Class 11th

Notes of Ch 7 Natural Hazards and Disasters| Class 11th Geography

What is Disaster?

• “Disaster is an undesirable occurrence resulting from forces that are largely outside human control, strikes quickly with little or no warning, which causes or threatens serious disruption of life and property including death and injury to a large number of people, and requires therefore, mobilisation of efforts in excess of that which are normally provided by statutory emergency services”.

• For long time, disasters were considered as consequences of natural forces; and human beings were treated as innocent and helpless victims in front of the mighty forces of nature.

• However natural forces are not only the causes of disasters, but also they can be caused by human activities. There are some other activities of human begings that accelerate or intensityt disasters indirectly.Landslides and floods due to deforestation.The best way out is to emphasise on natural disaster mitigation and management.

Difference between Disaster and Natural Hazard

• Natural hazards are elements of circumstances in the natural environment that have the potential to cause harm to people or property or both.These may be swift or permanent aspects of the respective environmental setting like currents in the oceans.

• As compared to natural hazards, disasters, which are caused by natural forces or activities of human beings, are relatively sudden and cause large scale, widespread death, loss of property and disturbance to social life.

• Natural hazards may be swift or permanent aspects of the respective environmental settings like currents in the ocean , steep slope and unstable structural features in the Himalayas or extreme climatic conditions in deserts or glaciated areas.

• Any event can be classed as disaster when the magnitude of destruction and damage caused by it is very high. Every disaster is unique in terms of the local socio-economic factors that control it, the social response it generates and the way each social group negotiates with it.

Facts about Disaster

• Firstly, the magnitude, intensity, frequency and damages caused by natural disasters have Increased over the years.

• Secondly, there is a growing concern among people the world over to deal with the menace created by these so that the loss of human life and property can be minimised.

• Finally, significant changes have taken place in the pattern of natural disasters over the years.

Modern changes in perception of natural disasters and hazards

• There has also been a change in the perception of natural disasters and hazards.

• Previously hazards and disasters were seen as two closely associated and interrelated phenomena i.e. areas prone to natural hazards, were more vulnerable to disasters. Hence people avoided intensification of their activities in such areas and that is how disasters were less damaging.

• Technological power has given large capacity to human intervention in nature.

• Consequently, now, human beings tend to intensify their activities into disaster prone areas increasing their vulnerability to disasters.

Yokohama Strategy and Plan of Action for a Safer World

• All the member states of the United Nations and other states met at the World Conference on Natural Disaster Reduction in the city of Yokohama from May 23rd-27th 1994.

• The resolution of the World Conference on Natural Disasters Reduction is as mentioned below:

(i) It will note that each country has the sovereign responsibility to protect its citizens from natural disasters;

(ii) It will give priority attention to the developing countries, particularly the least developed, land-locked countries and small-island developing states;

(iii) It will develop and strengthen national capacities and capabilities and, where appropriate, national legislation for natural and other disaster prevention, mitigation and preparedness, including the mobilisation of non-governmental organisations and participation of local communities;

(iv) It will promote and strengthen sub-regional, regional and international cooperation in activities to prevent, reduce and mitigate natural and other disasters, with particular emphasis on:
(a) human and institutional capacity-building and strengthening;
(b) technology sharing: the collection, the dissemination and utilisation of information; and
(c) mobilisation of resources.

• It also declared the decade 1990-2000 as the International Decade for Natural Disaster.

Natural Disasters And Hazards In India

Earthquakes

• Earthquakes are by far the most unpredictable and highly destructive of all the natural disasters.

• Earthquakes that are of tectonic origin have proved to be the most devastating and their area of influence is also quite large.

• These earthquakes result from a series of earth movements brought about by a sudden release of energy during the tectonic activities in the earth‘s crust.

• As compared to these, the eart hquakes ass oci at ed with volcanic eruption, rock fall, landslides, subsidence, particularly in the mining areas, impounding of dams and reservoirs, etc. have limited area of influence and the scale of damage.

• The Indian plate is moving at a speed of one centimetre per year towards the north and northeastern direction and this movement of plates is being constantly obstructed by the Eurasian plate from the north.

• As a result of this, both the plates are said to be locked with each other resulting in accumulation of energy at different points of time.

• Excessive accumulation of energy results in building up of stress, which ultimately leads to the breaking up of the lock and the sudden release of energy causes earthquakes along the Himalayan arch.

• Some of the most vulnerable states are Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Sikkim, and the Darjiling and subdivision of West Bengal and all the seven states of the northeast.

• Recently, some earth scientists have come up with a theory of emergence of a fault line and energy build-up along the fault line represented by the river Bhima (Krishna) near Latur and Osmanabad (Maharashtra) and the possible breaking down of the Indian plate.

• National Geophysical Laboratory, Geological Survey of India, Department of Meteorology, Government of India, along with the recently formed National Institute of Disaster Management, following five earthquake zones:
→ Very high damage risk zone
→ High damage risk zone
→ Moderate damage risk zone
→ Low damage risk zone
→ Very low damage risk zone.

• North-east states, areas to the north of Darbhanga and Araria along the Indo-Nepal border in Bihar, Uttarakhand, Western Himachal Pradesh (around Dharamshala) are in Very high damage risk zone.

• The remaining parts of Jammu and Kashmir, Himachal Pradesh, Northern parts of Punjab, Eastern parts of Haryana, Delhi, Western Uttar Pradesh, and Northern Bihar fall under the High Damage Risk Zone.

• Remaining parts of the country fall under moderate to very Low Damage Risk Zone. Most of the areas that can be considered safe are from the stable landmass covered under the Deccan plateau.

Socio-Environmental Consequences of Earthquakes

• It becomes a calamity when it strikes the areas of high density of population.

• It not only damages and destroys the settlements, infrastructure, transport and communication network, industries and other developmental activities but also robs the population of their material and socio-cultural gains that they have preserved over generations.

• It renders them homeless, which puts an extra-pressure and stress, particularly on the weak economy of the developing countries.

Effects of Earthquakes

On Ground	On Manmade Structure	On Water
Fissures	Cracking	Waves
Settlements	Slidings	Hydro-Dynamic
Landslides	Overturing	Pressure
Liquefaction	Buckling	Tsunami
Earth Pressure	Collapse
Possible Chain-effects	Possible Chain-effects	Possible Chain-effects

Apart from these , earthquakes also have some serious and far-reaching environment consequences.Earthquakes are also responsible for landslides and often these cause obstructions in the formation of reservoirs.

Earthquake Hazard Mitigation

Methods to decrease the effects of Earthquake

• Establishing earthquake monitoring centres (seismological centres) for regular monitoring and fast dissemination of information among the people in the vulnerable areas. Use of Geographical Positioning System (GPS) can be of great help in monitoring the movement of tectonic plates.

• Preparing a vulnerability map of the country and dissemination of vulnerability risk information among the people and educating them about the ways and means minimising the adverse impacts of disasters.

• Modifying the house types and building designs in the vulnerable areas and discouraging construction of high-rise buildings, large industrial establishments and big urban centres in such areas.

• Finally, making it mandatory to adopt earthquake-resistant designs and use light materials in major construction activities in the vulnerable areas.

Tsunami

• A tsunami is a series of waves caused by an earthquake, underwater volcanic eruption, landslide or other abrupt disturbance.

• The most common cause of atsunami is an earthquake, which is a sudden shifting of the earth’s crust, which releases energy.

• A tsunami can travel as fast as a jet plane in the deep ocean waters.

How is Tsunami formed?

• A tsunami is a series of waves generated in an ocean or other body of water by a disturbance such as an earthquake, landslide, volcanic eruption, or meteorite impact.

• Undersea earthquakes, which typically occur at boundaries between Earth’s tectonic plates, cause the water above to be moved up or down.

Regions affected by Tsunami

• Tsunamis are frequently observed along the Pacific ring of fire, particularly along the coast of Alaska, Japan, Philippines, and other islands of Southeast Asia, Indonesia, Malaysia, Myanmar, Sri Lanka, and India etc.

Effects of Tsunami

• After reaching the coast, the tsunami waves release enormous energy stored in them and water flows turbulently onto the land destroying port cities and towns, structures, buildings and other settlements.

• The effect of tsunami is more along the coast because the density of population is high.

Mitigation

• It is beyond the capacity of individual state or government to mitigate the damage. Hence, combined efforts at the international levels are the possible ways of dealing with these disasters as has been in the case of the tsunami that occurred on 26th December 2004 in which more than 300,000 people lost their lives.

• India has volunteered to join the International Tsunami Warning System after the December 2004 tsunami disaster.

Tropical Cyclone

• Tropical cyclones are intense low- pressure are as confined to the area lying between 30° N

and 30° S latitudes, in the atmosphere around which high velocity winds blow.

• Horizontally, it extends up to 500​- 1,000 km and vertically from surface to 12-14 km.

• A tropical cyclone or hurricane is like a heat engine that is energised by the release of latent heat on account of the condensation of moisture that the wind gathers after moving over the oceans and seas.

Initial conditions for the emergence of a tropical cyclone

• Large and continuous supply of warm and moist air that can release enormous latent heat.

