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Class 11 Geomorphic Processes: cheat sheet
CBSE Social Science. The forces that build up and wear down the land: diastrophism and volcanism, weathering, mass movements, erosion, and how soil forms.
Key ideas
- Endogenic forces from inside the earth build up the land; exogenic forces from the atmosphere wear it down; the sun’s energy drives all exogenic processes.
- Diastrophism includes orogeny (mountain building by folding), epeirogeny (uplift of large areas), earthquakes and plate tectonics.
- Weathering breaks rocks in place (in situ): chemical (solution, carbonation, hydration, oxidation, reduction), physical and biological.
- Mass movements carry debris downslope by gravity alone: creep, slump, debris slide, rockslide and rock fall.
- Erosion removes and carries material by agents such as running water, glaciers, wind and waves; denudation is all of these together.
- Soil forms from parent material, topography, climate, biological activity and time.
- Climate and biological activity are active factors; parent material, topography and time are passive.
Remember
| Gradient of a slope | rise ÷ horizontal distance × 100 (in %) |
| Soil loss | years = depth lost (in mm) ÷ loss per year (in mm); 1 cm = 10 mm |
| Soil formation time | years for 1 cm × number of cm |
| Kankar | calcium carbonate nodules in soils of intermediate rainfall |
| Desilication | silica washed out of soil in wet equatorial areas |
| Rhizobium | bacteria in legume root nodules that fix nitrogen |
| Waves | the only agent of erosion not controlled by climate |
Watch out
- Calling exfoliation by unloading chemical weathering (it is physical).
- Thinking mass movement needs weathering first: gravity moves any material.
- Mixing up orogeny (folding, mountains) and epeirogeny (broad uplift).
Worked example
Slope A rises 8 m over 100 m and slope B rises 40 m over 200 m. What is the gradient of each as a percentage, and on which are mass movements more likely?
Working: 8 ÷ 100 × 100; 40 ÷ 200 × 100
Answer: A 8%, B 20%; slope B, being steeper
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