Controls of Weathering

Question 1

How does rock type control weathering?

Answer 1

• influences rate + type due to:
  
  • chemical composition
  • nature of cements in sedimentary rocks
  • joints + bedding planes

e.g. limestone contains CaCO3: prone to carbonation/solution
e.g. granite contains feldspar: prone to hydrolysis

Question 2

Why is nature of cements crucial in sedimentary rocks?

Answer 2

• Fe2O3 based cements: prone to oxidation
• quartz cements: v resistant

Question 3

What factors of rock structure controls weathering?

Answer 3

• joint patterns: exert strong control on water movement
• grain size: influences speed of rocks weathering
• mineral type in rocks formed

Question 4

How does joint patterns exert a strong control on water movement?

Answer 4

• acts as lines of weakness, creating differential resistance in same rock type

Question 5

How does grain size influence speed of rocks weathering?

Answer 5

• coarse grained rocks: quickly - large void space + high permeability
• fine grained rocks: > SA for weathering - may be highly susceptible

Question 6

How does mineral type in rocks formed control weathering?

Answer 6

• resistant minerals (quartz, feldspar in granites): resist weathering
• weaker minerals: weather rapidly

Question 7

What factors of vegetation influence the nature + rate of weathering?

Answer 7

• moisture content
• root depth
• acidity of humus

Question 8

What are the 2 main ways vegetation weathers rocks?

Answer 8

• secretion of organic acids: helps chemically weather soil
• growth of roots: physically weathers soil

Question 9

How does depth of soil affect weathering?

Answer 9

• may protect rocks from further breakdown
• may inc. rate due to veg. it supports

Question 10

How does relief control weathering?

Answer 10

• slope too shallow: removal may not occur
• slope too steep: water may flow over surface
• medium slopes: may produce most weathering