1. Landforms and their Evolution

NCERT Questions:

  1. 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

Ans. a) Youth stage

 

 (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

Ans. d) Canyon

 

(iii) In which one of the following regions the chemical weathering processes is more dominant then the mechanical process?

a) Humid region

b) Limestone Region

c) Arid region

d) Glacier Region

Ans. b) Limestone Region

 

(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

Ans. a) A small to medium sized shallow depression

 

(v) A deep long and wide trough or basin with very steep concave high walls at its head as well as sides is known as:

a) Cirque

b) Glacier Valley

c) Lateral Moraine

d) Esker

Ans. a) Cirque

 

  1. Answer the following questions in about 30 words:

 

(i) What do incised meanders in rocks and meanders in plains of alluvium indicate?

Ans.

a) The streams that flow rapidly over steep gradients, normally erosion is concentrated on the bottom of the stream channel.

b) Where stream gradients are very gentle it is common to find meandering courses over flood plains and delta plains, lateral erosion on the sides of the valley is more.

c) But very deep and wide meanders can also be found cut in hard rocks.

d) Meandering loops developed over original gentle surface in the initial stages of development of streams and the same loops get entrenched into the rocks, normally due to erosion or slow continued uplift of the land over which they start.

e) They widen and deepen overtime and can be found as deep, gorges and canyons in hard rock.

 

 

(ii) Explain the evolution of Valley sinks or uvalas.

Ans.

a) Quite often the surface run off simply goes down through swallow and sink holes and flow as underground streams and re-emerges at a distance downstream through a cave opening.

b) When sinkholes and dough lines joined together because of slumping of materials along their margins or due to roof collapse of caves long narrow to wide trenches called valley sinks or uvalas form.

 

(iii) Underground flow of water is more common than surface runoff in limestone areas. Why?

Ans.

a) The result of the work of groundwater cannot be seen in all types of rocks. But in rocks like lime-stones or dolomites rich in calcium carbonate, the surface water as well as groundwater through the chemical process of solution and precipitation deposition develops varieties of landforms.

b) These two processes of solution and precipitation are active in limestone or dolomites occurring either exclusively or inter-bedded with other rocks.

c) Therefore, underground flow of water is more common than surface runoff in limestone areas.

 

 (iv) Glacier valley show up many linear depositional forms. Give their locations and names.

Ans.

a) Glacial valleys show up many linear depositional forms their locations and names are as follows:

b) Moraines: They are long range of deposits of glacial till. Lateral moraines form along the sides, parallel to the glacial valleys. The lateral moraines may join a terminal Moraine.

c) Eskers: When glaciers melt in summer the water flows on the surface of the ice, or seeps down along the margins, or even moves through holes in the ice. These waters accumulate beneath the glacier and flow like streams in a channel beneath the ice. Such streams flow over the ground with ice forming its banks. Very course materials like boulders and blogs, along with some minor fractions of rock debris carried into this stream, settle in the valley of ice beneath the glacier. And after the ice melts can be found as a sinus ridge called as eskers.

d) Outwash plains: The place at the foot of the glacier mountains are beyond the limits of continental ice sheets are covered with glacier fuel deposits in the form of broad, flat alluvial fans which may join to form. Outwash plains of gravel, silt, sand and clay.

e) Drumlins: Drumlins are smooth oval shaped, ridge like features, composed mainly of glacier till with some masses of gravel and sand. The long axes of drumlins are parallel to the direction of ice movement. They may measure up to one kilometre in length and 30 metres or so in height.

 

(v) How does wind perform its task in desert areas? Is it the only agent responsible for the erosional features in the deserts?

Ans.

a) The desert gets heated up too much and too quickly because of being dry and barren. The heated floors heat up the air directly above them and result in upward movement in the hot, lighter air with turbulence and any obstructions in its path sets up eddies whirlwinds updrafts and down drafts. These storm winds are very destructive. Winds cost deflation, abrasion and impact.

b) Deflation includes lifting and removal of dust and smaller particles from the surface of rocks in the transportation processes. Sand and silt act as effective tools to abrade the land surface.

c) Wind is not the only agent responsible for the erosional features in the deserts. The other one is rain or sheet washes.

 

  1. 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 arid climates. Explain.