• Strong Coriolis force that can prevent filling of low pressure at the centre (absence of Coriolis force near the equator prohibits the formation of tropical cyclone between 0°-5°latitude).

• Unstable condition through the troposphere that creates local disturbances around which a cyclone develops.

• Finally, absence of strong vertical wind wedge, which disturbs the vertical transport of latent heat.

Structure of Tropical Cyclone

• Tropical cyclones are characterised by large pressure gradients. The centre of the cyclone is mostly a warm and low-pressure, cloudless core known as eye of the storm.

• Generally, the isobars are closely placed to each other showing high-pressure gradients. Normally, it varies between 14​- 17mb/100 km, but sometimes it can be as high as 60mb/100km. Expansion of the
wind belt is about 10-150 km from the centre.

Spatio-temporal Distribution of Tropical Cyclone in India

• The tropical cyclones in India originate in Arabian sea in the west and Bay of Bengal in the east.

• Though most of the cyclones originate between 10°-15° north latitudes during the monsoon season, yet in case of the Bay of Bengal, cyclones mostly develop during the months of October and November. Here, they originate between 16°-2° N latitudes and to the west of 92° E. By July the place of origin of these storms shifts to around 18° N latitude and west of 90°E near the Sunderban Delta.

Consequences of Tropical Cyclones

• It was mentioned that the energy to the tropical cyclone comes from the latent heat released by the warm moist air. Hence, with the increase in distance from the sea, the force of the cyclone decreases.

• In India, the force of the cyclone decreases with increase in distance from the Bay of Bengal and the Arabian Sea. So, the coastal areas are often struck by severe cyclonic storms with an average velocity of 180 km/h.

• Often, tropical cyclone results in abnormal rise in the sea level known as Storm Surge. A surge is generated due to interaction of air, sea and land.

• The cyclone provides the driving force in the form of very high horizontal pressure-gradient and very strong surface winds.

• The sea water flows across the coast along with strong winds and heavy downpour. This results in inundation of human settlements, agricultural fields, damaging crops and destruction of structures created by human beings.

Floods

• Floods occur commonly when water in the form of surface run-off exceeds the carrying capacity if the river channels and streams and flows into the neighbouring low-lying flood plains.

Causes of Floods

• A flood occurs when a river bursts its banks and the water spills onto the floodplain.

• Flooding tends to be caused by heavy rain: the faster the rainwater reaches the river channel, the more likely it is to flood.

Regions affected by Floods

• Floods in the South, Southeast and East Asian countries, particularly in China, India and Bangladesh are frequent and equally disastrous.

Areas of India frequently affected by floods

Rashtriya Barh Ayog (National Flood Commission) identified 40 million hectares of land as flood- prone in India.

• Assam, West Bengal and Bihar are among the high flood- prone states of India.

• Most of the rivers in the northern states like Punjab and Uttar Pradesh are also ulnerable to occasional floods.

• States like Rajasthan, Gujarat, Haryana and Punjab are also getting inundated in recent decades due to flash floods.

• Tamil Nadu experiences flooding during November- January due to the retreating monsoon.

Consequence and Control of Floods

Frequent inundation of agricultural land and human settlement, particularly in Assam, West Bengal, Bihar and Eastern Uttar Pradesh (flooding rivers), coastal areas of Orissa, Andhra Pradesh, Tamil Nadu and Gujarat (cyclone) and Punjab, Rajasthan, Northern Gujarat and Haryana (flash floods) have the following consequences:

• Floods seriously affect the national economy and society.

• Floods destroy valuable crops every year.

• Floods also damage physical infrastructure such as roads, rails, bridges and human settlements.

• Millions of people are rendered homeless and are also washed down along with their cattle in the floods.

• Spread of diseases like cholera, gastro-enteritis, hepatitis and other water-borne diseases spread in the flood-affected areas.

• The only positive consequence of Flooding is deposition of fertile silt over agricultural fields which is good for the crops, every year. Majuli (Assam), the largest riverine island in the world, is the best example of good paddy crops after the annual floods in Brahmaputra.

Methods to Control the Floods

• In many countries, rivers prone to floods are often carefully managed. Defences such as levees, bunds, reservoirs, and weirs are used to prevent rivers from bursting their banks.

• When these defences fail, emergency measures such as sandbags or portable inflatable tubes are used.

• Coastal flooding has been addressed in Europe and the Americas with coastal defences, such as sea walls, beach nourishment, and barrier islands.

• A dike is another method of flood protection. A dike lowers the risk of having floods compared to other methods. It can help prevent damage; however it is better to combine dikes with other flood control methods to reduce the risk of a collapsed dike.

• A weir, also known as a lowhead dam, is most often used to create millponds, but on the Humber River in Toronto, a weir was built near Raymore Drive to prevent a recurrence of the flooding caused by Hurricane Hazel in 1954, which destroyed nearly two fifths of the street.

Droughts

• The term ‘drought’ is applied to an extended period when there is a shortage of water availability due to inadequate precipitation, excessive rate of evaporation and over-utilisation of water from the reservoirs and other storages, including the ground water.

Drought is a complex phenomenon as it involves elements of meteorology like

(i) Precipitation
(ii) Evaporation,
(iii) Evapotranspiration,
(iv) Ground water,
(v) Soil moisture,
(vi) Storage of water,
(vii) Surface run-off,
(viii) Agricultural practices, particularly the types of crops grown,
(ix) Socio-economic practices
(x) Ecological conditions

Types of Droughts

• Meteorological Drought: It is a situation when there is a prolonged period of inadequate rainfall marked with mal-distribution of the same over time and space.

• Agricultural Drought: It is also known as soil moisture drought, characterised by low soil moisture that is necessary to support the crops, thereby resulting in crop failures. Moreover, if an area has more than 30 per cent of its gross cropped area under irrigation, the area is excluded from the drought-prone category.

• Hydrological Drought: It results when the availability of water in different storages and reservoirs like aquifers, lakes, reservoirs, etc. falls below what the precipitation can replenish.

• Ecological Drought: When the productivity of a natural ecosystem fails due to shortage of water and as a consequence of ecological distress, damages are induced in the ecosystem.

Drought Prone Areas in India

• Droughts and floods are the two accompanying features of Indian climate.

• According to some estimates, nearly 19 per cent of the total geographical area of the country and 12 percent of its total population suffer due to drought every year.

• About 30 percent of the country’s total area is identified as drought prone affecting around 50 million people.

• It is a common experience that while some parts of the country reel under floods, there are regions that face severe drought during the same period.

• Also, it is also a common sight to witness that one region suffers due to floods in one season and experiences drought in the other. This is mainly because of the large-scale variations and unpredictability in the behaviour of the monsoon in India.

On the basis of severity of droughts, India can be divided into the following regions:

• Extreme Drought Affected Area: Most parts of Rajasthan, particularly areas to the west of the Aravali hills, i.e.. Marusthali and Kachchh regions of Gujarat fall in this category. Included here are also the districts like Jaisalmer and Barmer from the Indian desert that receive less that 90 mm average annual rainfall.

• Severe Drought Prone Area: Parts of eastern Rajasthan, most parts of Madhya Pradesh, eastern parts of Maharashtra, interior parts of Andhra Pradesh and Karnataka Plateau, northern parts of interior Tamil Nadu and southern parts of Jharkhand and interior Orissa are included in this category.

• Moderate Drought Affected Area: Northern parts of Rajasthan, Haryana, southern districts of Uttar Pradesh, the remaining parts of Gujarat, Maharashtra except Konkan, Jharkhand and Coimbatore plateau of Tamil Nadu and interior Karnataka are included in this category.

• The remaining parts of India can be considered either free or less prone to the drought.

Consequences of Drought

Droughts have both immediate as well as long term disastrous consequences on the social and physical environments.

• Crop failure leading to scarcity of food grains (akal) and fodder (trinkal), inadequate rainfall, resulting in shortage of water (jalkal), and often shortage in all the three, i.e. food grains, fodder and water (trikal) is most devastating.

• Large-scale death of cattle and other animals.

• Migration of humans and livestock are the most common sight to be seen in the drought affected areas.

• Scarcity of water compels people to consume contaminated water resulting in spread of many waterborne diseases like gastro-enteritis, cholera, hepatitis, etc.

Mitigation

• Provision for the distribution of safe drinking water.

• Medicines for the victims.

• Availability of fodder and water for the cattle.

• Shifting of the people and their livestock to safer places.

• Identification of ground water potential in the form of aquifers.

• Transfer of river water from the surplus to the deficit areas.

• Planning for inter-linking of rivers.

• Construction of reservoirs and dams.

• Remote sensing and satellite imageries can be useful in identifying the possible river-basins that can be inter-linked and in identifying the ground water potential.

• Dissemination of knowledge about drought-resistant crops and proper training to practice the same can be some of the long-term measures that will be helpful in drought-mitigation.

• Rainwater harvesting can also be an effective method in minimising the effects of drought.

Landslides

• Landslides are largely controlled by highly localised factors. Hence, gathering information and monitoring the possibilities of landslide is not only difficult but also immensely cost-intensive.

