Class 11 Geography: Landforms
A. Multiple Choice Questions (MCQs) - 1 Mark Each (Total: 15 Marks)
Which of the following landforms is primarily created by the depositional action of rivers?
a) V-shaped valley
b) Gorge
c) Delta
d) Waterfall
Answer: c) Delta
Hint: Consider the processes that occur when a river enters a large body of water.
Rationale: Deltas are formed at the mouth of rivers where sediments are deposited as the river's flow velocity decreases upon entering a larger water body. V-shaped valleys, gorges, and waterfalls are typically erosional features.
A U-shaped valley is a characteristic landform created by the erosional activity of:
a) Rivers
b) Glaciers
c) Wind
d) Ocean waves
Answer: b) Glaciers
Hint: Think about the powerful erosive force of moving ice.
Rationale: Glaciers, through processes like plucking and abrasion, erode valleys into a distinctive U-shape, unlike the V-shaped valleys typically formed by rivers.
Sinkholes, stalactites, and stalagmites are typical landforms found in which type of topography?
a) Desert topography
b) Glacial topography
c) Karst topography
d) Volcanic topography
Answer: c) Karst topography
Hint: These features are associated with soluble rock formations.
Rationale: Karst topography is characterized by features formed from the dissolution of soluble rocks such as limestone, dolomite, or gypsum by groundwater, leading to caves, sinkholes, and dripstones (stalactites and stalagmites).
A mushroom rock (pedestal rock) is a landform formed by the erosional action of:
a) Running water
b) Groundwater
c) Wind
d) Glaciers
Answer: c) Wind
Hint: Consider environments where wind abrasion is a dominant process.
Rationale: Mushroom rocks are typically found in arid or semi-arid regions where wind abrasion, concentrated near the base due to bouncing sand particles, erodes the lower part of a rock more than the top, creating a mushroom-like shape.
Which of the following is an example of an endogenic landform?
a) Fiord
b) Block Mountain
c) Sand Dune
d) Sea Arch
Answer: b) Block Mountain
Hint: Endogenic forces originate from within the Earth.
Rationale: Block mountains are formed by internal (endogenic) forces of faulting, causing blocks of crust to be uplifted (horsts) or down-dropped (grabens). Fiords, sand dunes, and sea arches are formed by exogenic (external) processes of glaciers, wind, and waves, respectively.
An Oxbow lake is a landform associated with the mature stage of a:
a) River
b) Glacier
c) Desert
d) Coast
Answer: a) River
Hint: This feature forms when a river's bend is cut off.
Rationale: Oxbow lakes form when a meander (bend) of a river becomes too pronounced, and the river eventually cuts across the narrow neck of the meander, leaving the isolated bend as a crescent-shaped lake.
Moraines are landforms created by the deposition of material transported by:
a) Wind
b) Glaciers
c) Rivers
d) Waves
Answer: b) Glaciers
Hint: These are ridges of till.
Rationale: Moraines are accumulations of glacial till (unsorted rock debris) that have been transported and deposited by glaciers. They can be terminal, lateral, medial, or ground moraines depending on their position.
What is the term for a natural bridge-like opening in a headland, formed by wave erosion?
a) Stack
b) Stump
c) Arch
d) Cave
Answer: c) Arch
Hint: This feature often precedes the formation of a stack.
Rationale: A sea arch is a natural opening formed when waves erode through a headland, often by exploiting weaknesses like cracks or softer rock layers. Continued erosion can lead to the collapse of the arch, leaving a stack.
The term 'Loess' refers to:
a) Volcanic ash deposits
b) Fine-grained, wind-blown silt deposits
c) Coarse gravel deposited by rivers
d) Glacial clay deposits
Answer: b) Fine-grained, wind-blown silt deposits
Hint: These deposits are typically fertile and cover vast areas.
Rationale: Loess is an aeolian (wind-blown) sediment consisting predominantly of silt-sized particles. It can form extensive, fertile plains, often found far from its source.
A 'horst' and 'graben' are associated with which type of tectonic structure?
a) Folding
b) Faulting
c) Volcanism
d) Subduction
Answer: b) Faulting
Hint: These terms describe uplifted and down-dropped blocks of crust.
