Master the complex earth-shaping mechanisms and ace your textbook exercises with our expertly crafted resource featuring New NCERT class 11 Geography Chapter-5: Geomorphic Processes Solutions. Designed to help you navigate intricate geological questions with absolute clarity, this guide provides structured, step-by-step answers to all chapter queries.
1. Multiple Choice Questions
(i) Which one of the following processes is a gradational process?
- (a) Deposition
- (b) Diastrophism
- (c) Volcanism
- (d) Erosion
Correct Answer: (d) Erosion
- Explanation: Gradation refers to the wearing down of relief variations on the Earth’s surface. While endogenic processes (diastrophism and volcanism) continuously build up landforms, exogenic erosion acts as the primary gradational process that degrades and evens out surface elevations.
(ii) Which one of the following materials is affected by hydration process?
- (a) Granite
- (b) Clay
- (c) Quartz
- (d) Salts
Correct Answer: (d) Salts
- Explanation: Hydration is a chemical weathering process where rock minerals chemically absorb water and expand in volume. Salts are heavily affected by hydration; absorbing moisture causes them to swell, exerts severe internal stress on rocks, and leads to eventual breakdown.
(iii) Debris avalanche can be included in the category of:
- (a) Landslides
- (b) Slow flow mass movements
- (c) Rapid flow mass movements
- (d) Subsidence
Correct Answer: (c) Rapid flow mass movements
- Explanation: A debris avalanche occurs on steep, humid slopes where saturated rock and earth material move downhill at high velocities along narrow tracks. Because the saturated mass behaves like a fast-moving fluid, it belongs to the category of rapid flow mass movements rather than simple sliding.
2. Answer the following questions in about 30 words.
(i) It is weathering that is responsible for bio-diversity on the earth. How?
Weathering breaks bedrock into regolith, forming deep weathering mantles required for soil formation. These nutrient-rich soil layers sustain forest vegetation, which serves as the foundational substrate for global biomes and terrestrial biodiversity.
(ii) What are mass movements that are real rapid and perceptible? List.
Rapid and perceptible mass movements involve swift downslope movement of earth materials driven directly by gravity. They include:
- Slumps
- Debris slides and debris falls
- Rockslides and rock falls
- Debris avalanches
(iii) What are the various mobile and mighty exogenic geomorphic agents and what is the prime job they perform?
The primary mobile geomorphic agents are running water, groundwater, glaciers, wind, waves, and ocean currents. Their prime job is acquiring, transporting, and depositing earth materials to continuously wear down reliefs and fill depressions.
(iv) Is weathering essential as a pre-requisite in the formation of soils? Why?
Yes, weathering is essential. It disintegrates and decomposes solid parent rock into a loose weathering mantle (regolith). This weathered mantle provides the primary physical input that pioneer organisms colonize to initiate soil development.
3. Answer the following questions in about 150 words.
(i) “Our earth is a playfield for two opposing groups of geomorphic processes.” Discuss.
The Earth’s surface represents a dynamic landscape shaped by two opposing geomorphic forces: endogenic and exogenic processes. Endogenic processes originate within the Earth’s interior, driven by geothermal heat, radioactivity, and primordial energy. They act as land-building forces that continuously elevate crustal blocks through diastrophism, faulting, folding, and volcanism. Conversely, exogenic processes originate in the atmosphere and are powered mainly by solar energy and gravity. These forces act as land-wearing mechanisms that continuously erode, degrade, and flatten surface elevations through weathering, mass wasting, and erosion.
| Force Type | Primary Energy Source | Core Action | Typical Examples |
| Endogenic | Internal geothermal heat | Land-building (Elevates crust) | Volcanism, Diastrophism |
| Exogenic | Solar energy & gravity | Land-wearing (Degrades relief) | Weathering, Erosion, Deposition |
As long as internal energy pushes the crust upward, external atmospheric forces attempt to level it down. This relentless interplay ensures that the surface remains dynamic and uneven over deep geological time.
(ii) Exogenic geomorphic processes derive their ultimate energy from the sun’s heat. Explain.
Sunlight serves as the primary engine for all atmospheric phenomena driving exogenic geomorphic processes across the globe. Thermal gradients created by differential solar heating power global atmospheric circulation, wind systems, and seasonal weather patterns. Solar energy also drives the hydrological cycle by evaporating surface water, which generates precipitation across continental landmasses.
