedingly high amount of shaking.