Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
Lithosphere II — Exogenetic Processes — Exercise Solutions Guide
Solve every exercise on your own first, then cross-check your answers here. Understanding why an answer is correct matters more than memorising it.
I. Multiple Choice Questions (MCQs)
**Q1. The breakdown of rocks without any movement of the broken material is called
(a) Erosion (b) Weathering (c) Mass movement (d) Deposition
**Q2. Which type of weathering is most common in hot and humid regions?
(a) Physical weathering (b) Chemical weathering (c) Biological weathering (d) Mechanical weathering
**Q3. A delta is formed at the
(a) Source of a river (b) Middle course of a river (c) Mouth of a river (d) Upper course of a river
**Q4. Which of the following is an erosional landform of a river?
(a) Delta (b) Floodplain (c) Waterfall (d) Levee
**Q5. Sand dunes are landforms created by the action of
(a) Rivers (b) Wind (c) Glaciers (d) Sea waves
**Q6. The process of peeling off concentric layers of rock due to temperature changes is called
(a) Frost action (b) Exfoliation (c) Carbonation (d) Hydration
**Q7. Which agent of gradation is responsible for the formation of stalactites and stalagmites?
(a) Wind (b) Glacier (c) Groundwater (d) Sea waves
**Q8. An oxbow lake is formed by
(a) Wind erosion (b) Glacial erosion (c) River meandering (d) Sea wave action
**Q9. Moraines are depositional features associated with
(a) Rivers (b) Wind (c) Glaciers (d) Sea waves
**Q10. Which of the following is NOT a chemical weathering process?
(a) Oxidation (b) Carbonation (c) Frost action (d) Solution
**Q11. The V-shaped valley carved by a river in its upper course is called a
(a) Gorge (b) Delta (c) Floodplain (d) Meander
**Q12. Mushroom rocks are formed by the erosional action of
(a) Rivers (b) Glaciers (c) Wind (d) Sea waves
II. True or False
1. Weathering involves the movement of rock material from one place to another.
2. Chemical weathering is dominant in cold and dry regions.
3. A delta is a depositional landform found at the mouth of a river.
4. Glaciers move very slowly, only a few centimetres to metres per day.
5. Exfoliation is a type of chemical weathering.
6. Sea cliffs are formed by the depositional action of sea waves.
7. Mass movement always requires a transporting agent like water or wind.
8. A meander is a bend in the course of a river.
9. Loess is a wind-deposited, fine-grained sediment.
10. Cirques are depositional features of glaciers.
III. Fill in the Blanks
1. The process of breaking down rocks in situ is called ___.
2. The type of weathering caused by temperature changes is called ___ weathering.
3. The triangular depositional landform at a river mouth is called a ___.
4. The process by which wind rolls small pebbles along the ground is called ___.
5. The steep cliff formed by sea wave erosion is called a ___.
6. The U-shaped valley formed by a glacier is called a ___.
7. The ridge of deposited sediment along a river bank during floods is called a ___.
8. The process of rusting of iron-rich rocks is called ___.
9. The mound of sand deposited by wind is called a ___.
10. The slow downhill movement of soil and rock under gravity is called ___.
IV. Match the Following
| Column A | Column B |
|---|---|
| 1. Stalactite | a. Glacial erosional feature |
| 2. Delta | b. Wind depositional feature |
| 3. Mushroom rock | c. River depositional feature |
| 4. Cirque | d. Cave depositional feature |
| 5. Sand dune | e. Wind erosional feature |
1 → d — Stalactites are icicle-shaped deposits of calcium carbonate hanging from the ceilings of limestone caves, formed by mineral-rich groundwater dripping through the cave roof.
2 → c — A delta is a fan-shaped depositional landform formed at the mouth of a river where it deposits sediment into a sea or lake. Examples include the Ganges-Brahmaputra delta and the Nile delta.
3 → e — Mushroom rocks are wind-carved erosional features found in deserts, where sand-laden wind erodes the lower portion of a rock more than the upper part, creating a mushroom-like shape.
4 → a — A cirque is an armchair-shaped erosional hollow carved by a glacier at the head of a mountain valley. When the glacier melts, it often forms a tarn (mountain lake).
5 → b — Sand dunes are mounds of sand deposited by wind action. They form in deserts and coastal areas where wind-transported sand accumulates around obstacles. Types include barchans, seifs, and transverse dunes.
V. Short Answer Questions (2-3 marks)
Q1. What is weathering? Name the three types.
Weathering is the process of breakdown and decomposition of rocks in situ (in their original place) by physical, chemical, or biological agents without any movement of the broken material. The three types are: (1) Physical (mechanical) weathering — caused by temperature changes, frost action, and abrasion; (2) Chemical weathering — caused by processes like oxidation, carbonation, hydration, and solution; (3) Biological weathering — caused by plant roots, burrowing animals, and lichen action.
