GEOGRAPHY- CLASS-11: FUNDAMENTALS OF PHYSICAL GEOGRAPHY
CHAPTER-6
Landforms and their Evolution
1. Multiple Choice Questions
(i) In which of the following stages of landform development, downward cutting is dominated?
Answer: (a) Youth stage
Explanation: During the youth stage of river development, vertical or downward erosion is dominant, resulting in deep valleys and gorges.
(ii) A deep valley characterised by steep step-like side slopes is known as
Answer: (d) Canyon
Explanation: A canyon is a deep, narrow valley with steep, step-like sides formed by river erosion in horizontally layered rocks.
(iii) In which one of the following regions is the chemical weathering process more dominant than the mechanical process?
Answer: (a) Humid region
Explanation: Chemical weathering is most active in warm and humid regions because abundant moisture and high temperatures accelerate chemical reactions.
(iv) Which one of the following sentences best defines the term 'Lapies'?
Answer: (d) An irregular surface with sharp pinnacles, grooves and ridges
Explanation: Lapies are small-scale limestone landforms produced by the solution action of rainwater, creating sharp 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:
Answer: (a) Cirque
Explanation: A cirque is a bowl-shaped depression formed by glacial erosion at the head of a valley.
2. Answer the following questions in about 30 words.
(i) What do incised meanders in rocks and meanders in plains of alluvium indicate?
Answer:
Incised meanders indicate renewed vertical erosion due to uplift of land, whereas meanders in alluvial plains indicate lateral erosion and deposition during the mature stage of a river.
(ii) Explain the evolution of valley sinks or uvalas.
Answer:
Uvalas are formed when several nearby sinkholes (dolines) enlarge and merge due to continuous limestone solution. They develop into large, irregular depressions in karst regions.
(iii) Underground flow of water is more common than surface run-off in limestone areas. Why?
Answer:
Limestone is highly porous and contains numerous joints and cracks. Rainwater easily seeps underground by dissolving the limestone, reducing surface runoff and increasing underground drainage.
(iv) Glacial valleys show up many linear depositional forms. Give their locations and names.
Answer:
Linear depositional landforms include lateral moraines along the valley sides, medial moraines at the centre where glaciers meet, and terminal moraines at the glacier's end.
(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 erodes, transports and deposits sand by deflation and abrasion. However, it is not the only agent. Running water also forms many erosional landforms in deserts during occasional heavy rainfall.
3. 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 most important geomorphic agent because it continuously erodes, transports and deposits sediments over the Earth's surface. In humid regions, rivers flow throughout the year due to abundant rainfall. They carve valleys, waterfalls, gorges, floodplains, meanders and deltas. In arid regions, although rainfall is infrequent, sudden heavy showers create powerful streams that carry large amounts of sediments and form landforms such as gullies, canyons, alluvial fans and playas. Running water also transports weathered materials from highlands to lowlands, gradually reducing relief differences. It shapes landscapes more effectively than other geomorphic agents because of its widespread occurrence and continuous action. Thus, whether in humid or arid climates, running water plays a dominant role in the evolution of landforms.
(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:
Limestone behaves differently because the amount of water available varies with climate. In humid regions, abundant rainfall absorbs carbon dioxide and forms weak carbonic acid, which dissolves limestone rapidly. As a result, solution is the dominant geomorphic process and produces characteristic karst topography. Common karst landforms include lapies, sinkholes (dolines), uvalas, poljes, caves, caverns, stalactites, stalagmites and limestone pillars. In arid regions, rainfall is scarce, so chemical solution is limited and mechanical weathering becomes comparatively more important. Therefore, karst features are poorly developed in dry climates. The process of solution is almost exclusive in limestone regions and is responsible for the formation of a wide variety of underground and surface landforms.
(iii) How do glaciers accomplish the work of reducing high mountains into low hills and plains?
Answer:
Glaciers are powerful agents of erosion in high mountain regions. As glaciers move slowly under the influence of gravity, they erode the underlying rocks by plucking and abrasion. Large rock fragments are removed and carried along with the ice, while smaller particles grind the rock surface like sandpaper. This process widens and deepens valleys, converting V-shaped river valleys into U-shaped glacial valleys. Glaciers also form cirques, arêtes, horns and hanging valleys. The eroded materials are transported and deposited as moraines, outwash plains and drumlins when the glacier melts. Continuous glacial erosion gradually lowers mountain peaks and reduces rugged landscapes into gentler hills and broad plains. Thus, glaciers play an important role in reducing high mountains and reshaping the Earth's surface.