page_title: Armero tragedy
section_title: Precursor
hierarchical_section_title: Armero tragedy / 1985 activity / Precursor
caption_attribution_description: English: In this photo, the volcano’s summit and upper flanks are covered by several glaciers that appear as a white mass surrounding the 1-kilometre-wide Arenas Crater; melt-water from these glaciers has incised the grey to tan ash and pyroclastic flow deposits mantling the lower slopes. A well-defined lava flow is visible at image lower right. This astronaut photograph was taken at approximately 7:45 a.m. local time, when the Sun was still fairly low above the horizon, leading to shadowing to the west of topographic high points.
context_page_description: The Armero tragedy was one of the major consequences of the eruption of the Nevado del Ruiz stratovolcano in Tolima, Colombia, on November 13, 1985. After 69 years of dormancy, the volcano's eruption caught nearby towns unaware, even though the government had received warnings from multiple volcanological organizations to evacuate the area after the detection of volcanic activity two months earlier.
  As pyroclastic flows erupted from the volcano's crater, they melted the mountain's glaciers, sending four enormous lahars down its slopes at 50 kilometers per hour. 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 tragedy, 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.
context_section_description: In late 1984, geologists noticed that seismic activity in the area had begun to increase. 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 Nevado del Ruiz's volcanic edifice.
  An Italian volcanological mission analyzed gas samples from fumaroles along the Arenas crater floor and found them to be a mixture of carbon dioxide and sulfur dioxide, indicating a direct release of magma into the surface environment. Publishing a report for officials on October 22, 1985, the scientists determined that the risk of lahars was unusually high. To prepare for the eruption, the report gave several simple preparedness techniques to local authorities. 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 Nevado del Ruiz became enriched with magnesium, calcium and potassium, leached from the magma.
  The thermodynamic equilibration temperatures, corresponding to the chemical composition of the discharged gases, ranged from 200 to 600 °C (400 to 1,100 °F); this is a measure of the temperature at which the gases equilibrated within the volcano. The extensive degassing of the magma caused pressure to build up inside the volcano in the space above the magma, which eventually resulted in the explosive eruption.
caption: Nevado del Ruiz seen from space. The summit ice cap and glaciers surround the dark Arenas crater.
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