How Volcanoes Work

 Image Described in Caption
 Tuff ring, Saudi Arabia -- This tuff ring was generated about 200,000 years ago by a hydrovolcanic eruption in the high central vent system of the Harrat Khaybar volcanic field, western Saudi Arabia. The light color of the erupted debris is typical attributed to the felsic nature of the erupting magma (a differentiated rock called comendite). Photo by Vic Camp