Photograph R.J. Janda on December 2, 1985

Armero, Colombia, destroyed by a lahar on November 13, 1985. The lahar was caused by the rapid melting of snow and ice on the volcano by hot pyroclastic flows and surges erupted from the summit crater. As floods of water descended the volcano, they picked up loose debris and soil from the canyon floors and walls, growing both in volume and density, to form hot lahars. In river valleys farther down the volcano's flanks, the lahars were as thick as 40 m and traveled as fast as 50 km/hour. Two and a half hours after the start of the explosive eruption, one of the lahars reached Armero, 74 km from the explosion crater.

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Last modified: February 5, 1999