Ans.

a) In humid regions which receive heavy rainfall, running water is considered the most important of the geomorphic agents in bringing about the degradation of the land surface. There are two components of running water.

b) One is overland flow on general land surface as a sheet another is linear flow as streams and rivers in valleys.

c) Most of the erosional landforms made by running water are associated with vigorous and youthful rivers flowing over steep gradients.

d) With time, stream channels over steep gradients turn gentler due to continued erosion and as a consequence lose their velocity, facilitating active deposition.

e) There may be depositional forms associated with streams flowing over steep slopes. But these phenomena will be on a small scale compared to those associated with rivers flowing over medium to gentle slopes. The gentler, the river channel gradient or slopes, the greater is the deposition. When the stream beds turn gentler due to continued erosion, downward cutting becomes less dominant and lateral erosion of banks increases and as a consequence the hills and valleys are reduced to planes.

f) In dry regions most of the landforms are formed by the erosion and deposition of flood sheet. Although in deserts rain is scarce it comes down torrentially in a short period of time. The desert rocks devoid of vegetation, exposed to mechanical and chemical weathering processes due to drastic diurnal temperature changes. Decay faster and the torrential rains help in removing the weathered materials easily. That means the weathered debris in deserts is moved by not only wind, but also by rain /sheet wash.

 

(ii) Lime stones 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?

Ans.

a) Many depositional landforms develop within the limestone caves.

b) The chief chemical in limestone is calcium carbonate, which is easily soluble in carbonated water that is carbon dioxide absorbed rainwater. This calcium carbonate is deposited when the water carrying it in solution evaporates or loses.

c) It is carbon dioxide as it trickles over rough rock surfaces. Stalactites, stalagmites and pillars are made.

d) Normally stalactites are broad at their base and taper down, showing up in a variety of forms. Stalagmites rise up from the floor of the caves. In fact, stalagmites formed due to dripping water from the surface or through the thin pipe of the stalactite immediately below it.

e) The two processes of solution and precipitation are active in limestone or dolomites occurring either exclusively or Inter-bedded with other rocks. Therefore, underground flow of water is more common than surface runoff in limestone regions.

 

(iii) How do glaciers accomplish the work of reducing high mountains into low hills and plains?

Ans.

a) Masses of ice moving a sheet over the land, or as linear flows down the slopes of mountains in broad trough like valleys are called glaciers. A glacier in its valley is slow, unlike water flow. The movement could be a few centimetres to a few metres a day, or even less or more. Glaciers move basically because of the force of gravity.

b) Erosion by glaciers is tremendous because of friction caused by sheer weight of the ice. The material plucked from the land by glaciers get dragged along the floors or sides of the valleys and cause great damage through abrasion and plucking. Glaciers can cause significant damage to even un-weathered rocks and can reduce high mountains into low hills and plains.

c) As glaciers continue to move, debris gets removed, device get lowered, and eventually the slope is reduced to such an extent that glaciers will stop moving, leaving only a mass of low hills and vast outwash plains, along with other depositional features.

Question Bank:

  1. Stream erosion aided by the abrasion of rock fragments cause:

a) Sinkhole

b) Pediments

c) Deflation hollows

d) Potholes

Ans. d) Potholes

Over the rocky beds of hill-streams, circular depression is caused by the abrasion of rocks and pebbles to form the potholes.

 

  1. Natural levees and point bars are associated with:

a) Beaches

b) Flood plains

c) Outwash plains

d) Pediplains

Ans. b) Flood plains

Natural levees are found at the parallel of coarse deposits and point bars are formed during the flooding of river and form a series of natural levees near the bank.

 

  1. Stalagmite and stalactites ultimately mingle and give rise to:

a) Lapis

b) Pillars

c) Pavements

d) Eskers

Ans. b) Pillars

Stalagmites form due to the dripping of water to the surface, whereas stalactites hang at the roof. They touch each other to form pillars.

 

  1. Heavy waves create hollows on cliffs and get widened to form:

a) Stacks

b) Terrace

c) Dunes

d) Caves

Ans. d) Caves

The pouring of wave breaks against the cliff base smashes the rock debris against the cliff and gets widen to form caves.

 

  1. The process of lifting and removal of dust from the earth’s crust surface is called:

a) Deflation

b) Impact

c) Abrasion

d) Aggradation

Ans. a) Deflation

Deflation is caused due to the winds in which the weathered debris is eroded from the earth surface.

