A Volcanic Mudflow Buries the Town of Armero

On November 13, 1985, the Nevado del Ruiz stratovolcano in the department of Tolima, Colombia, erupted explosively after nearly seven decades of dormancy. Beginning around 9:09 p.m., the mountain blasted tephra into the atmosphere and unleashed hot pyroclastic flows across its summit. These discharges rapidly melted the volcano's glaciers and snowcaps, sending a series of enormous debris flows known as lahars surging down river channels at high speeds. The resulting torrents of mud, meltwater, and fractured rock descended upon settled valleys below, sweeping directly toward the agricultural center of Armero.

Armero sat several tens of kilometers from the summit on an alluvial fan formed by historical volcanic mudflows. Settlers had long cultivated the surrounding countryside, drawn by fertile volcanic soil that made the town a major producer of rice, cotton, and coffee. However, the exact geography that supported its agriculture placed it directly in the path of drainage corridors. Similar lahars had flattened earlier settlements on the site in 1595 and 1845. When the mud reached Armero around 11:30 p.m. in successive pulses, it swallowed 85 percent of the town, crushing structures and giving residents almost no time to flee.