Which volcano’s 1985 eruption caused the Armero tragedy in Colombia?

Nevado del Ruiz’s 1985 eruption caused the Armero tragedy in Colombia.

On 13 November 1985, an eruption melted part of the volcano’s summit ice cap and snow. The resulting water mixed with loose volcanic material, producing fast-moving lahars—mudflows made of water, ash, rock, and debris.

The lahars traveled down river valleys and overwhelmed the town of Armero, killing more than 20,000 people. The disaster became one of the deadliest volcanic events of the 20th century.

Nevado del Ruiz is a glacier-covered stratovolcano in the Andes. A common mix-up is to call the disaster a lava-flow event; the town was primarily destroyed by lahars, not by a broad river of molten lava. The volcano remains active and is monitored closely.