Weathering

Question 1

Describe physical weathering

Answer 1

Involved disintegration or breaking of rocks into smaller pieces with no chemical change in their composition. The result is smaller, angular pieces of rock.
Take place in all regions where there are changes in temperature and is seen in hot tropical desert areas where there is a large daily temperature range
Two main types of physical weathering freeze-thaw action and exfoliation

Question 2

Describe freeze thaw action

Answer 2

Water from rainfall or melting snow and ice becomes trapped in the crack or joint in a rock
If the air temperature drops below freezing, the water will freeze and expand by 9 to 10% putting pressure on the rock so the rock crack
The ice will melt when the temperature rises above freezing , more water is able to enter the crack and then able to freeze again
This process continues, slowly breaking down the rock

Question 3

Describe exfoliation

Answer 3

Happen in areas with a high diurnal temperature range
During the day rock heat up and expand and during the night it cools down and contracts
These changes in temperature and shape cause the rock to weaken and as it is a poor conductor, the expansion and contraction only occur near the surface
-> outer layer heat and cool mote quickly than inner layer
-> cracks the rock
-> layers begin to peel off

Question 4

Describe chemical weathering

Answer 4

Involves the decomposition of rock by changing their chemical composition
Two types of chemical weathering: carbonation and oxidation

Question 5

Describe carbonation

Answer 5

Rain water combines with co2 in the air to form dilute carbonic acid
This attacks the rock surface as well as soaking into joints and bedding planes
The carbonic acid reacts with calcium carbonate in rocks such as limestone to make calcium bicarbonate -> this is soluble and gets carried away in solution in streams

Question 6

Describe oxidation

Answer 6

Oxygen in the air combines with metal, especially iron in rock -> produce a reddish brown coating known as rust
This expands and weaken the original rock

Question 7

Biological weathering

Answer 7

When plants and animal break down
Tree roots penetrate cracks in rock and force them to weaken and crack
Burrowing organisms contribute to the breaking up and loosening of rock

Question 8

How does climate affects rate of weathering

Answer 8

Hot temperature increase rate of reaction -> increase chemical weathering
High diurnal range -> increase in some physical weathering
Wet areas -> increase chemical weathering
Wet and warm area -> increase vegetation -> increase biological weathering
Humid tropical climate -> chemical wth dominates
Cold climate -> physical wth dominates

Question 9

How does rock feature affect rate of weathering

Answer 9

Rocks with cracks more likely to experience increase raye of physical and chemical wth
Soft rocks are much more vulnerable than strong rocks
Chemical composition of rocks is also important

Question 10

Why weathering is more rapid in humid tropical regions than in temperate regions

Answer 10

Large amount of rainfall -> increase chemical wth
Large amount of vegetation -> increase biological wth
Near equator -> high temperature -> faster rate of chemical reaction
Some area have higher diurnal temp. Range

Question 11

Define weathering

Answer 11

The break-up or breakdown and decomposition of rock in situ
No transport of material is involved while erosion is the breakdown of rocks by moving water, ice and wind and the broken rock is then transported away