Unlock a deeper understanding of how Earth’s magnificent surface features are shaped and transformed over time with our expertly crafted resource featuring New NCERT class 11 Geography Chapter 6: Landforms and their Evolution Solutions. Designed to help you navigate intricate geological questions with absolute clarity, this guide provides structured, step-by-step answers to all textbook exercises.
Multiple Choice Questions
(i) In which of the following stages of landform development, downward cutting is dominated?
- (a) Youth stage
- (b) Late mature stage
- (c) Early mature stage
- (d) Old stage
Answer: (a) Youth stage
- Explanation: During the youth stage, streams flow over steep gradients with high kinetic energy. Downward vertical cutting dominates over lateral bank erosion, removing surface irregularities like waterfalls and rapids while carving deep, shallow V-shaped valleys.
(ii) A deep valley characterised by steep step-like side slopes is known as
- (a) U-shaped valley
- (b) Gorge
- (c) Blind valley
- (d) Canyon
Answer: (d) Canyon
- Explanation: A canyon is a structural variant of a gorge. It is characterized by steep, step-like side slopes formed commonly in horizontally bedded sedimentary rocks. It is distinctly wider at the top than at its bottom, whereas a gorge has almost equal width at top and bottom.
(iii) In which one of the following regions the chemical weathering process is more dominant than the mechanical process?
- (a) Humid region
- (b) Limestone region
- (c) Arid region
- (d) Glacier region
Answer: (b) Limestone region
- Explanation: In limestone regions (Karst topography), rocks are rich in calcium carbonate (CaCO3). Surface water and groundwater enriched with dissolved carbon dioxide actively decompose and dissolve the rock through chemical solution and carbonation, making chemical weathering far more dominant than physical/mechanical breakdown.
(iv) Which one of the following sentences best defines the term ‘Lapies’?
- (a) A small to medium sized shallow depression
- (b) A landform whose opening is more or less circular at the top and funnel shaped towards bottom
- (c) A landform formed due to dripping water from surface
- (d) An irregular surface with sharp pinnacles, grooves and ridges
Answer: (d) An irregular surface with sharp pinnacles, grooves and ridges
- Explanation: Lapies are formed on limestone surfaces where differential chemical solution along parallel to sub-parallel joint planes eats away the rock, leaving behind a highly irregular surface featuring sharp points, ridges, and grooves.
(v) A deep, long and wide trough or basin with very steep concave high walls at its head as well as in sides is known as:
- (a) Cirque
- (b) Glacial valley
- (c) Lateral Moraine
- (d) Esker
Answer: (a) Cirque
- Explanation: A cirque is an erosional glacial hollow found at the head of a mountain valley. It is a deep, bowl-shaped trough with steep, concave walls dropping vertically at the head and sides. After the glacier melts, water often fills these hollows to form tarn lakes.
Answer the following questions in about 30 words.
(i) What do incised meanders in rocks and meanders in plains of alluvium indicate?
Answer:
- Meanders in Alluvium: Indicate low channel gradients, gentle slopes, and dominant lateral bank erosion during the mature or old age stage of river development.
- Incised Meanders in Rocks: Indicate landmass rejuvenation, where active vertical down-cutting carves deep sinuous channels into bedrock following tectonic uplift or base-level drops.
(ii) Explain the evolution of valley sinks or uvalas.
Answer:
Valley sinks (uvalas) evolve in Karst topography when adjacent solution sinks and collapse sinkholes (dolines) continuously enlarge over time. As their intervening margins slump or subterranean cave roofs collapse, these individual sinkholes merge to form long, wide, and shallow trench-like depressions.
(iii) Underground flow of water is more common than surface run-off in limestone areas. Why?
Answer:
Limestone rocks are highly jointed, permeable, and rich in soluble calcium carbonate. Surface runoff readily disappears into swallow holes and sinkholes created by chemical solution. Water percolates vertically through rock fissures to establish sub-surface cave networks rather than flowing as open surface streams.
(iv) Glacial valleys show up many linear depositional forms. Give their locations and names.
Answer:
- Lateral Moraines: Formed along the sides parallel to glacial valley walls.
- Medial Moraines: Located along the center of glacial valley floors where two lateral moraines merge.
- Terminal Moraines: Formed at the snout or toe of a glacier.
- Eskers: Sinuous ridges deposited along sub-glacial meltwater stream channels.
- Drumlins: Smooth, oval-shaped ridges aligned parallel to the direction of ice flow.
(v) How does wind perform its task in desert areas? Is it the only agent responsible for the erosional features in the deserts?
Answer:
Wind performs its task through deflation (lifting dust), abrasion (sand-blasting rock bases), and impact. No, wind is not the sole agent. Torrential sheet floods and running water wash are equally responsible for carving major desert landforms like pediments, inselbergs, and wadis.
Answer the following questions in about 150 words.
(i) Running water is by far the most dominating geomorphic agent in shaping the earth’s surface in humid as well as in arid climates. Explain.
Answer:
Running water is the principal geomorphic driver across diverse global climate regimes, operating through overland sheet flow and linear stream flow.