• It is always difficult to define in a precise statement and generalise the occurrence and behaviour of a landslide.

Controlling Factors

• Geology

• Geomorphic agents

• Slope

• Land-use

• Vegetation cover

• Human activities

Landslide Vulnerability Zones of India

India has been divided into a number of zones:

• Very High Vulnerability Zone: Highly unstable, relatively young mountainous areas in the Himalayas and Andaman and Nicobar, high rainfall regions with steep slopes in the Western Ghats and Nilgiris, the north-eastern regions, along with areas that experience frequent ground-shaking due to earthquakes, etc. and areas of intense human activities, particularly those related to construction of roads, dams, etc. are included in this zone.

• High Vulnerability Zone: Areas that have almost similar conditions to those included in the very high vulnerability zone are also included in this category. The only difference between these two is the combination, intensity and frequency of the controlling factors. All the Himalayan states and the states from the north-eastern regions except the plains of Assam are included in the high vulnerability zones.

• Moderate to Low Vulnerability Zone: Areas that receive less precipitation such as Trans Himalayan areas of Ladakh and Spiti (Himachal Pradesh), undulated yet stable relief and low precipitation areas in the Aravali, rain shadow areas in the Western and Eastern Ghats and Deccan plateau also experience occasional landslides. Landslides due to mining and subsidence are most common in states like Jharkhand, Orissa, Chhattisgarh, Madhya Pradesh, Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu, Goa and Kerala.

• Other Areas: The remaining parts of India, particularly states like Rajasthan, Haryana, Uttar Pradesh, Bihar, West Bengal (except district Darjiling), Assam (except district Karbi Anglong) and Coastal regions of the southern States are safe as far as landslides are concerned.

Consequences of Landslides

• Roadblock,

• Destruction of railway lines,

• Channel-blocking due to rock-falls have far-reaching consequences,

• Diversion of river courses due to landslides can also lead to flood,

• Loss of life and property,

• Difficult spatial interaction which adversely affects the developmental activities in these areas.

Mitigation

• Restriction on the construction and other developmental activities such as roads and dams,

• Limiting agriculture to valleys and areas with moderate slopes,

• Control on the development of large settlements in the high vulnerability zones,

• Promoting large-scale afforestation programmes

• Construction of bunds to reduce the flow of water.

• Terrace farming should be encouraged in the northeastern hill states where Jhumming (Slash and Burn/Shifting Cultivation) is still prevalent.

Disaster Management

• Disaster Management refers to how we can protect or preserve many lives and property.

• India has been traditionally vulnerable to the natural disasters on the account of its unique geo climatic conditions.

• Floods, droughts, cyclones, earthquakes and landslides would have been a recurrent phenomena.The steps that can help in minimising the damages of cyclones are:
→ Construction of cyclone shelters, embankments, dykes, reservoirs,
Afforestation to reduce the speed of the winds,
→ implementation of The Disaster Management Bill, 2005.

Conclusion

Mitigation and Preparedness

There are three stages involved in disaster mitigation and management:

(i) Pre-disaster management involves
• Generating data and information about the disasters,
• Preparing vulnerability zoning maps,
• Spreading awareness among the people about the disasters,
• Disaster planning,
• Preparedness and preventive measures are other steps that need to be taken in the
vulnerable areas.

(ii) During disasters, Rescue and relief operations such as evacuation, construction of shelters, relief camps, supplying of water, food, clothing and medical aids etc. should be done on an emergency basis.

(iii) Post-disaster operations should involve:
• rehabilitation
• recovery of victims.
• concentrate on capacity building in order to cope up with future disasters.

These measures have special significance to a country like India. Introduction of the Disaster Management Bill, 2005 and establishment of National Institute of Disaster Management are some examples of positive steps taken by Government of India.

Class 11 Geography Notes Chapter 6 Soils

Soil is the mixture of rock debris and organic materials which develop on the earth’s surface.

The major factors affecting the formation of soil are relief, parent material, climate, vegetation and other life-forms and time. Besides these, human activities also influence it to a large extent.

Components of the soil are mineral particles, humus, water and air. The actual amount of each of these depends upon the type of soil.

Soil is bifurcated into three layers called horizons. ‘Horizon A’ is the topmost zone, where organic materials have got incorporated with the mineral matter, nutrients and water, which are necessary for the growth of plants. ‘Horizon B’ is a transition zone between the ‘horizon A’ and ‘horizon C’, and contains matter derived from below as well as from above. It has some organic matter in it, although the mineral matter is noticeably weathered. ‘Horizon C’ is composed of the loose parent material. This layer is the first stage in the soil formation process and eventually forms the above two layers.

In ancient times, soils used to be classified into twro main groups – Urvara and Usara, which were fertile and sterile, respectively.

In the 16th century A.D., soils were classified on the basis of their inherent characteristics and external features such as texture, colour, slope of land and moisture content in the soil. Based on texture, main soil types were identified as sandy, clayey, silty and loamy, etc. On the basis of colour, they wrere red, yellow, black, etc.

On the basis of genesis, colour, composition and location, the soils of India have been classified into:

• Alluvial soils
• Black soils
• Red and Yellow soils
• Laterite soils
• Arid soils
• Saline soils
• Peaty soils
• Forest soils.

Alluvial Soils Alluvial soils are widespread in the northern plains and the river valleys. These soils cover about 40 per cent of the total area of the country. They are depositional soils, transported and deposited by rivers and streams.

The alluvial soils vary in nature from sandy loam to clay. They are generally rich in potash but poor in phosphorous. In the Upper and Middle Ganga plain, two different types of alluvial soils have developed, viz. Khadar and Bhangar.

Khadar is the new alluvium and is deposited by floods annually, which enriches the soil by depositing fine silts. Bhangar represents a system of older alluvium, deposited away from the flood plains.

Black soil covers most of the Deccan Plateau which includes parts of Maharashtra, Madhya Pradesh, Gujarat, .Andhra Pradesh and some parts of Tamil Nadu. In the upper reaches of the Godavari and the Krishna, and the north western part of the Deccan Plateau, the black soil is very deep.

Red soil develops on crystalline igneous rocks in areas of low rainfall in the eastern and southern part of the Deccan Plateau. Along the piedmont zone of the Western Ghat, long stretch of area is occupied by red loamy soil.

Laterite has been derived from the Latin word ‘Later’ which means brick. The laterite soils develop in areas with high temperature and high rainfall. These are the result of intense leaching due to tropical rains. With rain, lime and silica are leached away, and soils rich in iron oxide and aluminium compound are left behind.

Arid soils range from red to brown in colour. They are generally sandy in structure and saline in nature. In some areas, the salt content is so high that common salt is obtained by evaporating the saline water. Due to the dry climate, high temperature and accelerated evaporation, they lack moisture and humus.

Saline soils are also known as Usara soils. Saline soils contain a larger proportion of sodium, potassium and magnesium, and thus, they are infertile, and do not support any vegetative growth. They have more salts, largely because of dry climate and poor drainage. They occur in arid and semi-arid regions, and in waterlogged and swampy areas.

Peaty soils are found in the areas of heavy rainfall and high humidity, where there is a good growth of vegetation. Thus, large quantity of dead organic matter accumulates in these areas, and this gives a rich humus and organic content to the soil. Organic matter in these soils may go even up to 40-50 per cent.

Forest soils are formed in the forest areas where sufficient rainfall is available. The soils vary in structure and texture depending on the mountain environment where they are formed. They are loamy and silty on valley sides and coarse-grained in the upper slopes.

Soil degradation can be defined as the decline in soil fertility, when the nutritional status declines and depth of the soil goes down due to erosion and misuse. Soil degradation is the main factor leading to the depleting soil resource base in India. The degree of soil degradation varies from place to place according to the topography, wind velocity and amount of the rainfall.

The destruction of the soil cover is described as soil erosion. Forest and other natural vegetation are removed for human settlement, for cultivation, for grazing animals and for various other needs. Wind and water are powerful agents of soil erosion because of their ability to remove soil and transport it.

Soil erosion is a serious problem for Indian agriculture and its negative eff ects are seen in other spheres also. Eroded materials are carried down to rivers and they lower down their carrying capacity, and cause frequent floods and damage to agricultural lands.

Deforestation is one of the major causes of soil erosion. Plants keep soils bound in locks of roots, and thus, prevent erosion. They also add humus to the soil by shedding leaves and twigs. The salt lodged in the lower profiles of the soil comes up to the surface and destroys its fertility. Chemical fertilizers in the absence of organic manures are also harmful to the soil.

If soil erosion and exhaustion are caused by humans; by corollary, they can also be prevented by humans. Contour bunding, Contour terracing, regulated forestry, controlled grazing, cover cropping, mixed farming and crop rotation are some of the remedial measures which are often adopted to reduce soil erosion.

Experiments have been made to stabilize sand dunes in western Rajasthan by the Central Arid Zone Research Institute (CAZRI). The Central Soil Conservation Board, set up by the Government of India, has prepared a number of plans for soil conservation in different parts of the country.

