Nevado del Ruiz Volcanic Eruption – Colombia – November 13, 1985

Colombia’s Nevado del Ruiz erupted and mudflows swept down from a height of 17,500 feet.

On November 13, 1985, Colombia’s Nevado del Ruiz, South America’s most northerly active volcano, erupted close to midnight. Pyroclastic flows melted ice and snow at the 17,500-foot summit, forming mudflows that rushed down several river valleys. These mudflows, known locally as lahars, were as thick as 150 feet and they traveled at more than 65 mph, devastating houses and towns in their paths. The town of Armero, fifty miles from Colombia’s capital, Bogota, was completely covered by them, killing 21,000 of its population of 28,700. In all there were 23,000 deaths, 5,000 injuries, and the destruction of more than 5,000 homes.

There were hundreds of instances where people that were only a few feet apart were either killed or survived the massive mudflows. Among the terrible consequences for some survivors was that the high temperature of the mudflows had made them collectors of all kinds of pathogenic fungi and bacteria. Some survivors who had minor cuts were killed by the infections because they could not be treated with known antibiotics. The villagers had been warned of the impending disaster but, because of false information that had been circulating about it for some time, these warnings were ignored. The first sign of activity occurred in the afternoon of November 13 and local officials immediately ordered a general evacuation but then cancelled it within a couple of hours when the mountain became quiescent.

Nevado del Ruiz is an active volcano with a history of generating deadly volcanic mudflows from relatively small-volume eruptions. In 1595, a lahar swept down the valleys of the River Guali and the River Lagunillas, killing 636 people. In 1845, an immense lahar flooded the upper valley of the River Lagunillas, killing over 1,000 people. It continued for forty-five miles downstream before spreading across a plain in the lower valley floor. The young village of Armero was built directly on top of the 1845 mudflow deposit. Over the ensuing years, Armero grew into a vibrant town with over 27,000 residents. On November 13, 1985, history repeated itself for the third time in four hundred years, with another eruption and another deadly lahar racing down the River Lagunillas.

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. Several years later, the scarred sides of the creeks along which the lahar flowed were clearly visible from commercial aircraft. Even in the mid-1990s the town was covered with up to twenty feet of ash and debris. Local villagers harvested stones for building work. A few small trees were trying to grow, protected from wandering animals by makeshift fences. The eruption cost Colombia 7.7 billion dollars; about 20 percent of the country’s GNP for the year in question. Following the 1985 eruption, Nevado del Ruiz remained active for several more years, culminating in smaller eruptions in 1991 and 1992, well below the VEI of 3 that defined the 1985 eruption.

Ultimately, this was a tragedy that could have been averted. Nevado del Ruiz had served up a steady menu of minor earthquakes and steam eruptions for fifty-one weeks prior to the November 13 eruption. The on- going activity was just enough to keep people nervous, but not enough to convince authorities that the volcano provided a real threat to the communities surrounding the volcano. Since Colombia had no equipment to monitor the volcano, or geologists skilled in using such equipment, expertise could only come from other countries. A scientific commission and some journalists visited the crater in late February and soon after a report of the volcanic activity first appeared in the newspaper La Patria in early March.

By July, seismographs were obtained from several countries that would help in plotting the movement of rising magma beneath the volcano. Money was obtained from the Unified Nations to help map the areas that were thought to be at the greatest risk. The resulting report and volcanic hazards map were finished on October 7, but only ten copies were distributed. Based on the report, the National Bureau of Geology and Mines declared that a moderate eruption would produce a percent hundred percent probability of mudflows with the greatest danger for Armero.