The Rock Cycle and Volcanism

The rock cycle is the conceptual model geologists use to describe the continuous transformation of Earth materials among the three basic rock families: igneous, sedimentary, and metamorphic. Igneous rock forms when molten material, whether magma underground or lava at the surface, cools and solidifies. Weathering and erosion can break any exposed rock down into sediment, which, once compacted and cemented, becomes sedimentary rock. Any rock type, in turn, can be transformed into metamorphic rock if subjected to sufficient heat and pressure without fully melting, and any of the three types can be melted into magma and re-enter the cycle as a new igneous rock. Because the cycle has no fixed starting point and no true endpoint, it is best understood as a set of interconnected pathways, powered jointly by the internal heat driving plate tectonics and volcanism and by the energy of the Sun driving weathering, erosion, and deposition at the surface.