Weathering (1): p 71
1. The breaking down of rocks by air, water, and the heat of the Sun is called weathering.
2. Types of weathering: physical, chemical, biological.
3. Erode means to be worn away by the action of physical, chemical or biological weathering.
4. In very cold weather, water seeps into cracks in the road surface and then freezes. As it turns into
ice, it expands and forces the surface to split.
5. Plant roots spread into and under rocks causing stresses and strains to build up. Eventually cracks
appear which become larger as the plant continues to grow. This process is called biological
Weathering (2): the weathering of limestone: p 72
1. Carbon dioxide in the soil comes from the bacteria which feed on dead plant and animal material.
2. a) When carbon dioxide dissolves in water it forms carbonic acid.
b) carbon dioxide + water ‡ carbonic acid
3. a) When carbonic acid reaches limestone a chemical reaction takes place. Limestone is mainly made
up of calcium carbonate. When it reacts with carbonic acid it erodes.
b) calcium carbonate + carbonic acid ‡ calcium hydrogen carbonate solution.
Transporting weathered material: p 73
1. The carrying away of weathered rock such as pebbles, sand, mud and clay is called transport.
2. Tiny pieces of weathered rock are washed by rain into streams and rivers.
3. The flowing water causes the heavier rocks to roll along the river bed and form smooth round
4. The more energy and water a river has, the greater the amount and size of the material it can
5. During floods, larger pieces of materials like trees, cars, and huge boulders can be carried along as
the water has a lot of energy.
Depositing transported material: p 74
1. The heavier particles are deposited first, dissolved material is carried to the sea and the finest particles
are deposited last.
2. a) The deposition of different sized rock fragments in different places due to the changes in the
speed of a river is called sorting.
b) Fast flowing river water carries most sizes of rock fragments. A sudden slow down, will cause the
deposition of larger, heavier material such as large stones; only the lighter, finer particles will be
3. When a river slows down, it loses energy. As a result, it deposits the transported material as sediment. If
the river has enough energy, it will carry material out to sea, where it eventually falls to the sea floor.
From sediment to sedimentary rock: p 75
1. Over millions of years sediment will build up on river beds and at the bottom of the sea. With
increasing pressure from the weight of the sediment above, water is forced out of the lower layers
compacting the particles to form sedimentary rock.
2. A heavier layer on top of a fine layer could mean that at one time the river flooded and carried larger
3. a) Grade bedding is found on ocean floors.
b) Heavier particles sink faster than lighter ones.
4. Cross bedding is formed where layers of sediment lie at different angles. This is produced when the
wind or a river changes direction before depositing more material.
5. Ripple marks on sedimentary rock suggest that the sediment was shaped by a current of wind or
water after it was deposited.
Test yourself: p 76–77
1. a) ‘Weathered’ means the breaking down of rocks by the action of air, water, and the heat of the
b) This process is an example of physical weathering called frost shattering. Water seeps into cracks
in the rocks and then freezes. As it turns into ice it expands and forces the rock to split. Large
boulders fall apart and shatter to form scree at the foot of mountain slopes.
c) Plant roots can have a similar effect on rocks. As the plant grows, its roots spread into and under
rocks, causing stresses and strains to build up. Eventually cracks appear which become larger as
the plant continues to grow. This process is sometimes called biological weathering.
2. a) Physical and chemical weathering of igneous rocks.
b) Particles of igneous rocks carried by river.
c) Rock particles deposited under the seabed in layers.
d) Formation of sedimentary rocks.
3. Rock is worn away by wind and water.
Rock particles are transported by wind and water.
Rock particles are deposited at the mouth of rivers.
Rock particles build up on top of one another in layers.
Rock particles are squashed together to form rock.
4. a) 0.5 m/s
b) 0.1 m/s
c) It shows the size of particles carried.
d) Changes in the speed of a river are responsible for the deposition of different sized rock
fragments. Fast flowing water carries most sizes of rock fragments.
e) A sudden slow down will cause the deposition of larger, heavier material; only the lighter, finer
particles will be transported further.