Rationale: Horsts are uplifted blocks of land between parallel faults, while grabens are down-dropped blocks, forming rift valleys. Both are direct results of tensional forces leading to faulting.
Which landform is created when a river's course is interrupted by an abrupt drop in elevation?
a) Meander
b) Delta
c) Natural Levee
d) Waterfall
Answer: d) Waterfall
Hint: This feature is a vertical drop in a river's flow.
Rationale: Waterfalls form where a river flows over a vertical drop in its course, often due to variations in rock resistance or fault lines. Meanders, deltas, and levees are formed by lateral erosion, deposition, or overflow.
Inselbergs are isolated residual hills found in:
a) Glaciated regions
b) Coastal areas
c) Desert regions
d) Karst regions
Answer: c) Desert regions
Hint: These are 'island mountains' in a flat desert plain.
Rationale: Inselbergs are isolated steep-sided hills or mountains that rise abruptly from a gently sloping plain in arid or semi-arid regions. They are resistant remnants of erosion.
Which of the following is a depositional feature formed by glaciers?
a) Cirque
b) Arete
c) Drumlin
d) Horn
Answer: c) Drumlin
Hint: These are elongated, oval-shaped hills.
Rationale: Drumlins are streamlined, elongated hills composed of glacial till, deposited beneath a glacier and shaped by its movement. Cirques, aretes, and horns are erosional features.
The deposition of sediment along the banks of a river during floods leads to the formation of:
a) Alluvial fans
b) Meander loops
c) Natural Levees
d) River terraces
Answer: c) Natural Levees
Hint: These are raised banks flanking a river channel.
Rationale: Natural levees are raised embankments built up on either side of a river channel by the deposition of coarser sediments during floods, which settle quickly as the water overflows the banks.
What is the process by which rock fragments are dislodged and carried away by wind, water, or ice?
a) Weathering
b) Mass Wasting
c) Erosion
d) Deposition
Answer: c) Erosion
Hint: This process involves movement or transport.
Rationale: Erosion is the process of wearing away and transporting soil, rock, or dissolved material from one location on the Earth's crust to another. Weathering is breakdown in situ, mass wasting is downslope movement under gravity, and deposition is the laying down of material.
B. Short Answer Questions (2-3 Marks Each) - (Total: 20-30 Marks)
Differentiate between weathering and erosion.
Answer: Weathering is the in-situ (on-site) breakdown and decomposition of rocks and minerals by physical, chemical, or biological processes. Erosion is the process by which weathered material is picked up and transported by agents like wind, water, ice, or gravity from one place to another.
Explain the formation of a 'V-shaped valley' by river erosion.
Answer: A 'V-shaped valley' is formed by rivers primarily through downcutting (vertical erosion). In the youthful stage of a river, the dominant force is the vertical erosion of the riverbed, especially in mountainous or hilly terrains. The river cuts deeply into the rock, while weathering and mass wasting on the valley sides cause material to fall into the river, which is then carried away, resulting in a narrow, steep-sided, V-shaped profile.
What are sand dunes? Name two types of sand dunes.
Answer: Sand dunes are mounds or ridges of sand formed by the wind (aeolian process) in desert or coastal areas. They are created when wind transports sand particles and deposits them where the wind's velocity decreases or when an obstacle is encountered. Two types include Barchans (crescent-shaped, horns pointing downwind) and Seifs (longitudinal dunes, parallel to wind direction). Other types are transverse dunes, parabolic dunes, and star dunes.
Describe any two landforms created by the depositional work of glaciers.
Answer:
Moraines: These are accumulations of unsorted rock debris (till) transported and deposited by glaciers. They can be terminal (at the glacier's end), lateral (along its sides), medial (in the middle where two glaciers merge), or ground moraines (sheet of till on the valley floor).
Drumlins: These are elongated, oval-shaped hills of glacial till that are streamlined in the direction of ice flow. They often occur in fields and indicate the direction of the glacier's movement.
What is a 'Canyon'? How is it different from a 'Gorge'?