Q2. Distinguish between erosion and weathering.
Weathering is the in-situ breakdown of rocks without any transportation — the broken material stays where it forms. Erosion, on the other hand, involves both the wearing away of rocks and the transportation of the loosened material by agents such as water, wind, ice, or gravity. Weathering prepares material for erosion; erosion removes and carries it away.
Q3. What are the three courses of a river? Name one landform associated with each.
A river has three courses: (1) Upper course (Youthful stage) — characterised by steep gradients and vertical erosion; landforms include V-shaped valleys, gorges, and waterfalls. (2) Middle course (Mature stage) — characterised by lateral erosion and the beginning of deposition; landforms include meanders and oxbow lakes. (3) Lower course (Old stage) — characterised by a very gentle gradient and heavy deposition; landforms include floodplains, levees, and deltas.
Q4. How does wind erode the land? Name two wind erosional features.
Wind erodes through three processes: (1) Deflation — lifting and removing loose, fine particles (sand, dust) from the surface; (2) Abrasion — sand-blasting effect where wind-driven sand particles scour and polish rock surfaces; (3) Attrition — particles carried by wind collide and break each other down into finer particles. Two wind erosional features are mushroom rocks (or rock pedestals) and deflation hollows (blowouts).
Q5. What is mass movement? Name three types.
Mass movement (also called mass wasting) is the downslope movement of rock, soil, and debris under the influence of gravity, without the aid of a transporting agent like water or wind. Three types are: (1) Landslide — rapid sliding of a mass of rock or soil down a slope; (2) Mudflow — a flow of water-saturated soil and debris down a slope; (3) Soil creep — the very slow, imperceptible movement of soil downslope, often caused by alternate wetting and drying or freeze-thaw cycles.
Q6. How are sea cliffs and sea caves formed?
Sea cliffs are formed by the continuous erosive action of sea waves pounding against the base of a rocky coast. The waves undercut the rock through hydraulic action and abrasion, forming a notch. Over time, the overhanging rock collapses, creating a steep cliff face. Sea caves are formed when waves exploit lines of weakness (cracks and joints) in the cliff rock, eroding them into hollow chambers. If a sea cave extends through the headland, it forms a natural arch.
Q7. Name four depositional landforms of glaciers.
Four depositional landforms of glaciers are: (1) Moraines — ridges of unsorted till deposited by a glacier (lateral, medial, ground, and terminal moraines); (2) Drumlins — smooth, oval-shaped hills of glacial till with a steeper end facing the ice flow direction; (3) Eskers — long, winding ridges of sand and gravel deposited by meltwater flowing in tunnels under the ice; (4) Outwash plains — broad areas of sorted sediment deposited by meltwater streams flowing away from the glacier's terminus.
Q8. What is the work of a river in its lower course?
In the lower (old) course, the river flows over a nearly flat gradient with very low velocity. Its primary work is deposition — it deposits most of its sediment load because it lacks the energy to transport it. The river becomes wide and shallow, with extensive meanders. Depositional landforms formed include floodplains (flat areas of alluvium on either side), natural levees (raised banks), and deltas (fan-shaped deposits at the river mouth where it enters the sea or lake).
VI. Detailed Answer Questions (5 marks)
Q1. Explain the three types of weathering with examples.
Weathering is the breakdown of rocks in situ by physical, chemical, or biological agents. The three types are:
Physical (Mechanical) Weathering: The disintegration of rocks without any change in their chemical composition. It is caused by: (1) Temperature changes — in deserts, rocks expand during the day and contract at night, causing stress and cracking (exfoliation or onion weathering). (2) Frost action (freeze-thaw) — water enters rock cracks, freezes and expands by about 9%, exerting pressure and gradually splitting the rock. Common in cold, mountainous regions. (3) Abrasion — rocks grinding against each other due to wind, water, or gravity.
Chemical Weathering: The decomposition of rocks through chemical reactions that alter their mineral composition. Key processes include: (1) Oxidation — oxygen reacts with iron-rich minerals, causing rusting and weakening (e.g., iron turning reddish-brown). (2) Carbonation — rainwater containing dissolved CO2 forms carbonic acid, which dissolves limestone (calcium carbonate), forming caves and karst landscapes. (3) Hydration — minerals absorb water and expand, causing stress and cracking (e.g., feldspar hydrating to clay). (4) Solution — soluble minerals like rock salt and gypsum dissolve directly in water.
Biological Weathering: The breakdown of rocks by living organisms. This includes: (1) Plant roots — growing roots penetrate rock cracks, exerting pressure and splitting rocks apart. (2) Burrowing animals — rabbits, ants, and worms loosen soil and expose rock to weathering agents. (3) Lichens and mosses — secrete acids that chemically dissolve rock surfaces over time.
