CHAPTER NO.3 AGENTS OF CHANGE:DENUDATION AND TRANSPORTATION

CHAPTER NO.3 AGENTS OF CHANGE:DENUDATION AND TRANSPORTATION

The structure of Earth continuously changes by both, internal forces

(volcanoes, earth quakes etc.) and external forces (weathering, erosion, levelling of Earth’ s surface etc.)

Denudation : External forces work continuously on levelling of outer surface of Earth and this activity is known as denudation. Eroded materials settle down in lower areas,leading to levelling up of earth’s surface which is techmcally known as aggredation.

When external forces erode the level of outer surface of Earth the process, is

known as degradation. When these two activities of erosion and deposition occur simultaneously, itis known as Gradation.

Denudation takes place because of heat of sun and gravitationak pull. Weather

changes because of Sun’s heat which results in the break down of rocks. Rivers flow from higher level to lower level because of gravitation. This is known as Mass Wasting.Both weathering and erosion are the tools of denudation.

Let us discuss in detail :

Weathering : Weather plays an important roles in changing the structure of Earth. It works deep beneath the Earth’s surface and also occurs over the crust of Earth and all surfaces in different forms. Actually, the breakage of rocks because of weather on the surface of Earth is known as weathering.

In other words, weathering is the breaking of rocks by static agents of weather which include rain, frost, temperature changes etc. According to B. Sparks,“Weathering is the mechanical fracturing and chemical decomposition of rocks by the natuaral agents at the surface of Earth”.

Climate of a place, composition of Rocks, Flora etc. have huge effect on the process of weathering. Humidity, rains, frost are the important elements of weather,beceause of these the breaking, fracturing, expansion and contaction (shrinking) of rocks takes place. Process of weathering may be divided into three parts :—

1. Physical Weathering/Mechanical Weathering :In this type of weathering rocks are divided/disintegrated into different parts without any chemical change that is why it is known as mechanical weathering. Three agents work on this type of activity :—

(a) Insolation : This process takes place mostly in deserts as during day

time rocks expand due to high temperature and contract during night

with fall in temperature. Repetition of this activity results in disintegration of rocks. Sometimes rocks disintegrate into small pieces, whichis known as

Granular disintegration. Although main reason for physical weathering is

heat of sun yet winds and air pressures can also cause such process.

(b) Frost-heaving : Due to heat when cracks appear on rocks, rain water is filled in those cracks. At night, water freezes because of low temperature and expands due to which breakdown of rocks starts and they disintegrate into smaller parts. Mostly this process takes place in mountainous regions. Sometime small stones comes out from soil because of frost heaving and these stones make ring like structure.

(c) Exfoliation : This activity takes place in desert areas. Rise and fall in temperature on daily basis leads to disintegration of layers of rocks and due to high speed winds these fine eroded layers get transported to far-flunged areas. This process is known

as exfoliation.

2. Chemical Weathering : In this weathering chemical structure of rock changes.Gases in Atmosphere and rain lead to disintegration of rocks which brings physical as well as chemical changes. This process is known as chemical weathering. Chemical weathering also has various types :

(a) Oxidation : In this process oxygen reacts with the iron particles present in rocks because of which ferrous (rust) is formed. Due to oxidation, rocks attain red or yellow colour. Rust leads to the disintegration of rocks in small particals.

(b) Carbonation : When regions with high lime content receive rainfall, the

carbondioxide present in water reacts with lime and carbonic acid is formed. Because of carbonic acid cracks turn into enlarged deeps on rocks and continuity of this process disintegration of rocks takes place.

(c) Hydration : In this process in which rocks having metallic content absorb water which makes structural change in type of rocks. Some rocks expand due to water absorption like Feldspar changes into Kaolin. Vindheya Mountains situated near Jabalpur are formed by this process.

(d) Solution : Some minerals are easily dissolvable in water and rock salt, silica and gypsum like soft rocks does not lose vanish by dissolving in water. Rock salt which is mostly found in desert areas, carries on its identity because of less or negligible

rainfall in desert regions. Gypsum, which is not as dissolvable as salt continues with its identity in humid regions where rock salt dissolves.

3. Biological Weathering : If activities of plants, animals and human beings result in to disintegration of rocks, weathering caused is known as biological

weathering.

(a) Plants : Plants contribute important type in physical and chemical weathering. Expansion of roots with growth of plants, leads to cracking of rocks. Further expansion results in disintegration of rocks.

(b) Bacterial Action : Decomposition of leaves and roots form organic and nitric acids which on reaction cause chemical weathering. “‘Humus’ is also formed in such process only.

(c) Weathering by Animals : Cracks appear on rocks because of ‘burrows’ of

animals. Many animals make their Funnels’ by breaking rocks. All this results in the disintegration of rocks. Common animals and insects performing such acts are; Foxes,Rats, Rabbits, Earthworms, Mites, Ants etc.

(d) Human Actions : Activities like search for minerals, construction of buildings,leveling of land for agriculture, construction of roads results in disintegration of rocks.

Deep quarrying for fulfilling need of stones is also one of the agents that causes weathering results.

Weathering effect is not same or similar for all types of rocks. Various factors

like weather, atmosphere, structure etc. affect their process.

Mass wasting is also known as slope movement or mass movement, is a process by which soil, sand and rocks move downslope. This brings change in the structure of

rocks. The structure itself indicates the change which weathering brings in parent rock.Weathering process may be quite fast on some rocks while slow on others.

Sometimes due to gravitational pull, the debris stops at higher spot on a slope.

‘Creep’ is the type when debris is creeping downslope while fall at high speed is known as ‘Fall’. Falling big parts of broken rocks are known as “Talus’ and smaller ones as *Scree’.

When these broken rocks fall at high speed, huge loss of life and property

occurs. During rainfall these activities are very commonin hilly regions. Mud flows downslopes at the speed of 80 km/hr/50 mph. This process is known as mud flow.In other words, movement of soil and regolith that more resembles fluid behaviour is called a ‘flow’.

Erosion : Word ‘erosion’ has been derived from the word ‘erodese’ of Latin

Language, which means ‘to gnaw’. In simple words, it is a process in which rivers,glaciers, winds, undergroud water removes soil and rocks from one place and transport them to another place, where they are deposited. Weathering, Erosion and Denudation are deeply related to each other and depend on each other for their accomplishment. Means of erosion perform three task i.e. Removal, Transportation and Deposition.

(i) Denudation Works of River Structure of Earth changes continously due to erosion. Water which is near omni present, plays most important role in the process of erosion, even more than air. That is why itis soimportant that at first step we should known about works of rivers.When it rains or when ice melts on mountains, some part of water seeps down into Earth and rest of it starts flowing on the Earth surface through rivers. The starting point of river is known as source and the last point of river is known as mouth. For

example, the source of nver Ganga is Gangotari Glacier (Uttarakhand) and its mouth is its deltain Bay of Bengal. This is a perennial river. Perennial rivers are those rivers which flow throughout the year and their source is ice (Glacier). On the other hand,those nvers which flow only during rainy season, are known as “seasonal rivers’. Rivers

flow from high to low altitudes and act as ‘means’ of erosion, transportation and deposition of various particles.

Source of river Beas is Beas Kund in Himachal Pradesh while mouth is Satluj river

What are the sources of rivers of Punjab. Prepare a list.

Small rivulets or streams falling in a river are known as tributaries. The drainage basin or watershed of a particular stream is whole the area that contributes overland

flow, stream flow and groundwater to that stream.

Denudational work of River :

(A) Erosion : Erosion by any river is very important aspect for mankind. Rate of erosionis higher in mountains as compared to that in plains. Rivers carry the particles/debris formed by weathering and deposit it at another place. The particles that rivers

carry are stones, rocks, sand particles etc., which help in erosional process. According to William Morris Davis the cycle of erosion is, “the period of time during which an uplifted land mass undergoes its transformation by the process of land sculpture ending

into a low featureless plain”.

