1. McKnight's Physical Geography
Chapter 15
Preliminaries to Erosion: Weathering and Mass Wasting
Modified by AJ Allred for Geography 1000
Salt Lake Community College
Original by Andrew Mercer
Mississippi State University
© 2014 Pearson Education, Inc.

2. Learning Goals of Chapter 15
Define denudation, weathering, mass wasting, and erosion.
Differentiate between mechanical, chemical, and biotic weathering.
Explain frost wedging, salt wedging, temperature changes, exfoliation, angle of repose, and oxidation.
Identify mass wasting, glaciation, landslide, slump, earthflow, mudflow, creep and solifluction.

3. The sun uses water & gravity to wear down landforms
Weathering
Mass wasting
Erosion

4. Weathering and Rock Openings
Notice how water gradually opens joints by gravity flow, freeze/expansion and chemically dissolving rocks.

5. More examples of weathering into joints

6. Weathering Agents Oxygen, carbon dioxide, and water
Temperature changes – freeze/thaw, expand/contract
Water penetration in bedrock openings
Biotic agents
Burrowing and/or plant roots
Chemical alteration
Three principal categories
Mechanical
Chemical
Biotic

7. Weathering Agents Mechanical Weathering Frost wedging
Physical disintegration of rock without changes to its chemical composition
Frost wedging
Freeze–thaw action of water
Ice wedges downward in openings
Ice melts and water falls farther into larger opening
Process repeats
Frost shattering

8. Weathering Agents Salt wedging Temperature changes
Salt left behind from evaporated water collects and pries apart rock openings
Temperature changes
Diurnal and seasonal temperature fluctuations modify volumes slightly
Fracturing of rock over long time scales

9. Weathering Agents Exfoliation Other mechanical weathering processes
Curved layers peel off of bedrock
Exfoliation dome
Unloading through erosion
Hydration
Other mechanical weathering processes
Chemical and biotic impacts on mechanical weathering

10. Biological Weathering Agents
Plant roots break apart rocks, and may also hold soils together.
Burrowing animals promote water entry and chemical change to soil and rock
Lichens slowly consumes rock, turning it into soil and dust.

11. Mass Wasting

12. Mass Wasting Fall Rockfall Talus/Scree
Uniform accumulation of rockfall material – talus apron
Material tends to collect in cone shaped heaps – talus cones
Talus cones grow up the mountain
Slow talus flow in glaciers – rock glaciers

13. Slumping – semi-wet material

14. Very wet soil can flow

15. Slow Creep
Walls, poles, head stones and other structures slowly move downhill over many years.