5. a) In poorly sorted sediment each layer shows a change in the type of sediment. In well sorted
sediment the heavier particles settle at the bottom and the lighter ones on top.
b) i) A heavy layer over a fine layer. ii) Fast flowing water carries larger particles.
c) Fast flowing water of a shallow stream carries most types of particles, which are deposited
d) i) Ripple marks on sedimentary rock suggest that the sediment was shaped by a current of
wind or water after it was deposited.
ii) Cracks are produced on the surface of sedimentary rock when the wind or a river changes
direction before depositing more material.
Workbook 2, chapter 8
1 a) i) Sedimentary rocks
ii) Igneous rocks
iii) Metamorphic rocks
b) i) Sedimentary rock
ii) Igneous rock
iii) Metamorphic rock
2. a) Physical weathering:
• rabbits digging burrows under a rock causing it to collapse
• water creeping into cracks in a rock face and freezing
• stalactites forming in a limestone
• gales blowing sand across the surface of a stone pillar
• granite being broken down to form china clay
• biological weathering
• a tree growing out of a crack on a rock face
b) i) Physical weathering
ii) Rocks can be eroded by force such as that of wind, water, etc.
3. a) To absorb water.
b) It freezes to form ice.
c) Ice expands and forces the rock to split.
4. a) i) They expand.
ii) They contract.
b) The heat of the Sun.
c) As the sun sets the night becomes cold.
d) The inside of the rock is most affected.
e) Physical weathering
f) At the foot of mountain slopes.
5. a) This happens in places where the river slows down.
b) i) 0.3 m/s
ii) 0.2 m/s
iii) They dissolve in the water and are carried out to the ocean.
iv) Fast flowing water carries most rock fragments. A sudden slow down will cause the deposition
of larger, heavier material.
v) Larger particles from 1.5 mm to 3 mm would be picked up.
Particle size in mm
less than 0.004
2 and over
7. a) i) A
b) The lowest layer must have been deposited first. Subsequent layers were deposited later.
c) i) This kind of shape is made by an intrusion of magma into rock.
ii) When very hot magma is pushed into rock it heats up the surrounding rock and different
layers of metamorphic rocks are made.
Problems to solve
1. Describe how a mountain is eroded?
2. What is sediment? Why do the mouths of rivers sometimes need to be cleared by dredgers?
3. Beach sand contains very small, smooth sand grains of different colours. How do you explain these
Solutions to problems
1. A mountain can be eroded by physical weathering such as frost shattering. Water seeps into cracks
in the rock and then freezes. As it turns to ice it expands and forces the rock to split. Large boulders
fall and shatter to form scree at the foot of mountain slopes.
2. Small pieces of dust and soil that have broken away from large pieces of land and rock and all the
shells of small sea animals, which are usually carried and dropped by water, wind or glaciers are
The speed of the river slows down at the mouth. Particles which were carried by the fast moving water
are deposited there and the mouth of the river becomes loaded with the deposition, so the mouth of
the river needs to be dredged.
3. The different colours of sand particles depend on the type of rock and where they originally came
Multiple Choice Questions
1. Which type of rock is granite?
2. When the Earth was first formed its surface consisted entirely of
A metamorphic rocks B sedimentary rocks C igneous rocks
D porous rocks
3. The average temperature beneath the surface of the Earth is well over
4. The breaking down of rocks due to the air, water and the heat from the Sun is called
5. Rain water becomes acidic because it dissolves
A carbon monoxide B sulphur dioxide
C nitrogen dioxide
6. Stalctites and stalagmites are formed due to the deposition of
A calcium sulphate
B calcium nitrate
C calcium phosphate D calcium carbonate
7. Changes in the speed of a river are responsible for the deposition of different sized rock fragments
in different places. This process is called
8. Which one of the following are steps in the formation of sedimentary rock?
A Rocks compacted by pressure‡ particles cemented together‡ formation of sedimentary rock
B Particles cemented together‡ formation of sedimentary rock ‡ rocks compacted by pressure
C Formation of sedimentary rock‡ particles cemented together ‡ rocks compacted by pressure
D Rocks compacted by pressure‡ formation of sedimentary rock‡ particles cemented by
9. Sand dunes are formed by the deposition of rock fragments by
10. What determines the type of sedimentary rock that is formed?
A The size and origin of the sediment particles.
B The size and origin of the river that carries the sediment.
C The place of deposition of the sediment.
D The angles at which the sediment is deposited.
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