Weathering
Weathering
What is weathering?
Weathering is the breakdown and alteration of
rocks and minerals near or at the Earth’s
surface.
The two types of weathering are:
1.
physical or mechanical weathering 2.
chemical weathering
Physical Weathering
• the breaking of rocks into smaller fragments
without changing their mineral or chemical
composition
• joints are cracks in rocks formed by tectonic
forces
Physical Weathering
1. frost action – rocks break as water freezes in
Click for
cracks
animation!
Physical Weathering
2. abrasion or impact weathering – rocks break
down when exposed to agents of erosion
Physical Weathering
2. abrasion or impact weathering – rocks break
down when exposed to agents of erosion
Physical Weathering
3. pressure release – rocks fracture as they
expand when exposed from beneath the
Earth’s surface
Physical Weathering
exfoliation – outer
layers of rock
peel off following
pressure release
or insolation
weathering
4. insolation weathering – rocks break due to exposure
of extremes of temperatures resulting in repeated
expansions and contractions
Click for
animation!
Physical Weathering
5. biological weathering
a. rocks break as plant roots grow in cracks
b. rocks and minerals break down as animals
burrow and move
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animation!
Chemical Weathering
• the minerals or chemicals in rocks are altered
and new substances are formed
• water is needed for chemical reactions to take
place
Chemical Weathering
iron
leaching
1. leaching – water dissolves chemicals in rocks
and washes them away
Chemical Weathering
2. hydration - certain minerals absorb water and
produce new substances (ex. feldspar +
water → kaolinite, a type of clay used in
pottery)
Click for
animation!
Chemical Weathering
Click for
animation!
3. oxidation – certain minerals combine with
oxygen in air or water forming oxides (ex.
iron + oxygen → rust)
Chemical Weathering
4. carbonation weathering – rocks with calcite (ex.
limestone) are dissolved away by carbonic acid
produced from water combining with CO2
Chemical Weathering
5. acid rain – sulfur and nitrogen oxide air
pollutants combine with rain droplets
forming acids that break down rocks
Chemical Weathering
6. biological weathering
a. chelation – organisms such as lichens and
moss produce acids that break down rocks
Chemical Weathering
6. biological weathering
b. organisms can influence environmental factors
that may enhance weathering (ex. moisture and
pH)
Rate of Weathering
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.
Rate of Weathering
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.
Products of Weathering
1.
2.
3.
4.
5.
6.
7.
rock fragments
rock formations
limestone caves
soil
sediment
nutritional minerals for plants
solutes in bodies of water
Exercise
Physical or chemical?
Vocabulary matching
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abrasion
chelation
exfoliation
oxidation
Vocabulary matching
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abrasion
chelation
exfoliation
oxidation
Vocabulary matching
•
•
•
•
abrasion
chelation
exfoliation
oxidation
Vocabulary matching
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•
•
•
abrasion
chelation
exfoliation
oxidation
Reflection:
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.
The End