WEATHERING AND MASS WASTING PROCESSES
I. Weathering
A. Combination of all processes that cause rock to disintegrate physically or
chemically due to exposure
B. Weathering processes possible due to:
1. Microscopic spaces between minerals
2. Joints or fissures in rock material
3. Faults in rock material
4. Lava Vesicles (gas bubbles)
5. Solution cavities (limestone)
II. Types of Weathering:
A. Physical (Mechanical) Weathering
1. Frost Action (Ice)
a. Frost Shattering/Ice Wedging
b. Frost heaving
c. Stone rings – Stone polygons
d. Pingos
2. Salt Crystal Action
a. Salt Wedging
3. Unloading
a. Exfoliation/Spalling
b. Sheeting Structure
4. Other
a. Bioturbation
(1) plant root action
(2) animal burrowing
b. Surface heating/cooling
B. Chemical Weathering
1. Hydrolysis – addition of H2O at molecular level/bonding
2. Oxidation – addition of dissolved O2 (from H2O)
3. Carbonation – reaction of limestone to Carbonic Acid
solution
C. Chemical Weathering Agents
1. Climate
2. Time
3. Composition of original rock material
III. Mass Wasting
A. Downslope movement of rock, soils and sediment under the influence of
gravity – water may or may not be present
1. Other factors:
a. Steepness of slopes
b. Composition of slope
(consolidated/unconsolidated)
c. Initial water content of slopes
© Vicki Drake
d. Vegetation present on slopes
e. Human/animal disturbances on slopes
B. Soil Creep
1. Slow, imperceptible downslope movement of
unconsolidated material – water not usually present
C. Earthflow
1. Solifluction – movement of tundra soils during Spring
thaw (slow)
2. Faster, water is present, shallow soil movement
downslope
3. Single cohesive unit along concave slip plane
4. Slump: Earthflow in series of terraces along multiple
slip planes
D. Mudflow
1. Fast, water is present
2. Lahar: Ash and mudflow from a volcano
3. Debris Flow: More rock and water, less mud – San
Gabriel Mountains, S. California
E. Landslide/Rockslide
1. Bedrock failure – fastest of all
2. Rigid mass of rock material displaced instantly – no
warning
a. Water may or may not be present
3. Granite cliffs: Yosemite
© Vicki Drake