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Title: 7.1 Weathering (Mechanical
Page #:48
Date: 1/2/13
 Students
will be able to identify the
factors that affect mechanical
 Weathering: The
process in which
materials on or near Earth’s surface
break down and change.
 Mechanical Weathering (Physical
Weathering): When rocks and minerals
break into smaller pieces. Only changes
the size and shape of the rock.
 Effect
of Temperature:
• Water expands when it freezes.
• Frost Wedging: When water in the cracks of a
rock freezes and expands causing the rock to
 Example: Potholes Result from freeze-thaw cycles of
moderate climates.
Frost Wedging
Frost Wedging: Potholes
Note: They all collect water!
Effect of Pressure:
1. Added Pressure: Causes Wedging and
 Example: Tree roots growing between cracks of
rocks, expand and break the rock.
Added pressure
Of tree roots
Breaks rocks
Effect of Pressure:
Removed Pressure: Large rocks form under Earth’s
When overlying rock is removed by erosion (or mining)
pressure on bedrock is reduced.
Removal of pressure allows bedrock surface to expand.
Expansion of bedrock causes cracks to form parallel to
the surface of the bedrock. Cracks are called joints.
Underground magma
When a batholith cools and is
Exposed to the Earth’s surface
It forms a large round rock like
Half Dome at Yosemite
National Park.
Removed Pressure:
Rock layers peel away from surface of rock like the skin
of an onion.
Exfoliation: The process by which outer rock layers are
stripped away.