Weathering, Erosion and Mass Movement
NCERT Class 11 - Fundamentals of Physical Geography, Chapters 5 and 6
Weathering, Erosion and Mass Movement
Exogenic processes wear the land down. They work in a sequence - weathering breaks rock in place, mass movement carries the loose material downslope by gravity, and erosion removes and transports it by rivers, ice, wind and waves.
Weathering and how it differs from erosion
- Weathering is the breakdown of rock in situ, that is, without any transport of the material.
- Erosion involves both the wearing away and the transport of material by a moving agent.
- Weathering therefore prepares the material that erosion then removes, which is why it is called the first step of denudation.
- The overall process of wearing down the land is called denudation, which includes weathering, mass movement, erosion and transport.
Types of weathering
| Type | Process | Where it dominates |
|---|---|---|
| Frost action | Water freezes in cracks and expands, splitting the rock | Cold mountains, high latitudes |
| Thermal expansion | Repeated heating and cooling peels off outer layers, called exfoliation | Hot deserts with large daily temperature range |
| Salt weathering | Salt crystals grow in pores and prise the rock apart | Arid and coastal areas |
| Unloading | Overlying rock is removed, the rock below expands and cracks | Areas of deep erosion and quarrying |
| Solution | Minerals dissolve directly in water | Limestone and salt regions |
| Carbonation | Carbon dioxide in rainwater forms weak acid that attacks limestone | Karst regions |
| Oxidation | Iron minerals react with oxygen and the rock reddens and crumbles | Humid warm regions |
| Hydrolysis and hydration | Minerals react with or absorb water and swell | Humid tropics |
- Physical weathering breaks rock without changing its chemistry; chemical weathering changes the minerals themselves.
- Biological weathering works both ways - roots widen cracks mechanically, while organic acids from lichens and decaying matter attack minerals chemically.
- Chemical weathering dominates in hot and humid climates, which is why tropical regions have deep weathered layers.
Mass movement
- Mass movement is the downslope movement of material under gravity, without a transporting medium such as running water.
- Creep - extremely slow movement of soil, visible only through tilted poles, bent trees and cracked walls.
- Solifluction - slow flow of water-saturated soil over frozen ground in cold regions.
- Landslide - rapid movement, including slump where material rotates along a curved surface, debris slide and rockslide.
- Mudflow and debris flow - saturated material moving quickly down a channel, common after heavy rain in the Himalayas.
- Rockfall and avalanche - free fall of rock or the rapid descent of snow and ice.
- Causes include steep slopes, heavy rain, weak or saturated material, loss of vegetation, earthquakes, and human activity such as road cutting, mining and construction on unstable slopes.
Soil formation
- Soil forms from weathered material called regolith, mixed with organic matter, water and air.
- The five factors controlling soil formation are parent material, climate, relief, organisms and time.
- Climate is generally the most important factor, since temperature and rainfall control the rate of weathering and the movement of material within the soil.
- A mature soil shows horizons - an upper layer rich in organic matter, a middle layer where material accumulates, and weathered parent rock below.
हिंदी संकेत: अपक्षय में पदार्थ अपनी जगह टूटता है और अपरदन में टूटकर हटाया भी जाता है। यही दोनों का निर्णायक अंतर है और सबसे अधिक पूछा जाता है।
Exam me kaise aata hai
Statement-based questions test the difference between weathering and erosion. Match-the-following links weathering process with the climate where it dominates. Application questions describe a slope failure and ask which type of mass movement it is.
UPSC / State PSC ke liye
Connect weathering to resources and hazards - deep chemical weathering in the humid tropics produces laterite and bauxite, while mass movement in the Himalayas is a major disaster risk made worse by deforestation and unplanned road construction. These links are what turn a descriptive answer into an analytical one.
Yahan confuse hote hain
✗ Weathering includes transport of material | ✓ Transport is erosion; weathering happens in place
✗ Exfoliation is a chemical process | ✓ It is physical, caused by repeated heating and cooling
✗ Mass movement requires running water to carry material | ✓ It is movement under gravity alone
Ek nazar me
- Denudation includes weathering, mass movement, erosion and transport.
- Weathering breaks rock in place; erosion also transports it.
- Physical weathering - frost action, thermal expansion, salt weathering and unloading.
- Chemical weathering - solution, carbonation, oxidation, hydrolysis and hydration.
- Chemical weathering dominates in hot humid climates and produces deep weathered layers.
- Mass movement includes creep, solifluction, landslide, mudflow, rockfall and avalanche.
- Soil forms from regolith under the influence of parent material, climate, relief, organisms and time.