 

  1. Long ridges of debris deposited at the end of glaciers are:

a) Lateral moraines

b) Ground moraines

c) Terminal moraines

d) Medial moraines

Ans. c) Terminal moraines

Terminal moraines have a ridge like accumulation of glacial and are deposited at the outermost edge of glaciers.

 

  1. The process of solution and precipitation are very active in:

a) Limestone

b) Sandstone

c) Granite stone

d) Quartz stone

Ans. a) Limestone

Limestone with its high calcium carbonate content is easily dissolved in carbonated water. When limestone interacts with underground water, it dissolves the limestone to form karst topography.

 

  1. Natural levees and point bars are depositional landforms of:

a) Glaciers

b) Waves

c) Winds

d) Rivers

Ans. d) Rivers

Natural levees are low, linear and parallel ridges of course deposits along the banks of river. Point bars are found on the convex side of meanders of large rivers.

 

  1. Over the rocky bed of hill streams more or less circular depression forms are known as:

a) Sinkholes

b) Potholes

c) Plunge pools

d) Swallow holes

Ans. b) Potholes

Potholes are small shallow depression formed when stream erosion is aided by the abrasion of rock fragments.

 

  1. A study of earth’s landform, its material and the processes that shape it is known as:

a) Geomorphology

b) Physiology

c) Anthropology

d) Geology

Ans. a) Geomorphology

Geomorphology deals with the origin and evolution of the earth’s landforms, both on the continents and within the ocean basins. It is concerned with the internal processes of the earth’s crust which constructs new landforms through tectonic activity and volcanic eruption, as well as modified landforms, driven by forces of wind, water, waves and glacial ice.

 

  1. An offshore bar which is exposed due to further addition of sand is termed as:

a) Spit

b) Beach

c) Terrace

d) Barrier

Ans. d) Barrier

Sand carried by the off-shore moving bottom current is deposited where the current reaches the wave break, representing the break point of even larger waves or the break point at low tide.

 

  1. A dune lying parallel to the prevailing wind with limited sand is:

a) Seif

b) Parabolic dune

c) Transverse dune

d) Longitudinal dune

Ans. d) Longitudinal dune

These types of dunes are short in height and extend as long ridges in the resultant direction of sand movement.

 

  1. The plains formed as a result of stream erosion are called:

a) Alluvial plains

b) Valley

c) Delta

d) Peneplains

Ans. d) Peneplains

The plains formed as a result of stream erosion is called Peneplains. They are almost flattened plains.

 

  1. Depositional landforms of Karst region are the:

a) Pools

b) Sinkholes

c) Caves

d) Stalactites

Ans. d) Stalactites

Stalactites are depositional features, which are formed due to the deposition of salts.

 

  1. In which of the following regions the chemical weathering process is more dominant than the mechanical process?

a) Desert region

b) Arid region

c) Limestone region

d) Glacier region

Ans. c) Limestone region

Limestone region is rich in calcium carbonate, which is easily dissolved in water, through which the chemical process of solution and precipitation deposition develops varieties of landforms.

 

  1. What is a deep and wide trough with very steep concave walls called?

a) Cirque

b) Lateral moraine

c) Glacier valley

d) Esker

Ans. a) Cirque

Cirque is an amphitheatre-like valley head, formed at the head of a valley glacier by erosion. A cirque may be a similarly shaped landform arising from fluvial erosion.

 

  1. A deep valley characterised by step like side slopes is known as:

a) U shaped valley

b) Blind valley

c) Gorge

d) Canyon

Ans. c) Gorge

Gorge is formed in the mountainous areas due to vertical cutting of rocks.

 

  1. Playas are the lakes in the:

a) Arid plains

b) Flood plains

c) Glacial plains

d) Alluvial plains

Ans. a) Arid plains

Playas are lakes formed in the centre of plains where water is retained for a short duration only.

 

  1. Cirque is:

a) V-shaped valley

b) Deep, long and broad trough

c) Hills

d) Plains

Ans. b) Deep, long and broad trough

They are found at the level of glacial valleys. The accumulated ice cuts these cirques.

 

  1. Cirque and horns are associated with:

a) Riverine erosion

b) Underground water erosion

c) Wind erosion

d) Glacial erosion

Ans. d) Glacial erosion

These landforms originate by the erosional activity of glaciers.

 

  1. An erosional landform of Karst region is:

a) Stalagmite

b) Pillar

c) Caves

d) Stalactite

Ans. c) Caves

When water percolates down, limestone gets dissolved to form caves.

