The rate of chemical weathering isn’t the same everywhere—it depends on factors like climate, rock type, water flow, and biological activity. Warmer, wetter conditions speed up reactions, while fractures in rocks allow water to seep in and break them down over time. Understanding these factors helps explain how landscapes evolve.
Factors controlling the rate of chemical weathering:
There are a number of factors controlling the rate of chemical weathering:
• Organic activity in soils generates soil acidity (CO2) through decomposition and aids the retention of water through the build-up of organic matter, and biological activity promotes permeability.
• Climate controls weathering reactions by affecting the chemical kinetics of temperature (Arrhenius-type equation), creating a latitudinal gross pattern of chemical weathering rates. Rainfall influences vegetation type, biological activity in the soil, and water’s activity as a solvent.
• Fractures facilitate the mechanical breakdown and the ingress of fluids that catalyze chemical weathering. They originate in the regolith and also through tectonic strains.
• The kinetics of mineral reactions show that chemical weathering requires pore waters to be undersaturated with respect to the mineral being weathered. Once saturation is achieved, increasing the flowrate will not cause further reaction.
In contrast, the rate of chemical weathering of evaporites depends on how quickly the saturated solution is removed by flushing. For relatively insoluble minerals, such as silicates, the rate of chemical weathering depends on the kinetics with which ions detach from crystal surfaces.
• The stability of the mineral components to weathering is controlled by bedrock composition through their degree of polymerization, as illustrated by the Goldich series. Monomer silicates, such as olivine, weather most easily, while framework silicates, like quartz, resist weathering the most.
• Topography influences the rate of removal of regolith by erosion, which invigorates chemical weathering by subjecting new, fresh bedrock to weathering. Topography also controls drainage and, therefore, rates of flushing. Flow rates on mountainous slopes are high but flat, poorly drained slopes have very low flow rates.
• Chemical changes take time to occur. Weathering profiles seldom reach equilibrium with surface conditions.
