1. Lesson 6

2. Rates of weathering
 The speed at which rock are
broken down.
This depends on several factors:
 Climate
 Rock Characterics
 Vegetation

3. CLIMATE
Chemical Weathering Physical Weathering
 Most intense in hot and wet  Particularly active in
climate
cold climates where
 Chemical reactions
frost shattering
promotes by high dominates
temperatures
 Heavy rainfall provides  Also active in desert
necessary moisture for the climates where
processes insolation weathering or
exfoliation dominates
 E.g: Deep weathering
profile and typical red soil in
tropical climate reflect
active oxidation

5. Climatic conditions
1. Strong Chemical Weathering – Hot and wet
 Temperature: 70C – 300C
 Rainfall : 1600 – 2500mm
2. Weak Chemical Weathering
 Temperature: -30C to -200C
 Rainfall : 0 – 900mm
3. Strong Physical Weathering
 Temperature: -50C to -100C
 Rainfall : 300 mm to 1300mm
4. Weak Physical Weathering
 Temperature: 00C to 90C
 Rainfall : 0 – 1700mm

7. Rock Characteristics
 Define the term joints and
bedding planes.
 Joints – fractures or cracks
that run through rocks
 Bedding planes –
the junctions between beds
of sedimentary rocks

10. Permeability and porosity
 Which of the following texture is easily weathered?

11. Vegetation
 Presence of vegetation promotes weathering
 Organic acids speed up hydrolysis
 Moss cling to rock surface, holding water
against them like a wet sponge 
encourage chemical weathering
 At the same time protect a rock surface from
temperature extreme which reduce physical
weathering