Summary of Introduction to Weathering Processes
Introduction to Weathering Processes: Types & Examples
Geomorphology: Weathering and Landform Change
Introduction
Weathering is the process that breaks down rocks and soil where they stand, changing their shape and sometimes their composition. It is the first step that prepares material for movement by erosion, but weathering itself does not move the material. In this guide you will learn the main types of weathering, how they work, and real-world examples and effects on landscapes and human structures.
Definition: Weathering is the breakdown of rocks and soils in place by physical, chemical, or biological processes.
Overview of Weathering Agents
- Main natural agents: temperature and water. Other important contributors include oxygen, carbon dioxide, acids, plants and animals.
- Weathering happens in place; erosion is the removal and transport of weathered material.
Types of Weathering
Weathering is grouped by how it breaks down material.
1) Mechanical (Physical) Weathering
- Mechanical weathering breaks rocks and soils into smaller pieces without changing their chemical composition.
- Common drivers: temperature changes, water, ice, pressure release, and abrasion.
Definition: Mechanical weathering is the physical disintegration of rock and soil without chemical change.
Key processes and examples:
- Freeze–thaw (frost) action
- Water collects in cracks and joints. When temperature drops, water freezes and expands by about 9%, forcing cracks wider. When it thaws, water moves deeper and the cycle repeats until pieces break off.
- Example: Mountain slopes where daily freeze–thaw cycles happen in cold climates.
- Exfoliation (sheeting)
- In hot, dry regions rock surfaces heat and expand by day and cool and contract at night. Repeated expansion and contraction causes outer layers to flake off in sheets.
- Example: Large dome-shaped granitic outcrops in deserts may peel like onion layers.
- Abrasion
- Wind, water or ice carrying particles scrape rock surfaces, wearing them down. Example: sandblasted rocks in deserts or polished rocks in glacial valleys.
Practical effects:
- Maintains and steepens slopes in cold climates due to freeze–thaw breakdown.
- Produces coarse fragments and gravel that become inputs to soil and sediment transport.
2) Chemical Weathering
- Chemical reactions change minerals in the rock, making them weaker and often soluble.
Definition: Chemical weathering is the breakdown of rocks and minerals through chemical reactions that change their composition.
Main processes:
- Carbonation
- Rainwater dissolves CO₂ to form weak carbonic acid $\ce{H2CO3}$. This acid reacts with calcium-bearing rocks (like limestone), converting calcium carbonate into soluble calcium bicarbonate which can be washed away.
- Example: Development of caves, sinkholes and karst landscapes where subsurface dissolution occurs.
- Oxidation
- Oxygen reacts with minerals that contain iron to form iron oxides (rust). This weakens rock and gives a reddish color to soils and weathered rock.
- Example: Red soils and weathered rock faces where iron-rich minerals are present.
- Hydrolysis
- Water reacts with minerals (especially silicate minerals) to form new clay minerals and soluble ions, gradually breaking down the rock structure.
Practical effects:
- Chemical weathering can damage buildings and statues made of limestone and dolomite.
- Creates fine particles (clay and dissolved ions) that influence soil fertility and water chemistry.
3) Biological Weathering
- Living organisms contribute to both mechanical and chemical weathering.
Definition: Biological weathering is the break down of rock and soil by plants, animals and microorganisms through mechanical or chemical means.
Examples:
- Plant roots grow into cracks and widen them mechanically.
- Lichens and microbes produce acids that chemically attack rock minerals.
- Burrowing animals mix soil and expose fresh surfaces to oth
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Weathering and Geomorphology
Klíčové pojmy: Weathering breaks rocks and soils in place without movement, Mechanical weathering breaks rock physically without chemical change, Freeze–thaw widens cracks as ice expands about 9% when freezing, Exfoliation peels outer rock layers due to thermal expansion and contraction, Chemical weathering alters mineral chemistry (e.g., carbonation, oxidation, hydrolysis), Carbonation: $\ce{H2CO3}$ dissolves calcium carbonate to form soluble calcium bicarbonate, Oxidation converts iron-bearing minerals to iron oxides (rust), weakening rock, Biological weathering includes root growth and acidic secretions from organisms, Mechanical produces fragments and gravel; chemical produces clays and dissolved ions, Weathering contributes to soil formation and supplies material for erosion and deposition, Understanding local weathering helps with construction, conservation and land use planning