GCE Geography 2024 Theory — Question 5

Model answer

(a) Three conditions that favour the development of karst topography: i. High rainfall: Abundant rainfall dissolves the rocks and creates underground drainage systems. ii. Warm temperatures: Warm temperatures enhance chemical reactions, increasing the rate of rock dissolution. iii. Presence of soluble rocks: Rocks like limestone, dolomite and gypsum are prone to dissolution by slightly acidic water. (Also acceptable: acidic water containing carbon dioxide, and topography with gentle to moderate slopes which allows water to flow slowly and have more time to erode the rock.) (b) A sinkhole is a depression or hole that forms in the ground when a layer of soil or rock is removed or collapses. Modes of formation: - Dissolution: Sinkholes often form in areas with soluble bedrock, such as limestone or gypsum. Groundwater gradually dissolves these rocks, creating underground voids and caverns. - Collapse: When the roof of an underground cavern becomes too thin to support the weight above it, it can suddenly collapse, forming a sinkhole. - Human activity: Construction, mining, groundwater withdrawal and other human activities can disturb the structural integrity of the ground, leading to sinkhole formation. Characteristics of sinkholes: - Shape and size: Sinkholes vary from small depressions to large, deep holes, in oval, circular or irregular shapes. - Depth: They range from a few feet to several hundred feet deep. - Edges: They can have steep and abrupt, or gently sloping edges. - Surface water: They may be filled with water to form ponds/lakes, or remain dry. - Subsoil exposure: They often expose bedrock and subsoil layers, revealing geological strata and sometimes underground water systems.