1. Title: 7.1 Weathering (Mechanical Weathering.) Page #:48 Date: 1/2/13
Table of Contents
Title: 7.1 Weathering (Mechanical Weathering.)
Page #:48
Date: 1/2/13

2. Objective
Students will be able to identify the factors that affect mechanical weathering.

3. Words of the Day
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.

4. Mechanical Weathering
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 break.
Example: Potholes Result from freeze-thaw cycles of moderate climates.

5. Mechanical Weathering
Frost Wedging

6. Mechanical Weathering
Frost Wedging: Potholes
Note: They all collect water!

7. Mechanical Weathering
Effect of Pressure:
Added Pressure: Causes Wedging and Cracking.
Example: Tree roots growing between cracks of rocks, expand and break the rock.

8. Mechanical Weathering
Added pressure
Of tree roots
Breaks rocks
Apart.

9. Mechanical Weathering
Effect of Pressure:
Removed Pressure: Large rocks form under Earth’s surface.
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.

10. Batholith:
Underground magma
Chamber.
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.

11. Mechanical Weathering
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.