How does internal heat create a volcano?
Internal planetary heat rises slowly toward the surface of a planet or moon through a process called convection (see “Convection Cells”). When the heat approaches the surface, it either passes directly through the rocky crust or it escapes via molten material that erupts through rifts in the crust (see “Rift Zone”). The passage or vent through which the hot material escapes is called a volcano. Molten rock and gases rise toward the surface because they are less dense than the surrounding cooler rock. As the cooler rock is eroded by the dynamic flow of the hot rock, chunks break off and sink into the flow where they dissolve. As the chamber of molten rock nears the surface it can form a bulge. Once the hot rock begins to flow above the surface it creates a volcanic peak. If the outflow of molten rock is later blocked by changes below, the chamber may collapse. Collapsed chambers form a geological feature called a caldera. Calderas formed by volcanoes are quite common on Earth. Crater La
