Id There Nothe Rrisk of the Nevado Ruiz Erupting Again

NEVADO DEL RUIZ (1985)

OVERVIEW

The Colombian volcano Nevado del Ruiz is an agile stratovolcano with a history of generating deadly volcanic mudflows ( lahars ) from relatively pocket-sized-volume eruptions. In 1595, a lahar swept downwards 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 1000 people. It continued for seventy kilometers 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 boondocks with over 27,000 residents. On November 13, 1985, history repeated itself for the third time in 400 years, with another eruption and some other mortiferous lahar racing down the River Lagunillas. This time, over 23,000 people were killed, including most of the residents of Armero. With proper planning, this tragedy could take been averted. Click volcanic hazards map for more information.

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LOCATION

Nevado del Ruiz is the northernmost of several Colombian stratovolcanoes in the Andes Volcanic Concatenation of western S America. The Andean volcanic belt is generated by the east subduction of the Nazca oceanic plate beneath the Southward American continental plate. Typically, such stratovolcanoes generate explosive Plinian eruptions with associated pyroclastic flows that can cook snow and glaciers near the elevation, thus producing devastating lahars.

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THE NEVADO DEL RUIZ VOLCANO

With a summit summit of v,389 thou (over 17,500 ft), Nevado del Ruiz is the highest of the Colombian volcanoes. Even though it is located only ~500 km from the Earth'due south equator, its loftier pinnacle is covered with ~25 foursquare kilometers of snowfall and ice. Its name, Nevado, means "snowfall-capped". During the volcanic outbursts of 1595, 1845, and 1985, large volumes of meltwater were derived from melting of the ice pack by hot pyroclastic flows erupting at the summit. Its chief crater, Arenas, lies about the northeastern edge of the ice pack. Because all three of these contempo eruptions were from the Arenas crater, it is not surprising that the resulting lahars invaded the valleys radiating northeastward from the elevation (see volcanic hazards map ).

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THE Nov xiii, 1985 ERUPTION

After nearly a yr of minor earthquakes and steam explosions from Nevado del Ruiz, the volcano exploded violently on November 13, 1985. The initial blast began at 3:06 p.m., and two hours afterwards pumice fragments and ash were showering down on Armero. Nevertheless, the citizens of Amero remained calm. They were placated by reassuring messages from the mayor over radio, and from a local priest over the church public accost organization. Nevertheless, the Cherry Cross ordered an evacuation of the town at vii:00 p.m. However, presently later on the evacuation guild the ash stopped falling and the evacuation was called off.

At nine:08 p.thousand., only as calm was being restored, molten rock began to erupt from the summit crater for the first time (all previous eruptions were steam explosions). The fierce ejection of this molten rock generated hot pyroclastic flows and airfall tephra that began to melt the summit water ice cap. Unfortunately, a storm obscured the summit area so that near citizens were unaware of the pyroclastic eruption. Meltwater speedily mixed with the erupting pyroclastic fragments to generate a serial of hot lahars. 1 lahar flowed downward the River Cauca, submerging the village Chinchina and killing 1,927 people. Other lahars followed the paths of the 1595 and 1845 mudflows. Traveling at 50 kilometers per hour, the largest of these burst through an upstream damn on the River Lagunillas and reached Armero two hours afterward the eruption began. About of the town was swept abroad or cached in but a few brusk minutes, killing three quarters of the townspeople.

Lahar inbound the outskirts of Armero	Amero was located in the center of this photograph

A few days before the disaster, a Colombian geology student, José Luis Restrepo, had come up to Armero on a field trip. Afterwards playing billiards, he was returning to his hotel at about ten:l p.m., when the lahar arrived. His recollection of events were recorded by Dr. Barry Voight:

"Nosotros didn't hear whatever kind of alarm, fifty-fifty when the ash was falling and we were in the hotel . . . we turned on the radio . . . The mayor was talking and he said not to worry, that it was a rain of ash, that they had not reported anything from the Nevado, and to stay calm in our houses. There was a local radio station and we were listening to it, when suddenly it went off the air . . . most fifteen seconds later, the electric power went out and that's when we started hearing the noise in the air, like something toppling, falling, and we didn't hear annihilation else, no warning . . . The priest from Armero had supposedly spoken on a loudspeaker [effectually six:00 p.m.] and had said the same thing: that at that place was no need to get out Armero . . . When we went out, the cars were swaying and running people down . . . in that location was full darkness, the just light was provided by cars . . . nosotros were running and were nigh to attain the corner when a river of h2o came downward the streets . . . we turned around screaming, towards the hotel, considering the waters were already dragging beds along, overturning cars, sweeping people abroad . . . we went back to the hotel, a 3-story building with a terrace, built of cement and very sturdy . . . Of a sudden, I heard bangs, and looking towards the rear of the hotel I saw something like foam, coming down out of the darkness . . . Information technology was a wall of mud approaching the hotel, and sure plenty, it crashed confronting the rear of the hotel and started burdensome walls . . . . Then the ceiling slab fractured and . . . the entire edifice was destroyed and cleaved into pieces. Since the edifice was made of cement, I thought that it would resist, but the boulder-filled mud was coming in such an overwhelming way, like a wall of tractors, razing the city, razing everything . . . . And then the university bus, that was in a parking lot next to the hotel, was higher than us on a wave of mud and on fire, and it exploded, and so I covered my confront, thinking this is where I dice a horrible decease . . . There was a picayune girl who I thought was decapitated, but . . . her head was cached in the mud . . . A lady told me, 'look, that girl moved a leg'. Then I moved toward her and my legs sank into the mud, which was hot just non burning, and I started to get the little girl out, simply when I saw her hair was caught, that seemed to me the virtually unfair thing in the whole world." -- from A. Scarth (1999)

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WHAT WENT WRONG?

When rescuers arrived at Armero on November 14, they were greeted by a horrible scene. They institute tangled masses of trees, cars, and mutilated bodies scattered throughout an sea of grayness mud. Injured survivors lay moaning in desperation while workers tried frantically to save them. Birthday, near 23,000 people and fifteen,000 animals were killed. Another 4500 people were injured and about 8000 people were made homeless. The estimated cost of the disaster is $1,000,000,000, or about one-fifth of the Republic of colombia'due south Gross National Product.

This is a tragedy that could have been averted. Nevado del Ruiz had served up a steady menu of small-scale earthquakes and steam eruptions for 51 weeks prior to the Nov thirteen eruption. The on-going action was just enough to keep people nervous, merely 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 to monitor earthquakes which would help in plotting the movement of rising magma beneath the volcano. Money was obtained from the Unified Nations to aid map the areas that were thought to exist at the greatest risk. The resulting report and volcanic hazards map were finished on October seven, just only x copies were distributed. Based on the report, the National Bureau of Geology and Mines (INGEOMINAS) declared that a moderate eruption would produce " . . . a 100 percent probability of mudflows . . . with smashing danger for Armero . . . Ambalema, and the lower function of the River Chinchina." However, some government officials dismissed the report as "besides alarming" and authorities did not want to evacuate people until they were assured of the necessity. Continuous earth tremors began beneath the volcano on November 10. This prompted a group of scientists to visit the crater on Nov 12. Notwithstanding, they saw goose egg to suggest eminent danger and they did not recommend an evacuation. The 23,000 people that would die the following day would underscore a tragic failure that led to the 2d near deadly eruption of the twentieth century.

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Source: http://sci.sdsu.edu/how_volcanoes_work/Nevado.html

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