Rock formation and erosion cycle. Cutaway artwork showing the cycle by which rocks are formed and eroded. At top, volcanic activity forms new rock on the Earths surface as molten rock (lava) rises from the Earths mantle (bottom). Weathering and erosion processes then slowly over thousands of years wear down the rock. Wind and water transport the eroded rock, and sediment is deposited at the mouths of rivers and on ocean beds. River deltas may form new land, but the layered ocean sediment is returned to the mantle (orange) at subduction zones, or lifted up by tectonic activity to be eroded once more.
