1. Weathering, Mass Wasting & Erosion
Chapter 15
Weathering, Mass Wasting & Erosion

2. Preliminaries to Erosion: Weathering and Mass Wasting
Denudation
Weathering
Breaking down of rock into smaller components by atmospheric and biotic agents
Mass Wasting
Involves the downslope movement of broken rock due to gravity
Erosion
More extensive and distant removal of fragmented rock material

3. Impacts of Weathering & Mass Wasting
Weathering = fragmentation of rock in place – no obvious movement
Mass Wasting = involves down slope movement – empty space above and debris strewn below
Erosion = wearing away of the land by the action of water, ice or wind

4. Denudation Weathering followed by mass wasting followed by erosion
Results in a lowering of the landscape over millions of years

5. Colorado River is major cause of erosion
Colorado River is major cause of erosion. Weather and mass wasting have also played a part in the carving of Grand Canyon

6. Weathering Jointing Weathering Agents Climate and Weathering
Mechanical Weathering
Chemical Weathering
Biological Weathering
Climate and Weathering

7. Weathering 1st step in external process of rock disintegration
Think of weathering as “aging of rock surfaces”
Where lithosphere and atmosphere meet (land/air interface)
Mechanical or chemical
Exposed bedrock is prone to weathering – it’s more “fragile”
Underlying rock is “stronger”

8. Faults and Joints faults = displacement of land
joints = no displacement of land
no displacement
displacement

9. Faults
The cracking and displacement of adjacent blocks of rock as a result of the severe stresses set up by tectonic activity

10. Jointing Vertical Horizontal
Cracks resulting from stress – very common
Show no displacement

11. Weathering Agents Mechanical Chemical Biological
Most are atmospheric – easy for gas to penetrate bedrock
Water can also penetrate
Temperature change
Biotic influence

12. Mechanical Weathering
Disintegration of rock material
No change in chemical composition
Mostly occurs at or near the surface
Frost Wedging = freeze/thaw action of water
Salt Wedging = salt crystallizes
Temperature change = heat expansion & cold contraction
Exfoliation = layers peel off

13. Frost Wedging
Water permeates cracks/fissures in rocks, then freezes, then melts

14. Exfoliation - single boulder
Curved layers peel off bedrock
Occurs at different scales
Exfoliation - hill
Exfoliation - single boulder

15. Impact of Mechanical Weathering
As rock is fragmented, the amount of rock surface increases
More surface area exposed = more fragmentation

16. Chemical Weathering Decomposition of rocks by alteration of minerals
Chemical weathering requires moisture
More in humid regions than arid
Requires oxygen, water & carbon dioxide
3 processes are:
Oxidation
Hydrolosis
Carbonation

17. Oxidation Oxidation is the combination of a substance with oxygen
Combines with metallic elements to form new compounds
Usually softer and more easily eroded

18. Oxygen combines with iron-bearing silicate minerals causing "rusting"
Red Rocks - Oxidation
Oxygen combines with iron-bearing silicate minerals causing "rusting"
Iron oxides are produced
Iron oxides are red, orange, or brown in color
"Georgia Red Clay" derives its color from the oxidation of iron bearing minerals

19. Hydrolysis Decomposition of a chemical compound by reaction with water
Igneous rock is very susceptible
Increases volume of rock and brings on disintegration

20. Carbonation Reaction between carbon dioxide in water & carbonate rocks
Produces calcium bicarbonate (very soluble)
Easily removed by runoff or percolation

21. Biological Weathering
Plants & Animals
Roots, lichens
Burrowing animals

22. Climate and Weathering
Weathering is enhanced by climate
More chemical weathering with high temperatures and lots of rain

23. Mass Wasting Fall Slide Flow Creep Landslide Slump Earthflow Mudflow
Debris Flow
Creep

24. Mass Wasting 2nd step in external process of rock disintegration
Movement of rock and soil downslope under the influence of gravity
Denudation: weathering followed by mass wasting followed by erosion

25. Fall: Falling of pieces of rock downslope
Slide: Landslide – instantaneous collapse of a slope
Flow: Gravity impelling force with water to bring section of a slope down i.e. mudflow
Creep: Slowest and least perceptible gradual downhill movement

26. Talus Slope
Pieces of rock become wedged in slope, then are loosened and fall to bottom

27. Visual Evidence of Creep

28. Freeze –Thaw Processes
Freezing lifts particle perpendicular, then melting deposits it further downslope