Physical, or mechanical, weathering is a geological process of breaking rocks apart without changing their chemical composition, according to the American Geosciences Institute. Ice wedging, plant activities and rapid moving water physically weather rocks as a result of extreme pressure or impact.
Learn more about Erosion & Weathering
- Ice wedgingAs small crevices of rock fill with water and the temperature dips below freezing, the fluid expands as it freezes, exerting substantial pressure on the rock. The ice behaves like a wedge, widening the crack. As the temperature rises, the water melts and the rock contracts. The repeated expansion and contraction can cause the rock to break apart.
- Plant activitiesThe pressure of the confined roots of plants growing in cracks in rocks can be tremendous. As the plant grows, the pressure can become great enough to expand the crack, ultimately breaking the rock apart. An everyday example is weeds growing in cracks in the sidewalk.
- Rapid moving waterRocks on the bottom of a stream can lift for brief periods of time as water moves swiftly. Their impact with other rocks causes physical weathering as small pieces break off.