Types of weathering

Physical Weathering

Physical weathering, also known as mechanical weathering, involves the disintegration of rocks without any change in their chemical composition. It reduces the size of rocks into smaller fragments.

• Freeze-Thaw Weathering: Water enters cracks in rocks, expands upon freezing (approximately 9% volume increase), and exerts pressure, widening the cracks. Repeated cycles lead to rock fracturing. Common in mountainous regions with fluctuating temperatures.
• Thermal Expansion and Contraction: Rocks expand when heated and contract when cooled. Repeated cycles create stress, leading to fracturing, especially in deserts with large diurnal temperature variations.
• Exfoliation (Pressure Release): As overlying rocks are eroded, the pressure on underlying rocks is reduced. This causes the rocks to expand and fracture in layers parallel to the surface, resulting in dome-shaped landforms (e.g., Stone Mountain, Georgia, USA).
• Salt Weathering: Salt crystals grow in pores and cracks of rocks, exerting pressure and causing disintegration. Common in arid and coastal regions.
• Abrasion: The wearing away of rocks by the mechanical action of other rocks and sediments carried by wind, water, or ice.

Chemical Weathering

Chemical weathering involves the decomposition of rocks through chemical reactions, changing their mineral composition. Water is a crucial agent in most chemical weathering processes.

• Solution: Some minerals dissolve directly in water (e.g., limestone dissolving in rainwater). This is particularly significant in karst landscapes.
• Hydrolysis: Reaction of minerals with water, leading to the formation of new minerals (e.g., feldspar altering to clay minerals). This is a major process in the formation of soils.
• Oxidation: Reaction of minerals with oxygen, often in the presence of water, leading to the formation of oxides (e.g., iron rusting).
• Carbonation: Reaction of minerals with carbonic acid (formed from dissolved carbon dioxide in water), leading to the formation of carbonates. Important in the weathering of limestone and chalk.

Biological Weathering

Biological weathering involves the breakdown of rocks by the actions of living organisms.

• Root Wedging: Plant roots grow into cracks in rocks, exerting pressure and widening the cracks.
• Burrowing Animals: Animals like earthworms and rodents burrow into the soil and rocks, loosening the material and increasing surface area for other weathering processes.
• Lichen and Moss: These organisms secrete acids that dissolve rock minerals.
• Microbial Activity: Microorganisms decompose organic matter, releasing acids that contribute to chemical weathering.

Comparative Table of Weathering Types

Type of Weathering	Mechanism	Resultant Landforms/Effects	Dominant Climate
Physical	Disintegration without chemical change	Scree slopes, rock fragments, exfoliation domes	Cold and arid regions
Chemical	Decomposition through chemical reactions	Karst topography, clay formation, altered rock surfaces	Warm and humid regions
Biological	Breakdown by living organisms	Soil development, weakened rock structures	Regions with abundant vegetation and animal life

It’s important to note that these types of weathering often operate simultaneously and interact with each other. For example, physical weathering increases the surface area available for chemical weathering, and biological weathering can accelerate both physical and chemical processes.