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 detected volcanic activity two months earlier.

The relief workers were horrified by the landscape of fallen trees, disfigured human bodies, and piles of debris from entire houses.

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.

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.

[4] 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.

[5] Built on top of an alluvial fan[6] that had been host to historic lahars, the town was previously destroyed by a volcanic eruption in 1595 and by mudflows in 1845.

[12] One week before the eruption, Marxist insurgents attacked and laid siege to the Palace of Justice in Bogotá, planning to hold a trial involving Colombian president Belisario Betancur.

[nb 1] This map highlighted the danger from falling material—including ash and rock—near Murillo, Santa Isabel, and Libano, as well as the threat of lahars in Mariquita, Guayabal, Chinchiná and Armero.

[21] Around 5:00 p.m. an emergency committee meeting was called, and when it ended at 7:00 p.m., several members contacted the regional Red Cross over the intended evacuation efforts at Armero, Mariquita, and Honda.

The storm's heavy rain and constant thunder may have overpowered the noise of the volcano, and with no systematic warning efforts, the residents of Armero were completely unaware of the continuing activity at Ruiz.

The lake's hot, acidic water significantly accelerated the melting of the ice, an effect confirmed by the large amounts of sulfates and chlorides found in the lahar flow.

[14] The lahars, formed of water, ice, pumice, and other rocks,[27] incorporated clay from eroding soil as they traveled down the volcano's flanks.

[31] The front of the lahar contained boulders and cobbles that would have crushed anyone in their path, while the slower parts were dotted by fine, sharp stones which caused lacerations.

Martí and Ernst state in their work Volcanoes and the Environment that they believe that many who survived the lahars succumbed to their injuries as they were trapped, or contracted hypothermia, though the latter is unlikely, given that survivors described the water as warm.

[36] The loss of life was exacerbated by the lack of an accurate timeframe for the eruption and the unwillingness of local authorities to take costly preventative measures without clear signs of imminent danger.

[37] Because its last substantial eruption had occurred 140 years earlier, it was difficult for many to accept the danger presented by the volcano; locals even called it the "Sleeping Lion".

The lahars had left behind a gray mass which covered the entire town, which was dotted with broken trees and horribly disfigured bodies.

[40] Scientists who later analyzed the seismograph data noticed that several long-period earthquakes (which begin strongly and then slowly die out) had occurred in the final hours before the eruption.

[41] The Nevado del Ruiz eruption occurred two months after the 1985 Mexico City earthquake, limiting the amount of supplies that could be sent to each of the disasters.

[46] The eruption was used as an example for psychiatric recuperation after natural disasters by Robert Desjarlais and Leon Eisenberg in their work World Mental Health: Problems and Priorities in Low-Income Countries.

One study showed that the victims of the eruption suffered from anxiety and depression, which can lead to alcohol abuse, marital problems and other social issues.

[45] Rafael Ruiz, a National Army major who briefly served as Armero's provisional mayor after the disaster, stated that there were survivors who, due to the trauma of the event, were "jittery", experienced "nightmares", and suffered from "emotional problems".

Armero had been built on an alluvial fan[6] that had been overrun by historic mudflows; authorities had ignored a hazard-zone map that showed the potential damage to the town from lahars.

She attracted the attention of the reporters at the site because of her sense of dignity and courage, and caused controversy when people wondered why the photographer had not saved her (which was impossible without equipment).

[48] An appeal to the government for a pump to lower the water around Sánchez was left unanswered, and she succumbed to gangrene and hypothermia after sixty hours of being trapped.

Her death epitomized the tragic nature of the Armero disaster – she could have been saved had the government responded promptly and addressed the concerns over the volcano's potency.

The mayor of Armero, Ramon Rodriguez, and other local officials had tried to bring the volcano's potential eruption to the attention of the Colombian government, but to no avail.

Rodriguez once referred to the volcano as a "time bomb" and told reporters that he believed an eruption would disrupt the natural dam above Armero, resulting in floods.

[53] Lahars pose a threat to the nearby towns of Honda, Mariquita, Chinchiná, Ambalema, Herveo, Villa Hermosa, Puerto Salgar and La Dorada.

All Colombian cities were directed to promote prevention planning to mitigate the consequences of natural disasters,[56] and evacuations due to volcanic hazards have been carried out.