How Volcanoes Work

 Image Described in Caption
 La Poruna scoria cone -- This monogenetic basaltic scoria cone located in northern Chile is a typical example of others worldwide. It's edifice is 300 m high and composed of loose scoria (cinder). It is probably only a few thousand years old and, therefore, well-preserved with a classic scoria-cone shape, having steep flanks and a large summit crater. Courtesy of Peter Francis.