1. Rocks and Weathering
Chapter 8.1

2. Weathering- the breaking of rock into smaller fragments
Mechanical weathering – breaks rock
apart without changing the chemical
composition
Examples:
Rocks colliding with other rocks in rivers
Tree roots lifting rock
Ice wedging caused by freezing and thawing

3. The composition of the rock is changed
Chemical weathering – reaction of air,
water and/or other substances with the
minerals in rock
The composition of the
rock is changed

4. Water is the main cause of chemical weathering
It dissolves away some minerals leaving a different composition behind
Compounds in air combine with water and react with minerals upon contact
Some metals react with oxygen and water
(oxidation)

5. Acids cause chemical weathering
Water and carbon dioxide form
carbonic acids which dissolve
calcite and create caves
Plant roots and decaying plants create acids that
dissolve minerals making rock weak

6. Climate effects the speed of weathering
- Chemical weathering is most rapid in warm, moist areas.
- Mechanical weathering is most rapid where freezing and thawing occur.

7. Chemical or Mechanical?
Colonies of lichens growing on the surface of rocks.
Chemical

8. Chemical or Mechanical?
The wedging of tree roots along natural joints in granite outcrops
Mechanical

9. Chemical or Mechanical?
Solution of limestone by acidic groundwater
Chemical

10. Chemical or Mechanical?
The oxidation of minerals which contain iron
Chemical

11. Chemical or Mechanical?
Animal burrows dug in rock which let in water and air
Mechanical

12. Chemical or Mechanical?
Repeated freezing and thawing of water cracks rock or joints
Mechanical

13. Chemical or Mechanical?
The action of water, salt and air on car fenders and panels

14. Chemical or Mechanical?
The action of water, salt and air on car fenders and panels
Chemical

15. Chemical or Mechanical?
The sun fading paint on houses and cars
Chemical

16. Chemical or Mechanical?
Formation of potholes in streets during severe winters
Mechanical

17. Chemical or Mechanical?
Lifted sections of sidewalk along tree-lined streets
Mechanical

18. How Soil Forms
Section 8.2

19. Soil Profile Soil – a mixture of weathered rock and
organic matter
- can take hundreds of years to form
- varies in thickness
Humus – decaying plants and animals that mix with weathered rock
Soil Profile - shows the layers of soil and
weathered rock

20. O-Horizon
Litter layer- leaves
A-Horizon
Top Soil – dark colored, sediment, decayed material, insects, worms
B-Horizon
Lighter color, little or no humus, contains minerals from leaching
C-Horizon
Some material leached from B-horizon, partly weathered rock, no humus
Solid rock below soil profile

21. Factors that influence soil profile
Climate
Slope of land
Length of time evolving
Type of rock
Amount of humus