Important Soils Found In India:

Class 11 Geography Notes Chapter 6 Important Terms:

• Soil: Soil is the mixture of rock debris and organic materials which develop on the earth’s surface.
• Bad land topography: A region with a large number of deep gullies or ravines is called a bad land topography.
• Horizons: When we dig a pit on land and look at the soil, we find that it consists of three layers. These are called horizons.
• Horizon A: It is the topmost zone, where organic materials have got incorporated with the • mineral matter, nutrients and water, which are necessary for the growth of plants.
• Horizon B: It is a transition zone between the ‘horizon A’ and ‘horizon C’, and contains matter derived from below as well as from above. It has some organic matter in it, although the mineral matter is noticeably weathered.
• Horizon C: It is composed of the loose parent material. This layer is the first stage in the soil formation process and eventually forms the above two layers.
• Soil profile: The arrangement of layers in three horizons, A, B and C is known as the soil profile.
• Parent rock: Underneath the three horizons there is the rock which is known as the parent rock or the bedrock.
• Estuary: The tidal mouth of a river where fresh and saline water get mixed.
• Gully erosion: It is the erosion of the soil and rock by the concentration of runoff into gullies.
• Humus: The dead organic content of the soil.
• Khadar: Khadar is the new alluvium and is deposited by floods annually, which enriches the soil by depositing fine silts.
• Bhangar: Bhangar represents a system of older alluvium, deposited away from the flood plains.
• Alluvial soil: They are depositional soils, transported and deposited by rivers and streams.
• Laterite soil: Laterite has been derived from the Latin word ‘Later’ which means brick. The laterite soils develop in areas with high temperature and high rainfall.
• Black soil: These soils are made from volcanoes. These soils are also known as the ‘RegurSoil’ or the ‘Black Cotton Soil’.
• Forest soils: Forest soils are formed in the forest areas where sufficient rainfall is available.
• Peaty soils: They are found in the areas of heavy rainfall and high humidity, where there is a good growth of vegetation.
• Soil erosion: The destruction of the soil cover is described as soil erosion.
• Soil degradation: Soil degradation can be defined as the decline in soil fertility, when the nutritional status declines and depth of the soil goes down due to erosion and misuse. Soil degradation is the main factor leading to the depleting soil resource base in India.
• Soil Conservation: Soil conservation is a methodology to maintain soil fertility, prevent soil erosion and exhaustion, and improve the degraded condition of the soil.

Notes of Ch 5 Natural Vegetation| Class 11th Geography

Introduction

• Natural vegetation refers to a plant community that has been left undisturbed over a long time, so as to allow its individual species to adjust themselves to climate and soil conditions as fully as possible.

• Himalayan heights are marked with the different types of vegetation according to altitude.

• The Western and Eastern Ghats and the Andaman Nicobar Islands have tropical rain forests while the deltaic regions have tidal forests (mangroves). The desert and semi-desert areas of Rajasthan are known for cactii, a wide variety of bushes and thorny vegetation.

• Depending upon the variations in the climate and the soil, the vegetation of India changes from one region to another.

• On the basis of certain common features such as predominant vegetation type and climatic regions, Indian forests can be divided into various groups.

Types of Forests

(i) Tropical Evergreen and Semi Evergreen forests
(ii) Tropical Deciduous forests
(iii) Tropical Thorn forests
(iv) Montane forests
(v) Littoral and Swamp forests

The Tropical Evergreen and Semi Evergreen forests

• These forests are found in the western slope of the Western Ghats, Eastern slopes of eastern Ghats, hills of the northeastern states and the Andaman and Nicobar Islands.

• They are found in warm and humid areas with an annual precipitation of over 200 cm and mean annual temperature above 22° C.

• Tropical evergreen forests are well stratified, with layers closer to the ground and are covered with shrubs and creepers, with short structured trees followed by tall variety of trees.

• Trees reach great heights up to 60 m or above.

• There is no definite time for trees to shed their leaves, flowering and fruition. As such these forests appear green all the year round.

• Species found in these forests include rosewood, mahogany, aini, ebony, etc.

Semi Evergreen Forest

• The semi evergreen forests are found in the less rainy parts of these regions.

• Such forests have a mixture of evergreen and moist deciduous trees.

• The under growing climbers provide an evergreen character to these forests.

• Main species are white cedar, hollock and kail.

• The oak forests in Garhwal and Kumaon were replaced by pine (chirs) which was needed to lay railway lines.

• Forests were also cleared for introducing plantations of tea, rubber and coffee.

Tropical Deciduous Forests

• These are the most widespread forests in India.

• They are also called the monsoon forests.

• They spread over regions which receive rainfall between 70-200 cm.

• On the basis of the availability of water, these forests are further divided into moist and dry deciduous.

Moist deciduous forests

• They are mostly found in the regions which record rainfall between 100-200 cm.

• These forests are found in the northeastern states along the foothills of the Himalayas, eastern slopes of the Western Ghats and Odisha.

• Teak, sal, shisham, mahua, amla, semul, kusum, and sandalwood etc. are the main species of these forests.

Dry deciduous forests

• Covers vast areas of the country.

• Rainfall ranges between 70 -100 cm.

• On the wetter margins, it has a transition to the moist deciduous, while on the drier margins to thorn forests.

• These forests are found in rainier areas of the Peninsula and the plains of Uttar Pradesh and Bihar.

• Parklands are found In the higher rainfall regions of the Peninsular plateau and the northern Indian plain.

• As the dry season begins, the trees shed their leaves completely and the forest appears like a vast grassland with naked trees all around.

• Tendu, palas, amaltas, bel, khair, axlewood, etc. are the common trees of these forests.

• In the western and southern part of Rajasthan, vegetation cover is very scanty due to low rainfall and overgrazing.

Tropical Thorn Forests

• Tropical thorn forests occur in the areas which receive rainfall less than 50 cm.

• These consist of a variety of grasses and shrubs.

• It includes semi-arid areas of south-west Punjab, Haryana, Rajasthan, Gujarat, Madhya Pradesh and Uttar Pradesh.

• In these forests, plants remain leafless for the most part of the year and give an expression of scrub vegetation.

• Important species found are babool, ber, and wild date palm, khair, neem, khejri, palas, etc.

• Tussocky grass grows upto a height of 2 m as the under growth.

Montane Forests

• In mountainous areas, the decrease in temperature with increasing altitude leads to a corresponding
change in natural vegetation.

• Mountain forests can be classified into two types, the northern mountain forests and the southern mountain forests.

• The Himalayan ranges show a succession of vegetation from the tropical to the tundra, which changes in with the altitude.

• Deciduous forests are found in the foothills of the Himalayas.

• It is succeeded by the wet temperate type of forests between an altitude of 1,000-2,000 m.

Littoral And Swamp Forests

• India’s wetlands have been grouped into eight categories:

(i) The Reservoirs of the Deccan plateau in the south together with the lagoons and other wetlands of southern west coast.

(ii) The vast saline expenses of Rajasthan Gujarat and the Gulf of Kachchhh.

(iii) Freshwater lakes and reservoirs from Gujarat eastward through Rajasthan (Keoladev National park) and Madya Pradesh.

(iv) The delta wetlands and lagoons of India’s east coast (Chilika Lake).

(v) The freshwater marshes of the Gangetic Plain.

(vi) The floodplains of the Brahmaputra, the marshes and swamps in the hills of northeast India and the Himalayan foothills.

(vii) The lakes and rivers of the montane region of Kashmir and Ladakh.

(viii) The mangrove forest and other wetlands of the island arcs of Andaman and Nikobar
Islands.

• In India, the mangrove forests spread over 6,740 sq. km which is 7 percent of the world’s mangrove forests. They are developed in Andaman and Nicobar Islands, Sunderbans of West Bengal, the Mahanadi, the Godavari and the Krishna deltas.

Notes of Ch 4 Climate| Class 11th Geography

Difference Between Weather And Climate

Weather	Climate
Weather is the momentary state of the atmosphere	Climate refers to the average of the weather condition over a longer period of time.
Weather changes quickly, may be within a day or week	Climate changes imperceptibly and may be noted after 50 years or even more

Unity And Diversity In The Monsoon Climate

Unity of The Climate

• The monsoon regime emphasizes the unity of India with the rest of southeast Asian region.

• This view of broad unity of the monsoon type of climate should not, however, lead one to ignore its regional variations which differentiate the weather and climate of different regions of India.

• The climate of Kerala and Tamil Nadu in the south are so different from that of Uttar Pradesh and Bihar in the north, and yet all of these have a monsoon type of climate.

Diversity of Climate

• The climate of India has many regional variations expressed in the pattern of:
→ Winds,
→ Temperature
→ Rainfall,
→ Rhythm of seasons
→ Degree of wetness or dryness.

Temperature Variation

• While in the summer the mercury occasionally touches 55°C in the western Rajasthan, it drops down to as low as minus 45°C in winter around Leh.

• Churu in Rajasthan may record a temperature of 50°C or more on a June day while the mercury hardly touches 19°C in Tawang (Arunachal Pradesh) on the same day.