1. Vertical Erosion : This is also known as downward (cutt) erosion,which results in deepening of valley.This, erosional activity 1s dominantly verticle. Rivers flow from mountains to low slopes, eroding the bed rocks

vertically. Because the flow is fast and slope (gradient) are steep, this process

goes on, till the river reaches its mouth and results in formation of *V’ shaped valleys.

2. Lateral Erosion : This is a sideway erosional process. It starts when river enters from mountains to plains. Speed of water/flow decreases and river starts “sideway’erosion and further it leads to widening of valley.

Factors controlling Erosion :

(i) Velocity of Running water : Process of erosion depends upon the velocity of

river. If the gradient 1s steep, velocity of river will be higher which leads to more erosion. In plains, the velocity of river is low, erosion is also comparatively less. There

is a law about erosional capacity of running water, if the velocity of river is doubled or multiplied by two its capacity of carrying the material rises by 64 times of its original capacity. This is known as ‘Gilbert’s sixth power law’. Erosion Capacity increases

during flooding while it lies low in dry patch of weather.

(11) Volume of water in river : Higher the volume of water in river, more will be erosion. As the volume increases the presence of rocks, stones, soil particles, debris etc. also rises. Higher volume results in deepening of river beds and broadening of

banks. All this leads to widerning of valley by eroding river bed and walls or sides of river.

(111) Load of River : If the amount of rocks, stones, soil particles 1s high in rivers, it will accelerate the process of erosion and friction.

(iv) Nature of Rocks : Erosion process on limestones and sand stones rocks is faster as these are soft rocks. On the other hand, the erosion process on Granite and Basalt is slow and tougher comparatively, these being hard rocks. Rivers carry out the process of erosion and friction on the basis of load, gradient and type of rocks.

B. Transportation : River carries rocks, stones, soil particles etc. from one place to another. This process of carrying materials is known as transportation. Basically itis

carried out in middle course of a river.

Rivers carry out debris in different ways :

(i) Traction : Large material such as boulders are rolled and pushed along the river bed by the force of river water.

(ii) Solution : Dissolved material are also carried by a river. This happens often in areas where the lime stone is dissolved by slightly acidic water. Some chemicals and salt also dissolve in river waters.

(iii) Load in suspension /Suspended load : When materials made of very fine particles such as clay and silt is lifted as the result of turbulence and transported by river.Faster flowing turbulent river carry more suspended materials, that is why rivers appear muddy.Transportation of fine material is

faster than coarse material.

(c) Deposition : This process begins when gradients are low and velocity of river water decreases. At this stage deposition of materials carried by river take place,which helps in leveling of low lying areas. The process of erosion and deposition is completed at this stage. Fast flowing rivers carry the material for longer time and distance. On the other hand, rivers which flow slow, start the deposition work on their

way. Sometimes when rivers change their directions, deposition process begins.

Parts of River and Cycle of Erosion

The erosion power of river varies from source to mouth. During this

process various landforms are formed.

Diagram showing all the parts of river is known as ‘Long Profile’.The first part is known as the Upper Course or Mountainous Course or youthful stage. Second part is known as Valley Stage or mature stage or Middle Course. Third part is known as Plain Stage or old age or Lower Course. The river course from source toits mouth is known as River Valley which may attain a depth ranging from some meters to 500 meters and even more than that.

1. The Upper Course/Mountain Course/

Youth Stage : It starts from the source of river. River flows from steep gradients to low gradients. In this part velocity of river water is high, erosion and friction power is also high. River carries the debris formed by weathering. Various stones roll on the sea bed and moreover friction between these

moving rocks results in formation of round shape rocks. Gravitational Pull and Rain water plays an important role at this part/stage of river. Rain water starts flowing downwards because of gravitational pull.Because of “down cutting’ erosion process at this stage various landforms are formed.The process of ‘land form’ formation is high in areas having soft rocks and in mountains

rocks are hard therefore down cutting is possible. Down cutting forms tight steep-side vallies and gorges.

Gorges/Canyons : Rivers like Satluj, Indus, Brahmaputra, Gandak, Kosi etc. form gorges in Himalayan mountains. In dry areas, canyons are formed by rivers. Canyons like letter ‘I’ and these are steep and narrow. Canyon made by Colorado river in U.S.A. is one of the finest examples. This is the largest canyon of world. Itis 480 kilometers long, 1828 kilometers deep and 6 to 16 kilometers wide.

(ii) V-Shaped Valley : Mostly the rivers formed ‘V’ shape valleys.Because of high rainfall, along with down cutting erosion, sides are also eroded. Due to this narrow valleys look like letter *V’ with the passage of time they become wider. We can easily understand this process from the figure.

(iii) Water Falls : River water flowing through a steep gradient area and falls from vertical gradient at high speed/velocity is known as water fall. Shiva Sundram (91 mtrs)and Jog (260 mtrs) on river Kaveri, while Dhuandhar (9 mtrs) on river Narmada are famous water falls in India. At me water from the fall lands on soft rock creating a

deep on the spot.

Do you know ?

Where are Niagara Falls and Victoria Falls are situated.

(iv) Rapids : These are the reactions of ariver where the bed has a relatively steep gradient,causing an increase in water velocity and turbulence. When a

river flows through an area of alternating bonds of resistant and

less resistant rocks, the less resistant rocks are eroded more quickly. Therefore, the soft rocks are at lower level compared to hard rocks which results in river falling in series of step along the bonds of hard rocks to form ‘rapids’. Rapids which are in a series of very short and fast falls are known as cascades. River Nile is a good example of rapid formation.

(v) Pot hole : When river flows it creates holes of various sizes. Some rocks are soft and they get eroded easily, resulting in deepening of holes. When water fills in the holes new landforms called ‘Pot holes’ are formed. They have ‘cylindrical’ shape and sometimes they look like ‘discs’. Their diameter may vary from centimeters to meters and they may be upto a few meters deep.These are considered very dangerous

because it is very hard to come out of these deeps. Because of this, these are

also known as ‘Devil Punch Bowls’.

2. The Middle Course : As river enters in plains from mountains, it starts deposition along with erosion because the volume of water 1s high but velocity decreases. This process results in formation of various landforms:

(i) Alluvial Cones : As the velocity of river decreases, its transportation capacity also decreases. Due to this decline deposition starts in Foot Hills. This deposition forms Alluvial Cones. This is the first landform/pasture which a river makes with deposition.Mostly the Alluvial Cones have stones, rocks and sand (coarse debris).

(ii) Alluvial Fans : While passing through alluvial cones, river is divided into various channels and alluvial cones convert into alluvial fans. Their size varies from some meters to various kilometers and they have semi circular shape. Cedar creek alluvial fan of

U.S.A. and Kosi Megafan are its best examples. Alluvial fan of nver Kosi 1s situated in foot hills of Himalayas and it is 151 kilometer long and 143 kilometer wide. Kosi river has recorded a continous westward shifting of around 113 KM in last 228 years.

(1) Alluvial Plains : These plains are formed by deposition of soil by rivers. Rivers bring soil particles of various rocks. With the continuous deposition of these soil particles layers are formed which further forms the fertile alluvial plains.

(iv) Natural Levees : With the continuous depositon of soil on the banks by the nver,the level of banks nses and they look like natural dams. These dams might rise upto 2 meters. Sometimes artificial Levees are also formed for the protection from floods.

(v) Flood Plains : “A flood plainis a feature of low relief build adjacent to

stream channel by the unconsolidated material derived from the related niver’’.In simple words, itis because of floods that layer of soil is depostied on the low lying areas near to the river. With the repetition of this process flood plains are formed. This process of flood plains formation is repeated annually,bi-annually or tri-annually.

3. Lower course of the river : At this stage river flows very slowly and almost there is no erosion and friction procedure. At this stage river starts deposition on its bed because of this the level of these parts rises. At this stage river meets its mouth forming

follwoing land forms :

(1) Ox-bow Lakes and Meanders : Word ‘Meander’ 1s basically related to Turkish language which means “small windling river’ . A river never flows completely straight,it flows in ‘S’ shaped (meanders). At low gradients, the deposition process is very common and width of river also increases. Due to obstacle in its way, river take turns

with which meanders are formed.

