Geomorphic ProcessesClass 11 Fundamentals of Physical Geography NCERT Solutions
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Q1_EXERCISES__
(iii) Debris avalanche can be included in the category of:
(a)
Landslides
(b)
Slow flow mass movements
(c)
Rapid flow mass movements
(d)
Subsidence
Solution
(c) Rapid flow mass movements
The textbook describes mass movements as ranging from slow to rapid and includes creep, flow, slide, and fall. It explicitly mentions that in the Himalayas, "debris avalanches and landslides occur very frequently." Landslides are defined as "relatively rapid and perceptible movements." A debris avalanche is a very fast-moving flow of rock, soil, and other debris, thus categorizing it as a rapid flow mass movement.
Q1_EXERCISES__
(ii) Which one of the following materials is affected by hydration process?
(a)
Granite
(b)
Clay
(c)
Quartz
(d)
Salts
Solution
(b) Clay
Hydration is a chemical weathering process where minerals absorb water, leading to expansion and decomposition. While the text does not specify which material is affected, clay minerals are known to expand significantly when they absorb water, making them highly susceptible to this process. Salts are primarily affected by solution, while granite and quartz are more resistant to chemical weathering.
Q1_EXERCISES__
Multiple choice questions. (i) Which one of the following processes is a gradational process?
(a)
Deposition
(b)
Diastrophism
(c)
Volcanism
(d)
Erosion
Solution
(d) Erosion
The source text defines gradation as "The phenomenon of wearing down of relief variations of the surface of the earth through erosion." While deposition is part of the overall process that levels the earth's surface, erosion is the specific process of wearing down, which is central to the concept of gradation. Diastrophism and volcanism are endogenic (land-building) processes, not gradational (land-wearing) ones.
Q2_EXERCISES__
Answer the following questions in about 30 words. (i) It is weathering that is responsible for bio-diversity on the earth. How?
Solution
Weathering is responsible for biodiversity because it breaks down rocks to form the weathering mantle, which is the basis of soil. The text states that forests and vegetation depend on the depth of this mantle. Forests, in turn, support a vast array of animal life, thus creating and sustaining biodiversity.
Q2_EXERCISES__
(iv) Is weathering essential as a pre-requisite in the formation of soils? Why?
Solution
Yes, weathering is an essential prerequisite for soil formation. The text states that soil formation, or pedogenesis, depends first on weathering. This is because weathering breaks down the parent rock into a fragmented layer called the weathering mantle, which is the basic input material upon which soil-forming processes can begin.
Q2_EXERCISES__
(iii) What are the various mobile and mighty exogenic geomorphic agents and what is the prime job they perform?
Solution
The mobile and mighty exogenic geomorphic agents are running water, glaciers (moving ice masses), wind, waves, and currents. Their prime job is to act as a medium to remove, transport, and deposit earth materials. This entire process of wearing down the landscape is known as erosion.
Q2_EXERCISES__
(ii) What are mass movements that are real rapid and perceptible? List.
Solution
Rapid and perceptible mass movements are generally categorized under landslides. The text lists several types:
- Slump
- Debris slide
- Debris fall
- Rockslide
- Rock fall Debris avalanches are also mentioned as frequent, rapid movements.
Q3_EXERCISES__
(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?
Solution
The process of soil formation, or pedogenesis, describes the actual sequence of events that transform parent material into mature soil. As described in the text, this involves the colonization of weathered material by organisms, the accumulation of organic matter (humus), the penetration of roots, and the development of a porous, sponge-like material. It is the 'how' of soil creation.
The soil-forming factors, on the other hand, are the controlling variables that influence the rate and nature of this process. They are the 'why' a particular soil forms in a certain way. The text lists five such factors: parent material, topography, climate, biological activity, and time.
Role of Climate: Climate is a crucial active factor.
