Weathering (Geology)
Weathering is the in-situ breakdown of rocks and minerals at or near Earth's surface through physical disintegration, chemical decomposition, and biological activity, without significant transport of the resulting material. Physical (mechanical) weathering fragments rock into smaller pieces without changing its mineral composition, while chemical weathering alters mineral chemistry through reactions with water, oxygen, and acids. Biological weathering involves living organisms such as plant roots, lichens, and bacteria accelerating both physical and chemical breakdown processes.
Types of Weathering with Processes and Examples
| Type | Process | Agent | Product | Example |
|---|---|---|---|---|
| Physical — Freeze-thaw | Water expands 9% on freezing, fracturing rock | Water/ice | Angular rock fragments | Scree slopes in alpine zones |
| Physical — Exfoliation | Pressure release causes concentric spalling | Stress relief | Rounded boulders | Granite domes, Yosemite |
| Chemical — Hydrolysis | Water reacts with silicate minerals | H₂O + acids | Clay minerals | Kaolinite from feldspar |
| Chemical — Oxidation | Oxygen reacts with iron-bearing minerals | O₂ + water | Iron oxides (rust) | Red laterite soils |
| Chemical — Carbonation | CO₂ + water dissolves carbonates | Carbonic acid | Calcium bicarbonate solution | Limestone karst caves |
| Biological | Root wedging, organic acid secretion | Plants, fungi, bacteria | Soil, clay residues | Lichen on granite |
Interactive Tools
PhET — States of Matter (Frost Weathering)
Explore water phase changes relevant to freeze-thaw weathering at the molecular level.
Open ToolKhan Academy — Weathering and Soil Formation
Comprehensive lesson on physical, chemical, and biological weathering with diagrams.
Open ToolWolfram Alpha — Silicate Hydrolysis Reactions
Look up chemical equations for feldspar hydrolysis and carbonate dissolution reactions.
Open Tool
Wikimedia Commons, CC BY-SA
Related Terms
Mineral
A mineral is a naturally occurring, inorganic, crystalline solid with a definite chemical composition and characteristic physical properties. Minerals are the building blocks of rocks and are classified by their crystal structure, hardness, luster, cleavage, and color. They are essential to industry, construction, and biological processes, with over 5,000 known mineral species recognized by the International Mineralogical Association.
Erosion
Erosion is the geological process by which rock, soil, and sediment are loosened and transported away from their original location by agents such as water, wind, ice, and gravity. It is a key component of the rock cycle that continuously reshapes Earth's surface by removing material from one location and depositing it elsewhere as sediment. Erosion rates are significantly influenced by climate, vegetation cover, rock type, and slope gradient, and accelerated erosion caused by deforestation or poor land management poses major environmental challenges.
Soil Formation
Soil formation (pedogenesis) is the process by which parent rock material is transformed into soil through the combined effects of weathering, biological activity, organic matter accumulation, and the movement of water and dissolved substances through the soil profile. The CLORPT model identifies five key soil-forming factors: climate, organisms, relief (topography), parent material, and time. The result is a layered soil profile with distinct horizons—O, A, B, C, and R—each reflecting the degree of weathering, organic content, and mineral alteration at different depths.
From Old English "weder" (weather, atmospheric conditions), reflecting the historical observation that atmospheric exposure breaks down rock. The scientific distinction between weathering and erosion was formalized by 19th-century geomorphologists, particularly through the work of Grove Karl Gilbert of the USGS in the 1870s–1890s.