Weathering is the process of alteration and breakdown of rock at or close to the Earth’s surface by chemical decomposition, biological degradation and physical disintegration that leads to the formation of soil. Weathering is most severe in humid tropical climates (Figure 11.1a and b) where it may extend to over 200 m beneath ground surface, whereas in more temperate climates, the process is much slower and less intense and may only affect the upper few metres of rock. The depth of weathering is controlled by the length of time that the decomposition has been active. During weathering, the constituent minerals in the rock become altered to clays, iron oxides and a plethora of other secondary minerals. Physical disintegration of the rocks through annual wetting and drying cycles, temperature changes and surface abrasion and fracturing are additional factors that can influence the intensity, distribution and rate of weathering. Weathering also involves the dissolution of soluble minerals within some rocks and the precipitation of new minerals from percolating groundwater. The formation of cave systems in carbonate-rich rocks is part of the overall weathering process and leads to the development of karst.