Mississippi river of U.S.A., Ganga of India and Po of Italy are famous for

“meanders” and *ox-bow’ lakes.

An Ox-bow lake is a U-shaped body of water which is formed when a river

creates a meander, due to the erosion of bank through abrasion. After a long period of time, meanders become very curved and eventually the neck of the meander becomes narrower and the river cuts through the neck during a flood, cutting of the meander and forming an ‘ox-bow lake’.

(11) Braided Stream : According to Miller, “A braided stream 1s one which does not flow in a single definite channel but rather a network of everchanging, branching and reuniting channels. At lower course, river starts depositing soil onits bed. Continuous

deposition forms soil layers. Because of this river is divided into small channels. With further deposition small ‘Bars’ or ‘Islands’ are formed which results in formation of

(i1) Delta : Greek historian ‘Herodotus’delta of river Nile (Egypt) for the first type. This delta resembles the fourth word of Greek language i.e. “A’.

When river flow reaches at its *mouth’, itis divided into various small

channels. Deltas are formed with deposition of sediments carried by a

river as the flow leaves its mouth. Its shape look like triangle *A’, that’s why

itis called “delta’.

The total area of Ganga-Brahmaputra delta is 1,25,000 sq. km. and is biggest

delta on the Earth. All the rivers of world do not form deltas because for such formation, certain necessities are there :

(i) Volume of water should be high at the first stage of river so that erosion and friction process also be high.

(i1) Some other rivers or streams i.e. tributaries should conjugate with the main niver so that amount of debris increases.

(iii) There should not be any obstacle at first stage of river like lake etc. so that river has a long bed.

(iv) Gradient should be low at last stage.

(v) Sea waves or Esturies should not act as obstacle in the natural flow and deposition process of river.

The rivers which do not form delta, they form “esturies’. This type of deltas are

formed in those rivers which have volcanic soil at its mouth. The mouth of such rivers get submerged into the sea. No river flowing to weatern coast of India forms delta.

Types of Delta :

(i) Estuary : Examples are Rhine, and Amazon rivers.

(ii) Arcurate (Fan shaped) : Examples are Nile & Niger rivers.

(ii) Cuspete (Pointed like tooth) : Examples are Ebro & Tiber rivers.

(iv) Bird’ s Foot (with fingering branches) : Examples is Mississippi river.

Activity :regions it passes through, and name its mouth also.

EXERCISE

1. Whatdo you mean by Denudation? What is the difference between Degradation

and Aggradation, explain in detail.

2. Give the answer to the following in 60-80 words.

(a) Physical weathering

(b) Oxidation

(d) Erosion

(e) Effect of human activities on weathering

(f) What do you mean by weathering ? Explain in detail.

3. Answer the following questions in a sentence or two :

(a) Whichis the largest delta of the world ?

(b) Whichis the largest canyon of the world ?

(d) What is the length and breadth of alluvial fan of river Kosi ?

(e) What is known as delta, write with example ?

4. Write the answer of the following in detail :

(a) Whatis the first stage of nver and which land forms are formed at this stage?

(b) What is the effect of river on topography during the proces of deposition?Explainin detail.

5. What is the difference between the following :

1. Waterfall - Rapids

2. Alluvial Cone - Alluvial Fan

3. Reservoir - Natural Levees

4, Flood Plains - Delta

Glaciers are the important source of denudation. If we look at history of the

Earth, we find that thousands of years ago, during Ice age, 20% part of Earth was covered by glaciers which has confined to only 10% part now. Global climate change is responsible for this. About 96% part of glaciers of the world is found in Antarctica and Greenland only. In Antarctica, thickness of glacial ice varies from 1500 meters to

4000 meters.

According to the research of NASA, the temperature of Antarctica has been

increasing by 0.12° per decade in last 50 years, owing to this, the layers of ice sheet are breaking continuously. This activity has resulted in rise of sea level by 73 meters.

Glaciers are found in mountains or near to high latitudes or at poles because

temperature at these regions is below freezing point. These regions receive snowfall continuously even in shape of snow flakes. Because of continuous snowfall and low temperature the lower layers of snow get hardened and is known as glacier.

Most of the regions in our world receive snowfall in winters. Snow melts

because of high temperature and when snow starts shifting because of rise in

temperature and melted parts start moving that is known as glacial movement.

According to Penguin Dictionary of Geography, “A glacier 1s an extensive body of land ice which exhibits evidence of downslope movement under the influence of gravity and which forms from the recrystallization of neve and firn.”. Holmes has defined glacier as “masses of ice which, under the influence of gravity, flow out

from snowfields where they originate”’. It makes clear that only a huge piece of ice/snow is not a glacier, nor is that frozen huge only which melts at increase of temperature.

Lious Agarriz proved in 1834 that the central part of glacier moves faster than its sides.

Transformation of Snow into Glacier :

At snowfall, snow is very soft single ice crystal or aggregation of ice crystals is known as snowflakes. with the continous process of combination of flakes, formation of granular snow begins. Water vapours start turning into solid form and low temperature helps in unifying of (firn) crystalized ice which further takes form of hardened snow. This is known as ice of glacier. Pores disappear at this stage and when this ice starts moving its solid form puts effect upon its speed also .

Sometimes it takes years to form of snow flakes firm and transformation of

snow into glacier may take three to five years.

The speed of glacier depends on the following aspects :

1. Bigger the size of glacier, faster it will move.

2. Glaciers may move at speed varing between some centimeters to 40 centimeters.

3. They move fast on steep gradients.

4, Their speed is high during summer.

Snow Fields and Snow Line :-Regions which are always covered by snow are known as snow fields.Glaciers start from snow fields. All the continents have snow feilds except Australia.The line above which, the rain water falls (as) in the form of snow is known as snow

line. In hot areas the height of snow line extends upto 5000 meters. In cold areas, it is even upto sea level. This line is also low in steep gradients of mountains.

Types of Glaciers :Glaciers are of various types on the bases of their size and structure. All the glaciers are divided/categorised on the bases of structure and temperature. AhImann

(1948) has divided glaciers into three categories:

1. Continental Glacier : Earlier, thousands of years back, North Europe, Asia and northern parts of America were covered long & wide by large glaciers but today their size has decreased. Presently such glaciers are found in Antarctica and Greenland.Their size is very large and they cover the whole continent. These are slow moving

glaciers.

2. Valley Glaciers : These glaciers start from snow covered mountains (ice caps).These are long but their breadth is less. These are also known as Alpine glaciers also.Because of their erosion process they create ups and downs. These type of glaciers are found in upper hills of Himalaya. The largest glacier of Indiais situated in Siachen

(72 km) in Karakoram Mountain range. Another important glacier of Indiais Gangotari (25.5 km-Uttarakhand). Valley glaciers are found in mountain valleys only. World’s largest glacier 1s situated in Alaska, i.e. ‘Hubbard Glacier’ (130 km).

3. Piedmont Glacier: Glaciers which conjugate and form a sheet like structure at the base of montains or in low lying areas are known as Piedmont glaciers. These are found at high altitudes. ‘Melaspina’ glacier of southern Alaska is the finest example of Piedmont Glacier.

Broken parts of glacier are known as ice bergs. These are formed during calving

process. Calving is a process, in which front portion of glacier (Snout) break from main glacier near the sea.

Works of Glacier : Glacier is a form of hard ice, which move and expands

continuously. It can move at speed of some centimeters in a year to 100 meters ina week. Their speed varies and it is different from each other. Some of the glaciers reach upto the sea while others melt before reaching there. Glaciers play animporant role in changing the structure of land/Earth. Glaciers also perform erosion, transportation and

deposition activities. When they move they carry stones, rocks, soil, vegetation etc.along with them. If the glacier is made up of ice only then its erosion capacity is nil. On the other hand glaciers having debris perform erosion activity more abundently. The

erosion process by glaciers is carried out in following ways :

(1) Plucking or Quarrying : This is the process in which glaciers move the rocks broken by weathering from one place to another. This activity is more vibrant at leeward slopes i.e. slopes facing away from the direction of ice movement.

