Geomorphic Processes
NCERT Solutions • Class 11 Geography • Chapter 51. Multiple Choice Questions
(i) Which one of the following processes is a gradational process?
(d) Erosion
Reason: Gradation involves wearing down relief variations. Erosion (and deposition) are exogenic processes that grade the land. Volcanism and Diastrophism are endogenic (building) processes.
Reason: Gradation involves wearing down relief variations. Erosion (and deposition) are exogenic processes that grade the land. Volcanism and Diastrophism are endogenic (building) processes.
(ii) Which one of the following materials is affected by hydration process?
(d) Salts
Reason: Hydration is the chemical addition of water. Many salts absorb water to become hydrated (e.g., Calcium Sulphate turns to Gypsum), expanding in volume.
Reason: Hydration is the chemical addition of water. Many salts absorb water to become hydrated (e.g., Calcium Sulphate turns to Gypsum), expanding in volume.
(iii) Debris avalanche can be included in the category of:
(c) Rapid flow mass movements
Reason: A debris avalanche acts much faster than a landslide and often involves water, making it flow rapidly like a liquid (e.g., snow avalanches).
Reason: A debris avalanche acts much faster than a landslide and often involves water, making it flow rapidly like a liquid (e.g., snow avalanches).
2. Short Answer Questions
(i) It is weathering that is responsible for bio-diversity on the earth. How?
Weathering breaks down rocks into finer particles, forming the soil mantle. This soil supports vegetation (forests), which is the base of the food chain. Without weathering, there would be no soil, no plants, and consequently, no terrestrial biodiversity.
(ii) What are mass movements that are real rapid and perceptible? List.
These are movements where soil and rock debris move down slopes visibly fast.
List:
List:
- Earthflow: Saturated clay/silt flowing down slopes.
- Mudflow: Rapid flow of thick mud in valleys (common in volcanic areas).
- Debris Avalanche: Very fast collapse of debris (common in humid regions).
- Landslides: Slump, Debris Slide, Rock Slide.
(iii) What are the various mobile and mighty exogenic geomorphic agents and what is the prime job they perform?
Agents: Running water (Rivers), Groundwater, Glaciers (Moving ice), Wind, and Waves/Currents.
Prime Job: They perform Erosion, Transportation, and Deposition. They wear down highlands (degradation) and fill up lowlands (aggradation), thus changing the surface configuration of the earth.
Prime Job: They perform Erosion, Transportation, and Deposition. They wear down highlands (degradation) and fill up lowlands (aggradation), thus changing the surface configuration of the earth.
(iv) Is weathering essential as a pre-requisite in the formation of soils? Why?
Yes, absolutely.
Weathering is the first step in soil formation. It breaks down solid parent rock into smaller fragments (regolith). Only after this mechanical and chemical breakdown can biological activity (humus addition) begin to turn the regolith into fertile soil.
Weathering is the first step in soil formation. It breaks down solid parent rock into smaller fragments (regolith). Only after this mechanical and chemical breakdown can biological activity (humus addition) begin to turn the regolith into fertile soil.
3. Long Answer Questions
(i) “Our earth is a playfield for two opposing groups of geomorphic processes.” Discuss.
The earth’s surface is constantly evolving due to the interplay of two opposing forces:
This continuous tug-of-war ensures the earth’s surface remains uneven and dynamic.
- Endogenic Processes (Internal Forces): Driven by earth’s internal heat (radioactivity, friction). They are force-building processes. They create relief features like mountains, plateaus, and volcanic cones (e.g., Volcanism, Diastrophism).
- Exogenic Processes (External Forces): Driven by solar energy and gravity. They are force-wearing (gradational) processes. They erode the elevated features created by endogenic forces and deposit the debris in low-lying basins (e.g., Weathering, Erosion by rivers/winds).
This continuous tug-of-war ensures the earth’s surface remains uneven and dynamic.
(ii) Exogenic geomorphic processes derive their ultimate energy from the sun’s heat. Explain.
The sun is the ultimate powerhouse for exogenic forces:
- Atmospheric Circulation: Solar heat causes differential heating, creating pressure belts and winds. Wind is a direct agent of erosion.
- Hydrological Cycle: Sun’s heat evaporates water, leading to rain and snow. This feeds rivers, glaciers, and groundwater—the most powerful geomorphic agents.
- Weathering: Temperature changes (insolation) cause physical weathering (expansion/contraction). Climate (determined by sun) dictates chemical weathering rates.
(iii) Are physical and chemical weathering processes independent of each other? If not, why? Explain with examples.
No, they are closely interrelated and often work together.
Physical weathering breaks rocks into smaller pieces, increasing the surface area exposed to chemical attack. Conversely, chemical weathering weakens the rock minerals (e.g., feldspar turning to clay), making it easier for physical forces to disintegrate them.
Example 1: In Exfoliation (Physical), outer layers peel off. This happens faster if hydration (Chemical) has already weakened the outer minerals.
Example 2: Frost Wedging (Physical) widens cracks, allowing acidic water (Chemical) to penetrate deeper into the rock, accelerating solution or oxidation.
Physical weathering breaks rocks into smaller pieces, increasing the surface area exposed to chemical attack. Conversely, chemical weathering weakens the rock minerals (e.g., feldspar turning to clay), making it easier for physical forces to disintegrate them.
Example 1: In Exfoliation (Physical), outer layers peel off. This happens faster if hydration (Chemical) has already weakened the outer minerals.
Example 2: Frost Wedging (Physical) widens cracks, allowing acidic water (Chemical) to penetrate deeper into the rock, accelerating solution or oxidation.
(iv) Distinguish between process of soil formation and soil-forming factors. Role of climate and biological activity?
Distinction:
- Soil Formation (Pedogenesis): The actual mechanism/action (e.g., weathering, humification, calcification) involved in creating soil.
- Soil-Forming Factors: The external agents or conditions that control these processes (Parent Material, Topography, Climate, Biological Activity, Time).
- Climate: The most active factor. Moisture (rain) enables chemical weathering and transporting nutrients. Temperature determines the rate of microbial activity. (e.g., Tropical soils are deep due to high rain/heat).
- Biological Activity: Plants cover the soil preventing erosion. Dead remains add humus (organic matter). Bacteria (Rhizobium) fix nitrogen. Ants/termites mix the soil (aeration).
Project Work
Guidance for Field Observation
(Student Activity)
To observe your local area:
To observe your local area:
- Climate: Note if it is humid, dry, or seasonal. (High rain = chemical weathering; Dry = physical weathering).
- Materials: Look at local rocks. Are they granites (exfoliation), limestones (holes/caves), or soft sedimentary rocks?
- Soil: Dig a small pit. Check the colour (Red = iron oxidation, Dark = humus). Check texture (sandy vs clayey).