Ch-6: Landforms & Evolution
1. Running Water (Humid Regions)
Most important agent of degradation. 3 Stages of River:
- Youth: V-shaped valleys, Waterfalls, Rapids. No floodplains.
- Mature: Wider valleys, Meanders, Floodplains appear.
- Old: Gentle gradient, Oxbow lakes, Natural levees, Vast floodplains.
Erosional Landforms (River):
- Valleys: Gorge (Steep sides, equal width top/bottom) vs Canyon (Step-like sides, wider at top).
- Potholes & Plunge Pools: Circular depressions in rocky beds.
- Incised Meanders: Deep meanders in hard rocks.
- River Terraces: Old valley floor levels marking former river beds.
Depositional Landforms (River):
- Alluvial Fans: Cone shaped deposit at foot of mountains.
- Deltas: Like fans but at river mouth (sea). Well sorted stratification.
- Floodplains: Active (River bed) & Inactive (Banks).
- Natural Levees: Low ridges along banks.
- Point Bars: Deposits on concave side of meanders.
2. Groundwater (Karst Topography)
Action of water on Limestone rocks (Solution & Deposition).
Erosional Forms:
- Swallow Holes/Sinkholes: Funnel shaped openings.
- Lapies: Irregular ridges & grooves.
- Caves: Horizontal gaps.
Depositional Forms (In Caves):
- Stalactites: Hang from roof.
- Stalagmites: Rise from floor.
- Pillars: Fused stalactite & stalagmite.
3. Glaciers (Ice Sheets)
Move due to gravity. Cause abrasion & plucking.
Erosional Forms:
- Cirque: Deep trough/basin at head of glacier (Armchair shape).
- Horns: Sharp peaks (e.g., Matterhorn).
- Glacial Valleys: U-Shaped troughs.
Depositional Forms:
- Moraines: Ridges of till. (Terminal, Lateral, Medial, Ground).
- Eskers: Sinuous ridges of boulders/sand.
- Drumlins: Oval shaped ridges (inverted boat).
4. Waves & Currents (Coastal)
Types of Coasts:
High Rocky: Submerged. Erosion dominant (Cliffs).
Low Sedimentary: Emerged. Deposition dominant (Lagoons, Deltas).
- Erosional: Cliffs, Terraces, Sea Caves, Stacks (Isolated rock).
- Depositional: Beaches (Sand), Dunes, Bars (Ridge), Spits (Attached to land), Lagoons.
5. Winds (Deserts)
Dominant in hot deserts. Causes Deflation, Abrasion & Impact.
Erosional Forms:
- Pediments: Gently inclined rocky floors at foot of mountains.
- Playas: Shallow lakes in basins.
- Mushroom Rocks: Rock with slender stalk & broad top.
Depositional Forms (Sand Dunes):
- Barchan: Crescent shape (wind constant).
- Seif: Single wing (wind shift).
- Parabolic: Reversed barchan (vegetation).
- Longitudinal/Transverse: Based on wind direction.
NCERT Solutions
Q1. Multiple Choice Questions
(i) Downward cutting dominated in?
Ans: (a) Youth stage
(ii) Deep valley with step-like slopes?
Ans: (d) Canyon
(iii) Chemical weathering dominant region?
Ans: (b) Limestone region
(iv) Definition of 'Lapies'?
Ans: (d) An irregular surface with sharp pinnacles...
(v) Deep trough with steep concave walls?
Ans: (a) Cirque
Q2. Short Answers (30 words)
(i) Incised Meanders vs Alluvial Meanders?
Incised meanders form in hard rocks due to vertical erosion. Alluvial meanders form on floodplains due to lateral erosion and deposition.
(ii) Evolution of Valley Sinks?
When sinkholes and dolines join together due to slumping or roof collapse of caves, long, narrow trenches called Valley Sinks or Uvalas are formed.
(iii) Why underground flow in Limestone?
Limestone is permeable and soluble. Water trickles down through joints/cracks and flows horizontally along bedding planes, dissolving the rock.
(iv) Glacial Depositional Forms?
Moraines: Ridges of till (Terminal/Lateral). Eskers: Sinuous ridges. Outwash Plains: Flat fans. Drumlins: Oval ridges.
(v) Wind action in Deserts?
Wind causes deflation, abrasion and impact. No, rain/sheet wash is also important for mass erosion in deserts.
Long Answers & Project
Q3. Long Answers (150 words)
(i) Running Water: Humid vs Arid
Running water is the most dominant agent.
Humid Areas: It degrades land through overland flow (sheet erosion) and linear flow (streams). Forms valleys, gorges, and peneplains.
Arid Areas: Even though rain is scarce, it comes torrentially. Desert rocks devoid of vegetation erode easily. Sheet floods remove weathered debris, aiding wind action.
(ii) Limestone: Humid vs Arid
Humid: Chemical process (Solution) is dominant. Rainwater absorbs CO2 and dissolves limestone, forming Karst topography (Caves, Sinkholes).
Arid: Lack of water prevents solution. Limestone behaves as a hard, resistant rock in deserts, often forming cliffs/hills.
(iii) Glaciers reducing Mountains
Glaciers erode through:
1. Plucking: Dragging large rock blocks.
2. Abrasion: Polishing the valley floor.
They deepen valleys (U-shaped), cut back headwalls (Cirques), and sharpen peaks (Horns). Continued erosion lowers divides, eventually reducing high mountains to low hills and plains.
Project Work
Identify Landforms:
Look around your area:
1. River: Is it meandering? Any sandy banks (Point bars)?
2. Hills: Any steep cliffs or rounded tops?
3. Coast (if nearby): Beach or rocky shore?