How Volcanoes Work

 Image Described in Caption
 Chao coulee -- Like other coulees, the Chao coulee in northern Chile is a cross between a lava flow and a lava dome. It is 14.5 km long, with flow fronts between 350 and 400 meters. This thick dacite extrusion spread laterally due to high shear stresses which exceed the flow's yield strength. The high shear stresses were partly the result of the lava advancing down a steep slope. The Chao coulee is less than 100,000 years old. Courtesy of Peter Francis.