L7- Chemical Weathering

Five types of weathering:
- Freeze-thaw
- Pressure release
- Salt weathering
- Chemical weathering
- Biological weathering
‘Frost shattering’ is also known as freeze-thaw weathering.
‘Thermal fracture’ is also referred to as thermal stress.
‘Dilatation’ is also known as pressure release.
Other types besides physical weathering include chemical weathering and biological weathering.

Task 1: Explain each of the 5 types of physical weathering with diagrams where appropriate.
Task 2: Submit a 15-mark answer extension.

Freeze-thaw: Erosion process where water enters joints in rock, expands when frozen, and exerts pressure, weakening the rock (4 marks total).
- Water enters rock joints (1)
- Expands upon freezing (1)
- Repeated cycles weaken the rock (1)
- Results in pressure release (1)
Vegetation root action: Growth of plant roots into rock joints forces rocks apart (3 marks total).
- Roots grow into rock joints (1)
- Forces rock apart (1)
- Continuous growth expands the crevice (1)

Key features:
- Primarily involves water.
- Most effective in subsurface layers due to acid-laden water from vegetation.
- Three main types: Hydrolysis, Hydration, and Carbonation/Solution.

Definition: Reaction where minerals in rocks interact with water acids, resulting in clay formation.
1. Granite consists of various minerals.
2. Feldspar reacts with acid in water to form kaolin (clay).
3. Potassium hydroxyl and silicic acid wash away, leaving clay.
4. Quartz remains unaffected and is left in the clay.

Definition: Process in which certain minerals absorb water and expand.
1. Anhydrite absorbs water and transforms into gypsum.

Definition: Reacts with calcium carbonate rocks.
1. Rain mixes with natural acids to form carbonic acid.
2. Reacts with calcium carbonate, dissolving it into calcium bicarbonate.
3. Caves form as rocks dissolve over time.
4. Calcium bicarbonate can deposit as stalagmites and stalactites in caves.

Task 1: Copy notes explaining the three types of chemical weathering.
Task 2: Document chemical reactions for hydrolysis, hydration, and carbonation (refer to p.81).
Factors influencing weathering:
- Increase: Rock structure weaknesses, allowing water penetration.
- Decrease: Impermeable rock structures.

3.1 Plate tectonics:
- Nature and patterns of tectonic plates.
- Types of plate boundaries: Divergent, Conservative, and Convergent.
- Related processes: Sea floor spreading, subduction, and volcanic landforms.
3.2 Weathering: Description of physical and chemical processes.
- Physical: Freeze-thaw, heating, salt crystal growth, pressure release, and vegetation action.
- Chemical: Hydrolysis, hydration, and carbonation.
Factors affecting weathering: Climate, rock type, structure, vegetation.
Slope Processes: Mass movement, water movement, and human impacts on slopes.