NCERT Solutions for Class 11 Geography Fundamentals of Physical Geography Chapter 5: Geomorphic Processes

Chapter at a glance

Exercise Questions

Question 1 (i)

Which one of the following processes is a gradational process?
(a) Deposition (b) Diastrophism (c) Volcanism (d) Erosion

Answer

Gradation (wearing down of relief) is mainly done by erosion (degradation).

4. Erosion

Question 1 (ii)

Which one of the following materials is affected by hydration process?
(a) Granite (b) Clay (c) Quartz (d) Salts

Answer

Hydration is the chemical addition of water; salts (e.g. calcium sulphate becoming gypsum) are most affected, swelling and causing rocks to crack.

4. Salts

Question 1 (iii)

Debris avalanche can be included in the category of:
(a) Landslides (b) Slow flow mass movements (c) Rapid flow mass movements (d) Subsidence

Answer

3. Rapid flow mass movements

Question 2 (i)

It is weathering that is responsible for bio-diversity on the earth. How?

Answer

Weathering breaks down rocks into regolith and soil, releasing nutrients. Soil supports vegetation, which in turn supports animals and micro-organisms. The depth of weathering mantle and the variety of soils depend on climate and rock; this variety of soils supports a variety of plants and animals. Hence weathering is the base of biodiversity.

Weathering forms soils and releases nutrients, which support plants and, through them, animals; varied soils support varied life.

Question 2 (ii)

What are mass movements that are real rapid and perceptible? List.

Answer

Rapid, perceptible mass movements are landslides, which include:

1. Slump — slipping of rock debris with backward rotation.
2. Debris slide — rapid rolling or sliding of earth debris without backward rotation.
3. Rockslide — sliding of individual rock masses down bedding, joint or fault surfaces.
4. Rockfall — free falling of rock blocks from steep slopes.

(Also rapid flows: earthflow, mudflow and debris avalanche.)

Landslides: slump, debris slide, rockslide and rockfall (plus rapid flows like mudflows and debris avalanches).

Question 2 (iii)

What are the various mobile and mighty exogenic geomorphic agents and what is the prime job they perform?

Answer

The mobile exogenic agents are running water, groundwater, glaciers, wind, waves and currents. Their prime job is erosion — removing and transporting weathered material — and later deposition, thereby lowering (degrading) the relief and filling up depressions (aggradation).

Running water, groundwater, glaciers, wind, waves and currents; their prime job is erosion, transport and deposition, which wears down relief.

Question 2 (iv)

Is weathering essential as a pre-requisite in the formation of soils? Why?

Answer

Yes. Weathering breaks down rocks into fine regolith (loose material), which is the parent material for soil. Without weathering, there would be no fine material on which plants, micro-organisms and humus can act to form soil. Soil formation begins with weathering.

Yes; weathering produces the loose, fine parent material (regolith) on which biological processes act to form soil.

Question 3 (i)

“Our earth is a playfield for two opposing groups of geomorphic processes.” Discuss.

Answer

The earth’s surface is shaped by two opposing groups of processes:

1. Endogenic processes (internal forces), driven by the earth’s internal heat — diastrophism (folding, faulting, uplift, subsidence, plate movements, earthquakes) and volcanism. They build up the surface, creating mountains, plateaus and depressions, and increasing unevenness.
2. Exogenic processes (external forces), driven by the sun’s energy and gravity — weathering, mass wasting, erosion and deposition by running water, groundwater, glaciers, wind, waves and currents. They wear down the high areas and fill the low areas, levelling the surface (gradation).

The two act continuously and simultaneously. As long as endogenic forces keep raising parts of the crust, exogenic forces keep wearing them down. The variety of landforms we see is the result of this continuous contest. That is why the earth is called a playfield of these opposing processes.

Endogenic forces (diastrophism, volcanism) build up relief while exogenic forces (weathering, erosion, deposition) wear it down; their continuous opposition shapes all landforms.

Question 3 (ii)

Exogenic geomorphic processes derive their ultimate energy from the sun’s heat. Explain.

Answer

• The sun’s heat creates temperature differences on the earth, which cause pressure differences and hence winds; wind erodes, transports and deposits material in deserts.
• Solar energy drives the hydrological cycle: evaporation, cloud formation and precipitation. This produces running water, groundwater and glaciers, the main agents of erosion.
• Temperature changes cause physical weathering (expansion and contraction, freezing and thawing), and heat and moisture speed up chemical weathering.
• Winds drive waves and ocean currents that shape coasts.
• Gravity helps these agents move material downslope, but the energy for moving water and air ultimately comes from the sun.

So all exogenic processes ultimately derive their energy from solar heat.

Solar heat creates winds, drives the water cycle (rain, rivers, glaciers), causes temperature changes for weathering and powers waves and currents; gravity then directs the movement.

Question 3 (iii)

Are physical and chemical weathering processes independent of each other? If not, why? Explain with examples.

Answer

No, they are interdependent and usually act together, though one may dominate depending on climate.

• Physical weathering breaks rocks into smaller pieces, increasing the surface area exposed to air and water, which speeds up chemical weathering. For example, frost wedging cracks a rock, and water entering the cracks then dissolves or oxidises minerals.
• Chemical weathering weakens rocks by changing minerals, making them easier to break physically. For example, hydration makes minerals swell, causing rocks to crack (physical); oxidation of iron weakens rock.
• Salt weathering involves both: salts crystallise (chemical change) and expand, breaking rocks (physical).
• In hot, humid regions chemical weathering dominates; in cold or dry regions, physical weathering dominates, but both are present.

No; physical breakdown increases surface area for chemical action, and chemical alteration weakens rocks for physical breakdown (e.g. frost cracks then dissolution, hydration-induced swelling, salt weathering).

Question 3 (iv)

How do you distinguish between the process of soil formation and soil-forming factors? What is the role of climate and biological activity as two important control factors in the formation of soils?

Answer

Soil formation (pedogenesis) is the process — the sequence of actions by which soil develops: weathering of rocks into regolith, followed by colonisation by plants and micro-organisms, addition of humus, and development of soil layers (horizons).

Soil-forming factors are the conditions that control this process: parent material, topography, climate, biological activity and time.

Role of climate

• Moisture (rainfall, evaporation, humidity) and temperature control the rate of weathering and the movement of materials within soil (leaching, eluviation, illuviation, capillary action).
• In hot, wet climates, chemical weathering and leaching are intense (laterite soils); in dry climates, salts may accumulate at the surface (saline soils).

Role of biological activity

• Vegetation and organisms add organic matter (humus), help retain moisture and nitrogen.
• Micro-organisms (bacteria, fungi) decompose dead matter; some fix nitrogen.
• Burrowing animals (earthworms, ants, termites) mix and aerate the soil.
• In humid tropics, bacterial activity is intense and humus is rapidly oxidised; in cold climates humus accumulates as peat.

Soil formation is the process (weathering, organic addition, horizon development); soil-forming factors are the controls (parent rock, topography, climate, biology, time). Climate governs weathering and leaching; biological activity adds humus, fixes nitrogen and mixes the soil.

Topic checklist

• Endogenic and exogenic processes
• Weathering: chemical, physical, biological; its significance
• Mass movements and landslides
• Erosion and deposition
• Soil formation and soil-forming factors

Total questions answered: 11 of 11