These three types often work together — physical weathering creates cracks that allow water entry, enabling chemical weathering, while biological weathering further widens cracks.
Q2. Describe the work of a river in its three courses — erosional, transportational, and depositional landforms.
A river performs three types of work — erosion, transportation, and deposition — with different processes dominating in each course:
Upper Course (Youthful Stage): The river flows rapidly down a steep gradient, so erosion dominates, especially vertical (downward) erosion. The river carves deep, narrow V-shaped valleys and gorges. Waterfalls form where the river flows over alternating bands of hard and soft rock — the soft rock erodes faster, creating a step. Interlocking spurs form as the river erodes the valley sides. Rapids occur where the gradient is steep but not enough for a waterfall. Transportation is active but deposition is minimal due to high velocity.
Middle Course (Mature Stage): The gradient decreases and the river begins to erode laterally (sideways) as well as vertically. Meanders develop — bends in the river where erosion occurs on the outer bank (cut bank) and deposition occurs on the inner bank (slip-off slope). Over time, meanders become more pronounced. When a meander loop is cut off, an oxbow lake forms. Some deposition begins as the river's energy starts to decrease on gentler slopes.
Lower Course (Old Stage): The river flows over a very gentle, nearly flat gradient with low velocity, so deposition dominates. The river deposits its load, forming wide floodplains on either side. During floods, the river overflows its banks and deposits coarse sediment near the channel, forming natural levees (raised banks). At the river mouth, where it enters the sea, the deposited sediment forms a delta — a triangular or fan-shaped landform. The river may split into multiple channels called distributaries across the delta.
Q3. Explain the work of wind as an agent of erosion, transportation, and deposition with landforms.
Wind is a powerful agent of gradation in arid and semi-arid regions (deserts) where vegetation is sparse and loose sediment is abundant.
Erosion by Wind: Wind erodes through three processes: (1) Deflation — the lifting and removal of loose, fine material like sand, silt, and dust from the surface. This can create deflation hollows (blowouts) and desert pavements. (2) Abrasion — wind-driven sand particles act like sandpaper, scouring, polishing, and shaping rock surfaces. This forms mushroom rocks (pedestal rocks), where the lower portion is eroded more because sand moves near ground level. Ventifacts (wind-faceted rocks) also form by abrasion. (3) Attrition — wind-transported particles collide and break down into finer pieces.
Transportation by Wind: Wind transports material in three ways: (1) Suspension — fine dust and silt particles are carried high in the air (dust storms); (2) Saltation — medium sand grains are lifted briefly and bounce along the surface; (3) Surface creep — larger pebbles roll along the ground pushed by the wind or the impact of saltating grains.
Deposition by Wind: When wind velocity decreases or encounters obstacles, it drops its sediment load. Depositional features include: (1) Sand dunes — mounds of sand deposited by wind, found in deserts and coastal areas. Types include barchans (crescent-shaped), seifs (longitudinal), and transverse dunes. (2) Loess — extensive deposits of fine, silt-sized wind-blown dust, forming fertile soils (e.g., in northern China and the Mississippi Valley). (3) Ripple marks — small wave-like patterns formed on sand surfaces by wind action.
Q4. Describe the work of glaciers — erosional and depositional landforms.
Glaciers are massive bodies of ice that move slowly under the influence of gravity. Despite their slow movement, they are powerful agents of erosion and deposition.
Erosion by Glaciers: Glaciers erode through two main processes: (1) Plucking (quarrying) — the glacier freezes around rock fragments and pulls them loose as it moves. (2) Abrasion — rock debris embedded in the glacier's base scrapes and grinds against the bedrock beneath, polishing, striating, and gouging the surface. Erosional landforms include: Cirques — armchair-shaped hollows carved at the head of a glacial valley; Aretes — narrow ridges between two cirques; Horns — pyramid-shaped peaks carved by multiple cirques (e.g., the Matterhorn); U-shaped valleys (glacial troughs) — wide, steep-sided valleys carved by glaciers; Hanging valleys — tributary glacial valleys that enter the main valley at a higher elevation, creating waterfalls; Fjords — drowned glacial valleys flooded by the sea; Roche moutonnee — asymmetric rock hills smoothed by glacial abrasion.
Deposition by Glaciers: When a glacier melts or retreats, it deposits the rock debris (till) it has been carrying. Depositional landforms include: Moraines — ridges of unsorted glacial till classified as lateral (along the sides), medial (where two glaciers merge), ground (deposited beneath), and terminal (at the glacier's furthest point); Drumlins — smooth, oval hills of till with a steeper end facing the ice direction; Eskers — long, winding ridges of sand and gravel deposited by meltwater streams in ice tunnels; Outwash plains — broad, flat areas of sorted sediment deposited by meltwater beyond the glacier's terminus; Erratics — large boulders transported by ice and deposited far from their source rock.
