HPU NCS2200 Earth Science for Elementary Education Majors Summer 2014 online course Weathering and erosion lecture

1. Chapter 10 – Weathering,
Soil and Erosion
Earth Science and the Environment (4th ed)
Thompson & Turk

2. 10.1 Weathering and erosion
►Weathering – processes that decompose
rocks into sediments
 Mechanical (physical) weathering – physical
disintegration without chemical change
 Chemical weathering – reaction with air/water
creates a product different physically and
chemically

3. 10.2 Mechanical weathering
► Pressure release
fracturing – formerly
buried rocks expand
when uncovered
► Frost wedging – water
in cracks expands
when frozen
► Abrasion – rock
particles moving in
contact wear each
other away

4. Weathering Con’t
► Organic activity – roots
► Thermal expansion /
contraction
Organic Action
Thermal Expansion

5. 10.3 Chemical weathering
► Dissolution – many
minerals dissolve to
some degree
► Hydrolysis – reaction
with water, new
mineral forms
► Oxidation – reaction
with oxygen, new
mineral forms

6. Destructional -Weathering
Landscapes broken down by
chemical & physical processes & erosion
Physical
► includes temperature
changes (freezing and
thawing, thermal
expansion), crystal
growth, pressure, plant
roots, burrowing animals
► causes disintegration of
parent material and
facilitates chemical
weathering
Chemical
► always in water
► includes hydration, hydrolysis,
oxidation, reduction,
carbonation and exchange
► examples :
 oxidation of Fe to form limonite,
deposited in joints, inhibits
groundwater flow
 hydrolysis of feldspars to form
clay (kaolin) - forms infill for
joints

7. Factors affecting the
RATE of weathering

8. Factors affecting
the RATE of Weathering
► Surface area
 Increases the areas exposed to water,
chemicals and wind.
► Time
 The longer a rock is exposed the more
weathering will occur
► Composition
 Some minerals are more susceptible to
chemical reaction
► Climate
 Chemical reactions are sped up with high
temperatures and moisture

9. Erosion
►Erosion is the
MOVEMENT of the
particles once they
have been
weathered.
►Erosion is caused by
both wind and
water.

10. Creation of Rock vs Soil
► Sedimentary Rock
formation follows
weathering and
erosion when the
particles undergo
compaction and
cementation this
usually occurs at the
bottom of lakes and
oceans but can occur
anywhere layers of
sediment accumulate
and are not disturbed.
►Soil formation
occurs when
weathered and
eroded rock
material mixes with
humus or organic
material and
accumulates.