1. Weathering and Erosion
Let's look at Gradational Processes.
These are the forces that are trying to
level the earth through weathering and
erosion.

2. Introduction
- erosion and weathering are part of the forces
of gradation which do battle with tectonic
forces
- tectonic forces: strive to build up rock
structures
- gradational forces: strive to bring rock
structures to a level or a uniform slope;
- this can be done in two ways:
- by tearing down (i.e. degradation
or erosion) or
- filling in (i.e. aggradation… think
“add” or deposition)

3. Erosion
 erosion can be divided into two processes:
a) the breaking up of rock masses (ie
weathering )
b) the carrying away of the weathered
rock fragments (i.e. transportation )
- cycle of gradation: weathering,
transportation, and deposition

4. Weathering Controls
 Chemical stability
 Rock structure (type of rock, joints, etc.)
 Climate
 Hot, wet favors chemical weathering
 Cold, dry favors physical weathering
 Presence of soil
 Soil acts as a lid, keeping water in
 Length of exposure

5. Factors Contributing to
Weathering

6. Weathering increases surface
area = more weathering

7. exfoliation or spheroidal
weathering or thermal expansion
and contraction or stress release
 daily variations in temperature cause rocks to expand
and contract
 various minerals in a rock expand and contract at
different rates; as a result there is a gradual splitting
apart of the rock
 in humid climates, running water tends to round off the
surface features causing the "skin" of the rock to peel
off
 this is also an important form of weathering in desert
areas where the daily temperature range can be high
 Bedrock that was formerly buried can expand when
overlying pressure is removed

8. Mechanical (or Physical)
Weathering
 the breaking up of rocks into smaller
fragments without any change in the
chemical composition of its minerals

9. Exfoliation
Notice the top layer of bedrock is cracking and separating from the
underlying bedrock

10. Coquihalla Hwy, BC

11. freeze-thaw or frost action or
frost shattering
 when the water in the
cracks and pore spaces of
rocks freezes, the force
created by its expansion is
tremendous
- rocks are literally split
apart resulting in shattering
 An example of the powerful
force of freeze thaw action
on a large boulder near
Vernon, BC.

13. The steep slopes of fractured rocks accumulating around Black
Tusk are a result of freeze-thaw action

14. Biological Weathering
 plants and roots  Animals
 tree roots, for  burrowing animals can
example, growing make the soil less
down into cracks can stable
exert powerful forces
- even mosses and
lichens can help to
split rocks apart

15. Biological Weathering

16. Chemical Weathering
 the decay of rock through actual
chemical change in the composition of
its minerals
 most common in warm and humid
climates where both water and heat
speed up chemical reactions
 Can be expedited by human influences
 (ie. Acid rain caused by industries)

17. Notice how the engravings on the tombstone on the right are no
longer clearly visible.

18. carbonation or solution
 occurs with limestone (easiest to erode)
 groundwater absorbs carbon dioxide to
form a slightly acidic solution
 destroys joints (joint: line of weakness
in a rock) and bedding planes to form
karst topography

19. When limestone interacts with underground water, the water dissolves the
limestone to form an amalgamation of caves, underground channels, and a
rough and bumpy ground surface.
Named for the Kras plateau region of eastern Italy and western Slovenia (Kras
is Karst in German for “barren land”)

20. hydrolysis
 occurs especially with
granite
 Minerals like feldspar
easily react with
slightly acidic water to
create clay and salts
 Clay is easily carried
away in solution by
water
 causes rock to whiten
(erodes slowly)

22. oxidation
 creates rusty red rock
 occurs especially with rock containing iron
nitrate
 erodes and forms soil

24. hydration
 occurs especially with rocks containing salt
minerals
 water is absorbed into the internal
structure of the rock causing swelling and
making it vulnerable to breakdown due to
pressure and potential chemical structure
changes
 a physical-chemical process
eg gypsum results from water being
added to anhydrite (CaSO4)

26. General Rule:
 igneous and metamorphic rocks are more
susceptible to chemical decomposition
than mechanical disintegration
 the reverse is true for sedimentary rocks =
more mechanical disintegration
 A notable exception to this is
limestone, a sedimentary rock that is
highly susceptible to chemical
weathering.

27. Weathering vs Erosion
 Weathering: The general process by which
rocks are broken (physically and
chemically) at the Earth’s surface
 Erosion: The process by which the surface
of the Earth is worn away (encompasses
weathering and transport)