2. Weathering vs. Erosion
Weathering the decomposition of earth rocks, soils
and their minerals through direct contact with the
planet's atmosphere. Weathering occurs in situ, or
quot;with no movementquot;, and thus should not to be
confused with erosion, which involves the movement
and disintegration of rocks and minerals by agents
such as water, ice, wind, and gravity.
3. Formation of the Grand Canyon
http://www.youtube.com/watch?v=ktf73HNZZGY
Debris flows
shown in this clip
erode rock along
the walls of the
canyon.
8. Physical Weathering
Mechanical or physical
weathering involves the
breakdown of rocks and
soils through direct
contact with atmospheric
conditions such as heat,
water, ice and pressure.
Badlands, SD
9. Abrasion
The primary process in
mechanical weathering
is abrasion (the
process by which clasts
and other particles are
reduced in size).
Talus at the base of Rocky Mountains in Canada
10. Physical Processes of Weathering
Frost Action
Pressure Release
Thermal Expansion and
Contraction
Salt Crystal Growth
Activities of Organisms
13. Pressure Release (Unloading)
Granite (igneous
rock) crystallizes far
below the surface, so
when it is uplifted
and the overlying
material is eroded, its
contained energy is
released by outward
Exfoliation at Stone Mountain, Georgia
expansion.
14. Thermal Expansion (Exfoliation)
Slabs of granitic
rock bounded by
sheet joints in the
Sierra Nevada, CA
Rock is a poor
conductor of heat, so
its outside heats up
more than its inside;
the surface expands
more than the
interior.
Often occurs in areas, like
deserts, where there is a large
diurnal temperature range.
Fig. 6-4a, p. 173
15. Salt Weathering (haloclasty)
Mechanical
Derives from an external source
(capillary rising ground water,
eolian origin, sea water along
rocky coasts, atmospheric pollution).
Favored by dry conditions in arid
climates.
The expanding salt crystals exert a
pressure on the walls of the rock
pores that exceeds the tensile Marine Abrasion of Granite.
strength of the rock.
17. Biological Weathering from Plants
Trees and other plants in
Lassen Volcanic National
Park, CA help break down
parent material into smaller
pieces and contribute to
mechanical weathering.
Fig. 6-6b, p. 174
19. Chemical Weathering
Chemical weathering, involves the direct effect of
atmospheric chemicals, or biologically produced
chemicals (also known as biological weathering), in
the breakdown of rocks, soils and minerals.
20. Organisms
Lichens are part
fungi and part
algae. They derive
their nutrients from
the rock and
contribute to
chemical
weathering.
Fig. 6-6a, p. 174
21. Decomposition of Earth’s Materials
Dissolution (minerals dissolve in water,
limestone dissolves to form caves)
Hydrolysis (hydrogen ions in water
dissociate and attack minerals in rocks, ex.
forms hard water)
Oxidation (minerals react with oxygen, ex.
formation of rust)
22. Factors Affecting Chemical Weathering
Presence of Fractures
Particle Size
Climate
Parent Material
Granite rocks in Joshua Tree
National Park, CA. Chemical
weathering is more intense along
fractures.
24. Temperature and Chemical Weathering
Chemical
processes proceed
more rapidly at
high temperatures
and in the
presence of
liquids.
Chemical
weathering can
extend to
depths of 10s of
meters in the
tropics, but only
a few inches in
arid or cold
climates
Fig. 6-11, p. 180
31. Soil Profile
Parent material, in soil
science, means the
underlying geological
material (generally bedrock
or a superficial or drift
deposit) in which soil
horizons form.
Fig. 6-14b, p. 183
32. Variables in Soil Production
parent material
time
climate
atmospheric composition
topography
organisms