1. Mechanical and Chemical
Weathering
Mechanical
and
Chemical

2. First step to forming soil and sedimentary rock
Breakdown of rock into smaller pieces
The smaller pieces do not move to a new location until erosion carries them away
What is Weathering?

3. What is Mechanical Weathering?
Breakdown of rock into smaller pieces, without any change in the chemical composition of its minerals Rock is torn apart by physical force. Sometimes called “physical” weathering
What is Mechanical Weathering?

4. What is Ice Wedging? Water fills joints of rocks and freezes.
Water expands 10% when it freezes, pushing rock apart.
Repeated freeze and thaw cycles over the years cause rock to break along the joint.
What is Ice Wedging?

5. What are other forms of Mechanical weathering?
Exfoliation
Rock breaks off into sheets along joints which are parallel to the surface.
What are other forms of Mechanical weathering?

6. What are other forms of Mechanical weathering? Cont.
Thermal Expansion
Repeated daily heating of rock causes expansion, cooling causes contraction, causing the rock to split.
What are other forms of Mechanical weathering? Cont.

7. What are other forms of Mechanical weathering? Cont.
Biotic
Weathering caused by living organisms
Plant roots act as a wedge and widen cracks.
Other causes of biotic weathering:
burrowing animals
microscopic plants
Animals
Algae
fungi
What are other forms of Mechanical weathering? Cont.

8. What is Chemical Weathering?
Chemical reactions break down the bonds holding the rocks together, causing them to fall apart.
Rock reacts with water, gases. and solutions.
What is Chemical Weathering?

9. What are the types of Chemical weathering?
Oxidation
oxygen combines with other elements in rocks to form new types of rock.
rock softer than original
easier for other forces to break rock apart
“rusting” of the rock
color change in the rock
What are the types of Chemical weathering?

10. What are the types of Chemical weathering? Cont.
Carbonation
when carbon dioxide (CO2 ) in the air mixes with rain,
carbonic acid is formed. This weak acid breaks down rock.
acid is too weak to harm plants and animals but slowly causes feldspar and limestone to decompose.
What are the types of Chemical weathering? Cont.