2.6 - Mass Movement And Weathering

Question 1

What is weathering

Answer 1

weathering is the breakdown of rock in its place of origin

Question 2

Types of mechanical weathering

Answer 2

When rocks break down with no chemical changes

• Freeze thaw: water expands by 9% in volume when freezing which exerts a force within cracks and fissures, repeated expansion and contraction causes further crack until rock breaks apart
• Wetting and drying: happens in warmer climates where rocks rich in clay expand when they get wet and contract when they dry, this repeated process causes them to crack and break over time
• Salt crystallisation: happens when sea spray gets through cracks in rocks, when the water evaporates it leaves behind salt crystals, the growth of these crystals in cracks and pore spaces can exert a breaking force, the salt can also corrode rocks
• Exfoliation/onion skin: when rocks warm up during the day the rock expands, at night the rock cools and contracts, overtime this causes very thin layers of rock to flake off

Question 3

Types of biological weathering

Answer 3

rocks break down due to organic activity

• Rock boring: many marine molluscs live on coastal rocks, scraping away at the rock surface to get food or boring a hole in the rock to make a home
• Plant roots: trees and plants roots grow into cracks and fissures forcing rocks apart
• Animals: dig burrows into the cliff breaking rocks

Question 4

Types of chemical weathering

Answer 4

rocks break down due to a chemical reaction
- Carbonation: as rain is slightly acidic, it reacts with carbonate rocks such as limestone causing them to dissolve
- Oxidation: when iron minerals in the rock react with oxygen in the air causing t=rust and the breaking down the rock
- Solution: when other salt minerals in the rock are dissolved
- Hydrolysis: the break down of minerals to form new clay minerals due to the effects of water and dissolved carbon dioxide

Question 5

What is mass movement

Answer 5

Mass movement is the downslope movement of material (rock and soil) under the force of gravity
Mass movement is classified based on: speed, water content and nature of material

Question 6

What are the 4 types of mass movement

Answer 6

• Rock fall: a rapid from of mass movement, blocks can be dislodged by mechanical weathering or hydraulic action, undercutting leads to large falls
• Slide: blocks of rockslide down a dip slope towards the sea, a very low angle dip will prevent rockfalls
• Flow: saturated soil and rock debris lose their cohesion and flow downslope, heavy rainfall and high tides can contribute to this
• Slump: huge masses of material can slowly rotate downslope over periods from days to years, can occur along a curved surface

Question 7

What is a rotational scar

Answer 7

• Curved, Un-weathered, Un-vegetated
• Forms as a result of rotational slumping
• The section that has detached is at the base of the cliff often with vegetation attached

Question 8

What is a talus scree slope

Answer 8

• A talus scree slope is a fan-shaped mound of material, often having a concave profile
• Made of block-fall debris which has accumulated at the foot of a cliff

Question 9

What is a terraced cliff profile

Answer 9

• The profile of the cliff is stepped
• This is the result of the lithology or fractures in the rock