Ch-5: Geomorphic Processes
1. Forces affecting Earth's Surface
Endogenic Forces (Internal): Originating from within earth. (Diastrophism, Volcanism). Mainly land building forces.
Exogenic Forces (External): Originating from atmosphere (Sun energy). (Weathering, Erosion). Mainly land wearing forces.
Gradation: Phenomenon of wearing down of relief variations through erosion.
2. Weathering
Disintegration of rocks by weather & climate. It is an in-situ process (no motion).
Types of Weathering:
- Chemical: Solution, Carbonation, Hydration, Oxidation. (Decomposition).
- Physical: Gravitational forces, Expansion (Temperature), Water pressure. (Disintegration). Ex: Exfoliation (Flaking).
- Biological: By organisms (earthworms, termites, plant roots).
3. Mass Movements
Transfer of rock debris down slopes under direct influence of Gravity. (No agent like water/wind needed).
Types:
- Slow Movements: Creep, Solifluction.
- Rapid Movements: Earthflow, Mudflow, Debris Avalanche.
- Landslides: Slump (backward rotation), Debris Slide, Rock Fall.
4. Soil Formation (Pedogenesis)
Soil is result of decay and medium for growth. Pedology is soil science.
5 Basic Control Factors:
- Parent Material: Passive factor. Texture & structure depends on rock.
- Topography: Passive factor. Soils thin on steep slopes, thick on flat areas.
- Climate: Active factor. Moisture & Temperature.
- Biological Activity: Adds humus, Nitrogen fixation (Rhizobium).
- Time: Determines maturity of soil profile.
NCERT Solutions
Q1. Multiple Choice Questions
(i) Which is a gradational process?
Ans: (d) Erosion
(ii) Material affected by hydration?
Ans: (d) Salts
(iii) Debris avalanche category?
Ans: (c) Rapid flow mass movements
Q2. Short Answers (30 words)
(i) Weathering & Bio-diversity?
Weathering creates soil (regolith). Forests/Vegetation depend on depth of weathering mantles. Thus, it is the basis for bio-diversity.
(ii) Rapid Mass Movements?
These are perceptible movements of wet/dry materials. Examples: Earthflow, Mudflow, Debris avalanche, Landslides (Slump, Debris slide, Rockslide).
(iii) Exogenic Agents & Job?
Wind, Running water, Glaciers, Waves and Ground water. Their prime job is Erosion (wearing down) and Transportation of earth materials.
(iv) Is weathering prerequisite for soil?
Yes. Weathering breaks down rocks into smaller fragments (weathering mantle), which is the basic input for soil formation.
Long Answers & Project
Q3. Long Answers (150 words)
(i) "Earth is playfield for two opposing forces"
The earth's surface is uneven because of two forces:
1. Endogenic Forces: Operate from within (Radioactivity, Heat). They are land Building forces (elevate crust, build mountains).
2. Exogenic Forces: Operate from outside (Sun energy). They are land Wearing forces (degrade relief, erode mountains).
Thus, the surface is always changing due to this continuous interaction.
(iv) Soil Formation Process vs Factors
Process: It is the actual action (Weathering → Bacteria colonization → Humus accumulation → Plant growth).
Factors: These control the process (Parent material, Topography, Climate, Biology, Time).
Role of Climate: Rainfall provides moisture for chemical activity; Temperature affects bacterial growth.
Role of Biological Activity: Adds organic matter (humus); Nitrogen fixation; Ants/Termites mix the soil.
Project Work: Observation
Activity: Observe your local area.
1. Topography: Is it flat or hilly?
2. Soil: Check color (Red/Black) and texture (Sandy/Clayey).
3. Weathering: Look for cracked rocks or exfoliated surfaces nearby.