Answer: Both canyons and gorges are deep, narrow valleys with steep sides, typically carved by rivers. A gorge is generally narrower and deeper with very steep to vertical walls, often cut through hard rock. A canyon is typically larger in scale, wider, and longer than a gorge, often characterized by step-like slopes due to varying resistance of rock layers. The Grand Canyon is a classic example.
Explain the role of solution in forming karst topography.
Answer: Solution is the primary process in forming karst topography. It involves the chemical weathering of soluble rocks, mainly limestone (CaCO 3), by acidic groundwater. Rainwater absorbs carbon dioxide from the atmosphere and soil to form carbonic acid, which then dissolves the limestone along joints and bedding planes, enlarging cracks, forming sinkholes (dolines), underground caves, and eventually intricate drainage systems characteristic of karst landscapes.
What are 'alluvial fans' and 'alluvial cones'? Where are they typically found?
Answer: Alluvial fans and alluvial cones are fan-shaped or cone-shaped deposits of sediment formed where a high-gradient stream emerges from a mountain front onto a flatter plain or valley. The stream's velocity decreases abruptly, causing it to drop its sediment load. Alluvial cones are steeper and smaller versions of fans, typically formed by coarser material. They are typically found at the base of mountains or hills, particularly in arid or semi-arid regions.
Briefly describe how a 'sea stack' is formed.
Answer: A sea stack is a vertical column of rock in the sea near a coast. It is formed by the continuous erosional action of waves on a headland. Initially, waves exploit weaknesses in the headland to form sea caves. If the caves on opposite sides of a headland meet, they form a sea arch. Continued erosion by waves on the arch's base eventually causes the top of the arch to collapse, leaving an isolated pillar of rock—the sea stack.
What are 'fiords'? What process leads to their formation?
Answer: Fiords (or fjords) are long, narrow, deep inlets of the sea, typically with steep, rocky sides. They are formed by the erosional action of glaciers. During glacial periods, glaciers flow down existing river valleys, significantly deepening and widening them into a U-shape. As the glaciers retreat, these U-shaped valleys are inundated by seawater, creating fiords. They are common in high-latitude coastal regions like Norway, Chile, and New Zealand.
Differentiate between physical and chemical weathering.
Answer: Physical (or Mechanical) Weathering involves the breakdown of rocks into smaller fragments without any change in their chemical composition (e.g., frost wedging, exfoliation, granular disintegration). Chemical Weathering involves the decomposition of rocks through chemical reactions, altering their mineral composition (e.g., carbonation, oxidation, hydrolysis, solution).
C. Long Answer Questions (5-6 Marks Each) - (Total: 10-12 Marks)
Describe the major landforms created by the erosional and depositional work of rivers, explaining their formation processes in detail.
Answer:
Rivers are powerful agents of denudation, constantly shaping the landscape through erosion, transportation, and deposition.Erosional Landforms by Rivers:
V-shaped Valleys, Gorges, and Canyons: In their youthful stage, rivers primarily engage in vertical erosion (downcutting). As the river rapidly cuts into its bed, the valley sides are simultaneously affected by weathering and mass wasting, leading to the characteristic V-shaped profile. Gorges are deep, narrow valleys with very steep sides cut through hard rock, while canyons are larger, often multi-layered versions formed in arid regions with horizontal rock strata.
Waterfalls and Rapids: These are formed where there is an abrupt change in the gradient of the riverbed or where the river flows over alternating layers of hard and soft rock. The softer rock is eroded more quickly, leaving a step over which the water plunges (waterfall) or flows turbulently (rapids).
Potholes: These are circular depressions formed in the riverbed due to the abrasion caused by pebbles and boulders carried by the swirling water in eddies.
River Terraces: These are flat steps found on either side of the present river valley, representing old floodplains or valley floors. They are formed when a river undergoes rejuvenation, either due to a drop in sea level or tectonic uplift, causing it to cut down into its own previously deposited alluvium.
Depositional Landforms by Rivers:
Alluvial Fans and Cones: As rivers emerge from mountainous areas onto flatter plains, their velocity decreases abruptly. This causes the stream to deposit its coarser sediment load in a fan-shaped accumulation known as an alluvial fan (or a steeper alluvial cone).
Floodplains: These are flat, low-lying areas adjacent to a river channel that are regularly inundated during floods. During floods, the river overflows its banks, depositing fine sediments (alluvium) over a wide area, which builds up the floodplain over time.
