Which Colombian volcano erupted in 1985, producing the lahar that buried the town of Armero?

Nevado del Ruiz erupted in 1985, producing the lahar that buried the Colombian town of Armero. On 13 November, a relatively modest eruption melted snow and ice near the summit, generating torrents of mud, rock, and water.

The lahars travelled through river valleys for many kilometres and reached Armero during the night. The town was overwhelmed, and about 23,000 people died. The disaster became one of the deadliest volcanic events of the 20th century.

Scientists had recognized the danger from the volcano’s ice cap and had issued warnings. However, communication problems, uncertainty, and delayed action meant that many residents were not evacuated in time. The tragedy influenced later volcanic hazard planning in Colombia and elsewhere.

Nevado del Ruiz is a glacier-covered stratovolcano in the northern Andes. It remains active, and its snow and ice make lahars a particularly serious hazard even when an eruption itself is not exceptionally large.