• On a December night, temperature in Drass (Jammu and Kashmir) may drop down to minus 45°C while Thiruvananthapuram or Chennai on the same night records 20°C or 22°C.

• In Kerala and in the Andaman Islands, the difference between day and night temperatures may be hardly seven or eight degree Celsius. But in the Thar desert, if the day temperature is around 50°C, at night, it may drop down considerably up to 15°-20°C.

The Regional Variations In Precipitation

• While snowfall occurs in the Himalayas, it only rains over the rest of the country.

• While Cherrapunji and Mawsynramin the Khasi Hills of Meghalaya receive rainfall over 1,080 cm in a year, Jaisalmer in Rajasthan rarely gets more than 9 cm of rainfall during the same period.

• Tura situated in the Garo Hills of Meghalaya may receive an amount of rainfall in a single day which is equal to 10 years of rainfall at Jaisalmer.

• While the annual precipitation is less than 10 cm in the northwest Himalayas and the western deserts, it exceeds 400 cm in Meghalaya.

• The Ganga delta and the coastal plains of Odisha are hit by strong rain-bearing storms almost every third or fifth day in July and August while the Coromandal coast, a thousand km to the south, goes generally dry during these months.

• Most parts of the country get rainfall during June-September, but on the coastal areas of Tamil Nadu, it rains in the beginning of the winter season.

Factors Determining The Climate Of India

• It can be broadly divided into two groups factors:
→ Factors related to location and relief
→ Factors related to air pressure and winds

Factors related to Location and Relief

• Latitude: Northern part of the India lies in sub-tropical and temperate zone and the part lying south of the Tropic of Cancer falls in the tropical zone. The tropical zone being nearer to the equator, experiences high temperatures throughout the year with small daily and annual range. Area north of the Tropic of Cancer being away from the equator experiences extreme climate with high daily and annual range of temperature.

• The Himalayan Mountains: The lofty Himalayas in the north along with its extensions act as an effective climatic divide. The towering mountain chain provides an invincible shield to protect the
subcontinent from the cold northern winds. The Himalayas also trap the monsoon winds, forcing them to shed air pressure causes reversal in the direction of monsoon winds.

• Distance from the Sea: With a long coastline, large coastal areas have an equable climate. Areas in the interior of India are far away from the moderating influence of the sea. Such areas have extremes of climate their moisture within the subcontinent.

• Distribution of Land and Water: India is flanked by the Indian Ocean on three sides in the south and girdled by a high and continuous mountain-wall in the north. As compared to the landmass, water heats up or cools down slowly. This differential heating of land and sea creates different air pressure zones in different seasons in and around the Indian subcontinent.

• Difference in Altitude: Temperature decreases with height. Due to thin air, places in the mountains are cooler than places on the plains.

• Relief: The physiography or relief of India also affects the temperature, air pressure, direction and speed of wind and the amount and distribution of rainfall. The windward sides of Western Ghats and Assam receive high rainfall during June-September whereas the southern plateau remains dry due to its leeward situation along the Western Ghats.

Factors Related to Air Pressure and Wind

• Distribution of air pressure and winds on the surface of the earth.

• Upper air circulation caused by factors controlling global weather and the inflow of different air masses and jet streams.

• Inflow of western cyclones generally known as disturbances during the winter season and tropical depressions during the south-west monsoon period into India, creating weather conditions favourable to rainfall.

Mechanism of Weather in the Winter Season

Surface Pressure and Winds

• In winter months, the weather conditions over India are generally influenced by the distribution of pressure in Central and Western Asia.

• A high pressure centre in the region lying to the north of the Himalayas develops during winter. This centre of high pressure gives rise to the flow of air at the low level from the north towards the Indian subcontinent, south of the mountain range.

• The surface winds blowing out of the high pressure centre over Central Asia reach India in the form of a dry continental air mass. These continental winds come in contact with trade winds over northwestern India.

Jet Stream and Upper Air Circulation

• Higher up in the lower troposphere, about three km above the surface of the earth, a different pattern of air circulation is observed.

• The variations in the atmospheric pressure closer to the surface of the earth have no role to play in the making of upper air circulation.

• All of Western and Central Asia remains under the influence of westerly winds along the altitude of 9-13 km from west to east.

• These winds blow across the Asian continent at latitudes north of the Himalayas roughly parallel to the Tibetan highlands. These are known as jet streams. branch blows in an eastward direction, south of the Himalayas.

• It has its mean position at 25°N in February at 200-300 mb level. It is believed that this southern branch of the jet stream exercises an important influence on the winter weather in India.

Direction of Winds in India in Winter at the Height of 9-13 km

Western Cyclonic Disturbance and Tropical Cyclones

• The western cyclonic disturbances which enter the Indian subcontinent from the west and the northwest during the winter months, originate over the Mediterranean Sea and are brought into India by the westerly jet stream.

• An increase in the prevailing night temperature generally indicates an advance in the arrival of these cyclones disturbances.

• Tropical cyclones originate over the Bay of Bengal and the Indian ocean.

• These tropical cyclones have very high wind velocity and heavy rainfall and hit the Tamil Nadu, Andhra Pradesh and Orissa coast.

• Most of these cyclones are very destructive due to high wind velocity and torrential rain that accompanies.

Mechanism of Weather in the Summer Season

Surface Pressure and Winds

• As the summer sets in and the sun shifts northwards, the wind circulation over the subcontinent undergoes a complete reversal at both, the lower as well as the upper levels.

• By the middle of July, the low pressure belt nearer the surface [termed as Inter Tropical Convergence Zone (ITCZ)] shifts northwards, By this time, the westerly jet stream withdraws from the Indian region.

• It is generally believed that there is a cause and effect relationship between the ictz and jet stream.

• The ITCZ being a zone of low pressure, attracts inflow of winds from different directions.

• The maritime tropical airmass (mT) from the southern hemisphere, after crossing the equator, rushes to the low pressure area in the general southwesterly direction. It is this moist air current which is popularly known as the southwest monsoon.

Jet Streams and Upper Air Circulation

• An easterly jet stream flows over the southern part of the Peninsula in June, and has a maximum speed of 90 km per hour.

• In August, it is confined to 15oN latitude, and in September up to 22o N latitudes. The easterlies normally do not extend to the north of 30o N latitude in the upper atmosphere.

Easterly Jet Stream and Tropical Cyclones

• The easterly jet stream steers the tropical depressions into India.

• These depressions play a significant role in the distribution of monsoon rainfall over the Indian subcontinent.

• The tracks of these depressions are the areas of highest rainfall in India.

• The frequency at which these depressions visit India, their direction and intensity, all go a long way in determining the rainfall pattern during the southwest monsoon period.

The Inter Tropical Convergence Zone (ITCZ)

• A low pressure zone located at the equator where trade winds converge, and so, it is a zone where air tends to ascend.

• In July, the ITCZ is located around 20°N-25°N latitudes (over the Gangetic plain), sometimes called the monsoon trough.

• This monsoon trough encourages the development of thermal low over north and northwest India.

• Due to the shift of ITCZ, the trade winds of the southern hemisphere cross the equator between 40° and 60°E longitudes and start blowing from southwest to northeast due to the Coriolis force. It becomes southwest monsoon.

• In winter, the ITCZ moves southward, and so the reversal of winds from northeast to south and southwest, takes place. They are called northeast monsoons.

The Nature Of Indian Monsoon

(i) The onset of the monsoon.

(ii) Rain-bearing systems (e.g. tropical cyclones) and the relationship between their

frequency and distribution of monsoon rainfall.

(iii) Break in the monsoon.

Onset of the Monsoon

• During April and May when the sun shines vertically over the Tropic of Cancer, the large landmass in the north of Indian ocean gets intensely heated. This causes the formation of an intense low pressure in the northwestern part of the subcontinent.

• Since the pressure in the Indian Ocean in the south of the landmass is high as water gets heated slowly, the low pressure cell attracts the southeast trades across the Equator.

• These conditions help in the northward shift in the position of the ITCZ. The southwest monsoon may thus, be seen as a continuation of the southeast trades deflected towards the Indian subcontinent after crossing the Equator. These winds cross the Equator between 40°E and 60°E longitudes.

Entry of Monsoon into India

• The southwest monsoon sets in over the Kerala coast by 1st June and moves swiftly to reach Mumbai and Kolkata between 10th and 13th June. By mid July, southwest monsoon engulfs the entire subcontinent.

Rain-bearing Systems and Rainfall Distribution

• Bay of Bengal Branch
• Arabian sea branch

The rainfall distribution is based on two factors:

(i) The offshore meteorological conditions.

(ii) The position of the equatorial jet stream along the eastern coast of Africa.

EI-Nino and the Indian Monsoon

• EI-Nino is a complex weather system that appears once every three to seven years, bringing drought, floods and other weather extremes to different parts of the world.

• The system involves oceanic and atmospheric phenomena with the appearance of warm currents off the coast of Peru in the Eastern Pacific and affects weather in many places including India.

