Rock cycle, illustration. This sequence of six images shows stages of the cycle of rock formation and destruction on Earth. At upper left, a volcanic eruption produces lava (molten rock) that cools to form igneous rock. At upper centre, this igneous extrusion is still molten but trapped below the overlying rock as it cools. At upper right, the igneous extrusion has solidified and erosion is wearing away the overlying rock to expose the hard igneous rocks. At lower left, continued erosion is wearing down the rocks, producing and transporting sediments that collect in layers under an ocean. The lower layers start to compress to form sedimentary rocks. At lower centre, sedimentary rocks under an ocean (oceanic crust) are subducted at a tectonic plate boundary (yellow arrows) to be melted as they reach the mantle. The cycle concludes at lower right, with tectonic compression and renewed volcanic activity producing metamorphic rocks.