1. 5.1 Weathering

2. 2 types of weathering Mechanical Weathering
Occurs when physical forces break rock into smaller & smaller pieces without changing the rock’s mineral composition
Chemical Weathering
The transformation of rock into 1 or more new compounds

3. Mechanical Weathering
Breaking a rock into smaller pieces increases the total surface area
more SA is exposed to chemical weathering
Unloading
Exfoliation (layers of onion)
Causes the outer layers of the rock to expand more than the rock below
Igneous rock may be exposed by uplift & erosion of overlying rocks. Pressure exerted on the igneous rock is reduced.
Frost Wedging
Water freezes and expands
Frozen water in rocks expand cracks
Freeze – thaw cycles = rock breaks into pieces

4. Chemical Weathering Water Most important factor in CW
Absorbs gases in the atmosphere & ground
Chemical Weathering of Granite
Can change the properties of rocks
Chemical Weathering of Silicate Minerals
Make up most of Earth’s crust
Na, Ca, K, Mg they contain dissolve & are carried away by groundwater
Spheroidal Weathering
Form of CW
Corners & edges become more rounded by CW

5. Rate of Weathering Differential Weathering
Different parts of rock mass often weather at different rates
Factors that affect the rate of chemical weathering:
Rock Characteristics
Climate
Temperature, Moisture
High Temps. & high moisture are best for chemical weathering
Mechanical Weathering
By breaking rock into small pieces MW accelerates CW by increasing the SA