On November 13, residents of Armero felt the earth tremble and heard a series of rumbling explosions emanating from a 17 453-foot stratovolcano volcano. Although it emitted an ominous cloud from the mountain’s crater and rained 3,5 x 10^10 kilograms of dacite and andesite tephra ash down on Armero, the citizens of the farming community were told that it “wasn’t anything serious”.
It was a relatively small eruption causing only small pyroclastic flows and surges. 5% of the ice and snow covering the uppermost reaches of the peak melted, with the ice-cap extending over an area of about 19km2. The blasts, however, were powerful enough to collapse a steep buttress down the summit crater, triggering a major lahar. Rock, snow and ice swept down the slopes of Nevado del Ruiz from an elevation of 15 000-feet. The avalanche liquefied and gathered momentum as it rocketed into the valley bottom at speeds up to 90 miles per hour.
This wreaked havoc on the landscape, as it wiped out a natural dam and sending a enormous mudslide downvalley. The community of Armero and Chinchina were thus immediately flooded and buried beneath 30 feet of gray-brown mud and concrete. It was the worst natural disaster ever recorded in Colombia’s history, killing approximately 21 000 people. While Colombia’s impact was a result of the lahar, it was the eruptions of El Chichon that had a direct impact. Approximately 0.3 km3 of tephra was ejected, causing 187 confirmed deaths and leaving 60 000 people homeless. No lava flow was reported, but pyroclastic flows surges were noted during April eruptions. The first eruptions were characterized by the emission of large amounts of ash, moderate amounts of pumice, and lesser amounts of lithic fragments.
A visible plume was emitted to an altitude of 0.7 km, having a width of 3 km approximately 1 km downwind from the crater rim. This was one of the largest eruptions of the century, and was the worst volcanic disaster ever known in Mexico.
Accumulations of ash also made many roads impassable and forced the closure of airports at the cities of Villahermosa and Tuxtla Gutiérrez, located about 75 km and 70 km, respectively, from the volcano summit. Not surprisingly, a totally unexpected eruption coming in the middle of the night terrified and panicked the local inhabitants. Dozens of people were killed by the ashfalls, and many hundreds began to flee the villages closest to the volcano, seeking the refuge of larger, more distant settlements.