NCERT Solutions - Geomorphic Processes

Q1: Multiple choice questions.
(i) Which one of the following processes is a gradational process?
(a) Deposition
(b) Diastrophism
(c) Volcanism
(d) Erosion
Ans: (d)
Explanation: Erosion is a gradational process because it wears down elevated landforms and reduces relief by removing rock and soil from higher areas and transporting them elsewhere. Over time this action tends to level the landscape, which is the essence of gradation.

(ii) Which one of the following materials is affected by hydration process?
(a) Granite
(b) Clay
(c) Quartz
(d) Salts
Ans: (d)
Explanation: Hydration involves the addition of water molecules into the mineral structure, producing hydrated minerals and causing expansion or chemical change. Salts commonly form hydrates (for example, gypsum) and are therefore particularly susceptible to hydration.

(iii) Debris avalanche can be included in the category of:
(a) Landslides
(b) Slow flow mass movements
(c) Rapid flow mass movements
(d) Subsidence
Ans: (c)
Explanation: A debris avalanche is an extremely rapid, high-velocity movement of soil, rock and vegetation down a slope. Its sudden, fluidised behaviour places it among rapid flow mass movements rather than slow flows or simple subsidence.

Q2: Answer the following questions in about 30 words.
(i) It is weathering that is responsible for bio-diversity on the earth. How?
Ans: Weathering breaks down rocks into finer material and forms soils that store water and nutrients. These soils support plant growth, which creates habitats and food chains, thus promoting greater biodiversity.

(ii) What are mass movements that are real rapid and perceptible? List.
Ans: The mass movements that are rapid and easily perceptible are:

• Earth flow
• Mud flow
• Landslide

(iii) What are the various mobile and mighty exogenic geomorphic agents and what is the prime job they perform?
Ans: The main exogenic agents are weathering, mass movement, erosion, transportation and deposition. Their prime job is to modify the earth's surface by wearing down relief, moving material and building up new landforms through deposition.

(iv) Is weathering essential as a pre-requisite in the formation of soils? Why?
Ans: Yes. Weathering breaks parent rock into smaller mineral particles and releases nutrients. Combined with organic matter and biological activity, these weathered materials form the mineral and humus components of soil.

Q3: Answer the following questions in about 150 words.
 (i) "Our earth is a playfield for two opposing groups of geomorphic processes." Discuss.
Ans:

• Our planet's surface is shaped by two opposing sets of forces: endogenic (internal) and exogenic (external). Endogenic forces, powered by Earth's internal heat, uplift and build relief by tectonic movements, volcanism and folding. Exogenic forces, driven ultimately by the sun's energy, wear down and level the surface through weathering, erosion, transportation and deposition.
• Because these groups act simultaneously, the landscape is never static. Endogenic uplift produces highs and lows; exogenic processes reduce these differences by removing material from highs and filling lows. In general terms, endogenic processes are land-building, while exogenic processes are land-wearing, and their interaction creates the variety of landforms we observe.

(ii) Exogenic geomorphic processes derive their ultimate energy from the sun's heat. Explain.
Ans: The sun's heat controls the atmosphere and the hydrological cycle, which drive many exogenic agents. Solar energy creates temperature differences that form winds, powers evaporation and precipitation, and sets climate patterns. Wind, running water and glaciers (through snowfall and melt) are therefore driven indirectly by solar energy. While gravity is essential for movement of materials (for example, in mass movements and river flow), the climatic and atmospheric motions that do the transporting and eroding ultimately trace back to the sun's heat.

• Weathering: Temperature and moisture changes-both controlled by climate-cause physical and chemical breakdown of rocks.
• Mass movement: Gravity moves material downslope; weathering often prepares material for movement.
• Erosion and deposition: Wind, rivers and glaciers, all dependent on climate, acquire, transport and deposit sediments.

(iii) Are physical and chemical weathering processes independent of each other? If not, why? Explain with examples.
Ans:

• No. Physical and chemical weathering are closely linked and commonly operate together. Physical processes fragment rock and expose fresh surfaces; chemical processes then act faster on these newly exposed surfaces.
• Example: Freeze-thaw (a physical process) breaks rock into smaller pieces, increasing surface area for chemical agents like water and oxygen to act on. Conversely, chemical weakening (for example, oxidation of iron minerals) makes rock more friable and easier to break by physical means.

(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?
Ans:

• The process of soil formation (pedogenesis) is the sequence of changes that turn weathered rock and organic matter into soil layers-breaking of rock, accumulation of organic matter, mixing by organisms and development of horizonation.
• Soil-forming factors are the conditions that control this process. The five classic factors are: parent material, topography, climate, biological activity and time. These act together to determine soil properties.
• Role of climate: Moisture and temperature govern rates of chemical reactions, biological activity and leaching. High rainfall promotes eluviation and deeper weathering; temperature speeds up chemical and biological processes.
• Role of biological activity: Plants, animals and microbes add organic matter (humus), mix the soil, aid nutrient cycling and influence soil structure. Vegetation protects the soil surface and helps retain moisture, while microbes drive decomposition and nutrient release.