(ii) Abrasion : Glaciers get power of erosion and friction when they carry debris with them. Big rocks move beneath the layers of ice and with the movement of glaciers these big rocks performs the friction acitivity on the banks and bed of valley, resulting in the increase of depth and breadth of valley.

(iii) Attrition : This is a process in which size of broken rocks decreases, because of their friction with each other or with Earth. Such frictional activity is called attrition.

Following land forms are formed due to the erosion process of

glaciers :

1. Crevasses : When a glacier moves, the speed 1s higher at central part as compared to its outer parts i.e.sides. The path on which glacier moves eroding it while moving, is known as pavement. During its movemet as glacier approaches some higher hindrance, it climbs over and then proceeds climbing down.

In this process the upper layer of glacier develops vertical cracks which expand with passage of time. Such cracks are known as Crevasses. As a glacier proceeds further average or steep slope, these crevasses enjoin each other and glacier takes smooth form. These crevasses are very dangerous for tourists, because when these are covered by fresh snow, no one can judge that they might be 2 meter broad and 50 to 200 meters deep.

2. Cirque : ‘Cirque’ is a word from French language. If pits are formed by rivers on steep gradients, their size is increased by erosion process of glaciers. Further they are filled by ice and hence known as ice reservoirs. Their shape looks like ‘resting chair’ .

These are also known as Berg-Schrund. Their size increases further because of

freezing of ‘Frost’ and Snow. Sometimes a lake is formed in the centre of cirques,known as Torn. ‘Cirque-de-Cavernic’ is the world famous cirque. In Scotland, cirques are known as ‘Corrie’, in Germany as ‘Karren’, is Norway as ‘Cron’ and in Scandenevia these are known as ‘Kessel’.

3. Horn: As ice accumulates in a cirque at a particular height and takes form of huge ice reservoir, the breadth of cirque increases because of freezing of ice, resulting in erosion of rocks which fall in its path. In such conditions, sides of central point erodes and only the central point is left uneroded, which looks like a “horn’. ‘Matter horn

Peak’ of Switzerland is the finest example of horn. When the ice of horn melts, a steep rock appears which is known as ‘Nunatak’. These forms are found in Greenland and Antarctica.

4, Col or Pass : When cirques are formed on both sides of mountain, some part of

central Ridge also falls down with passage of time forming way/path whichis known as “Pass”. In Alpas mountains various passes have been formed by glacial activity.These are used for transportation purposes. ‘Indira Col’, situated in the nothern India,

has big strategic importance for India, Pakistan, Afghanistan, Tajakistan and China.

5. Comb Ridge or Arete : When, on the both sides of ridge of the mountain, cirques have formed several horns and they look like Comb, that 1s known as Comb Ridge.Sometimes tips of high mountains also look extremely sharp and are known as Arete.

6. U-shaped Valley : When glacier moves in a pre-formed valley, the breadth of

valley increases because of the erosion by the glacier. Due to this process valley looks like the shape of Roman alphabet *U’. That is why it is known as U-shaped Valley.

7, Hanging Valley : Like rivers, glaciers too have tributaries. Main glacier increases the depth and breadth of its valley, the other glaciers moving towards this valley conjugate with main glacier, and form a steep gradient. After melting of ice, the level

of valley formed by main glacier decreases as compared to that of glacial tributaries.Tributaries conjugate with main glacier as ‘fall’. In this situation valley of tributary seems to be hanging in the valley of main glacier. Itis known as hanging valley.

8. Sheep Rocks or Roche Moutonnes : “Roche Moutonnes’ is a word of French

language which means ‘Fleecy Rock’. Sometimes there are big rock forms in the path of a moving glacier, which cannot be broken easily. Glacier moves up on this rock and with erosion and friction,decreases its height without stopping at this point. This whole process results in the leveling of the

windward side of rock and the leeward side becomes rough and steep. Due to this it looks like a sheep and is known as ‘Sheep Rock’. From a distance it looks like back of a sitting sheep.

Transportation

Glaciers carry rocks, stones, soil, vegetation etc. along with them. The erosion process of glacier depends upon the debris it is carrying. Glacier performs the task of transportation in several ways. Debris comes on the surface of glacier because of weathering. The heavy part of debris moves down through the cracks. Due to the formation of other layers of ice on the top heavy debris keeps deposited in the lower layers but it also moves with the movement of glacier while moving various types of erosion and friction process are carried out by the glacier. Glacier can move heavy rocks weighing upto several tonnes, from one place to another.Depositional work of a Glacier : As glacier melts or stops moving, it deposits the debris on the surface and its sides, which is known as glacier drift. When glacier looses

its capability of carrying ‘glacier dnift’, the debris is deposited which results in formation of various land forms :—

1. Moraines : On melting, glacier deposits its debris in the form of a

heap. Rocks deposited are not uniform, and are of several types and different colours e.g. Soft rocks, which are also known as glacier flour, triangular shaped pieces, big rocks, whose diameter varies from some centimeters to 20

meters, are found in this debris. This debris is known as Till or Morains.

Following are the types of Moraines :

(a) Lateral Moraines : When pieces of rocks are deposited on the both sides of the glacier and are sometimes higher than even 100 feet. This form is known as Lateral Moraines. The thickness of moraines in Alaska, extends upto 350 meters.

(b) Medial Moraines : When two glaciers conjugate, the moraines of their sides also conjugate forming a single moraine. Huge variation is found in the width of these moraines.

2. Esker : Sometimes, ice melts at the lower parts of the glacier and water starts flowing beneath the ice forming tunnels in the glacier. Debris gets deposited in these tunnels. With the passage of time both water and ice disappears, leaving behind the debris in the shape of long lines. This is known as ‘Esker’. Its length varies from 10

meters to 100 kilometers and their breadth also varies from some meters to kilometers.These are found in Finland, Sweden, North England and Scotland.

3. Kettle Holes : When glacier moves, pieces of rocks or stones fell on it. After sometimes with the melting of ice, small holes are formed in glacier. These holes are known as ‘Kettle Holes’. These are found in North American Prairies.

4. Kame : When glacier melts, the soil and other items of debris deposited in the cracks, get deposited in form of mound. Itis known as Kame. Examples of these are found in the parts of Scotland, Finland and Canada.

5. Outwash Plain : When a glacier passes through the ice tunnels and deposits the

sediments at a distance or in simple words when a glacier make its last moraine, the melted part of the glacier takes away light soil and deposits it in the form of layers and such deposits attain the form of plains. This is known as ‘Outwash Plain’. This particular name is given to this landform because all the material has been taken from

the last moraine. In Icelands these are known as ‘Sandur’.

Are we still living in ‘Ice Age’ or it has been finished ? (The time Period of 25 lakh years ago is accepted as “Ice age’). Presently also, the region covered with snow/ice give us the answer ‘Yes’. But if the human activities continously act as areason behind the melting of ice then definitely we will loose the glaciers. Global warming and

Green house gases are major cause of melting of ice.

In India, Himalayan mountains are house of snow. Total area of Himalayas is

5 Lakh Km? out of which 33,000K m? is covered by snow. This mountain region has 15,000 glaciers ‘Siachin’ glacier which is situated in Nurba valley, is the largest glacier (after poles). It covers the area of 450 sqaure kilometers. Gangotari glacier is the

source of river Ganga. Baltoru and Godwin Austin are also big and important glaciers.

Activity ;Write the names of seven biggest glaciers of the world and paste their pictures in your note book.

EXERCISE

1. Answer these in a sentence or two :

(a) Whichis the largest glacier in India?