In humid regions, abundant, regular rainfall feeds dense river networks. Streams erode valleys vertically during youth and laterally during maturity. Over time, running water lowers drainage divides, flattens rugged relief, and converts mountainous landscapes into low-relief peneplains featuring isolated monadnocks.
In arid regions, despite low overall rainfall, precipitation falls in rare but intense downpours. Devoid of protective vegetative cover, desert surfaces undergo severe sheet wash and flash flooding. Torrential runoff cuts broad channels, strips weathered mantle, and causes slope backwasting. This parallel retreat of mountain fronts carves broad pediments and eventually merges them into vast pediplains.
Thus, while wind transports fine particles, running water performs the heavy work of mountain reduction and large-scale landscape degradation in both wet and dry climates.
(ii) Limestones behave differently in humid and arid climates. Why? What is the dominant and almost exclusive geomorphic process in limestone areas and what are its results?
Answer:
Limestones behave differently based on moisture availability because calcium carbonate (CaCO3) requires water and carbon dioxide to undergo chemical solution:
- Humid Climates: Rainwater absorbs atmospheric and soil carbon dioxide, forming weak carbonic acid. Limestone reacts readily, dissolving along joints to form weak, subterranean-drained Karst lowlands.
- Arid Climates: Lack of water prevents chemical solution. Limestone behaves as a hard, highly resistant, cliff-forming caprock.
Dominant Process & Results: The dominant process in limestone regions is chemical solution and carbonation.
Groundwater dissolves bedrock along joint planes and bedding fractures, creating Karst topography.
| Geomorphic Category | Key Results & Landforms |
|---|---|
| Erosional Features | Swallow holes, solution sinks, collapse sinks (dolines), uvalas, lapies, limestone pavements, and underground caves. |
| Depositional Features | Dripstone formations inside caverns, including hanging stalactites, rising stalagmites, and fused pillars/columns. |
(iii) How do glaciers accomplish the work of reducing high mountains into low hills and plains?
Answer:
Glaciers degrade high mountain relief through the immense force of gravity and the weight of moving ice. They accomplish landscape reduction through two primary mechanical mechanisms:
- Plucking: Meltwater freezes into rock joints along the glacier bed. As the massive ice sheet moves, it pulls angular rock fragments directly out of the mountain floor.
- Abrasion: Dragged angular boulders and rock debris act like coarse sandpaper, scouring, gouging, and scratching the bedrock floor and valley walls.
Progressive Landscape Reduction:
- Valley Transformation: Glaciers convert narrow V-shaped river valleys into broad, flat-floored U-shaped troughs.
- Divide Lowering: Radiating glaciers cut headward via cirque expansion, sharpening peaks into horns and narrowing divides into serrated arêtes. Continuous ice erosion shears off mountain spurs into truncated facets.
- Outwash Plain Creation: As ice melts and retreats, glacio-fluvial streams carry till and outwash sediment outward, depositing broad outwash plains that submerge former mountain bases under thick sediment layers.
Project Work
Field Study Area: Indo-Gangetic Alluvial Plain & Yamuna Basin (Delhi-NCR Region)
This project report documents the prominent landforms, surface materials, and active geomorphic processes observed across the urbanized alluvial plain and its adjacent relict quartzite ridges.
1. Landforms Identified
- Active Floodplain (Khadar): Low-lying land directly adjacent to the river channel, subject to annual monsoon flooding and fresh silt accumulation.
- Older Alluvial Terrace (Bhangar): Elevated plain above current flood levels, representing higher former riverbed levels.
- Natural Levees & Point Bars: Low linear ridges of coarse sand along the river banks and inner curves of meanders.
- Relict Ridges (Monadnocks): Weathered quartzitic extensions of the Aravalli Range standing out as isolated, highly denuded hills above the surrounding flat plain.
2. Material Composition
| Landform Zone | Material Type | Physical Characteristics |
| Active Floodplain | Fresh Alluvium | Fine sand, silt, and soft clay; well-sorted and light in color. |
| Older Plain | Mature Alluvium & Kanker | Heavy clay-loam containing sub-surface calcium carbonate nodules (kanker). |
| Ridge Outcrops | Quartzite Bedrock | Hard, highly jointed, fractured metamorphic rock with iron oxide stains. |
| Channel Beds | Coarse Bedload | Medium to coarse river sand, rounded pebbles, and organic detritus. |
3. Geomorphic Processes at Work
- Fluvial Erosion & Deposition: High monsoon river discharge drives lateral bank erosion, while receding post-monsoon waters deposit extensive sandbars and silt sheets.
- Thermal Weathering: Large diurnal temperature ranges during summer cause physical expansion and contraction along jointed ridge quartzites, leading to block disintegration.
- Chemical Solution & Leaching: Seasonal rainfall percolates through upper soil layers, leaching soluble minerals downward and precipitating calcium carbonate (kanker) in lower horizons.
- Wind Deflation & Abrasion: Pre-monsoon dry winds lift fine dust particles from dry riverbeds, shifting loose surface material across open agricultural and urban patches.