2.4. Weathering

Question 1

What is weathering?

Answer 1

The breakdown of rocks in situ (in the same place with no major movement of rock materials involved

Question 2

What are sub-aerial processes?

Answer 2

Land based processes which alter the shape of the coastline.
These are a combination of weathering and mass movement.

Question 3

What do all processes involve?

Answer 3

All processes involve energy transfer from the sun or rain.
Weathering is responsible for the transfer (flow) of material

Question 4

What are the links to other natural systems?

Answer 4

• carbon cycle
• water cycle

Question 5

What is an example of a positive feedback loop for weathering?

Answer 5

If the rate of debris removal exceeds the rate of weathering and mass movement, positive feedback may operate- rate of weathering and mass movement could increase

Question 6

What is an example of a negative feedback loop for weathering?

Answer 6

If debris removal is slow and ineffective, it will lead to a build up of debris that reduces the exposure of the cliff face as it extends up the cliff face- weathering and mass movement rates decrease

Question 7

What is biological weathering?

Answer 7

This involves the break up of rock by organic activity

Question 8

BW- plant roots

Answer 8

• Thin plant roots grow into small cracks in cliff face
• Cracks widen as roots grow and break up rock

Question 9

BW- decaying vegetation

Answer 9

Water running through decaying vegetation becomes acidic, which leads to increased chemical weathering

Question 10

BW- birds and animals

Answer 10

Birds and animals dig burrows into cliffs

Question 11

BW- marine organisms

Answer 11

Marine organisms are capable of burrowing into rocks or secreting acids

Question 12

What is mechanical weathering?

Answer 12

The break up of rocks without any chemical changes taking place

Question 13

What is freeze-thaw weathering?

Answer 13

• Mechanical

1. water enters a crack or joint in rock when it rains and freezes in cold weather
2. when frozen, water increases by approx 10%
3. expansion exerts pressure on rock so crack widens
4. with repeated freezing and thawing, fragments of rock break away and collect at the base of the cliff as scree

Question 14

What is crystallisation?

Answer 14

• mechanical
• salt water evaporates, leaving salt crystals behind
• these can grow over time and exert stresses on the rock, causing it to break up
• salt can also corrode rock

Question 15

What is wetting and drying?

Answer 15

• mechanical
• rocks rich in clay expand when they get wet and contract when they dry
• this causes them to crack and break up

Question 16

What is chemical weathering?

Answer 16

Involves a chemical reaction where salts may be dissolved or a clay-like deposit may result which is then easily eroded

Question 17

What is carbonation?

Answer 17

• chemical
• rainwater absorbs Co2 from air to form weak carbonic acid
• this reacts with calcium carbonate in rocks to form calcium bicarbonate, which is easily dissolved
  -cooler the temp of rainwater, the more Co2 is absorbed

Question 18

What is oxidation?

Answer 18

• reaction of rock minerals with oxygen
• e.g. iron reacts with oxygen to form rust red powder which leaves rocks more vulnerable to weathering

Question 19

What is solution?

Answer 19

The dissolving of rock minerals, such as halite