Mechanical (Physical) Weathering What causes it? What happens? What do the effects look like? 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.  Mechanical Weathering is…  …the physical breaking down of rock is into smaller pieces.

What can cause mechanical weathering?  Pressure release  Ice wedging/ freezing & thawing  Animals burrowing  Plant roots  Abrasion by wind or water  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  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)  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  Abrasion by:  Wind  Water