In November 1985, a volcanic eruption composed of many layers of lava alternating with hardened volcanic ash and other pyroclastic rocks, producing swift moving currents of hot gas and rock which causes mud and debris flows which threaten human life and the environment, occurred. Its intensity was such that the hot gas was able to melt off mountain snow-caps, and adding large quantities of water to flow.

It is located on the border of the departments of Caldas and Tolima in Colombia, about 129 kilometers west of the capital city Bogota. The eruption buried the town of Armero causing 2, 500 deaths. It also caused atmospheric warming, and still poses a threat to nearby towns.