(b) Whichis the largest glacier in the world ?

(d) Where is ‘Indira Pass’ situated ?

(e) What is the increase rate of temperature of Antarctica per decade ?

2. Explain the difference :—

(a) Lateral — Medial Moraines

(b) Drumlines — Esker

3. Give the answer to the following questions in detail :

(a) What is a glacier and what are its types ?

(b) Glacier is animportant source of denudation. How ?

(d) What are the landforms that take shape by erosion process of glaciers,

Explain.

iii) Denudation Works of Wind

Air moves because of atmospheric pressure and this moving air is known as

wind. Winds blows because of vanations in air pressure. Wind always blows from high pressure to low pressure. The direction from which wind is coming gives it the name of same direction. Winds perform denudation activity also but their erosion and transportation capacity is low as compared to water. They work well in dry and desert

areas. Desert areas receive rainfall less than 25 centimeters annually and have high temperature. Because of these conditions these areas do not have any vegetation and moreover there are not many obstacles in the flow of wind. Most of the deserts of the world are situated on the western side of continents (20° to 30° N & S latitudes). The south western semi-arid part of Punjab also resembles to desert region. Winds helpin

the process of denudation in desert areas generally because of following reasons :

(i) Deserts are completely different to moist regions. Chemical weathering is common in moist or wet areas but in dry areas only regional weathering is possible. ‘Salt wedging’ is one ofits example.

(ii) Desert regions which receive low rainfall and have low vegetation, help winds to carry out denudation process easily.

(iii) Large regions in deserts are impermeable because of which the underneath layer of Earth has no moisture.

(iv) Deserts which have high soil content, expand because of heavy winds and scanty rain. Their size increases continuously.

(v) Most of the rivers of such regions are seasonal or ephemeral. They flow during rainfall sessions and for short span of time. So, because of less rainfall, vegetation in desert areas is very less and winds feel free play important role in denudation process.

Only thorns and shrubs are found in desert areas.

On the basis of erosional and depositional works by winds, deserts may be classified into three types :

(1) Soil Desert : Sand in the major constituent in such deserts. Wind easily

transports sand particles. In Sahara, these are known as *Ergs’. In Turkmeinistan,these are known as *Koun’. The biggest erg is situated in Khalis, Saudi Arabia. Its area is 5,60,000 sq. km.

(2) Stony Desert : These are formed by rocks, stones etc. Reg in Algeriais its finest example.

(3) Rocky Desert : These are barren regions, where the upper soft layer vanishes,leaving behind only rock heights/rocks and barren land. Hammada (Barren Bed Rock)in Saharais its example. Its name ‘Hammada’ also originates from Sahara.

Sahara is the largest desert of world which is situated in Africa. Thar desert of India is a hot desert which includes parts of Rajasthan, Gujarat, South West Punjab and Pakistan (Punjab and Sindh). Some cold deserts are also found in Central Asia.Atacama desert of South Africa is the driest desert of world, it receives annual rainfall less than 1mm.

Wind Erosion : Like other means of denudation, winds also perform erosion and friction activity. Winds carry rock and soil particles from one place and when their speed reduces they deposit those particles. Erosion process may be divided into three stages:

1. Deflation : High speed winds pick up soil and rock particles, resulting in the decrease or shrinking of upper layers. This process is known as deflation. Sometimes due to this process hollows are formed, which are mostly small in size but their diameter

may extend from 1 to 15 kms.

2. Abrasion : High speed winds carry soil and rock particles, small pieces of rocks etcs. This debris act as ‘sand paper’ and performs erosion and friction activity on other rocks which is known as abrasion. These are also known as tools of wind.

3. Attrition : Sand particles carried by winds, start friction process with in itself and because of this their size reduces. This is known as attrition. Erosion process of high speed winds is also fast.Soft rocks break down easily but on the other hand erosional process is long in case of hard rocks. Small particles are transported upto long distances but big rocks and stones (of 5 to 8 centimeter radius) cover only small distance. Wind erosion results in

the formation of various land forms, which are as follows :

1. Oasis : During deflation the upper layers of stones are eroded by high speed winds and rocks having water appear on the surface. Because of this underground water oozes out (comes out) which is known as Oasis. Any type of vegetation and human life is possible around oasis. These landforms are found in desert regions of Algeria, Libya

and Thar in India.

2. Needles : Complete to erosion of soft rocks by high speed winds allows steep

gradient rocks stand uneroded and still. They look like needles and therefore known as rocky Needles.

3. Mushroom or Pedstal rocks : Wind erosion takes place at the average height of 1 meter from the Earth’ s surface. While above height of average 2 meters,erosional process is again very low.Resultently middle portion of vertical rocks is eroded by high speed winds and after erosion rocks look like

mushrooms. In Sahara desert such land forms are known as ‘Gaur’ and in Germany these are known = as

Pitzfelsen’. In India, these are found in ‘North-West’ Jaisalmer (Rajasthan)

generally.

4. Zeugen : *Zeugen’ is a word from German language which means “Like Table’.When soft rocks covered by hard rocks are eroded by winds, hard rocks left behind looks like table and known as *Zeugen’. Their length may vary from 1 meter to 30 meters. Along with winds, rainfall and weathering also help in formation of *“Zeugen’.

5. Yardangs : Winds blowing continuously in one direction result in the erosion of zeugen in one direction/side only. Zeugens are eroded much from winward side and less from leeward side. This process forms a very queer structure of these rocks.The ratio of these structures (length and breadth) varies from 3:1 and 4:1 and average height is around 8 meters.In India such landforms are found in Jaisalmer (Rajasthan).

6. Stone Lattice : At times rocks are formed by the combination of both

soft and hard types of stones. Soft rocks and soft parts of such formations get eroded by winds and only hard parts are left behind which make formations look like ‘net’.These are known as Stone Lattice.

7. Driekanter : The direction of winds is never fixed and in the absence of vegetation in adesert, various rocks get eroded continuously in the direction of wind. With such continuous and all directional erosion, rocks attain a triangular shape and these are

known as Driekanter.

8. Window & Bridge : Continuous erosion by high velocity winds forms

holes in the rocks. Such holes are called Wind Windows. Further, the combined action of deflation and abrasion makes the wind windows larger and wider which assumes an arch like shape with solid roof over them. Such land forms are called Wind Bridges.

9. Demoislle : Some hard rocks are wrapped all round by soft rocks. With the continuous wind erosion soft rocks get vanished leaving behind the hard rock, which looks like a pillar. This pillar formation is known as Dermoislle.

10. Lag Deposits : Fast blowing wind carries lighter particles like sand, small pebbles and stones with it. While heavier stones and other big particles lag behind. These particles look like a layer of heavy stones and rubble. Such layers are very commonin desert regions. In Sahara desert such lag deposits are known as ‘Hamada’ in local language.

11. Inselberg : Wind erosion makes desert appear/look like plain but at some places some small mountains of solid rocks are found. These mountains are kwnon as Inselbergs. Mt. Aabu (Graynite Inselberg) and Sendra near Pali are the finest examples.

Transportation by Winds : Wind transports pieces of rocks, soil, stones etc., like rivers and glaciers, from one place to another. Although winds erosion is less effective as compare to that by rivers but it may be seen clearly in deserts. Transportation of particles takes place in different ways. High velocity winds can transport heavy debris from one place to another but on the other hand slow speed winds transport light weight particles only. Sometimes heavy and large pieces of rocks are not picked by winds but they roll on ground along the wind direction.

A dust storm having diameter of 500 km can pick up 100 million (10 Crore)

tons of soil. It has a capacity of forming a 30 meters high mountain with a base of 3 kilometers. Delhi experienced a dust storm on November 14, 2014. Its speed was 90mph and resulted in loss of life and property. Thick dust storms in Thar, sometimes reduce the visibility to hardly three feet and the particles being transported by such storms cause heavy losses also. The size of particles moving with high vilocity winds

decreases because of friction produced in itself. When the speed of wind decreases,debris starts depositing.

