1. Unit 4: Weathering and Soils

2. Weathering
the breaking down and changing of rocks at or near the Earth’s surface
2 Types:
Mechanical
Chemical

3. Mechanical Weathering
Occurs when physical forces break rock into smaller and smaller pieces without changing the rock’s mineral composition
Mechanical weathering increases surface area

4. Three processes that cause mechanical weathering
Frost Wedging
caused by the expansion of freezing water in cracks and crevices.
wedged loose rocks may tumble into large piles called talus, found at the bases of steep, rocky cliffs

5. Three processes that cause mechanical weathering
2. Unloading/Exfoliation
Reduced pressure on igneous rock causes it to expand and allows slabs of outer rock to break off in layers in a process called exfoliation

6. Three processes that cause mechanical weathering
3. Biological Activity
The activity of organisms, including plants, burrowing animals, and humans

7. Chemical Weathering
is the transformation of rock into one or more new compounds

8. Processes of chemical weathering
Water (dissolved gases)
oxygen (Fe + O2 = rust!)
CO2 (carbonic acid)
sulfur/nitrogen oxides (acid rain)

9. Processes of chemical weathering
2. Spheroidal Weathering
causes the corners and edges of rock to be more rounded (edges weather faster than curves)

10. Rates of Weathering Affected by:
Rock characteristics (cracks, minerals)
Climate (temperature, moisture, vegetation)
Chemical weathering is most effective in warm, humid climates
Differential Weathering (caused by variations in composition)

11. Soil Erosion Affected by: Solutions: Climate, slope, vegetation
Human activities that remove natural vegetation, such as farming, logging, and construction
Solutions:
windbreaks – planting rows of trees
terracing hillsides
plowing along contours of hills
rotating crops

12. Mass Movements Transfer of rock and soil downslope due to gravity
Triggers - anything that makes a slope more susceptible to gravity

13. Triggers of Mass Movement
Water – heavy rain, rapid melting of snow – saturates surface materials
Oversteepened slopes – stable up to 25-40 (depending on size/shape of particles)
Ex: waves on cliff, excavating, road construction
Removal of Vegatation – roots bind soil
Earthquakes – dislodge rock and unconsolidated material

14. Mass Movement Types
Rockfall: rocks fragments fall freely through the air

15. Mass Movement Types
Slide: a block of material moves suddenly along a flat, inclined surface.

16. Mass Movement Types
Slump: downward movement of a block of material along a curved surface.

17. Mass Movement Types
Flows - mass movements of material containing a large amount of water (acts like river)
Mudflows - move quickly and carry a mixture of soil, rock, and water that has a consistency of wet concrete
Earthflows - move relatively slowly and carry clay-rich sediment

18. Mass Movement Prevention
Retaining walls
Vegetation
Bolts
Fencing
Stepping
Diversion chutes