SAJC Cluster 2.2 Lecture 8 Notes (Geomorphic Processes Pt.2: Weathering Processes)

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2 Cluster 2_Lecture 11_2025/pg1 Lecture 11 Geomorphic Processes (II): Weathering Processes KEY QUESTIONS: ✓ What influences the weathering of rocks? With the completion of this lecture, attached readings and tutorial, you should be able to understand the: • Various chemical and physical weathering processes acting on rocks in the tropics • Factors influencing the weathering of rocks in the tropics Lecture Outline 11.1 Introduction 11.1.1 Types of Weathering Processes 11.2 Chemical Weathering Processes 11.2.1 Carbonation 11.2.2 Hydrolysis 11.2.3 Oxidation and Reduction 11.2.4 Solution 11.3 Physical Weathering Processes 11.3.1 Thermal Weathering 11.3.2 Freeze Thaw 11.3.3 Salt Weathering 11.3.4 Pressure Release 11.4 Factors Influencing Weathering of Rocks 11.4.1 Climate a) Cold regions (e.g. high altitudes in the Tropics) b) Hot and arid regions c) Hot and wet regions 11.4.2 Rock Characteristics (or Geology) a) Rock Composition b) Rock Structure c) Rock Texture 11.4.3 Vegetation a) Bio-physical weathering b) Bio-chemical weathering 11.4.4 Topography a) Steepness of slope 11.4.5 Human Activities a) Mining activity b) Construction of roads and residential areas c) Urbanised impermeable land surfaces d) Emissions from industries and automobiles 11.5 Conclusion

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2 Cluster 2_Lecture 11_2025/pg2 11.1 Introduction 11.1.1 Types of Weathering Processes • Weathering is the process of breakdown of rock by disintegration and decomposition in situ (in its original position), at or near, the earth’s surface. Weathering does not involve the removal of the weathered material. Weathering is a slow process, especially in resistant rocks, but its effects are evident on any exposed rock mass. • There are two main types of weathering processes namely chemical and physical weathering which can be further divided into sub-processes (see Fig. 1): Fig. 1: Weathering Processes in the Tropics o Chemical weathering occurs when the original mineral in the rock decomposes or decays in situ due to chemical alteration of those minerals (see Section 11.2). o Physical weathering occurs when rocks are broken and disintegrated into smaller pieces in situ without any chemical alteration (see Section 11.3). • Although both types of weathering may occur together, usually one predominates. The type and degree of weathering depends on the local climate, vegetation, structure and mineral composition of the rocks and the length of time during which the weathering process operate. • The pattern and products of weathering are therefor