Weathering and Erosion
~9 min read
- Weathering: Breakdown of rocks in situ (no movement). Three types: physical (mechanical), chemical, biological.
- Erosion: Wearing-away PLUS movement of broken material by an agent (water, wind, ice, gravity).
- Difference: Weathering = breakdown without moving. Erosion = breakdown + transport.
Weathering breaks rocks; erosion carries them away. Together they shape Earth's surface over geological time. NDA tests the difference between the two and the specific weathering processes.
Three Types of Weathering
| Type | Process | Example |
|---|---|---|
| Physical (mechanical) | Rock breaks into smaller pieces without chemical change | Frost wedging, exfoliation, thermal expansion |
| Chemical | Minerals dissolve or react chemically | Carbonation (limestone in CO₂-rich water), oxidation (iron rusts), hydrolysis (granite → clay) |
| Biological | Living organisms cause breakdown | Roots widening cracks, lichens dissolving minerals, burrowing animals |
Physical Weathering Processes
- Frost action / freeze-thaw: Water enters cracks, freezes, expands by 9%, widens cracks. Common in cold mountains.
- Exfoliation: Outer layers peel off curved rock surfaces, often due to pressure release as overlying rock erodes.
- Thermal expansion: Daily heating/cooling causes outer layers to expand/contract differently, leading to flaking. Common in deserts.
- Salt crystallisation: Salt crystals grow in cracks and pry rocks apart. Common near coasts.
Chemical Weathering Processes
- Carbonation: CO₂ + water → carbonic acid → dissolves limestone, forms caves (Borra caves, Andhra Pradesh; Meghalaya caves).
- Oxidation: Iron minerals + oxygen → rusty iron oxides. Red soils of South India show oxidation weathering.
- Hydrolysis: Water reacts with silicate minerals → clay. Granite → kaolinite (clay).
- Solution: Soluble minerals (rock salt, gypsum) dissolve directly in water.
Agents of Erosion
| Agent | Landforms produced |
|---|---|
| Running water | Valleys, gorges, meanders, deltas, alluvial plains |
| Glaciers | U-shaped valleys, fjords, moraines, cirques |
| Wind | Sand dunes, yardangs, mushroom rocks, ventifacts |
| Sea waves | Cliffs, sea arches, stacks, beaches |
| Groundwater | Caves, sinkholes (karst topography) |
NDA PYQ Examples
Q: Exfoliation is an example of:
(a) Chemical weathering (b) Physical weathering (c) Biological weathering (d) Erosion
Answer: (b) Physical weathering — pressure release peels outer layers.
Q: The conversion of limestone caves is caused by:
(a) Oxidation (b) Hydration (c) Carbonation (d) Wind erosion
Answer: (c) Carbonation — CO₂-rich water dissolves limestone.
Drill Weathering and Erosion for NDA
NDA-pattern items on Weathering and Erosion with answer keys and explanations.
Start Free Mock TestFrequently Asked Questions
What is the main difference between weathering and erosion?
Weathering breaks rocks in place (no movement). Erosion includes the transport of broken material away from its source by water, wind, ice or gravity.
Which type of weathering is dominant in deserts?
Physical weathering — daily temperature swings cause thermal expansion; salt crystallisation in arid soils. Chemical weathering is slow because of low water availability.
Which type of weathering is dominant in humid tropics?
Chemical weathering — abundant water and high temperatures speed up reactions like hydrolysis and oxidation. This is why tropical soils are deeply weathered.
What is exfoliation?
Peeling-off of curved outer layers of rock, often due to pressure release as overlying rocks erode. Common on granitic domes.
What is karst topography?
Landforms produced by chemical weathering (carbonation) of limestone — caves, sinkholes, underground rivers. Named after the Karst region of Slovenia.