Natural Levees: These are raised embankments or ridges of sediment (typically coarser sand and silt) that run parallel to the river channel on its banks. They are formed when the river overflows its banks during a flood, and the sudden decrease in water velocity causes the coarser sediment to be deposited immediately along the channel's edge.
Meanders and Oxbow Lakes: In the mature stage, rivers reduce their vertical erosion and begin to erode laterally, developing sinuous bends called meanders. Over time, as a meander loop becomes extremely curved, the river may cut across the narrow neck of the loop during a flood. The abandoned loop then forms a crescent-shaped oxbow lake.
Deltas: These are large, triangular or fan-shaped landforms built up at the mouth of a river where it enters a standing body of water (like an ocean, sea, or lake). As the river's velocity drops drastically upon entering the still water, it deposits its entire sediment load, forming a network of distributaries and accumulating land over time (e.g., Ganges-Brahmaputra Delta).
Discuss the formation of major landforms associated with arid (desert) regions, distinguishing between erosional and depositional features.
Answer:
Arid (desert) regions are characterized by extreme temperatures, sparse vegetation, and limited precipitation, where wind is a dominant geomorphic agent, along with occasional flash floods.
Erosional Landforms in Deserts (primarily by Wind and Ephemeral Streams):
Mushroom Rocks (Pedestal Rocks): These are isolated rock pillars with a narrower base and a wider top. They are formed by wind abrasion (corrasion), where wind-borne sand particles are most concentrated near the ground, eroding the lower part of the rock more effectively than the upper part.
Deflation Hollows/Basins: These are large depressions formed by the removal of fine, loose surface material (silt and sand) by strong winds (deflation). As the wind removes more material, the hollow deepens until it reaches the water table or resistant rock.
Inselbergs (Island Mountains): These are isolated, steep-sided residual hills or mountains that rise abruptly from a gently sloping desert plain. They represent remnants of a formerly more extensive landscape that have resisted long-term weathering and erosion.
Yardangs: These are streamlined, elongated ridges of rock, typically formed in arid regions where differential wind erosion has carved away softer rock layers, leaving more resistant ones as ridges, parallel to the dominant wind direction.
Mesas and Buttes: These are flat-topped, steep-sided landforms characteristic of layered sedimentary rock in arid regions. Mesas are larger, while buttes are smaller, isolated remnants of mesas that have undergone further erosion.
Wadis (Arroyos/Dry Channels): These are steep-sided, flat-bottomed ephemeral river channels found in deserts. They are typically dry but can experience sudden, powerful flash floods after infrequent rainfall, acting as significant erosional agents during those short periods.
Depositional Landforms in Deserts (primarily by Wind and Ephemeral Streams):
Sand Dunes: These are the most common depositional landforms in deserts. They are mounds or ridges of sand accumulated by wind action. Various types exist depending on wind direction, sand supply, and vegetation:
Barchans: Crescent-shaped dunes with horns pointing downwind, formed with limited sand supply and consistent wind.
Seifs (Longitudinal Dunes): Long, parallel ridges of sand aligned with the dominant wind direction.
Transverse Dunes: Long ridges of sand perpendicular to the wind direction, formed where sand is abundant.
Parabolic Dunes: Crescent-shaped, but with horns pointing upwind, often stabilized by vegetation.
Loess: This refers to extensive, thick deposits of fine-grained, yellowish, wind-blown silt. Loess deposits are highly porous and fertile, often found far from their desert source areas, forming significant agricultural regions (e.g., parts of China, Central USA).
Alluvial Fans and Bajadas: As ephemeral streams carrying sediment flow from mountain ranges onto flatter desert plains, their velocity decreases, depositing coarser sediments in fan-shaped structures called alluvial fans. When several adjacent alluvial fans merge along a mountain front, they form a continuous apron of sediment called a bajada.
Playas (Salt Flats): These are flat, barren basins in the lowest parts of desert depressions, which periodically fill with water from rainfall or runoff, forming temporary lakes. As the water evaporates, it leaves behind a flat plain covered with fine sediments and a crust of evaporite minerals (salts).