 

  1. Karst topography is associated with:

a) Running water

b) Underground water

c) Glaciers

d) Winds

Ans. b) Underground water

Karst topography is developed by ground water, through the process of solution and deposition. Example: the topography developed in the limestone rocks of Karst region in Balkans.

 

  1. An important geomorphic agent that makes the features in the areas rich in calcium carbonate is:

a) Running water

b) Underground water

c) Glaciers

d) Winds

Ans. b) Underground water

Limestone with underground water makes solution and erodes them through its activity.

 

  1. Which one of the following landform is associated with the old stage of the river?

a) Gorges

b) Canyons

c) Floodplains

d) Delta

Ans. d) Delta

Delta is a triangular shaped landform made up of fine silt; it is formed in the last stage of river cycle when river is going to merge in the ocean.

 

  1. The depositional landforms consist of:

a) Levees

b) Gorge

c) River terrace

d) Valley

Ans. a) Levees

Natural levees are found along the river bank as low, linear and parallel ridges are deposited during the flooding of the same river.

 

  1. Erosion causes:

a) Changes

b) No change

c) Uplift

d) Construction of land

Ans. a) Changes

Erosion transforms surface from high to low, irregular to regular and vice-versa.

 

  1. One of the geomorphic agents is:

a) Mountains

b) Glaciers

c) Plateaus

d) Valleys

Ans. b) Glaciers

A glacier is a geomorphic agent. It forms various erosional and depositional landforms.

 

  1. The erosional landform consists of:

a) Valleys

b) Floodplains

c) Deltas

d) Alluvial fans

Ans. a) Valleys

Valleys start as small and narrow rills. They gradually develop into long and widen gullies. This further deepens widens and lengthens to give rise to a valley.

 

  1. The activity dominated by glaciers is:

a) Sheet erosion

b) Gully erosion

c) Peneplains

d) Washout plains

Ans. d) Washout plains

Washout plains are formed at the foot of the glacial mountains.

 

  1. In the humid regions which of the following geomorphic agents play an important role in the evolution of landforms?

a) Glaciers

b) Winds

c) Running water

d) Waves

Ans. c) Running water

In the humid regions running water play an important role in the evolution of landforms as these areas receive heavy rainfall.

 

  1. The controlling factor for the evolution of landforms is:

a) Atmosphere

b) Forests

c) Climate

d) Atmospheric pressure

Ans. c) Climate

Climate, tectonic stability of landmass, stability of sea level is few controlling factors for the evolution of landforms.

 

  1. Every landform passes through:

a) Three stages

b) Single stage

c) Four stages

d) Two stages

Ans. a) Three stages

Like the stages of life, a landmass also passes through three stages. They are youth, mature and old.

 

  1. A landform is a result of the:

a) Tectonic activities

b) Vegetation

c) Soil

d) Atmospheric pressure

Ans. a) Tectonic activities

Landforms are the out product of the Endogenic and Exogenic processes of earth.

 

  1. A landform is a:

a) Piece of land

b) Oceans

c) Atmosphere

d) Piece of water body

Ans. a) Piece of land

A landform may be a mountain, a valley, a plateau etc. landforms are the result of geomorphic processes.

 

  1. Erosional landforms are the:

a) Levees

b) Deltas

c) Braided channels

d) River terraces

Ans. d) River terraces

River terraces are basically products of erosion as they result due to vertical erosion by the stream into its own depositional floodplains.

 

  1. Depositional landforms are the:

a) Valleys

b) Potholes and plunge pools

c) Mushroom rocks

d) Alluvial fans

Ans. d) Alluvial fans

Alluvial fans are the result of deposition made by rivers in the foothills of the mountains.

 

  1. River terraces are formed by the streams due to:

a) Lateral erosion

b) Vertical erosion

c) Horizontal erosion

d) Slow erosion of land

Ans. Vertical erosion

River terraces are basically products of erosion as they result due to vertical erosion by the streams into its own depositional floodplains.

 

  1. Deflation and abrasion activities are associated with:

a) Waves

b) Rivers

c) Winds

d) Glaciers

Ans. c) Winds

Winds cause deflation and abrasion. Deflation includes lifting and removal of dust and smaller particles from the surface of rocks. In the transportation process sand and silt act as effective tools to abrade the land surface. The impact is simply sheer force of momentum, which occurs when sand is blown into or against a rock surface.

