The Armero tragedy ( ) occurred following the eruption of the Nevado del Ruiz stratovolcano in Tolima, Colombia, on November 13, 1985. The volcano's eruption after 69 years of dormancy caught nearby towns unprepared, even though volcanological organizations had warned the government to evacuate the area after they had detected volcanic activity two months earlier.
As pyroclastic flows erupted from the volcano's crater, they melted the mountain's glaciers, sending four enormous lahars (volcanically induced mudflows, landslides, and debris flows) down the slopes at . The lahars picked up speed in gullies and engulfed the town of Armero, killing more than 20,000 of its almost 29,000 inhabitants. Casualties in other towns, particularly Chinchiná, brought the overall death toll to 23,000. Footage and photographs of Omayra Sánchez, a young victim of the disaster, were published around the world. Other photographs of the lahars and the impact of the disaster captured attention worldwide and led to controversy over the degree to which the Colombian government was responsible for the disaster. A banner at a mass funeral in Ibagué read, "The volcano didn't kill 22,000 people. The government killed them."
The relief efforts were hindered by the composition of the mud, which made it nearly impossible to move through without becoming stuck. By the time relief workers reached Armero twelve hours after the eruption, many of the victims with serious injuries were dead. The relief workers were horrified by the landscape of fallen trees, disfigured human bodies, and piles of debris from entire houses. This was the second-deadliest volcanic disaster of the 20th century, surpassed only by the 1902 eruption of Mount Pelée, and is the fourth-deadliest volcanic event recorded since 1500.
The event was a foreseeable catastrophe exacerbated by the populace's unawareness of the volcano's destructive history; geologists and other experts had warned authorities and media outlets about the danger in the weeks and days leading up to the eruption. Hazard maps for the vicinity were prepared but poorly distributed. On the day of the eruption, several evacuation attempts were made, but a severe storm restricted communications. Many victims stayed in their houses as they had been instructed, believing that the eruption had ended. The noise from the storm may have prevented many from hearing the sounds of the eruption until it was too late.
Nevado del Ruiz has erupted several times since 1985, and continues to threaten up to 500,000 people living along the Combeima, Chinchiná, Coello-Toche, and Guali river valleys. A lahar (or group of lahars) similar in size to the 1985 event might travel as far as from the volcano and could be triggered by a small eruption. To counter this threat, the Colombian government established a specialized office which administers the national system for identification, prevention, preparedness and management of natural disasters, the National Unit for Management of Disasters Risk (). The United States Geological Survey also created the Volcano Disaster Assistance Program and the Volcano Crisis Assistance Team, which evacuated roughly 75,000 people from the area around Mount Pinatubo before its 1991 eruption. All Colombian counties, by law, have a territorial plan that includes the identification of natural threats, treatment for building permits and preparedness for the prevention and management of natural disasters through planning programs which have helped save lives in many natural disasters since Armero's tragedy.
In 1988, three years after the eruption, Stanley Williams of Louisiana State University stated that, "With the possible exception of Mount St. Helens in the state of Washington, no other volcano in the Western Hemisphere is being watched so elaborately" as Nevado del Ruiz. Communities living near the volcano have become wary of volcanic activity: when it erupted in 1989, more than 2,300 people living around it were evacuated.
Background
Armero, located from the Nevado del Ruiz volcano and from Colombia's capital of Bogotá, was the third largest town in Tolima Department, after the towns of Ibagué and Espinal. A prominent farming town before the eruption, it was responsible for roughly one-fifth of Colombia's rice production and for a large share of the cotton, sorghum, and coffee crops. Much of this prosperity can be attributed to Nevado del Ruiz, as the fertile volcanic soil stimulates agricultural growth.
Built on top of an alluvial fan In the 1595 eruption, three distinct Plinian eruptions produced lahars that claimed the lives of 636 people.
Ruiz has undergone three distinct eruptive periods, the first beginning 1.8 million years ago. During the present period (beginning 11,000 years ago), it has erupted at least twelve times, producing ashfalls, pyroclastic flows, and lahars. The historically recorded eruptions have primarily involved a central vent eruption (in the caldera) followed by an explosive eruption, then the formation of lahars. Ruiz's earliest identified Holocene eruption was in about 6660 BC, and further eruptions occurred around 1245, 850, 200 BC, and in about 350, 675, in 1350, 1541 (perhaps), 1570, 1595, 1623, 1805, 1826, 1828 (perhaps), 1829, 1831, 1833 (perhaps), 1845, 1916, December 1984 through March 1985, 1987 through July 1991, and possibly in April 1994. Many of these eruptions involved a central vent eruption, a flank vent eruption, and a phreatic (steam) explosion. Ruiz is the second-most active volcano in Colombia after Galeras.
1985 activity
Precursor
thumb|Nevado del Ruiz seen from space. The summit ice cap and glaciers surround the dark Arenas crater.
In late 1984, geologists noticed that seismic activity had begun to increase in the area around Nevado del Ruiz. Increased fumarole activity, deposition of sulfur on the summit of the volcano, and phreatic eruptions also alerted geologists to the possibility of an eruption. Phreatic events, when rising magma encounters water, continued well into September 1985 (one major event took place on September 11, 1985), shooting steam high into the air. Activity began to decline in October, probably because the new magma had finished ascending into Ruiz's volcanic edifice. Another team gave the local officials seismographs, but no instructions on how to operate them.
Volcanic activity increased again in November 1985 as magma neared the surface. Increasing quantities of gases rich in sulfur dioxide and elemental sulfur began to appear in the volcano. The water content of the fumaroles' gases decreased, and water springs in the vicinity of Ruiz became enriched with magnesium, calcium, and potassium, which leached from the magma.
Preparation and attempted evacuation
thumb|A recent hazard map prepared for Nevado del Ruiz and vicinity, showing all of the major disaster zones affected by the eruption
In September 1985, as earthquakes and phreatic eruptions rocked the area, local officials began planning for an evacuation. In October, a hazard map was finalized for the area around Ruiz.