Which Colombian volcano's 1985 eruption destroyed the town of Armero?

Nevado del Ruiz was the Colombian volcano whose 1985 eruption destroyed the town of Armero.

On November 13, 1985, an eruption melted portions of the volcano’s summit glaciers and snow. The resulting lahars—fast, concrete-like mudflows carrying volcanic debris—raced down river valleys and engulfed Armero, killing more than 20,000 of its roughly 29,000 residents.

The disaster followed nearly seven decades of dormancy. Scientists had detected renewed activity and warnings had been issued, but hazard maps were poorly distributed, communication was disrupted by a storm, and many residents were not evacuated in time.

The event is often called the Armero tragedy, but the volcano itself was Nevado del Ruiz. Mount St. Helens and Cotopaxi are also famous explosive volcanoes, yet neither caused the 1985 destruction of this Colombian town.