 

  1. In deserts, shallow lakes are called:

a) Blow outs

b) Caves

c) Deflation hollows

d) Playas

Ans. d) Playas

In deserts, shallow lakes are called playas where water is retained only for short duration due to evaporation and quite often the playas contain good deposition of salts.

 

  1. The total number of wings a seifs has is:

a) One

b) Three

c) Five

d) Six

Ans. a) One

Seif is similar to barchans with a small difference. Seif has only one wing or point. This happens when there is shift in wind conditions. The alone wing of seifs can grow very long and high.

 

  1. Cliffs, terraces, caves and stacks are the erosional landforms of:

a) Waves

b) Rivers

c) Winds

d) Glaciers

Ans. Waves

Most of the changes along the coast are accomplished by waves. When waves break, the water is thrown with great force onto the shore and simultaneously, there is a great churning of sediments on the sea bottom. Constant impact of breaking waves drastically affects the coasts. Cliffs, terraces, caves and stacks are the erosional landforms of waves.

 

  1. Important landforms associated with floodplains are:

a) Lapies

b) Point bars

c) Sinkholes

d) Caves

Ans. b) Point bars

Point bars develop where stream flow is locally reduced because of friction and reduced water depth. In a meandering stream, point bars tend to be common on the inside of a channel bend.

 

  1. Transverse dunes are aligned:

a) Horizontal to wind direction

b) Against wind direction

c) Parallel to wind direction

d) Perpendicular to wind direction

Ans. d) Perpendicular to wind direction

Transverse dunes are aligned perpendicular to wind direction. These dunes form when the wind direction is constant and the source of sand is an elongated feature at right angles to the wind.

 

  1. In the middle stages, erosion of valley sides is:

a) Vertical

b) Lateral

c) Gradual

d) Negligible

Ans. b) Lateral

In the middle stages, streams cut their beds slower and lateral erosion of valley sides becomes severe. Gradually the valley sides reduce to lower and lower slopes.

 

  1. Smooth oval shaped ridge like features composed mainly of glacial till is called:

a) Moraines

b) Outwash plains

c) Eskers

d) Drumlins

Ans. Drumlins

Drumlins are smooth oval shaped ridge like features composed mainly of glacial till with some masses of gravel and sand. The long axes of drumlins are parallel to the direction of ice movement.

 

  1. Overflow causes:

a) Sheet erosion

b) Monadnocks

c) Peneplains

d) River terraces

Ans. Sheet erosion

Sheet erosion is responsible for extensive soil erosion in both cultivated and non-cultivated environments. Sheet erosion occurs as a shallow ‘sheet’ of water flowing over the ground surface, resulting in the removal of a uniform layer of soil from the soil surface.

 

  1. Barchans are:

a) Crescent shaped dunes

b) Large holes at the bottom of waterfall

c) Bedrock without alluvial deposits

d) Plain formed due to stream erosion

Ans. a) Crescent shaped dunes

Barchans are crescent shaped dunes produced by the action of wind predominantly from one direction. One of the commonest types of dunes occurs in sandy deserts all over the world.

 

  1. Masses of moving ice as sheets on land are called:

a) Icebergs

b) Moraines

c) Debris

d) Glaciers

Ans. d) Glaciers

Glaciers form high in mountain valleys (valley glaciers) and in Polar Regions (continental glaciers) where the snow falls but never melts. The heavy snow crushes the layers below and forms a mountain of ice. As the glaciers move slowly down the mountain, it grinds against the ground and the walls of the valley to make it deep and wide. Glaciers cover about six million square miles which is about 3% of the earth’s surface.

 

  1. Stream erosion aided by the abrasion of rock fragments cause:

a) Sinkholes

b) Pediments

c) Deflation hollows

d) Potholes

Ans. d) Potholes

Over the rocky beds of hill-streams, circular depression is caused by the abrasion of rocks and pebbles to form the potholes.

 

  1. Landforms

Question Bank:

  1. Name some depositional landforms of running water.

Ans. Some depositional landforms of running water are:

a) Alluvial fans

b) Meanders

c) Flood plains

d) Natural levees

e) Point bars

f) Deltas

 

  1. Define potholes.

Ans. Over the rocky beds of hill streams more or less circular depressions called pot holes form because of stream erosion aided by the abrasion of rock fragments.

 

  1. What are continental glaciers?

Ans. Continental glacier or piedmont glacier is a vast sheet of ice and is spread over at the foot of mountains. It is found in Polar Regions of Antarctica and Greenland.

