How Volcanoes Work

 Image Described in Caption
 Andesite flows on Lascar Volcano -- Located in Chile, the Lascar volcano is the most active stratovolcano in the central Andes. The most impressive features on the flanks of the volcano are two massive andesite flows exhibiting thick flow margins tens of meters high and well-developed lava levees. The transverse ridges on the central andesite flow are called ogives. They develop as folds perpendicular to the direction of flow, which are sometimes ramped upward along faults generated by brittle deformation of the flow interior. Courtesy of Peter Francis.