Mechanical (Physical)
Weathering
What causes it?
What happens?
What do the effects look like?
What is Mechanical
Weathering?
 Mechanical Weathering is…
 …the physical breaking down of rock is
into smaller pieces.
What can cause mechanical
weathering?
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

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Pressure release
Ice wedging/ freezing & thawing
Animals burrowing
Plant roots
Abrasion by wind or water
Mechanical weathering by release of pressure
 This is an example of exfoliation
Exfoliation is a kind of mechanical weathering that happens
the pressure or stress on the rock is reduced (usually by the
erosion of whatever was on top)
Another example of
exfoliation:
 Look for this kind of weathering in the core of mountain chains
like the Appalachians Look for this kind of weathering
in New Hampshire
The Onion
 This shows a kind of exfoliation too
Another onion…
 … the release of pressure on the outside of the rock allows the
outer layers to spall
Mechanical weathering can be caused
by plants

In this picture, the tree growth has enlarged the crack in the rock
Mechanical weathering by plants
 Roots growing in the cracks in the rock force it apart
Mechanical Weathering by
Plants
The growth of tree roots forces rocks apart
Mechanical Weathering by
Plants
Root wedging
Mechanical Weathering by Ice
Ice forces rock apart because it expands as it freezes
Mechanical Weathering by Ice
 Example of an environment in which weathering by ice occurs:
Mechanical Weathering by
Wind Abrasion
 The wind carries sand, and acts like sandpaper!
Mechanical Weathering by
Wind Abrasion
Wind abrasion has produced gorgeous landscapes on the
Colorado Plateau west of the Rockies!
Mechanical Weathering by
Water Abrasion
 Sediment carried by water can scour rock like sandpaper!
Mechanical Weathering by
Water Abrasion
 These beach rocks are scoured and polished by wave action:
Mechanical Weathering:
Review
 Rocks physically broken into smaller pieces:
 Pressure release (exfoliation, spalling)
Mechanical Weathering:
Review
 Plants and Animals:
Mechanical Weathering:
Review
 Ice Wedging and Freeze/ Thaw
Mechanical Weathering:
Review
 Abrasion by:
 Wind
 Water