How Volcanoes Work

 Image Described in Caption Tephra and littoral cone on Kilauea, Hawaii -- The episodic steam-driven explosion shown here is one of several tephra jets generated by incoming waves that disrupt lava exiting from a lava tube on the south coast of Kilauea. The basalt tephra accumulates into a littoral cone, the domal mass in the background. Note also the thin pahoehoe flow advancing toward the sea in at the base of the littoral cone. Courtesy of L. Kesthelyi, USGS.