The first signs were not spectacular, which is part of why they were dangerous. In September 1985, Nevado del Ruiz began to show increasing seismic unrest, and by late October and early November the volcano was sending a sequence of warnings that geologists could interpret but no community could easily live with. Earthquakes, ash emissions, fumarolic activity, and the warming of crater lakes all pointed to pressure rising beneath the summit. The mountain was not yet erupting in a way the public could see from the valleys, but the system was no longer quiet. Its language was technical before it was visible, and that made it easy to underestimate.
What made the situation especially grave was not simply that the volcano had awakened, but that its warnings came in a form requiring translation. On 7 October 1985, a hazard map was issued identifying zones at risk from lahars generated by an eruption. The map did not emerge from guesswork or hindsight. It was based on known topography, on the volcano’s structure, and on the historical behavior of mudflows that had already shown how quickly volcanic debris could funnel into valleys. It was, in the plainest sense, a map of consequences. Yet a hazard map is only effective if the people who receive it can read it as a forecast rather than as an abstract cartographic exercise. In the case of Nevado del Ruiz, the information existed, but its meaning had not yet become a command.
By early November, concern had become formalized. The volcano’s activity drew increasing attention from Colombian authorities and from the volcanological community. International experts, including those linked to the United Nations system and the US Geological Survey, had reason to worry that ice-melt combined with pyroclastic activity could unleash lahars capable of reaching populated areas far downstream. The issue was not whether such flows were physically possible. That had already been established. The issue was whether the warning could be translated into public action before the mountain changed from a source of concern into a source of death.
The hazard was not hypothetical in the technical sense, but it remained socially unreal to many of the people most exposed to it. In Armero, the signs of distant unrest were filtered through daily life. People prepared for ordinary rain, not volcanic mud. Families shopped in the market. Children went to school. Streets were used, not evacuated. Shops opened, accounts were tallied, meals were cooked, and the town’s routines proceeded with the confidence of habit. That was the great vulnerability of the moment: a community can hear that a mountain is angry and still believe its own streets are too far away to matter. The distance between scientific knowledge and human readiness was not measured in kilometers alone. It was measured in trust, in authority, and in the ability of warnings to interrupt ordinary time.
The public record of this phase shows a widening gap between what scientists knew and what officials were prepared to require. The warnings did not become mass evacuation. In part, that was because the threat was not a single force but a sequence of possible outcomes, and because officials feared the social cost of moving tens of thousands on incomplete certainty. Evacuating a town before an eruption is not just a logistical act; it is a political one. It can expose officials to accusations of alarmism if the event subsides. It can disrupt work, school, transport, and commerce. But the volcano did not pause for administrative caution. In a mountain town, uncertainty feels like postponement; in a volcano, postponement can be fatal.
The communications chain itself became part of the danger. Scientists and civil authorities were trying to push a message through government offices, local radio, and regional decision-makers while the volcano continued to vent steam and ash. The pressure was no longer merely geological. It was administrative. Who had authority to order evacuation? Who would bear the blame if the eruption weakened? Who would answer if people were sent home from work and school for a threat that had not yet fully materialized? Those are not rhetorical questions in a disaster archive; they are the questions that determine whether a warning becomes a life-saving order or an after-action report.
In this phase, the named institutional figures and documents mattered because they were supposed to convert knowledge into response. The 7 October hazard map is one of the central documents of the warning period, a formal artifact that tied risk to geography. The volcanic unrest documented in September, late October, and early November gave that map urgent relevance. Yet the existence of the document did not guarantee use. The problem was not the absence of evidence. It was the failure of evidence to compel decisive movement on the ground.
The tension intensified as the days passed. Authorities and scientists were not discussing a remote possibility but the mechanics of a likely disaster: glacier ice in the summit area, volcanic heat, sudden meltwater, and the long channels by which lahars could race into settled valleys. International experts linked to the United Nations system and the US Geological Survey were concerned precisely because the physics were unforgiving. Once a lahar forms, its movement is determined by gravity and topography, not by human wishes. The town of Armero sat in the path of that logic. Its vulnerability had already been mapped; what remained uncertain was whether the map would become action before the mountain forced the issue.
The human decisions in those hours mattered because the threat was approaching at the pace of physics. On the evening of 13 November, the summit erupted. That was the instant the mountain stopped being a warning and became a machine for destruction. The eruption itself was comparatively modest by the standards of volcanic history, but modest is a misleading word when applied to a glacier-clad cone above inhabited valleys. A small eruption can still be enough to melt ice, mobilize sediment, and send lethal slurries roaring outward. The disaster did not require a gigantic explosion. It required only enough heat and force to activate the landscape already primed for catastrophe.
Before the eruption, there was one more hour of normalcy, the kind communities later describe with unbearable clarity: a final meal, a last errand, a radio broadcast heard and not acted upon, a schoolhouse still lit, a street still dry. The scientists had already calculated the hazard; the town had not yet fully accepted it. In the documentary record, this is the hinge moment, the place where preventability becomes visible in retrospect. The volcano was now in motion, and the next act would belong to force.
The key figure who carried the burden of this warning phase was Luis Eduardo Larios, then director of civil defense in the region. He stood at the point where technical warning was supposed to become public safety action. His responsibilities were procedural and political at once: to weigh incomplete information, to navigate administrative hesitation, and to judge whether the danger warranted moving people who had not yet seen any direct sign of disaster in their own streets. The role was not glamorous. It was the uncelebrated work of turning forecasts into orders. The record of the failure to evacuate Armero before the eruption cannot be reduced to one official alone, but Larios stood inside the chain of authority where urgency was meant to become action, and where delay proved disastrous.
That is why the warning signs of late 1985 matter so much in the history of Nevado del Ruiz. They were not vague omens. They were measurable events: seismic unrest beginning in September, the hazard map issued on 7 October, growing concern by early November, and the eruption on 13 November. Each step narrowed the window. Each document and report sharpened the stakes. Each delay made the same truth harder to escape: the evidence had existed before the catastrophe, but the response did not rise fast enough to match it.
By nightfall, the mountain had made its choice. The eruption began, and the valleys below had only minutes to learn what the warning signs had meant.