Abrasion is another type of mechanical weathering. With abrasion, one rock bumps against another rock. Gravity causes abrasion as a rock tumbles down a slope. Moving water causes abrasion it moves rocks so that they bump against one another ( Figure below ). Strong winds cause abrasion by blasting sand against rock surfaces. Finally, the ice in glaciers cause abrasion. Pieces of rock embedded in ice at the bottom of a glacier scrape against the rock below. If you have ever collected beach glass or pebbles from a stream, you have witnessed the work of abrasion.
John liked to walk by the creek near his house. His favorite thing about exploring the creek was looking for pebbles to add to his collection. John liked watching the water pass over the rocks. Sometimes the rocks rolled into each other.
Were the rocks smaller or bigger in the past?