Rain and snow push loose rock and soil or sediment down a mountain or along a stream Soil washes away Gravity pulls tons of rocks and soil down a slope in a kind of erosion called mass wasting When moving water or wind speed slows the sediments drop Soil deposits can build up land like deltas and wetlands Large rock piles from rockfalls create cone-shaped talus at mountain bases 6
Heat from the core melts the rock in the middle layer the mantle This heat sets up currents that move the molten rock The motion slowly moves the plates on top of the crust The plate motions create disturbances in the crust Crust Upper Mantle Lower Mantle Outer Core Inner Core 7
Some changes cause mountains to form and land to break apart Different forces break apart rock The rock bits crumble and are deposited on ocean floors in layers Others slip beneath the crust Moving water wind and ice then carry off the crumbling rock The endless force of erosion continues as great mountains crumble and tons of sediments are carried away Volcano Magma Trench Crust Mantle New rock forms when layers of sediment pile on the ocean floor and volcanoes hurl magma out to cool The formation of the three groups of rock and their erosion make the rock cycle 8
Earthquakes and Volcanoes Heavy ocean plates sink below the lighter continental plates Their rocky layers melt into the mantle The motion and the sinking crust causes earthquakes Some rock is forced up making mountain ranges Land uplifts Magma under pressure erupts forming volcanoes 9