Q5. Explain the work of sea waves — erosional and depositional landforms.
Sea waves are powerful agents of coastal erosion and deposition, constantly shaping coastlines through their relentless action.
Erosion by Sea Waves: Waves erode through four processes: (1) Hydraulic action — the sheer force of waves compressing air in rock cracks, causing them to widen and fracture; (2) Abrasion (corrasion) — waves hurl pebbles and sand against cliffs, scouring and grinding the rock surface; (3) Attrition — rock particles carried by waves collide and break into smaller, rounder pieces; (4) Solution (corrosion) — seawater dissolves soluble rock, especially limestone. Erosional landforms include: Sea cliffs — steep rock faces formed by wave undercutting; Sea caves — hollows excavated in cliffs by waves exploiting lines of weakness; Natural arches — formed when a sea cave is eroded right through a headland; Stacks — isolated rock pillars left when an arch collapses; Stumps — the eroded remains of stacks at sea level; Wave-cut platforms — flat, rocky surfaces left behind as a cliff retreats landward.
Deposition by Sea Waves: Waves deposit sediment when their energy decreases. Depositional landforms include: Beaches — accumulations of sand and pebbles along the coast; Spits — long, narrow ridges of sand extending from the coast into the sea; Bars — spits that grow across a bay, connecting two headlands and enclosing a lagoon; Tombolos — sand bars connecting an island to the mainland; Sand dunes — mounds of wind-blown sand formed behind beaches; Barrier islands — long, narrow islands parallel to the coast formed by wave deposition.
Common Mistakes
1. Confusing weathering and erosion: Weathering breaks rocks in place (no movement); erosion breaks rocks and transports the material. Think of weathering as preparing material and erosion as carrying it away.
2. Calling exfoliation a chemical process: Exfoliation (onion weathering) is a physical weathering process caused by temperature changes. The rock layers peel off due to expansion and contraction, not chemical reactions.
3. Saying deltas form in the upper course of a river: Deltas form at the mouth (lower course) of a river where it enters the sea or lake and its velocity drops, causing deposition. The upper course is dominated by erosion (V-shaped valleys, waterfalls).
4. Confusing moraines with drumlins: Moraines are ridges of unsorted glacial till deposited along the sides, middle, or end of a glacier. Drumlins are smooth, oval-shaped hills of till that indicate the direction of ice flow. Both are depositional, but moraines are linear ridges while drumlins are streamlined hills.
5. Saying sea caves are depositional features: Sea caves, arches, stacks, and stumps are all erosional features carved by wave action. Beaches, spits, bars, and tombolos are the depositional features.
6. Confusing stalactites and stalagmites: Stalactites hang down from cave ceilings (remember: "stalactites hold tight to the ceiling"). Stalagmites rise up from cave floors. When they meet, they form a column.
7. Forgetting that mass movement operates without a transporting agent: Mass movement (landslides, soil creep, mudflows) moves material downslope by gravity alone. Water may lubricate the process, but it is not the transporting agent. This distinguishes mass movement from erosion by rivers, wind, or glaciers.
Exam Checklist
- [ ] Can define and distinguish weathering, erosion, and deposition
- [ ] Can explain physical, chemical, and biological weathering with at least two examples each
- [ ] Can name and describe the three courses of a river with associated landforms
- [ ] Can list and explain river erosional landforms (V-shaped valley, waterfall, gorge, meander)
- [ ] Can list and explain river depositional landforms (delta, floodplain, levee, oxbow lake)
- [ ] Can describe wind erosion (deflation, abrasion, attrition) and wind landforms (mushroom rock, sand dune, loess)
- [ ] Can describe glacial erosional landforms (cirque, arete, horn, U-shaped valley, hanging valley, fjord)
- [ ] Can describe glacial depositional landforms (moraine, drumlin, esker, outwash plain, erratic)
- [ ] Can describe coastal erosional features (sea cliff, cave, arch, stack, stump, wave-cut platform)
- [ ] Can describe coastal depositional features (beach, spit, bar, tombolo, barrier island)
- [ ] Can explain mass movement types (landslide, mudflow, soil creep)
- [ ] Can distinguish between stalactites and stalagmites as groundwater depositional features
Internal Links
- [Class 9 Social Science — Lithosphere II Exogenetic Processes Guide](/school/tamil-nadu-state-board/class/9/social/lithosphere-ii-exogenetic-processes)
- [All Class 9 Social Solutions](/school/tamil-nadu-state-board/class/9/social/solutions)
- [Class 9 Social Science Subject Guide](/school/tamil-nadu-state-board/class/9/social)