Shifting of Sand Dunes : Direction of wind is not fixed because of this sand dunes are not stable, they shift according to the direction of wind. Shifting sand dunes is harmful

for fertile plains. Fast growing and deep root plants are planted in desert regions to control this process. They may shift from 5 to 30 meters per year.

Depositional Work of Wind : Deposition work of wind may be divided into two parts namely :

1. Sand Deposition and

2. Clay Deposition.

(1) Sand Deposition : Following landforms comeup under this head :—

(a) Ripples : Low speed winds deposit the particles in the shape of waves, which are known as layers of sands or sand ripples.The inter-difference between these waves may vary from few centimeters to few meters. The windward side of Ripples is generally angular at 8° to 10° while leeward side is angular at 20° to 30°. Their height rises to a few centimeters only.

(b) Sand Dunes : Velocity of wind carrying sand decreases when it faces

some obstacle and therefore wind it starts depositing the sand particles on the spot of obstacle only. Resulting in the formation of sand dunes. Any shrub, big rock, skeleton of an animal, upland area can act as such obstacle. The height of sand dunes may vary from some meters to 150 meters and their length may vary between 3 kilometers to 150 kilometers. Sand dunes may be of

many types :—

(1) Barkhan : Half moon and crescent shaped sand dunes are known as Barkhans.

These are convex on windward side and steeper and concave on leeward side. They might be high upto 30 meters and their length varies from 150 meters to 200 meters.

(ii) Seif or Longitudinal Sand Dunes : Seif is an Arabic word which means ‘Sword’.These sand dunes are generally oriented in a direction parallel to prevailing wind but when the dunes blow out, sand gets deposited in parallel forms. These may raise to 100 meter high and their breadth varies from 500 to 600 meters. These are not shifting sand

dunes. These are found in areas where high velocity winds blow. These are foundin Sahara Desert (Africa), Thar Desert (India).

(iii) Coastal Dunes : High velocity winds blow in coastal areas because of this, waves deposit sand on the coasts of oceans. Blowing wind gives it a form of “Sand Dune’.With the growth of vegetation in these areas, curved sand dunes are formed and sometimes they also look like Barkhans. These are found in Atlantic coastal regions. In Southern France, there is 240 kilometers long dune along the coast covering 3 to 10

kilometers in inland areas. On the Western coast of India, sand dunes (coastal areas) of Goa are famous for their beauty.

2. Loess Plains : Winds deposit light and soft soil over a large area like a blanket,these are known as plains of Loess. ‘Loess’ is a word of German language which means yellow colour, porous soil with very soft particles. Generally, these particles are

of same size.This soil does not have layers and itis frable. When we press it crumbles easily. During rainfall it becomes very sticky, on the other hand in summer it becomes very dry. Loess is found in China, Europe, North America, South America and Africa.The name “Yellow river’ in Chinais also given on the basis of their soil because when

it mixes with river water, water appears to be yellow in colour.

Wheat and Maize is grown in Loess plains and more over soil erosion is also very (low/less) in these plains. In India this soilis found in Kashmir andin Pakistan itis found in

Potwar plateau.

Activity :

Show the ‘Thar Desert’ in the map of India

Make a model of Landform that is made by winds.

EXERCISE

1. Answer the following in few words only :

(a) Whichis the largest desert of world ?

(b) How many types of deserts are there ? Wnite their name also?

(d) Are the sand dunes always stable ?

(e) Whiatis the colour of Loess soil and which crops are grown in this soil?

(f) Whiatis the difference between air and wind ?

(g) What do you mean by porous rocks ?

(h) How the coastal sand dunes are formed ?

2. What is the difference between the following :

(a) Barkhan — Loess

(b) Stone Lattice — — Driekanter

(d) Oasis — __Inselberg

(e) Rockydesert — Stony desert

3. Write the answer of the following in 100 words :

(a) Winds are the source of erosion in deserts, Explain.

(b) Which are the landforms that are made by soils during erosion process ?

Explain.

(iv) Denudation works of Underground Water

Water plays an important role in changing shapes over the land although. Its amount is not uniform at all places. At some places it is found an abundance and at other its quantity is very small. When Surface water seeps into Earth through porus rocks, itis known as underground water. Although flow of underground water is similar

to that of overground water yet, the speed of flow of underground water is too less and because of this its geographical weathering activity is also low while chemical weathering activity is high. Moreover, clean water does not involve in any activity but while seving into Earth various chemicals get mixed init. We find the work of underground water in the regions with rich chalk, Limestone and Dolomite contents.

A geographical distribution of the location of water on earth :Works of underground water are not much visible on the upper layer of Earth.Mankind extracts it out to fulfill their various needs. e.g. Agricultural and house hold,

etc. Sometimes it naturally comes out from Earth through natural openings like springs,wells, Geysers, etc.

[fin any region, rainfall is high and rate of evaporation is low then the level of underground water will be high.

(A) Springs : When the water oozes out naturally from Earth1.e. on the upper and outer most surface, that flow is known as ‘spring’. Mostly springs are found at the junction or fissures and joints of Porus and Nonporus rocks. In India these are found inhilly regions of Jammu Kashmir, Manikaran (Himachal Pradesh), Bihar and Assam.

There are various kinds of springs :

(i) Hot water spring / Thermal water spring : These springs have hot water and are found in volconic regions. In Himachal Pradesh, langar is cooked with the help of heat generated by such springs at Manikaran Sahib.Indiais planning to install its first geothermal plant, which will produce power upto

3to5 MW.

(ii) Cold Water Springs : These springs provide cold water and are mainly found in Himalayas, Western Ghats and Mountains of Chhota Nagpur Plateau.

(11) Mineral Springs : These springs have mineral and salts in their water. These are very helpful in the treatment of skin discases. Such springs are found in Manikaran,Manali (District Kullu), Sahashtradhara (Dehradun), Tilsma Rajasthan when water flows continuously from a spring, itis known as Permanent spring.

(iv) Geysers : When lots of steam oozes out as fountain alongwith hot water, such form is known as geyser. These might raise 30 to 60 meters high. The old faithful geysers of Yellow Stone National Park, Situated in Rocky Mountains of USA, comes active for four minutes after sleeping for 65 minutes at average. Iceland, parts of Rocky

Mountains of USA, North Island of Newzealand and Yellow stone park of wayoming state in USA are known for Geysers and Hot water springs. Total number of geysers in the world is 425 and out of these, 225 are situated in Yellow Stone Park of (USA America) This region has 24000 springs of hot water and around 100 geysers.Some Geysers continuously ooze out on the Earth’s surface and their temperature is 100°C (or 212°F). Some Geysers collect very less debris and some of them make acone like nozzle. Most of the Geysers spread mineral deposits on the area around

them.

(B) Well : When underground water flows beneath the surface through a hole, that

is known as ‘well’. If the well is not deep then the water does not come out

continuously and that is known as “Intermittent well’

(C) Aquifer : This is a word of Latin language which means ‘to bear water’. An underground permeable rock is present which contains water and = an impremeable rock is situated below the permeable rock, thus a reserviour of underground water is created. “Aquifer” is a natural filter which purifies various types of sediments and bacteria. ‘Aquifers’ get pollutedif waste material is thrown in them and moreover septic tanks, medical waste (Injections, Medicine), Fertilizers etc. also create problems if constructed or piled near the aquifers.