Rainfall and melting snow fuel running water and glaciers. These mobile geomorphic agents acquire kinetic energy as gravity pulls them down slopes created by tectonic uplift. Solar radiation dictates diurnal temperature swings that trigger thermal expansion and contraction in surface rocks. Furthermore, plant growth depends directly on solar insolation. Vegetation cover indirectly regulates erosion rates, weathering intensity, and moisture retention in surface soils. Without solar heat, atmospheric circulation would halt. Geomorphic agents like wind, running water, and ice would lose their driving energy, freezing all exogenic landscape evolution.
(iii) Are physical and chemical weathering processes independent of each other? If not, why? Explain with examples.
Physical and chemical weathering processes are not independent. They operate synergistically, where each process accelerates and enhances the efficiency of the other.
Physical weathering mechanically fractures massive bedrock into smaller fragments without altering chemical composition. This physical breakdown drastically increases the total exposed surface area available for chemical attack. Conversely, chemical weathering alters mineral matrices, loosening inter-grain bonds and weakening structural integrity. This chemical decay renders rocks far more susceptible to physical fracturing, spalling, and frost wedging.
- Example 1: In cold, humid regions, chemical hydration causes salt crystals within rock crevices to absorb water and swell. This volumetric expansion creates intense pressure, allowing physical frost wedging to crack the rock apart easily.
- Example 2: Chemical carbonation dissolves limestone along joint planes. As these joints widen chemically, physical gravitational forces cause large unsupported rock faces to collapse.
Both processes work together continuously to convert solid bedrock into loose, unorganized regolith.
(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?
The distinction lies between active mechanisms and environmental controls. Soil-forming processes are the physical, chemical, and biological actions—such as weathering, humification, leaching, eluviation, and illuviation—that transform loose regolith into structured soil. In contrast, soil-forming factors are the conditions (climate, biological activity, parent material, topography, and time) that regulate the speed, intensity, and direction of those processes.
Climate and biological activity are the primary active control factors:
- Climate: Temperature and precipitation determine chemical reaction speeds and moisture availability. High rainfall drives intense downward leaching (eluviation) and silica removal (desilication), producing deep tropical profiles. Arid climates cause capillary action, drawing groundwater upward to leave behind surface salt crusts (hardpans).
- Biological Activity: Plants and microorganisms add organic matter, converting raw minerals into nutrient-rich humus. Cold climates suppress bacterial activity, leading to peat accumulation. Tropical heat accelerates bacterial oxidation, leaving low humus content. Soil bacteria like Rhizobium fix atmospheric nitrogen into plant-usable forms, directly enriching soil fertility.
Project Work: Field Observation Report
Location Context: Indo-Gangetic Alluvial Plain (Sub-tropical Semi-Arid Belt / Delhi-NCR Region)
1. Topography & Relief
- Terrain Type: Low-relief flat alluvial plain with gentle regional slopes toward river courses.
- Geomorphic Features: Active floodplains (Khadar), older alluvial terraces (Bhangar), and localized quartzite ridges (southern Aravalli spur).
2. Climatic Parameters
- Temperature Range: Severe seasonal contrast. Summer highs cross 45°C, while winter lows dip to 4°C. High diurnal temperature range during dry months.
- Precipitation: Highly seasonal monsoonal rainfall (600 mm – 800 mm annually), concentrated heavily between July and September.
- Evaporation Rate: High evaporation rates during dry pre-monsoon summer months.
3. Weathering Processes Observed
| Weathering Type | Driving Mechanism | Field Evidence |
| Physical (Thermal) | Alternate heating and cooling cycles | Granular disintegration and surface flaking on exposed Ridge quartzite rocks. |
| Physical (Salt Expansion) | High summer evaporation pulling sub-surface salts upward | Surface salt efflorescence (reh/kallar) visible on uncultivated dry patches. |
| Chemical (Solution & Oxidation) | Heavy moisture availability during monsoons | Rusting of iron-bearing minerals in exposed rock outcrops and soil staining. |
| Biological | Vegetation expansion and anthropogenic activity | Root wedging in rock joints, urban soil compaction, and agricultural tillage. |
4. Soil Characteristics & Contents
- Soil Type: Mature to semi-mature alluvial soil (Inceptisols/Entisols).
- Texture: Fine sandy loam near active channels; silt-clay loam across mature older plains.
- Color: Light grey in active floodplains to dark reddish-brown in older alluvial tracts.
- Sub-Surface Horizons: Presence of calcium carbonate concretions (kanker nodules) in subsoil layers due to capillary precipitation.
- Organic Content: Moderate to low humus content resulting from rapid high-temperature bacterial oxidation during summer months.