WEATHERING
Unit 1: The concept of weathering
Page 56
Notes:
● Weathering is the process of wearing away rocks and soil due to the effects
of natural forces.
● The primary agents of weathering are temperature and water.
● There are three main types of weathering: physical, biological, and
chemical.
● Physical weathering is caused by physical forces such as frost and
temperature changes.
● Biological weathering results from the actions of plants and animals.
● Chemical weathering involves chemical changes that weaken rocks.
● Weathering is a slow process that affects the shape and composition of
rocks and soil over time.
Questions:
1. What is weathering, and what are its primary agents?
2. Name and describe the three main types of weathering.
3. Give an example of physical weathering caused by temperature changes.
4. How do plants and animals contribute to biological weathering?
5. Explain the process of chemical weathering and its impact on rocks.
6. Why is weathering considered a slow process?
7. How does weathering affect the landscape over time?
Answers:
,1. Weathering is the process of wearing away rocks and soil by the action of
natural forces. Its primary agents are temperature and water.
2. The three main types of weathering are:
- Physical weathering, caused by physical forces such as frost and temperature
changes, which break rocks into smaller pieces.
- Biological weathering, resulting from the actions of plants and animals, like
tree roots growing into cracks in rocks.
- Chemical weathering, involving chemical changes that weaken rocks, such as
the dissolution of minerals in water.
3. An example of physical weathering caused by temperature changes is when
water seeps into cracks in rocks, freezes, and expands, causing the cracks to
widen and the rock to break apart.
4. Plants and animals contribute to biological weathering by actions like tree
roots growing into rock crevices, which can gradually split rocks apart. Animals
can burrow into the ground, aiding in the breakdown of soil and rocks.
5. Chemical weathering occurs through chemical reactions that weaken rocks. For
instance, when minerals in rocks react with water or acids, they may dissolve or
change composition, making the rock more susceptible to erosion.
6. Weathering is considered a slow process when compared to a human lifetime
because it takes place over a long period, often thousands or millions of years,
gradually altering the landscape and rock formations.
7. Weathering affects the landscape over time by reshaping the landforms,
breaking down rocks into smaller particles, and altering the composition of soils.
This leads to the creation of valleys, canyons, and other geological features as
rocks and soil are eroded and transported by natural processes like wind, water,
and gravity.
Unit 2: Physical Weathering
Page 57
Notes
Physical Weathering:
● Involves physical forces that break up rocks.
, ● Examples: Freeze thaw action and exfoliation.
Freeze Thaw Action:
● Water collects in cracks in rocks.
● When water freezes, it expands (about 9% larger than liquid water).
● Ice puts pressure on crack walls.
● Repeated freezing and thawing weakens rocks.
● Over millions of years, it can wear away mountains in cold climates.
Exfoliation:
● Occurs in dry areas with large day-night temperature changes.
● Outer layers of rocks expand during the day and contract at night.
● Repeated expansion and contraction causes outer layers to peel off.
Local Places for Physical Weathering:
1) Freeze Thaw Action:
a) Weathering agents: Water and temperature changes.
b) Places in South Africa: Mountainous regions, like the Drakensberg
Mountains.
2) Exfoliation:
● Conditions: Dry areas with significant day-night temperature fluctuations.
● Places in South Africa: Karoo Desert, Richtersveld, and other arid regions.
Questions
1. a. What are the two weathering agents that affect freeze thaw action?
b. Name a location in South Africa where freeze thaw action occurs.
2. What are the conditions required for exfoliation to occur, and can you name a
place in South Africa where exfoliation takes place?
3. Explain exfoliation in your own words and provide an everyday example that
illustrates its effects, similar to freeze thaw action.
4. Explain how the process of freeze thaw action weakens rocks over time.
Answers:
1. a. The two weathering agents that affect freeze thaw action are water and
temperature changes.
b. Freeze thaw action takes place in locations like the Drakensberg Mountains in
South Africa.
, 2. Exfoliation occurs in dry areas with significant day-night temperature
fluctuations. Places in South Africa where exfoliation takes place include the
Karoo Desert, Richtersveld, and other arid regions.
3. Exfoliation is a type of physical weathering where the outer layers of rocks
expand during the day due to heat and contract at night when it cools. This
repeated expansion and contraction cause the outer layers to peel off. An
everyday example of this effect is the peeling of paint on a wall due to
temperature changes.
4. Freeze thaw action weakens rocks by the repeated expansion of water when it
freezes in cracks, creating pressure on the crack walls. Over time, this constant
freezing and thawing cause the rocks to crack and break apart.
Unit 3: Chemical Weathering
Page 58 and 59
Notes
Chemical Weathering
● Chemical weathering changes the chemical composition of rocks and
weakens them.
● Key reactions in chemical weathering: carbonation, hydrolysis, and
oxidation.
1) Carbonation
● Rainwater contains carbon dioxide (CO2), forming carbonic acid (H2CO3).
● Carbonic acid reacts with rocks containing calcium carbonate (CaCO3),
turning it into soluble calcium bicarbonate (Ca(HCO3)2).
● Soluble calcium bicarbonate dissolves in water and is washed away.
● Carbonation is more pronounced in colder climates and can damage
buildings.
2) Oxidation
● Oxidation occurs in rocks and iron-containing objects, leading to rust.
● Water contains oxygen that reacts with iron in rocks, forming iron oxide.
● Oxidation weakens rocks and objects.
