On November 13, 1985, Nevado del Ruiz erupted. Pyroclastic flows melted ice and snow at the summit. This melt formed lahars that rushed down several river valleys. The lahars were up to 50 meters thick and travelled more than 100 kilometers.
Many houses and towns were devastated by the lahars. The town of Armero, Colombia was completely covered by debris. Approximately 21,000 people (out of 28,700) died in Armero. The eruption caused an estimated 23,000 deaths, 5,000 injuries, and destroyed more than 5000 homes.