• EI-Nino is merely an extension of the warm equatorial current which gets replaced temporarily by cold Peruvian current or Humbolt current (locate these currents in your atlas). This current increases the temperature of water on the Peruvian coast by 10°C. This results in:
(i) the distortion of equatorial atmospheric circulation;
(ii) irregularities in the evaporation of sea water;
(iii) reduction in the amount of planktons which further reduces the number of fish in the sea.

• The word EI-Nino means ‘Child Christ’ because this current appears around Christmas in December. December is a summer month in Peru (Southern Hemisphere).

• EI-Nino is used in India for forecasting long range monsoon rainfall. In 1990-91, there was a wild EI-Nino event and the onset of southwest monsoon was delayed over most parts of the country ranging from five to twelve days.

Break in the Monsoon

• During the south-west monsoon period after having rains for a few days, if rain fails to occur for one or more weeks, it is known as break in the monsoon.

• These dry spells are quite common during the rainy season. These breaks in the different regions are due to different reasons:

(i) In northern India rains are likely to fail if the rain-bearing storms are not very frequent along the monsoon trough or the ITCZ over this region.
(ii) Over the west coast the dry spells are associated with days when winds blow parallel to the coast.

The Rhythm Of Seasons

The climatic conditions of India can best be described in terms of an annual cycle of seasons. Four seasons are:
(i) The cold weather season
(ii) The hot weather season

(iii) The southwest monsoon season

(iv) The retreating monsoon season

The Cold Weather Season

• Found from November to February

• December and January are the coldest months in the northern plain.

• The mean daily temperature remains below 21°C, over most parts of northern India.

• The night temperature may be quite low, sometimes going below freezing point in Punjab and Rajasthan.

There are three main reasons for the excessive cold in north India during this season:
(i) States like Punjab, Haryana and Rajasthan being far away from the moderating influence of sea experience continental climate.

(ii) The snowfall in the nearby Himalayan ranges creates cold wave situation; and

(iii) Around February, the cold winds coming from the Caspian Sea and Turkmenistan bring cold wave along with frost and fog over the northwestern parts of India.

Pressure and Winds:

• By the end of December (22nd December), the sun shines vertically over the Tropic of Capricorn in the southern hemisphere.

• The weather in this season is characterized by feeble high pressure conditions over the northern plain. In south India, the air pressure is slightly lower respectively.

• As a result, winds start blowing from northwestern high pressure zone to the low air pressure zone over the Indian Ocean in the south. Due to low pressure gradient, the light winds with a low velocity of about 3-5 km per hour begin to blow outwards.

• By and large, the topography of the region influences the wind direction. They are westerly or northwesterly down the Ganga Valley. They become northerly in the Ganga-Brahmaputra delta. Free from the influence of topography, they are clearly northeasterly over the Bay of Bengal.

• During the winters, the weather in India is pleasant.

• The pleasant weather conditions, however, at intervals, get disturbed by shallow cyclonic depressions originating over the east Mediterranean Sea and travelling eastwards across West Asia, Iran, Afghanistan and Pakistan before they reach the northwestern parts of India.

Rainfall:

• Winter monsoons do not cause rainfall as they move from land to the sea.

• It is because firstly, they have little humidity;

• Secondly, due to anti cyclonic circulation on land, the possibility of rainfall from them reduces. So, most parts of India do not have rainfall in the winter season.

However, there are some exceptions to it:

• In northwestern India, some weak temperate cyclones from the Mediterranean sea cause rainfall in Punjab, Haryana, Delhi and western Uttar Pradesh. Although the amount is meagre, it is highly beneficial for Rabi crops. The precipitation is in the form of snowfall in the lower Himalayas. It is this snow that sustains the flow of water in the Himalayan rivers during the summer months. The precipitation goes on decreasing from west to east in the plains and from north to south in the mountains.

• Central parts of India and northern parts of southern Peninsula also get winter rainfall occasionally.

• Arunachal Pradesh and Assam in the northeastern parts of India also have rains between 25 mm and 50 mm during these winter months.

• During October and November, northeast monsoon while crossing over the Bay of Bengal, picks up moisture and causes torrential rainfall over the Tamil Nadu coast, southern Andhra Pradesh, southeast Karnataka and south east Kerala.

The Hot Weather Season

• With the apparent northward movement of the sun towards the Tropic of Cancer in March, temperatures start rising in north India.

• April, May and June are the months of summer in north India. In most parts of India, temperatures recorded are between 30°-32°C.

• In March, the highest day temperature of about 38°C occurs in the Deccan Plateau while in April, temperature ranging between 38°C and 43°C are found in Gujarat and Madhya Pradesh.

• In May, the heat belt moves further north, and in the north-western part of India, temperatures around 48°C are not uncommon.

• Temperatures remain between 26°C and 32°C. Due to altitude, the temperatures in the hills of Western Ghats remain below 25°C.

Pressure and Winds:

• The summer months are a period of excessive heat and falling air pressure in the northern half of the country.

• Roughly, this elongated low pressure monsoon trough extends over the Thar desert in the
north​west to Patna and Chotanagpur plateau in the east-southeast.

• The location of the ITCZ attracts a surface circulation of the winds which are southwesterly on the west coast as well as along the coast of West Bengal and Bangladesh.

• They are easterly or southeasterly over north Bengal and Bihar.

• In the heart of the ITCZ in the northwest, the dry and hot winds known as ‘Loo’, blow in the afternoon, and very often, they continue to well into midnight.

• Dust storms in the evening are very common during May in Punjab, Haryana, Eastern Rajasthan and Uttar Pradesh.

• These temporary storms bring a welcome respite from the oppressing heat since they bring with them light rains and a pleasant cool breeze.

• Occasionally, the moisture-laden winds are attracted towards the periphery of the trough.

• A sudden contact between dry and moist air masses gives rise to local storms of great intensity.

• These local storms are associated with violent winds, torrential rains and even hailstorms.

Some Famous Local Storms of Hot Weather Season

• Mango Shower: Towards the end of summer, there are pre-monsoon showers which are a common phenomena in Kerala and coastal areas of Karnataka. Locally, they are known as mango showers since they help in the early ripening of mangoes.

• Blossom Shower: With this shower, coffee flowers blossom in Kerala and nearby areas.

• Norwesters: These are dreaded evening thunderstorms in Bengal and Assam. Their notorious nature can be understood from the local nomenclature of ‘Kalbaisakhi’, a calamity of the month of Baisakh.

• These showers are useful for tea, jute and rice cultivation. In Assam, these storms are known as “Bardoli Chheerha”.

• Loo: Hot, dry and oppressing winds blowing in the Northern plains from Punjab to Bihar with higher intensity between Delhi and Patna.

The Southwest Monsoon Season

• Due to high temperature there is lo to attract the trade winds of Southern Hemisphere coming from the Indian Ocean.

• These southeast trade winds cross the equator and enter the Bay of Bengal and the Arabian Sea,.

• After crossing the equator, they follow a southwesterly direction. That is why they are known as southwest monsoons.

• The rain in the southwest monsoon season begins rather abruptly. One result of the first rain is that it brings down the temperature substantially.

• This sudden onset of the moisture-laden winds associated with violent thunder and lightning, is often termed as the “break” or “burst” of the monsoons.

The monsoon approaches the landmass in two branches:
(i) The Arabian Sea branch
(ii) The Bay of Bengal branch

Monsoon Winds of the Arabian Sea

The monsoon winds originating over the Arabian Sea further split into three branches:

(i) Its one branch is obstructed by the Western Ghats. These winds climb the slopes of the Western Ghats from 900-1200 m. Soon, they become cool, and as a result, the windward side of the Sahyadris and Western Coastal Plain receive very heavy rainfall ranging between 250 cm and 400 cm. After crossing the Western Ghats, these winds descend and get heated up.
(ii) Another branch of the Arabian sea monsoon strikes the coast north of Mumbai. Moving along the Narmada and Tapi river valleys, these winds cause rainfall in extensive areas of central India. The Chotanagpur plateau gets 15 cm rainfall from this part of the branch. Thereafter, they enter the Ganga plains and mingle with the Bay of Bengal branch.

(iii) A third branch of this monsoon wind strikes the Saurashtra Peninsula and the Kachchh. It then passes over west Rajasthan and along the Aravalis, causing only a scanty rainfall. In Punjab and Haryana, it too joins the Bay of Bengal branch. These two branches, reinforced by each other, cause rains in the western Himalayas.

Monsoon Winds of the Bay of Bengal

• The Bay of Bengal branch strikes the coast of Myanmar and part of south east Bangladesh. But the Arakan Hills along the coast of Myanmar deflect a big portion of this branch towards the Indian subcontinent.

• The monsoon, therefore, enters West Bengal and Bangladesh from south and southeast instead of from the south-westerly direction. From here, this branch splits into two under the influence of the Himalayas and the thermal low is northwest India.

• Its one branch moves westward along the Ganga plains reaching as far as the Punjab plains. The other branch moves up the Brahmaputra valley in the north and the northeast, causing widespread rains. Its sub-branch strikes the Garo and Khasi hills of Meghalaya. Mawsynram, located on the crest of Khasi hills, receives the highest average annual rainfall in the world.

