Nevado del Ruiz Eruption (1985)

On November, 11, 1985, a small volcanic eruption generated destructive lahars (mudflows), burying the town of Armero, killing over 23,000 persons, injuring 4,000, and rendering homeless another 7,000. Infrastructure was severely damaged. The lahars destroyed over 8,400 acres of agricultural land, destroying industrial plants, schools, roads, bridges, and houses. Damage was estimated in excess of $1 billion. The cost to the Colombian economy was $7.7 billion, one-fifth of the country's Gross Domestic Product (GDP).

Located in the South American Andes, Nevado del Ruiz, a stratovolcano, stands at 16,200 feet. Known locally as “the sleeping lion,” the volcano had lain dormant for over 100 years prior to the 1985 eruption. Lahars have been generated by past eruptions, most notably in 1595, in which over 600 were killed; and 1845, where the town of Ambalema was destroyed and 1,000 people were left dead. Armero had been built on the solidified remains of the 1845 lahars.

Initial volcanic activity began in November 1984, when minor earthquakes no greater than magnitude 4.0 were detected on the upper flanks of the volcano. A minor explosion of ash rock fragments shooting 650 feet into the air occurred on December 22. The first few months of 1985 saw a series of small eruptions. After numerous recommendations from scientists, a network of seismic monitoring stations was installed in July and August by Instituto Colombiano de Minería y Geología (INGEOMINAS) and the Volcanic Risk Committee in Manizales. A small eruption on September 11 lasted for seven hours, causing minor ash to shower on the town of Manizales. A small lahar was generated and flowed 88 feet down the Azufrado river valley, but no damage was reported. Work on a volcanic hazard map outlined the areas that would be affected by lahars should Nevado del Ruiz erupt.

A month later, INGEOMINAS scientists declared with 100 percent probability that an eruption would melt the ice cap and generate mudflows, posing a grave danger to Armero. Colombian scientists published a volcanic hazard map on October 7, highlighting the areas at high risk of lahars, namely Armero and Chinchina. Due to a rebel attack in Bogota, the publication of the new hazard map was postponed to November 15.

[Page 446]On November 13, just after 9:00 P.M. local time, a more serious plinian eruption spewed 65 million cubic feet of hot ash and rocks across the volcano's snow-covered glacier, triggering the melting of approximately 10 percent of the volcano's glacial ice cap. This in turn generated 165-foot-wide lahars, which rushed down the steep river valleys at speeds of up to 30 miles per hour. The lahars entered river channels with extreme flooding exacerbated by heavy rainfall, then overwhelmed the town of Armero. The town was left buried 10–25 feet deep in mud, with the largest lahar measuring greater than 148 feet deep. Two hospitals, 50 schools, over 5,000 homes, and 8,400 acres of agricultural land were buried or destroyed by lahars. Rescue efforts were hampered by impassable roads and destroyed bridges.

The death toll could have been greatly averted if the warnings from geologists and scientists had been taken seriously, and the surroundings towns had been evacuated. Instead the disaster embodies all the hallmarks of human error. The local authorities were not willing to evacuate the area, possibly for the fear of a false alarm, social displacement, or potential economic losses. The government and agencies failed to respond to the looming and increased threat of eruption, despite warnings from scientists. Information between INGEOMINAS, the Volcanic Risk Committee in Manizales, local media, and government were not disseminated or communicated in the appropriate fashion. Prior to the disaster, public perception of the looming threat changed daily, and reports were conflicting and changing on a daily basis. Leading figures from the local community openly criticized the media coverage, accusing the local press of spreading “volcanic terrorism.” The chamber of commerce in Manizales blamed the media coverage for potentially causing economic losses in the region, adding that the volcanic hazard map was damaging local property prices.

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