(D) Artesian Well : The word Artesian has been derived from the word * Artois’,which was the name of a province of France where first Artesian well on the Earth was dug in 1126. Itis a limited Aquifer in which water comes out through well because of pressure even without using a pump. Great Artesian basin is the world’s largest and

deepest Artesian basin, which extends over 23% part of Australian continent. Australia has 9000 Artesian wells, maximum in the world. In India these are found in Indora Tehsil of District Kangra (HP), Mukenan Tehsil of District Hoshiarpur (Punjab), Tarai,Pudduchery, Tamilnadu, Alluvial soil areas of Gujrat etc.Underground water as an agent of denudation Underground water also performs erosion, transportation and deposition activities.The speed of underground water is very low. If “KM/Hr’ unit is used for speed of river

then ‘meter per day’ is used for underground water. Because of this its activities may be seen only in regions having soft rocks or regions with Limestone, Dolomite etc. As

topography, underground water forms “Karst topography’ in areas which have

limestones. In India this is found in Chirapoonji, Jammu-Kashmir, Himachal Pradesh,Panch Marhi (M.P.), Bastar (Chattisgarh and Coastal areas near Vishakhapatnam.

Karst means barren land. This word has been derived from Kars or Kua, which

is a plateau region situated in Slovenia (former Y ogoslavia).‘Karst topography’ is also found in the areas having Dolomite, Gypsum or Halite,(Rock-salt).

Following land forms are formed by denudation activity of underground water :

1. Lapies : In German language these are known as *Karren’ and in English these are

known as ‘clint’ while Lapies is a french word. When underground water contains Carbondi oxide init, dissolving process of ‘lime stone’ rocks begins. Because of this breadth of cracks and joints increases, which are known as “Lapies’.

2. Sink holes : Sometimes Lapies gets deep like funnel forming a sink hole. Its depth may vary from a few centimeters to some meters.

3. Swallow holes : When the size of sink holes increases, these are called swallow holes.

4. Doline : Due to high chemcial activity on swallow holes, their size and depth increases. Its diameter may extend upto some kilometers and depth may run upto 100 meters. Mostly such forms are found in tropical regions.

5. Karst Lakes : When the lower part of Dolite is blocked because of debris formed by its own erosion, water gets collected as reservoir. This is known as ‘Karst Lake’.

6. Uvalas : A reservoir is formed with the conjugation of many sink holes. This is known an Uvala.

7. Ponar : When Uvalas are filled with water, high erosion activity converts it into a tunnel like structure, which is known as ponar.

8. Caverns : In lime stone regions the flow of rivers are not outwards but is inwards.it dissolves its own bed and forms a large cave called ‘cavern’. The roofs of such structures are called Chambers. In India these are found in Chattisgarh and Chirapoonji.

9. Natural bridge : When roofs of caverns collapse, some of its parts are left behind,which look like a bridge. This is called natural bridge.

Depositional work of Underground Water :

Underground water dissolves the rocks but when it deposits this dissolved materials various types of forms are created :-

1. Stalactite and Stalagmite : These are fromed in a region nch with lime stone,

where caverns have been formed. Lime water seeps down-ward from these caverns

during this activity some of drops hang with the ceiling of cavern. Due to evoporation,water gets evaporated and the hanging structure of lime is left, which is known as *stalactite’. Its breadth is more near the ceiling as compared to its tip.The drops of lime water which fell on ground, get evaporated and only a structure

made of lime is left behind. This is known as ‘Stalagmite’. Its width on the ground iS More as compare to its tip. Sometimes both stalactite and stalagmite combine to form a pillar which gives an impression of acavern on the whole. “Zenolan lane’ in Sydney (Australia) is its fine example whichis around 100 kms deep. Another natural cave or cavernis at Tirlokpur falling on Pathankot-Dharmshala Highway, which is thousands

of years old.China, India and USA are top three nations which use underground water for agriculture the most. Central Ground Water B oard, established in 1970, has carried out 21 pilot projects to recharge the underground water artifically in Amritsar,Jalandhar, Patiala and Sangrur districts of Punjab.

Underground water is very important and it must be used properly. In Punjab the level of underground water is decreasing day by day (continuously). Its level is extremely down in 85% part of the state. Low rainfall is one of the pn mary reaons behind the situation. Annual average rainfall has been decreased upto 45-50%. Annual rainfallin 1990 was 755 mm. which has come down to 375 mm in year 2004. In 2009 it was 420 mm and in 2014 it was recorded 600 mm.Cultivation of ‘Rice’ is another reason. Rice is planted on 2/3 part of Punjab before

June 15 ever year, which increases the need of irrigation and moreover during this period evaporation is also fast due to hot weather. In these conditions underground water is used to fulfill the requirement of water, Around 73% Irrigation depends on the underground water and all this has resulted in banning of use of underground water

at a few places. Hence it is our duty to use underground water properly.ctivity ; What can we do to save underground water for our future generation’Discuss this in the your class with the help of your teacher and also collect the information about the number of wells and tubewells in your area.

EXERCISE

1. Give the answer to the following questions in one or two words :

(a) In which State of France, first ever Artesian well was dug ?

(b) Write the names of hot water springs of Kullu Valley.

(d) At which places of India, cold water springs are found ?

(e) What was the Annual/Monsoon rainfall of Punab in 2014?

2. Write the answer of the following questions in detail :-

(a) Underground water is a source of denudation, How? Write in detail.

(b) What is the depositional process of underground water and what landforms

are created by this process ? Explain with [Hustrations.

3. What is the difference between the following :

a. Lapies - Doliane

b. Stalactite - Stalagmite

c. Well - Artesian Well

d. Geyser - Spring

(4) Denudation Works of Sea

Like river water, sea water also performs denudation acitivity in the form of waves, currents and tides. Because of this various landforms are formed but obviously this process takes place only in coastal regions. Coastal regions are totally different to

non-coastal regions.

The speed and velocity of waves depends on the speed of winds. Sea water

rises because of direction, pressure and friction of winds. The part of water, which rises is ‘crest’ and the lower one 1s known as ‘trough’. Rocks, stones, sand, soil etc., present in high speed waves increase the erosion capacity of waves. Sea water also performs erosion, transportation and deposition activities.

Coastline is a place where Hydrosphere, Lithosphere and Atmosphere meet.

Erosional work of Sea Waves: Erosional work depends on the speed and power of

waves, gradient and height of the coast and moreover depth of sea. Erosion process 1s not uniform at all the places.

Erosion of hard rocks is slow but incase of soft rocks it is very fast. During

rainfall water level increases which accelerates erosion. Plants and animals reduce the strength of rocks by making holes in them. Presence of sand, soil, rocks, stones etc. in waves increases the erosion. Any hindrance in the way of waves gives it the name as ‘braker waves’. A number of braker waves when flow towards coast, these are known

as ‘surfing waves’. At times the “might” of these surfing waves 1s to such an extent that these exert a presence of 3000 kilometers per square meter to 30,000 km per sq.meter on the costal rocks.

Waves can perform erosion activity in four ways :

(a) Hydraulic Action: Rocks are broken when waves having debris (rocks, soil, sand,stones etc.) strike with huge force.

(b) Abrasion: When both waves and currents break the rocks this happens when waves strike with rocks again and again. It is a frictional force and known as abrasion.

(c) Attrition: It 1s because of waves, when the size of pieces of rocks decreases or they are grained, this process is known as Attrition.

(d) Solution: Soluble rocks like limestone, dolomite, chalk etc. dissolve in sea water.This solvent action is limited to certain areas only.

When a wave strikes it starts erosion process, resulting in the formation of following forms:

1. Sea Cliff: Waves erode the lower part of the coastal rocks, first because these are at sea level. Sometimes the lower parts of rocks are soft and get easily eroded. The upper part of these rocks look ‘high’, whichis known as cliff. It has a steep gradient.

Sometimes waves make a hole in lower part of the cliff with erosion activity, know as *notch’. The size of notch increases with the passage of me and seacaves are formed.

Cliffs situated on the western coast of India are the finest examples.

2. Sea Caves: With the passage of time, size of ‘Notch’ increases due to erosion and a large pitis formed in the lower part of cliff. This is known as seacave.

3. Arch or Natural Bridges: If at any coast, Waves strike on both sides of caves and form a hole, such structure is known as sea arch, moreover it looks like a natural bridge.

4. Stack: Natural arch collapses due to erosion, leaving steep and often vertical columns of rock, whichis known as ‘stack’.

