Weathering & Erosion
Notes
Weathering is the in-situ breakdown and decay of rocks by atmospheric agents (temperature, water, frost, plants, gases). There is no transport of material. Erosion is the removal and transport of weathered material by agents such as running water, glaciers, wind, waves and groundwater.
Types of weathering
- Physical (mechanical): disintegration without chemical change. Dominant in arid and cold regions.
- Temperature changes (insolation): repeated heating and cooling cause granular disintegration, block disintegration and exfoliation (onion-peel weathering).
- Frost wedging: water freezes in cracks and expands.
- Salt weathering: salt crystals grow in pores.
- Pressure release (unloading): removal of overlying rock causes sheeting.
- Chemical: decomposition by reactions with water and gases. Dominant in warm, humid regions.
- Solution: minerals dissolve (rock salt).
- Carbonation: carbonic acid reacts with limestone, producing karst features.
- Hydration: minerals absorb water and swell (anhydrite to gypsum).
- Oxidation: iron minerals form rust (red and yellow colours).
- Reduction: in waterlogged conditions (grey-blue colours).
- Hydrolysis: feldspar breaks down into clay minerals (kaolinite).
- Biological: roots widening cracks, burrowing animals, lichens and organic acids.
Mass wasting (mass movement): downslope movement of weathered material under gravity: slow (soil creep, solifluction) and rapid (rockfall, landslides, mudflows, debris avalanches).
Erosion: carried out by running water (the most important), glaciers, wind, waves and groundwater. Denudation is the sum of weathering, mass wasting, erosion and transport.
Basis | Weathering | Erosion |
|---|---|---|
Movement of material | No (in situ) | Yes (transport) |
Agents | Climate, organisms | Water, ice, wind, waves |
Result | Regolith and soil | Landforms (valleys, deltas) |
Significance: formation of soil, enrichment of ores (bauxite, iron), and creation of landforms; excessive erosion causes soil loss and gullying.
Key Points
- Weathering is in situ; erosion involves transport.
- Physical weathering dominates in arid and cold regions; chemical in warm, humid regions.
- Carbonation produces karst on limestone; oxidation gives red soils.
- Exfoliation and frost wedging are physical processes.
- Mass wasting is gravity-driven movement.
MCQs
Q1. Which weathering process is most important in the formation of karst topography?
(a) Oxidation
(b) Carbonation
(c) Hydration
(d) Exfoliation
Ans: (b).
Q2. Weathering differs from erosion because:
(a) It is carried out by running water
(b) It involves no transport of material
(c) It occurs only in deserts
(d) It is a chemical process only
Ans: (b).
Q3. Exfoliation is a type of:
(a) Chemical weathering
(b) Physical weathering
(c) Biological weathering
(d) Mass wasting
Ans: (b).