How Volcanoes Work

 Image Described in Caption
 The November 13, 1985 lahar from Nevado del Ruiz -- The lahar deposit forms the flat plane at the base of the River Lagunillas canyon. The lethal lahar killed over 23,000 people, most of which were from the town of Armero, located about 70 kilometers from the summit of the volcano. Courtesy of R.J. Janda, USGS.