5. Stumps: When stacks get eroded by the waves, they collapses, leaving behind a

stump. Stump usually forms a small rockisland, low enough for a big tide to submerge.

6. Spouting horns or Blow holes: Due to erosion, the cracks of seacaves form a

hole in the roof of the cave, whichis known as spouting horn or blow hole. Actually when the water rises into sea cave, already available air starts dashing out through the hole incave roof, creating whistling sound. This sound gives it the name, Spouting horn

7. Breaking of Sea caves: When high speed waves strike with huge force on cave,they create pressure on the internal air upto such extent that cave break down into pieces. Inspite of this sometimes large number of blow holes are formed in caves because of which it losses its strength and collapses. With the break down of cave a narrow inlet

is formed whichis known as ‘geo’.

8. Caves: Sometimes on the coast, soft and hard rocks are situated parallel to each other. When soft rocks are eroded faster with the hard rocks surrounding them, small gulfs are formed which are known as caves.

9. Creeks and Bays: When soft and hard rocks are situated in vertical positionand continous erosion by waves erodes soft part of these rocks resulting in formation of deep and narrow inlets known as ‘creek’. With the passage of time their depth and breadth increases whichis known as “Bay”.

10. Headland or Cape: Sometimes a hard rock is surrounded by soft rocks and

erosional activity of waves leaves only hard rock standing vertically ahead of it surrounding. Such form is known as headland or cape.

Transportation by Sea Waves :

Waves pick up the rocks, stones, soil etc. formed by the process of weathering and bring them in sea water. High speed waves bring shells and other materials on the coast, people collect these for manufacturing of material used for decoration purposes.

Shells are direct source of Calcium Carbonate and it is used for increasing the level of calcium in the soil, manufacturing of musical instruments, poultry feed and for making ornamens.

Depositional work : While transporting the debris, as carrying capacity of waves reduces, debris is deposited on the coast. Because of which various forms take shape.

1. Sea Beach : Beaches are formed by deposition of soil, rocks, stones etc. on the coast by sea wavess. The size of a beach depends upon the debris deposited, more the debris, larger will be the beach. Beaches may be of various types. life curp beach,Gokarna and Kovalam, Linear Beaches, Marina beach Chennai, Rock beaches and Sand beaches. Marina beach is second longest beach in the world. Beach formation is possible during low velocity of waves or swift moving wave or thunder storms destroy

beach deposits.

2. Sandbar : Sand bars are formed if sand gets deposited parallel to the waves. These are extended parallel on the front side of the hard rocks near the coast. When its size increases it is called as offshore or longshore sandbar. Sometimes gulf is blocked due to the huge deposition of soil, offshore bars which act or blockers, get combined with

each other and are known as Tied Island. The Islands also have various types e.g. Bay bar, Tombolo, Hook, Loop etc.

3. Spit : Deposition of sand and rocks at some distance from sea coast is known as spit. According to O.F. Evans, (1942), as pitis a “Ridge of embankment of sediment attached to land at one end and terminating in open at other’Spits are commonly found on the eastern and western coast of India. Around 50 KM

long spit is situated on the mouth of Chilka lake and 60 KM long spit is situated in the east of Policot lake. When two spits conjine, it is known as “Looped bar’.

4. Lagoon : Water collected between the sand bar and coast is known as Lagoon.

These are very commonin low coasts. “Chilka’ on the easter coast and *Vembanad’situated on the coast of Kerala are the important examples of ‘lagoons’

5. Dunes : Sand dunes are also get formed in coastal areas. Waves deposit the sand and winds transport this sand and deposit it at another place because of which sand dunes are formed. Such sand dunes are found on eastern and western coasts of India.Sea waters carry unimaginable energy. Various land forms of the eastern and western coasts of India, formed by Oceanic waters are its biggest example. Total length of

Indian coast is 7,516.6 kilometers, including Andeman and Nicobar (Bay of Bengal)and Lakshdweep (Arabian Sea).

EXERCISE

1. Give the answer to the following questions in one or two words :

(a) What are the higher parts of waves known as?

(b) Whatis the length of Indian coast?

(d) Whatis the name of formation developed as conjugation of two spits ?

2. Write a note on the following :

(a) Spit (b) Sea Beach

(e) What is the difference between the following :

1. Crest - Trough

2. Sandbar-Lagoon

3. Give the answer to the following questions in detail :

(a) Explain Erosional of work of sea and which land forms are created by such

erosion ?

more erosion. In plains, the velocity of river is low, erosion is also comparatively less. There

during flooding while it lies low in dry patch of weather.

banks. All this leads to widerning of valley by eroding river bed and walls or sides of river.

(111) Load of River : If the amount of rocks, stones, soil particles 1s high in rivers, it will accelerate the process of erosion and friction.

B. Transportation : River carries rocks, stones, soil particles etc. from one place to another. This process of carrying materials is known as transportation. Basically itis

carried out in middle course of a river.

Rivers carry out debris in different ways :

(i) Traction : Large material such as boulders are rolled and pushed along the river bed by the force of river water.

faster than coarse material.

way. Sometimes when rivers change their directions, deposition process begins.

Parts of River and Cycle of Erosion

The erosion power of river varies from source to mouth. During this

process various landforms are formed.

1. The Upper Course/Mountain Course/

rocks are hard therefore down cutting is possible. Down cutting forms tight steep-side vallies and gorges.

deep on the spot.Do you know ?

Where are Niagara Falls and Victoria Falls are situated.

(iv) Rapids : These are the reactions of ariver where the bed has a relatively steep gradient,causing an increase in water velocity and turbulence. When a

river flows through an area of alternating bonds of resistant and

because it is very hard to come out of

these deeps. Because of this, these are

also known as ‘Devil Punch Bowls’.

(v) Flood Plains : “A flood plainis a feature of low relief build adjacent to

follwoing land forms :

with which meanders are formed.

Mississippi river of U.S.A., Ganga of India and Po of Italy are famous for

“meanders” and *ox-bow’ lakes.

An Ox-bow lake is a U-shaped body of water which is formed when a river

deposition forms soil layers. Because of this river is divided into small channels. With further deposition small ‘Bars’ or ‘Islands’ are formed which results in formation of

(i1) Delta : Greek historian ‘Herodotus’delta of river Nile (Egypt) for the first type. This delta resembles the fourth word of Greek language i.e. “A’.

When river flow reaches at its *mouth’, itis divided into various small

channels. Deltas are formed with deposition of sediments carried by a

river as the flow leaves its mouth. Its shape look like triangle *A’, that’s why

itis called “delta’.

The total area of Ganga-Brahmaputra delta is 1,25,000 sq. km. and is biggest

delta on the Earth. All the rivers of world do not form deltas because for such formation, certain necessities are there :

(i) Volume of water should be high at the first stage of river so that erosion and friction process also be high.

(i1) Some other rivers or streams i.e. tributaries should conjugate with the main niver so that amount of debris increases.

(iii) There should not be any obstacle at first stage of river like lake etc. so that river has a long bed.

(iv) Gradient should be low at last stage.

(v) Sea waves or Esturies should not act as obstacle in the natural flow and deposition process of river.

The rivers which do not form delta, they form “esturies’. This type of deltas are

formed in those rivers which have volcanic soil at its mouth. The mouth of such rivers get submerged into the sea. No river flowing to weatern coast of India forms delta.

Types of Delta :

(i) Estuary : Examples are Rhine, and Amazon rivers.

(ii) Arcurate (Fan shaped) : Examples are Nile & Niger rivers.

(ii) Cuspete (Pointed like tooth) : Examples are Ebro & Tiber rivers.

(iv) Bird’ s Foot (with fingering branches) : Examples is Mississippi river.

Activity :regions it passes through, and name its mouth also.

EXERCISE

1. Whatdo you mean by Denudation? What is the difference between Degradation

and Aggradation, explain in detail.

2. Give the answer to the following in 60-80 words.

(a) Physical weathering

(b) Oxidation