- Moisture: Precipitation provides water for chemical reactions and helps transport minerals down through the soil profile (eluviation). In wet climates, this can lead to leaching of minerals, while in dry climates, evaporation can bring salts to the surface, forming hardpans.
- Temperature: It controls the rate of chemical and biological activity. Higher temperatures in tropical regions lead to rapid decomposition and deeper soil profiles, whereas cold temperatures slow down these processes.
Role of Biological Activity: This is another important active factor.
- Organic Matter: Dead plants and animals decompose to form humus, which enriches the soil and produces acids that help break down minerals.
- Nitrogen Fixation: Bacteria convert atmospheric nitrogen into a form that plants can use, which is essential for growth.
- Mechanical Mixing: Burrowing organisms like earthworms and rodents rework the soil, improving its porosity and structure.
Q3_EXERCISES__
Answer the following questions in about 150 words. (i) "Our earth is a playfield for two opposing groups of geomorphic processes." Discuss.
Solution
The statement that our earth is a playfield for two opposing groups of geomorphic processes refers to the continuous interaction between endogenic (internal) and exogenic (external) forces.
Endogenic Forces: These originate from within the earth and are primarily land-building forces. Processes like diastrophism (mountain building and continental uplift) and volcanism create relief by elevating or building up portions of the earth's crust. They are responsible for the large-scale features like mountains, plateaus, and continents.
Exogenic Forces: These originate from the earth's atmosphere and are powered by solar energy. They are mainly land-wearing forces. Processes like weathering, mass wasting, erosion, and deposition work to wear down the elevated landforms (degradation) and fill in the basins and depressions (aggradation).
The uneven and dynamic surface of the earth is a direct result of this ongoing conflict. While endogenic forces build up the relief, exogenic forces constantly work to level it. This balance ensures that variations on the earth's surface remain as long as both forces are active.
Q3_EXERCISES__
(ii) Exogenic geomorphic processes derive their ultimate energy from the sun's heat. Explain.
Solution
Exogenic geomorphic processes, which include weathering, erosion, and deposition, are driven by energy from the earth's atmosphere, which is ultimately derived from the sun. The sun's heat is the primary engine of the Earth's climate system.
Solar energy creates temperature differences across the globe due to factors like latitude and the distribution of land and water. These thermal gradients create pressure differences in the atmosphere, which in turn generate wind. Wind is a powerful agent of erosion and transportation.
Furthermore, solar energy drives the hydrological cycle. It causes evaporation of water from oceans and other water bodies. This water vapor condenses to form clouds and returns to the surface as precipitation (rain and snow). This precipitation results in running water (rivers) and the formation of glaciers, two of the most powerful exogenic agents that shape the landscape through erosion and deposition. Therefore, the actions of wind, water, and ice, which are the main exogenic agents, are all powered by the ultimate energy source: the sun.
Q3_EXERCISES__
(iii) Are physical and chemical weathering processes independent of each other? If not, why? Explain with examples.
Solution
No, physical and chemical weathering processes are not independent of each other. They often work together, and one process can enhance the effectiveness of the other. The textbook states, "Very rarely does any one of these processes ever operate completely by itself."
Physical weathering aids chemical weathering by increasing the surface area of the rock. When a rock is broken into smaller fragments by processes like thermal expansion or frost wedging, more of its surface is exposed to air and water. This allows chemical reactions like oxidation, carbonation, or solution to occur at a much faster rate.
Example: A large block of granite is fractured by thermal stress (physical weathering). Water can now penetrate these cracks, accelerating the chemical decomposition of minerals like feldspar into clay (chemical weathering).
Conversely, chemical weathering can aid physical weathering by weakening the rock. When minerals within a rock are chemically altered or dissolved, the overall structure of the rock becomes weaker and more susceptible to being broken apart by physical forces.
Example: The dissolving of cementing materials in a sandstone by acidic water (chemical weathering) loosens the sand grains, making it easy for the rock to crumble and be carried away by wind or water (physical erosion).