Recognise that weathering involves the breakdown of rock in
situ and, as such, should be distinguished from erosion. Describe
what is meant by different types of weathering physical/mechanical
(freeze-thaw action, exfoliation), chemical (carbonation,
oxidation) and biological. Explain the main factors influencing the
type and rate of weathering climate and rock features (mineral
composition, grain size of the rock, presence of lines of
weakness). The influence of climate on the rate of weathering could
be illustrated with reference to simple explanation as to why
weathering is more rapid in humid tropical regions of the world
than in temperate regions.
Slide 3
Weathering is the breakdown of rock in situ Erosion involves
the removal of weathered material by the action of gravity, water,
wind or ice
Slide 4
The two types of weathering are: 1. physical or mechanical
weathering 2. chemical weathering 3. Biological weathering
Slide 5
the breaking of rocks into smaller fragments without changing
their mineral or chemical composition joints are cracks in rocks
formed by tectonic forces
Slide 6
1. frost action rocks break as water freezes in cracks Click
for animation!
Slide 7
2. pressure release rocks fracture as they expand when exposed
from beneath the Earths surface
Slide 8
3. insolation weathering rocks break due to exposure of
extremes of temperatures resulting in repeated expansions and
contractions Click for animation! exfoliation outer layers of rock
peel off following pressure release or insolation weathering
Slide 9
4. biological weathering a. rocks break as plant roots grow in
cracks b. rocks and minerals break down as animals burrow and move
Click for animation!
Slide 10
the minerals or chemicals in rocks are altered and new
substances are formed water is needed for chemical reactions to
take place
Slide 11
1. leaching water dissolves chemicals in rocks and washes them
away iron leaching
Slide 12
2. hydration - certain minerals absorb water and produce new
substances (ex. feldspar + water kaolinite, a type of clay used in
pottery)
Slide 13
3. oxidation certain minerals combine with oxygen in air or
water forming oxides (ex. iron + oxygen rust)
Slide 14
4. carbonation weathering rocks with calcite (ex. limestone)
are dissolved away by carbonic acid produced from water combining
with CO 2
Slide 15
5. acid rain sulfur and nitrogen oxide air pollutants combine
with rain droplets forming acids that break down rocks
Slide 16
6. biological weathering a. chelation organisms such as lichens
and moss produce acids that break down rocks
Slide 17
6. biological weathering b. organisms can influence
environmental factors that may enhance weathering (ex. moisture and
pH)
Slide 18
1. The bigger and more numerous the joints in a rock, the
faster is the rate of weathering. 2. Climate affects the rate of
weathering. a. Frost action depends on rain, snowfall and
temperature ranges. b. Chemical weathering is enhanced in humid
climates.
Slide 19
Slide 20
3. The mineral composition of a rock may make it more or less
susceptible to weathering. a. Quartz is resistant to both physical
and chemical weathering. b. Calcite is easily dissolved away by
carbonic acid.
Slide 21
1. rock fragments 2. rock formations 3. limestone caves 4. soil
5. sediment 6. nutritional minerals for plants 7. solutes in bodies
of water
Slide 22
Slide 23
Slide 24
abrasion chelation exfoliation oxidation
Slide 25
abrasion chelation exfoliation oxidation
Slide 26
abrasion chelation exfoliation oxidation
Slide 27
abrasion chelation exfoliation oxidation
Slide 28
Watch the following slideshow in silence. Look at each picture.
Be sensitive to the feelings and ideas each one evokes. Choose the
picture that made the most impact on you. Describe it. How did it
make you feel? What thoughts and ideas came to you? Write a short
reflection (5 to 10 sentences) about it.