Nevado del Ruiz

Nevado del Ruiz is a broad, glacier-covered volcano located in west-central Colombia. It is the highest active volcano in the Andes Mountains, reaching an elevation of 17,717 feet (5,400 meters). Located about 80 miles (128 kilometers) west of the Colombian capital of Bogota, the Nevado del Ruiz is one of several stratovolcanoes in the Andes volcanic chain of western South America. The term stratovolcano means it takes the shape of a composite cone, with gentle lower slopes rising steeply near the summit producing an overall concave shape. Although more picturesque, stratovolcanoes can also be among the most deadly. An eruption on Nevado del Ruiz in 1985 was the fourth-deadliest volcanic eruption ever recorded and the deadliest in modern times, killing more than twenty-three thousand people, including most of the residents of the nearby town of Armero.

Background

Eruptions on Nevado del Ruiz, which is sometimes referred to as Mount Ruiz, have been relatively infrequent; however, the volcano does have a history of producing damaging and deadly volcanic events. The most common threat from Nevado del Ruiz are lahars, which consist of debris or mud flows produced by volcanic ash, loose soil, and rock flowing down the sides of the volcano. Because the volcano is covered by glaciers, when it has a volcanic eruption, the heat from the magma melts the glaciers, resulting in a torrent of floodwater that mixes with dirt and debris on the mountain.

Prior to the deadly 1985 eruption, there were two other major events caused by eruptions on Nevado del Ruiz. Geological evidence indicates a major eruption occurred on the mountain in 1595, shortly after the arrival of Spanish colonists, and killed more than six hundred and left a path of destruction extending from central Colombia north to the southern border of Panama. Later, an eruption in 1845 resulted in mudslides and flooding that claimed the lives of more than one thousand people. After the 1845 eruption, the mountain was quiet for 140 years and many forgot about the destruction that had taken place. The town of Armero was built directly on top of the mudflow deposit from the 1845 event, and by 1980, it had grown to become a town of nearly thirty thousand people.

At the time of the catastrophic 1985 eruption, scientists had been monitoring Nevado del Ruiz and pathways that the deadly lahars were likely to take were identified. Nearby communities, including Armero, were warned of the danger. The deadly eruption began in the afternoon of November 13, 1985, with small explosions in the volcano's crater. A minor amount of ash began to fall on Armero, but evacuations were never ordered. The volcano's eruption grew in intensity throughout the evening resulting in the formation of deadly lahars. Later that night, as many in the town of Armero were sleeping, the mudflows overwhelmed the entire city, killing the majority of its inhabitants and people in nearby villages.

Overview

The eruption of Nevado del Ruiz on November 13, 1985, resulted in the melting of an estimated 10 percent of the ice from the glaciers covering the volcano. The resulting floodwater produced massive lahars, which grew in volume and density until they were more than 130 feet (36 meters) thick and traveling at speeds of up to 30 miles (40 kilometers) per hour. It took the lahars less than three hours to reach the city of Armero. Many of the river valley's residents, including those in Armero, would have survived had they moved to higher ground. However, warnings from scientists studying the volcano at the time went unheeded.

The volcano first began showing signs of an imminent eruption more than a year before the deadly 1985 incident. The presence of vapor on Nevado del Ruiz's summit was noted by scientists in addition to a small glacial lake that began filling the bottom of the crater caused by the volcano's heat melting the thick ice pack. In November of 1984, strong earthquake activity began, likely caused by the slow rise of magma within the volcano. Volcanic activity on Nevado del Ruiz increased between December of 1984 and September of 1985. The 1985 eruption and resulting lahars from Nevado del Ruiz resulted in the deaths of more than twenty-three thousand people; injured more than five thousand; destroyed more than five thousand homes, schools, hospitals, and other structures; and cost the country of Colombia more than $1 billion in damages.

Because the tragedy could have been avoided, an intense debate began after over who was to blame for the destruction. A hazard map compiled of the area by scientists—one of the first to be made in Colombia—was widely ignored and misinterpreted. The map and a report issued by the scientists were completed on October 7, 1985, more than a month before the deadly eruption. Upon analyzing the report, the National Bureau of Geology and Mines warned that even a moderate eruption of Nevado del Ruiz would produce a high probability of dangerous lahars, but some government officials dismissed the report. Authorities had also been warned that Armero was built on the deposits made by the deadly 1845 lahar and that a similar disaster could happen again.

Despite warnings from scientists, Armero and other nearby towns were never evacuated. However, the disaster resulted in a greater respect for and further study of volcanic sites. The government of Colombia even created a special program aiming to prevent such catastrophes in the future. Greater effort was also made to more continuously monitor Nevado del Ruiz. Automated networks monitoring seismic and other activity on the mountain were implemented and stationed at the Manizales observatory in Caldas, Colombia. The observatory was declared a permanent international volcano observatory by the Colombian government in early 1986.

Bibliography

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