 

  1. How are Uvalas formed?

Ans. When sinkholes or swallow holes join together due to slumping of materials, along with their margins or due to the collapse of the roof in caves, they result in the formation of long and narrow trenches, known as Uvalas.

 

  1. What type of landforms dominates the eastern and western coast of India?

Ans. The western coast of India is characterised by high rocky retreating coast and hence, erosional landforms dominate the west coast. However, the eastern coast of India is a low sedimentary coast, largely dominated by depositional landforms.

 

  1. How is delta formed?

Ans. Delta is formed at a mouth of a river and is featured as a low, watery land with a triangular shape. It is formed from silt, sand and small rocks that flow downstream in the river and are deposited in the delta. These deposits are well stratified as the coarsest materials deposited; first followed by finer fractions. River distributaries increase in length as delta grows.

 

  1. What are drumlins?

Ans. Drumlins are smooth oval shaped ridge like features composed mainly of glacial till with some masses of gravel and sand. The long axes of drumlins are parallel to the direction of ice movement. They may measure up to 1 Km in length and 30 Mt or so in height.

 

  1. What are glacial troughs?

Ans. Glaciated valleys are trough like with floors and steep sides. They include debris as moraines with swampy appearance and lakes, hanging valleys on one or both sides of it. When these valleys are filled with sea water in this trough forms fiords.

 

  1. How are cirques formed?

Ans. Cirque is semi-circular hollows at the sides of a mountain. The moving ice produces a depression on the slopes of mountains. An armchair shaped basin with back wall is formed. These are known as cirques.

 

  1. What do entrenched meanders indicate?

Ans. Meander loops develop over original gentle surfaces in the initial stages of development of streams and the same loops get entrenched into rocks normally due to erosion or slow, continued uplift of the land over which they start. They give an indication on the status of original land surfaces over which streams have developed.

 

  1. Mention different types of sand dunes.

Ans. The different types of sand dunes are:

a) Barchans

b) Seif

c) Parabolic

d) Transverse

e) Longitudinal

 

  1. Underground water is more common than surface runoff in limestone areas. Why?

Ans. Underground flow of water is more common than surface runoff in limestone areas. It is because the chief constituent of limestone is calcium carbonate, which is soluble in pure water and easily soluble in carbonate water. Surface runoffs and infiltration into the ground starts the solution process along the fractures and joints.

 

  1. What is sinkhole?

Ans. A sinkhole is an opening more or less circular at the top and funnel shaped towards the bottom with sizes varying in area from a few sq. metres to a hectare and with depth from a less than half a metre to thirty meters or more. A dolines is a collapsed sinkhole. When sinkhole and do-line join together, they may become collapse valley sinks.

 

  1. Define landforms.

Ans. Small to medium tracts or parcels of the earth’s surface are called landforms. Several related landforms together make up landscapes-the larger tracts of the earth’s surface. Landforms once formed may change in their stage, size and nature slowly or quickly due to the continued action of geomorphic processes and agents.

 

  1. Explain the evolution of landforms.

Ans. Evolution of landforms involves different stages of transformation of either a part of earth’s surface from one landform into another or transformation of individual landforms after they are once formed. Each and every landmass experience some changes and development with passing time. They also have developmental stages in their life span as youth, mature and old and get changed in their shape, size and nature.

 

  1. What is the difference between gorge and canyon?

Ans. A gorge is a deep valley with very steep to straight sides and a canyon is a characterized by steep step like side slopes and may be as deep as a gorge. A gorge is almost equal in width at its top as well as its bottom. In contrast, a canyon is wider at its top than its bottom. A canyon can be termed as a variant of gorge.

 

  1. How are river terraces formed?

Ans. River terraces are surfaces marking old valley floor or flood plain levels. They may be bedrock surfaces without any alluvial cover or alluvial terraces consisting of stream deposits. They are basically products of erosion as they result due to vertical erosion by stream into own depositional flood plains. The terraces may result due to:

a) Receding water after a natural flow

b) Change in hydrological regime due to climatic changes

c) Tectonic uplift of land

d) Sea level changes in case of rivers closer to the sea.

