Mechanical Weathering

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6 Terms

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Physical/Mechanical Weathering

The breaking down of rocks into smaller particles.

  • Does not change the chemical composition of rocks

  • Generally in places w/ little vegetation and extreme climates.

  • E.g. mountainous regions or deserts

Main types

  1. Freeze thaw Action

  2. Exfoliation

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  1. Freeze-Thaw Action

Most common type

Occurs in mountainous areas where the temperature between day and night is drastically different.

In these areas the temperature frequently rises above and falls below freezing point.

The changing temperature and plentiful rainfall creates the conditions for freeze-thaw action.

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How it Happens

  1. Rainfall can seep into the cracks of rocks.

  2. The water freezes when temps drop below freezing.

  3. As water freezes it can expand by about 10%.

  4. The expansion puts pressure onto the rock and causes the crack to widen.

  5. During the daytime the ice melts with increasing temperatures.

  6. More rainfall can enter the widened cracks

  7. Overtime, the repeated freezing, expanding, thawing and rainwater, will crumble and shatter the rock.

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Onion Weathering

A.K.A. Exfoliation

Specific type of mechanical weathering that occurs in rocks with alternating layers of soft and hard material.

Named after the way onion layers peel away.

The weathering of the rock layers separate in a similar fashion.

Temperature is crucial for exfoliation.

Usually in regions w/ a wide diurnal temperature range

E.g. deserts

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How

  1. In these regions temps soar as high as 50 degrees C.

  2. Causes rocks to expand.

  3. At night temps drop to below 0.

  4. Causes rocks to contract.

  5. A repetition of expansion and contraction.

  6. The rock weakens.

  7. The outer layer shatters and peels off.

  8. The broken layers collect at the base of the rock.

  9. Forms scree.

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Significance

Exfoliation has significant geological and environmental implications.

  • Contributing to the formation of soil.

  • Influencing the stability of slopes and rock formations,

  • Affecting engineering and construction projects.