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How are rocks worn away?

Weathered bouldersWeathered bouldersRocks may appear to be solid and unchanging, but they are being slowly worn away. They are always under “attack” by the weather. Rainwater, frost or even just changes in the temperature can all break up rocks. This is called weathering. Rocks may also be ground down by erosion. This is the removal of rock fragments by water, ice or wind.

How rock is weathered by freezing rainwaterHow rock is weathered by freezing rainwater

Weathering

How does the weather break down rocks? Rocks heat up and expand in the sunshine during the day. At night, they cool down and contract (get smaller). This expansion and contraction, repeated day after day, causes the rock’s surface to crack. Pieces flake off and are blown or washed away. Over many years, the rock disappears. Hard rocks take longer to break down than softer ones.

Rainwater seeps into cracks in the rock. If it later freezes, it expands with great force and splits off pieces of rock. On slopes or cliffs, rockfalls or slides are often the result. Piles of fallen rocks, called scree, build up at the bottom.

Cliffs created by weathering and wind erosionCliffs created by weathering and wind erosion

Deposition

Deforestation (cutting down forest trees) and overgrazing (allowing cattle to graze the land for too long) can speed up the forces of erosion and strip the land of soils.

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