Describe two forms of mechanical weathering.

1.Frost Wedging (Freeze-Thaw)

Water expands by 9 percent when it freezes. As it expands, it exerts up to 4.3 million pounds per square foot of pressure. Since water seeks low points, repeated freezing and thawing can lead to deep vertical fissures as cracks are extended downward. Cracks that allow entry of roots lead to similar wedging.

2.Crystal Formation

Crystal formation cracks rock in a similar way. Most water contains dissolved salts. When water in rock fissures evaporate, the salt concentration increases, which leads to crystallization. This occurs in arid regions where the humidity fluctuates widely, so that the salt can be redissolved and carried into new fissures.

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