• Here it is important to know why the Tamil Nadu coast remains dry during this season.

There are two factors responsible for it:
(i) The Tamil Nadu coast is situated parallel to the Bay of Bengal branch of southwest monsoon.
(ii) It lies in the rain shadow area of the Arabian Sea branch of the south-west monsoon.

Characteristics of Monsoonal Rainfall

• Rainfall received from the southwest monsoons is seasonal in character, which occurs between June and September.

• Monsoonal rainfall is largely governed by relief or topography. For instance the windward side of the Western Ghats register a rainfall of over 250 cm. Again, the heavy rainfall in the north -eastern states can be attributed to their hill ranges and the Eastern Himalayas.

• The monsoon rainfall has a declining trend with increasing distance from the sea. Kolkata receives 119 cm during the southwest monsoon period, Patna 105 cm, Allahabad 76 cm and Delhi 56 cm.

• The monsoon rains occur in wet spells of few days duration at a time. The wet spells are interspersed with rainless, interval known as ‘breaks’. These breaks in rainfall are related to the cyclonic depressions mainly formed at the head of the Bay of Bengal, and their crossing into the mainland. Besides the frequency and intensity of these depressions, the passage followed by them determines the spatial distribution of rainfall.

• The summer rainfall comes in a heavy downpour leading to considerable run off and soil erosion.

• Monsoons play a pivotal role in the agrarian economy of India because over three-fourths of the total rain in the country is received during the southwest monsoon season.

• Its spatial distribution is also uneven which ranges from 12 cm to more than 250 cm.

• The beginning of the rains sometimes is considerably delayed over the whole or a part of the country.

• The rains sometimes end considerably earlier than usual, causing great damage to standing crops and making the sowing of winter crops difficult.

Season of Retreating Monsoon

• October and November are known for retreating monsoons.

• By the end of September, the southwest monsoon becomes weak as the low pressure trough of the Ganga plain starts moving southward in response to the southward march of the sun.

• The monsoon retreats from the western Rajasthan by the first week of September.

• It withdraws from Rajasthan, Gujarat, Western Ganga plain and the Central Highlands by the end of the month.

• By the beginning of October, the low pressure covers northern parts of the Bay of Bengal and by early November, it moves over Karnataka and Tamil Nadu.

• By the middle of December, the centre of low pressure is completely removed from the Peninsula.

• The retreating southwest monsoon season is marked by clear skies and rise in temperature.

• The land is still moist. Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive. This is commonly known as the ‘October heat’. Here, October and November are the rainiest months of the year.

• The widespread rain in this season is associated with the passage of cyclonic depressions which originate over the Andaman Sea and manage to cross the eastern coast of the southern Peninsula.

Traditional Indian Seasons

Seasons	Months (According to the Indian Calendar)	Months (According to the Indian Calendar)
Vasanta	Chaitra-Vaisakha	March-April
Grishma	Jyaistha-Asadha	May-June
Varsha	Sravana-Bhadra	July-August
Sharada	Asvina-Kartika	September-October
Hemanta	Margashirsa-Pausa	November-December
Shishira	Magha-phalguna	January-February

Distribution of Rainfall

The average annual rainfall in India is about 125 cm, but it has great spatial variations.

• Areas of High Rainfall : The highest rainfall occurs along the west coast, on the Western Ghats, as well as in the sub-Himalayan areas is the northeast and the hills of Meghalaya. Here the rainfall exceeds 200 cm. In some parts of Khasi and Jaintia hills, the rainfall exceeds 1,000 cm. In the Brahmaputra valley and the adjoining hills, the rainfall is less then 200 cm.

• Areas of Medium Rainfall : Rainfall between 100-200 cm is received in the southern parts of Gujarat, east Tamil Nadu, northeastern Peninsula covering Odisha, Jharkhand, Bihar, eastern Madhya Pradesh, northern Ganga plain along the sub-Himalayas and the Cachar Valley and Manipur.

• Areas of Low Rainfall : Western Uttar Pradesh, Delhi, Haryana, Punjab, Jammu and Kashmir, eastern Rajasthan, Gujarat and Deccan Plateau receive rainfall between 50-100 cm.

• Areas of Inadequate Rainfall: Parts of the Peninsula, especially in Andhra Pradesh, Karnataka and Maharashtra, Ladakh and most of western Rajasthan receive rainfall below 50 cm.Snowfall is restricted to the Himalayan region.

Climatic Regions of India

Major climatic types of India based on Koeppen‘s scheme: Koeppen based his scheme of Climatic classification on monthly values of temperature and precipitation. He identified five major climatic types, namely:

(i) Tropical climates, where mean monthly temperature throughout the year is over 18°C.

(ii) Dry climates, where precipitation is very low in comparison to temperature, and hence, dry. If dryness is less, it is semi arid (S); if it is more, the climate is arid(W).

(iii) Warm temperate climates, where mean temperature of the coldest month is between 18°C and minus 3°C.

(iv) Cool temperate climates, where mean temperature of the warmest month is over 10°C, and mean temperature of the coldest month is under minus 3°C.

(v) Ice climates, where mean temperature of the warmest month is under 10°C.

Class 11 Geography Notes Chapter 3 Drainage System

On the basis of discharge of water (orientations to the sea), it may be grouped into:

• The Arabian Sea drainage; and
• The Bay of Bengal drainage.

Nearly 77 per cent of the drainage area consisting of the Ganga, the Brahmaputra, the Mahanadi, the Krishna, etc. are oriented towards the Bay of Bengal while 23 per cent comprising the Indus, the Narmada, the Tapi, the Mahi and the Periyar systems discharge their waters in the Arabian Sea.

On the basis of the size of the watershed, the drainage basins of India are grouped into three categories:

• Major river basins with more than 20,000 sq. km of catchment area. It includes 14 drainage basins such as the Ganga, the Brahmaputra, the Krishna, the Tapi, the Narmada, the Mahi, the Penner, the Sabarmati, the Barak, etc.
• Medium river basins with catchment area between 2,000-20,000 sq. km incorporating 44 river basins such as the Kalindi, the Periyar, the Meghna, etc.

Minor river basins with catchment area of less than 2,000 sq. km include fairly good number of rivers flowing in the area of low rainfall.

The Indus System is one of the largest river basins of the world, covering an area of 11,65,000 sq. km (in India it is 321, 289 sq. km) and a total length of 2,880 km and in India its length is 1,114 km.

The Jhelum, an important tributary of the Indus, rises from a spring at Verinag situated at the foot of the Pir Panjal in the south-eastern part of the valley of Kashmir. It flows through Srinagar and the Wular lake before entering Pakistan through a deep narrow gorge. It joins the Chenab near Jhang in Pakistan.

The Chenab is the largest tributary of the Indus. It is formed by two streams, the Chandra and the Bhaga, which join at Tandi near Keylong in Himachal Pradesh. Hence, it is also known as Chandrabhaga.

The Ravi is another important tributary of the Indus. It rises west of the Rohtang pass in the Kullu hills of Himachal Pradesh and flows through the Chamba valley of the state.

The Beas is another important tributary of the Indus, originating from the Beas Kund near the Rohtang Pass at an elevation of 4,000 m above the mean sea level. The river flows through the Kullu valley and forms gorges at Kati and Largi in the Dhaoladhar range.

Satluj river flows almost parallel to the Indus for about 400 km before entering India, and comes out of a gorge at Rupar. It passes through the Shipki La on the Himalayan ranges and enters the Punjab plains. It is an antecedent river. It is a very important tributary as it feeds the canal system of the Bhakra Nangal project.

The Ganga System rises in the Gangotri glacier near Gaumukh (3,900 m) in the Uttarkashi district of Uttarakhand. Here, it is known as the Bhagirathi. It cuts through the Central and the Lesser Himalayas in narrow gorges. At Devprayag, the Bhagirathi meets the Alaknanda; hereafter, it is known as the Ganga. The Alaknanda has its source in the Satopanth glacier above Badrinath.

The Alaknanda consists of the Dhauli and the Vishnu Ganga which meet at Joshimath or Vishnu Prayag. The other tributaries of Alaknanda such as the Pindar joins it at Kama Prayag while Mandakini or Kali Ganga meets it at Rudra Prayag.

The Ganga river has a length of 2,525 km. It is shared by Uttarakhand (110 km) and Uttar Pradesh (1,450 km), Bihar (445 km) and West Bengal (520 km).

The Ganga basin covers about 8.6 lakh sq. km area in India alone. The Ganga river system is the largest in India having a number of perennial and non-perennial rivers originating in the Himalayas in the north and the Peninsula in the south, respectively. The Son is its major right bank tributary. The important left bank tributaries are the Ramganga, the Gomati, the Ghaghara, the Gandak, the Kosi and the Mahananda.

The Yamuna is the western most and the longest tributary of the Ganga. It has its source in the Yamunotri glacier on the western slopes of Banderpunch range (6,316 km). It joins the Ganga at Prayag in Allahabad. It is joined by the Chambal, the Sind, the Betwa and the Ken on its right bank which originates from the Peninsular plateau while the Hindan, the Rind, the Sengar, the Varuna, etc. join it on its left bank.



