How Volcanoes Work

 Image Described in Caption Mt. Augustine, Alaska -- A pyroclastic flow from the 1996 eruption of Mt. Augustine in the Aluetian Islands. The glowing avalanche races down the flanks of the volcano at hurricane-force speeds. The avalanche is partly disguised by the more bouyant, billowing ash cloud that rises above it. Courtesy of M.E. Yount, USGS.