 

  1. What are braided channels?

Ans. Channels develop braided pattern particularly in arid or semi-arid climates, where lateral erosion dominates and valleys widen. They are also found over alluvial fans and in large rivers, especially in their lower reaches. It is found when river is flowing over very gentle gradient, where the discharge is less and load is more, then bars of sand gravel develop on the floor of the channel and water is divided into multiple threads. These threads like streams of water re-join and get subdivided repeatedly to give a typical braided pattern. Eg. Brahmaputra river.

 

 

  1. How are flood plains and natural levees formed?

Ans. Flood plains: it is formed due to the river deposition. Sediments are brought down by rivers during floods, excessive water spills over banks. Then sediments get deposited along the river to form a floodplain.

Natural levees: they are found along the large bank of rivers. They are low, linear and parallel ridges of coarse deposits. They are formed when flood water reduce its velocity and deposits the sediments in the river’s immediate bank.

 

  1. What are moraines? Give their types.

Ans. Moraines are long ridges of deposits of glacial till. There are different types of moraines such as:

  1. a) Terminal moraine: it is a long ridge of debris deposited at the end of the glaciers.
  2. b) Lateral moraine: it forms along the sides parallel to the glacial valleys.
  3. c) Ground moraine: it is an irregular sheet of till left by retreating moraines.
  4. d) Medial moraines it is found in the centre of the glacial valley.

 

  1. What are eskers?

Ans. An esker is a long, narrow, steep-sided ridge composed of irregular stratified sediment deposited in contact with ice (glacial) in either an open channel or enclosed. When the glaciers melt in summer, water accumulates beneath the glaciers flows like streams beneath the ice. Very coarse material like boulders and blocks along with some rock debris carried into this stream and settle in the valley ice, beneath the glacier. After the ice melts, they can be found as a ridge.

 

  1. What are erosional landforms of winds in a desert?

Ans. Winds are one of the dominant agents of weathering in hot deserts. They move along the desert floors with great speed and obstruction in their path creates turbulence. A number of interesting landforms are created by the erosional activities of winds in deserts:

  1. a) Pediments: Gentle rocky floor at the foot of mountains with or without debris cover.
  2. b) Pediplains: Low featureless plain in deserts.
  3. c) Playas: Shallow lakes formed in the centre of a basin in desert.
  4. d) Mushroom rock: Rocks having broad upper part and narrow base resembling a mushroom shape in the desert.
  5. e) Deflation hollows: shallow depression in the bare soil or rocks, created by the continuous erosion in one direction.

 

  1. What is alluvial fan?

Ans. Alluvial fans are formed when streams flowing from higher levels break into foot slope plains of lower gradient. When coarse load, carried by streams becomes too heavy for the streams to be carried over gentler gradients and gets dumped and spread as a broad low to high cone shaped deposit called alluvial fans.

 

  1. What are barchans?

Barchans are crescent or moon shaped sand dunes formed in a perpendicular direction to the wind. The windward side is convex and gentle while the leeward side is steep. Its ends are called ‘horns’. Most of the dunes in the deserts shift and a few of them get stabilized especially near human habitation.

 

  1. How do glaciers accomplish the work of reducing high mountains into low hills and plains?

Ans. Erosion of glacier is tremendous because of the friction caused by sheer weight of the ice. The material plucked from the land by glaciers get dragged along the floor of the valley and cause great damage through abrasion and plucking. Glaciers can cause damage to un-weathered rocks and can reduce high mountains into hills and plains.

 

  1. Running water is the most dominating geomorphic agent engaged in shaping the earth’s surface in humid as well as arid climates. Explain.

Ans. In humid regions, the important components of running water, i.e., overland flow and linear flow are engaged in changing and shaping the earth’s surface as they develop a number of erosional landforms. During their youthful stage, they make V-shaped valleys, gorges and canyons. In their middle stage, they make river terraces, alluvial fans, flood plains and natural levees. They make deltas during old stage.

 

  1. Name the soil forming factors.

Ans. Five basic factors that control the formation of soil are:

a) Climate

b) Topography

c) Parent material

d) Biological activity

e) Time

 

  1. How is young soil distinguished from mature soil?

Ans. The length of time soil forming processes operate, determines maturation of soils and profile development. A soil becomes mature when all soil forming process act for a sufficiently long time developing a profile. Soils developing from recently deposited alluvium are considered young and they exhibit no horizon or poorly developed.

 

  1. How is a cliff formed?

Ans. Cliffs are formed by the processes of erosion and weathering. Weathering happens when soft rocks are hit by strong wind or sea waves. The hard racks are left behind as cliffs.

 

 

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