Rocks and weathering 3.2

Question 1

What is weathering?

Answer 1

The decay and disintegration of rocks.

Question 2

Physical weathering: freeze thaw

Answer 2

• Process of water getting into cracks during the day before freezing overnight, expanding by about 10%.
• The crack is widened as force of expansion is greater than the resistance of the rock.

Question 3

Physical weathering: thermal fracture

Answer 3

• Large ranges in temperature in deserts cause rocks and minerals to expand and contract, resulting in disintegration.

Question 4

Physical weathering: salt crystal growth

Answer 4

• When salt solutions such as sodium carbonate in the pores or joints of a rock crystallise.
• Temperatures of around 27 degrees is optimum and can produce expansion rates of up to 300%.

Question 5

Physical weathering: pressure release

Answer 5

• Process when ground surface is lowered by erosion which reduces weight of load.
• This leads to expansion of rocks below which forms cracks.

Question 6

Chemical weathering: hydrolysis

Answer 6

• When a mineral is broken down by reactions with water.
• This causes a change in chemical composition where the rock becomes more unstable.
• Occurs on rocks containing feldspar.

Question 7

Chemical weathering: hydration

Answer 7

Wetting and drying of rocks adds and removes water causing expansion or contraction.

Question 8

Chemical weathering: carbonation

Answer 8

• Process which affects carbonate minerals where rainwater containing carbonic acid attacks carbonate minerals.
• This forms chalk and limestone.

Question 9

Chemical weathering: organic action

Answer 9

• Process of roots working their way into cracks in rocks.

- As roots become bigger, cracks widen and deepen, breaking up bedrock.

Question 10

Which 5 factors affect weathering?

Answer 10

• Climate
• Vegetation
• Relief
• Rock structure
• Rock type

Question 11

Factors affecting weathering: climate

Answer 11

• Determines which weathering processes occur and rate at which they occur.

Question 12

Factors affecting weathering: vegetation

Answer 12

• Type: larger vegetation such as trees are more likely to break apart rocks with larger roots.
• Structure: high density of vegetation increases organic action

Question 13

Factors affecting weathering: relief

Answer 13

• Steep: types of weathering caused by rain is less prevalent
• Gentle: subjected to standing water and infiltration which increases rates of weathering.

Question 14

Factors affecting weathering: rock structure

Answer 14

• Soft/hard: softer and more permeable rocks are more susceptible to weathering
• Layers: more vulnerable to weathering.
• Joints and bedding planes: allows increase in water penetration.

Question 15

Factors affecting weathering: rock type BDS

Answer 15

• Basalt: often highly weathered
• Dolerite: joints allow water penetration
• Slate: chemically resistant