Nevado del Ruiz is the northernmost great volcano of the Andes, its 5,300-metre summit capped with glacial ice. The town of Armero — a prosperous cotton and rice centre of about 29,000 people — sat 48 kilometres away in the valley of the Lagunilla river, built directly on the deposits of mudflows that had destroyed earlier settlements on the site in 1595 and 1845.
The volcano woke in late 1984. Through 1985, scientists — Colombian and international — monitored the unrest and warned of exactly the danger that history recorded: an eruption would melt the ice cap and send lahars (volcanic mudflows) down the river valleys. In October 1985 a hazard map was completed showing Armero in the path of mudflows with high probability. Its publication was criticized in places as alarmist; distribution was limited; committees deliberated.
13 November 1985
At 15:06 a moderate eruption dusted the region with ash. Officials debated evacuation through the afternoon; radio broadcasts and the local priest reassured Armero’s residents. Rain kept people indoors.
At 21:09 the main eruption came — modest by volcanic standards, perhaps a hundredth the size of Mount St Helens 1980. It was enough. Pyroclastic flows melted roughly a tenth of the ice cap. Meltwater, ash, and debris churned down the valleys, gathering soil and boulders, growing into lahars tens of metres thick moving at up to 50 km/h.
Shortly after 23:30 the first wave reached Armero, preceded by a flood as a natural dam upstream broke. Successive pulses of grey concrete-like mud rolled over the town for more than an hour. By morning about 85 per cent of Armero was gone. Around 23,000 people died there, with some 2,000 more killed in other valleys, including at Chinchiná on the volcano’s far side.
Omayra
Rescue was improvised, slow, and short of everything. Its symbol became Omayra Sánchez, a 13-year-old girl trapped to the neck in water and debris, pinned by the wreckage of her own house. For nearly three days she spoke calmly with rescuers and journalists — no pump capable of freeing her arrived in time — before she died on 16 November. Frank Fournier’s photograph of her final hours won World Press Photo of the Year and forced a global reckoning with how preventable it had all been.
The eruption had been predicted in kind, in path, and nearly in scale. The failure was administrative: warnings diluted, maps shelved, the cost of a false alarm feared more than the hazard. Colombia created a national disaster-preparedness system in direct response, and “Armero” became volcanology’s shorthand for the gap between knowing and acting.