Omahyra

Loss of life was exacerbated by the authorities' failure to take costly preventive measures in the absence of clear signs of imminent danger. There had been no substantial eruption of the volcano since 1845, which contributed to complacency; locals called the volcano the "Sleeping Lion".

The death toll was increased by the lack of early warnings, unwise land use, as villages were built in the likely path of lahars, and the lack of preparedness in communities near the volcano. Colombia's worst natural disaster, the Armero tragedy (as it came to be known) was the second-deadliest volcanic disaster of the 20th century (surpassed only by the 1902 eruption of Mount Pelée). It was the fourth-deadliest eruption recorded since 1500 AD. Its lahars were the deadliest in volcanic history.

In September 1985, as earthquakes and phreatic eruptions rocked the area around the volcano, officials began planning for evacuation. A hazard map was prepared in October; it highlighted the danger from falling ash and rock near Murillo, Santa Isabel, and Líbano, as well as the threat of lahars in Mariquita, Guayabal, Chinchiná, and Armero. The map was poorly distributed to those at highest risk: many survivors had never heard of it, though several major newspapers had featured it. Henry Villegas of the Colombian Institute of Mining and Geology stated that the maps clearly demonstrated Armero would be affected by the lahars, but had "met with strong opposition from economic interests." He said that the short time between the map's preparation and the eruption hindered timely distribution.

The picture later won the World Press Photo of the Year for 1986.

For Example, a punk rock band formed in Chile in 2008 named themselves Omayra Sánchez; they express their "discontent that they feel with the negligence on the part of the people who in this day and age run the world". Adiós, Omayra: La catástrofe de Armero (1988), written by Eduardo Santa as a response to the eruption, depicts the girl's last days of life in detail and cites her in its introduction as an eternal symbol of the catastrophe. In No Morirás (1994), Germán Santa María Barragán writes that of all the horrors he saw at Armero, nothing was more painful than seeing the face of Omayra Sánchez under the ruins of her house. Isabel Allende's short story, "And of Clay Are We Created" ("De barro estamos hechos"), is told from the perspective of a reporter who tries to help a girl trapped under the fireplace of her ruined home. Allende later wrote, "Her [Sánchez's] big black eyes, filled with resignation and wisdom, still pursue me in my dreams. Writing the story failed to exorcise her ghost."

Omayra Sánchez lived in the neighborhood of Santander with her parents Álvaro Enrique, a rice and sorghum collector, and María Aleida, along with her brother Álvaro Enrique and aunt María Adela Garzón. Prior to the eruption, her mother had traveled to Bogotá on Business. The night of the disaster, Omayra and her family were awake, worrying about the ashfall from the eruption, when they heard the sound of an approaching lahar. After it hit, Omayra became trapped under her home's concrete and other debris and could not free herself. When rescue teams tried to help her, they realized that her legs were trapped under her house's roof. Sources differ as to the degree to which Sánchez was trapped. Zeiderman (2009) said she was "trapped up to her neck", while Barragán (1987) said that she was trapped up to her waist.

The Nevado del Ruiz volcano is still active, according to the Volcano Watch Center in Colombia. Melting only 10 percent of the ice would produce mudflows with a volume of up to 200,000,000 cubic meters (7.06×10 cu ft)—similar to the mudflow that destroyed Armero in 1985. Such lahars can travel up to 100 kilometers (62 mi) along river valleys in a few hours. Estimates show that up to 500,000 people living in the Combeima, Chinchiná, Coello-Toche, and Guali valleys are at risk, and 100,000 of these are considered to be at high risk. The city of Armero no longer exists. The site was commemorated as a memorial with Christian crosses and a small monument to Sánchez.

Frank Fournier, a French reporter who landed in Bogotá on November 15, took a photograph of Sánchez in her final days, titled "The Agony of Omayra Sánchez". When he reached Armero at dawn on the 16th, a farmer directed him to Sánchez, who by then had been trapped for nearly three days and was near-deserted. Fournier later described the town as "very haunting," with "eerie silence" punctuated by screaming. He said that he took the photograph feeling that he could only "report properly on the courage and the suffering and the dignity of the little girl" in his attempt to publicize the disaster's need for relief efforts, feeling otherwise "powerless".