SAJC Cluster 2.2 Lecture 13 Notes (Karst Landforms in the Humid Tropics)

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2 Cluster 2_Lecture 13_2025/pg1 Lecture 13 Karst Landforms in the Humid Tropics KEY QUESTION: ✓ What landforms can be found in the humid tropics? ✓ What factors influence the formation of karst landforms in the humid tropics? ✓ What is the importance of karst landforms in the humid tropics? With the completion of this lecture, attached readings and tutorial, you should be able to: • Identify the different karst landforms and describe their features • Discuss the role of geomorphic processes in the formation of karst landforms • Discuss the ecosystem services provided by karst landforms • Discuss the impact of human activities on ecosystem services provided by karst landforms Lecture Outline 13.1 Introduction 13.2 Global Distribution of Karst Landforms 13.3 Features of Karst Landforms 13.3.1 Cockpit Karsts 13.3.2 Tower Karsts 13.3.3 Caves 13.4 Role of Geomorphic Processes in the Formation of Karst Landforms 13.4.1 Role of Geomorphic Processes in the Formation of Cockpit Karst 13.4.2 Role of Geomorphic Processes in the Formation of Tower Karst 13.4.3 Role of Geomorphic Processes in the Formation of Caves 13.5 Factors Influencing the Formation of Karst Landforms 13.5.1 Climate 13.5.2 Vegetation 13.5.3 Rock Characteristics of Limestone 13.5.4 Tectonic Activity 13.5.5 Human Activities 13.6 Importance of Karst Landforms in the Humid Tropics 13.6.1 Ecosystem Services Provided by Karst Landforms (a) Provisioning Services (b) Regulating Services (c) Cultural Services (d) Supporting Services 13.6.2 Impact of Human Activities on Ecosystem Services Provided by Karst Landforms 13.7 Summary: Conditions Favouring the Development of Karst Landforms 13. 8 Conclusion

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2 Cluster 2_Lecture 13_2025/pg2 13.1 Introduction • In geomorphology (i.e. the study of characteristics, origins and development of landforms), karst landforms (see Fig. 1) are a set of landforms mostly developed in carbonate rocks due to their high solubility. Karst landforms therefore only develop in limestone under favourable conditions. Fig. 1 Different Karst Landforms • Characteristics of Limestone o Limestone is made up of calcium carbonate. Calcium carbonate is insoluble in water; it is highly soluble in acid. o The concentration of calcium carbonate may vary from area to area. Limestone which has high concentration (80% or more) of calcium carbonate is highly susceptible to the processes of carbonation and solution (see Lect. 11). o Limestone is a permeable rock. It has lines of weaknesses such as joints and bedding planes (see Fig. 2). Thus, limestone allows acidic water to pass through its lines of weaknesses, enabling weathering, fluvial erosion and mass movement to occur along these lines of weaknesses, thereby contributing to the formation of karst landforms. The density of joints may vary over place and time and thus so will the rate of weathering. The rate of weathering is most intense where two or more joints and bedding planes intersect (intersecting joints) or where joints and bedding planes are more dense. Fig. 2 Lines of weaknesses in limestone • It has been suggested that certain karst landforms are more common in the humid tropics. Thus, their formation is influenced by climatic conditions. To understand such relationships, we need to become familiar with the characteristics of limestone, and the processes capable

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2 Cluster 2_Lecture 13_2025/pg3 of weathering it into distinctive landforms. Also, we need to consider the role of fluvial erosion and mass movements involved. Thus, all three geomorphic processes play a role in the formation of karst landforms. 13.2 Global Distribution of Karst Landforms • Karst landforms are common in southern China and countries of Southeast Asia such as northern Vietnam, Thailand, Indonesia, Sabah and Sarawak. Karst landforms are also found in south-eastern parts India, Central and South America, Australia and several European countries, including the UK, France and Slovenia (see Fig. 3). For our syllabus, we would focus on karst landforms found in the humid tropics mainly in parts of India, Vietnam, Thailand, Indonesia, Southern China, Malaysia etc. Fig. 3 Global distribution of limestone regions 13.3 Features of Karst Landforms • The karst landforms as specified in the syllabus are: o Cockpit karsts (Section 13.3.1) o Tower karsts (Section 13.3.2) o Caves (Section 13.3.3) • These landforms can be differentiated based on surface and sub-surface location. They can also be distinguished based on their features like shape, height, slope angle etc. • These surface and sub-surface landforms are the result of prolonged and extensive weathering, fluvial erosion and mass movement of limestone regions.

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2 Cluster 2_Lecture 13_2025/pg4 13.3.1 Cockpit Karsts • Cockpit karsts consist of star-shaped depressions called cockpits separated from each other by roughly equally spaced conical/cone-shaped hills (cone karst) (see Fig. 4 and 5), with local relief that is anything from 30 to 300 metres. o Often been labelled as egg-box topography (see Fig. 4 and 5). • The cones or conical hills are generally symmetrical, and their slopes measured between 45° and 60°, regardless of their structure. Conical hills are 30 to 120 m tall and occur with a density of 15 to 30 hills/km2. (Compare these numbers with tower karst later). • Example of cockpit karst is Chocolate Hills, Bohol, Philippines (see Fig. 6). Fig. 4 Cockpit Karst Fig. 5 Star-shaped depression Fig. 6 Cockpit Karsts: Chocolate Hills, Bohol, Philippines

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2 Cluster 2_Lecture 13_2025/pg5 13.3.2 Tower Karsts • Tower karsts are a steeper variety of karst risers than cone karsts. In general, towers are steeper and higher than cones and have a bigger height-diameter ratio. These residual hills come in a range of shapes, though a common dominant feature is their sharp rise from the surrounding plains. • Tower karsts are steep-sided limestone hills that rise above a plain, formed in humid tropics due to the further deepening of cockpits (see Section 13.3.1). o Tower karsts are much more variable in size than the cone karst (see Section 13.3.1), and their heights may reach over 150 m in Sarawak and even 300 m elsewhere such as Vietnam (see Fig. 7) and southern China (see Fig. 8). They occur with a density of 5-10 hills/km2, which is relatively much lower than cockpit karst. o Form in hard limestone with pronounced vertical jointing and almost horizontally bedded. o Tower karsts are characterised by steep sides (between 60° and 90°) with cliffs and overhangs, and with cave and solution notches at their base. Tower karsts usually occur in groups and are separated from each other by an alluvial plain or swamp or river. • Thus, in general, tower karsts are steeper and higher than cones in cockpit k