The Chambal rises near Mhow in the Malwa plateau of Madhya Pradesh and flows northwards through a gorge up wards of Kota in Rajasthan, where the Gandhisagar dam has been constructed. From Kota, it traverses down to Bundi, Sawai Madhopur and Dholpur, and finally joins the Yamuna.

The Gandak comprises two streams, namely Kaligandak and Trishulganga. It rises in the Nepal Himalayas between the Dhaulagiri and Mount Everest and drains the central part of Nepal.

The Brahmaputra is one of the largest rivers of the world. It has its origin in the Chemayungdung glacier of the Kailash range near the Mansarovar lake.

The Brahmaputra receives numerous tributaries in its 750 km long journey through the Assam valley. Its major left bank tributaries are the Burhi Dihing and Dhansari (South) whereas the important right bank tributaries are the Subansiri, Kameng, Manas and Sankosh.. The Subansiri which has its origin in Tibet, is an antecedent river.

The Peninsular drainage system is older than the Himalayan one. This is evident from the broad, largely-graded shallow valleys, and the maturity of the rivers.

Most of the major Peninsular rivers except Narmada and Tapi flow from west to east. The Chambal, the Sind, the Betwa, the Ken, the Son, originating in the northern part of the Peninsula belong to the Ganga river system. The other major river systems of the Peninsular drainage are – the Mahanadi, the Godavari, the Krishna and the Kaveri. Peninsular rivers are characterised by fixed course, absence of meanders and non- perennial flow of water.

Three major geological events in the distant past have shaped the present drainage systems of Peninsular India:

• Subsidence of the western flank of the Peninsula leading to its submergence below the sea during the early tertiary period.
• Upheaval of the Himalayas when the northern flank of the Peninsular block was subjected to subsidence and the consequent trough faulting.
• Slight tilting of the Peninsular block from north-west to the south-eastern direction gave orientation to the entire drainage system towards the Bay of Bengal during the same period.

There are some problems in river water usage. Some of these are:

• No availability in sufficient quantity.
• River water pollution.
• Load of silt in the river water.
• Uneven seasonal flow of water.
• River water disputes between states.
• Shrinking of channels due to the extension of settlements towards the thalweg.

Class 11 Geography Notes Chapter 3 Important Terms:

• Drainage: The flow of water through well-defined channels is known as ‘drainage.’
• Drainage System: The network of drainage channels is called a ‘drainage system’.
• Dendritic Drainage System: The drainage pattern resembling the branches of a tree is known as “dendritic” the examples of which are the rivers of northern plain.
• Radial Drainage System: When the rivers originate from a hill and flow in all directions, the drainage pattern is known as ‘radial’. The rivers originating from the Amarkantak range present a good example of it.
• Trellis: When the primary tributaries of rivers flow parallel to each other and secondary tributaries join them at right angles, the pattern is known as ‘trellis’.
• Centripetal Drainage System: When the rivers discharge their waters from all directions in a lake or depression, the pattern is known as ‘centripetal’.
• Catchment area: A river drains the water collected from a specific area, which is called its ‘catchment area’.
• Drainage Basin: An area drained by a river and its tributaries is called a drainage basin.
• Watershed: The boundary line separating one drainage basin from the other is known as the watershed.
• Sorrow of Bengal: River Damodar is also known as the ‘Sorrow of Bengal’ as it changes its course very frequently and causes floods in Bihar.
• Sorrow of Bihar: River Kosi is called Sorrow of Bihar.
• River System: A river or a river system is a body of water flowing in a channel through the surface of the earth. It consists of four important parts: river course, river source, tributaries and river mouth.
• River Source: A place at which begins or originates. This is usually found in mountainous areas. The source may be melting snow from the top of a mountain on a lake with stream flowing out of it. A river flow downhill from its source due to the force of gravity
• River Course: The path on which the river flows along.
• Singi Khamban or Lion’s mouth: Kailash Mountain range is known as ‘Singi Khamban; or Lion’s mouth in Tibet.
• Regime: The pattern of flow of water in a river channel over a year is known as its regime.
• Cusecs: It means cubic feet per second.
• Cumecs: It stands for cubic metres per second.

Class 11 Geography Notes Chapter 2 Structure and Physiography

These geological regions broadly follow the physical features:

• The Peninsular Block
• The Himalayas and other Peninsular Mountains
• Indo-Ganga-Brahmaputra Plain.

The northern boundary of the Peninsular Block may be taken as an irregular line running from Kachchh along the western flank of the Aravali Range near Delhi and then roughly parallel to the Yamuna and the Ganga as far as the Rajmahai Hills and the Ganga delta. Apart from these, the Karbi Anglong and the Meghalaya Plateau in the north-east and Rajasthan in the west are also extensions of this block.

The Peninsula is formed essentially by a great complex of very ancient gneisses and granites, which constitutes a major part of it. The rift valleys of the Narmada, the Tapi and the Mahanadi and the Satpura block mountains are some examples of it. The Peninsula mostly consists of relict and residual mountains like the Aravali hills, the Nallamala hills, the Javadi hills, the Veliconda hills, the Palkonda range and the Mahendragiri hills, etc.

Most of the east flowing rivers form deltas before entering into the Bay of Bengal. The deltas formed by the Mahanadi, the Krishna, the Kaveri and the Godavari are important examples.

The Himalayas along with other Peninsular mountains are young, weak and flexible in their geological structure unlike the rigid and stable Peninsular Block. Consequently, they are still subjected to the interplay of exogenic and endogenic forces, resulting in the development of faults, folds and thrust plains.

The third geological division of India comprises the plains formed by the river Indus, the Ganga and the Brahmaputra. Originally, it was a geo-synclinal depression which attained its maximum development during the third phase of the Himalayan mountain formation approximately about 64 million years ago. Since then, it has been gradually filled by the sediments brought by the Himalayan and Peninsular rivers. Average depth of alluvial deposits in these plains ranges from 1,000-2,000 m.

India can be divided into the following physio-graphic divisions:

• The Northern and North-eastern Mountains
• The Northern Plain
• The Peninsular Plateau
• The Indian Desert
• The Coastal Plains
• The Islands.

The North and North-eastern Mountains consist of the Himalayas and the North-eastern hills. The Himalayas consist of a series of parallel mountain ranges. Some of the important ranges are the Greater Himalayan range, which includes the Great Himalayas and the Trans-Himalayan range, the Middle Himalayas and the Shiwalik.

The approximate length of the Great Himalayan range, also known as the central axial range, is 2,500 km from east to west, and their width varies between 160-400 km from north to south.

On the basis of relief, alignment of ranges and other geomorphological features, the Himalayas can be divided into the following sub-divisions:

• Kashmir or North-western Himalayas.
• Himachal and Uttaranchal Himalayas.
• Darjeeling and Sikkim Himalayas.
• Arunachal Himalayas.
• Eastern Hills and Mountains.

Kashmir or North-western Himalayas comprise a series of ranges such as the Karakoram, Ladakh, Zaskar and Pir Panjal. The north-eastern part of the Kashmir Himalayas is a cold desert, which lies between the Greater Himalayas and the Karakoram ranges.

The word shiwalik has its origin in the geological formation found in and around a place called Sivawala near Dehra Dun which was once a headquarter of the Imperial Survey and which subsequently established its permanent headquarters at Dehra Dun.

The Himachal and Uttarakhand Himalayas lies approximately between the Ravi in the west and the Kali (a tributary of Ghaghara) in the east. In this section of Lesser Himalayas, the altitude between 1,000-2,000 m specially attracted to the British colonial administration, and subsequently, some of the important hill stations such as Dharamshala, Mussoorie, Shimla, Kaosani and the cantonment towns and health resorts such as Shimla, Mussoorie, Kasauli, Almora, Lansdowne and Ranikhet, etc. were developed in this region.

The two distinguishing features of this region from the point of view of physiography are the ‘Shiwalik’ and ‘Dun formations’, Some important duns located in this region are the Chandigarh – Kalka Dun, Nalagarh Dun, Dehra Dun, Harike Dun and the Kota Dun.

In the Great Himalayan range, the valleys are mostly inhabited by the Bhotia’s. These are nomadic groups who migrate to ‘Bugyals’ (the summer glass lands in the higher reaches) during summer months and return to the valleys during winters. The famous ‘Valley of flowers’ is also situated in this region. The places of pilgrimage such as the Gangotri, Yamunotri, Kedarnath, Badrinath and Hemkund Sahib are also situated in this part.

Sikkim and Darjeeling Himalayas are also known for their scenic beauty and rich flora and fauna, particularly various types of orchids.

An important aspect of the Arunachal Himalayas is the numerous ethnic tribal community inhabiting in these areas. Some of the prominent ones from west to east are the Monpa, Daffla, Abor, Mishmi, Nishi and the Nagas. Most of these communities practise Jhumming. It is also known as shifting or slash and burn cultivation. This region is rich in biodiversity which has been preserved by the indigenous communities. Due to rugged topography, the inter-valley transportation linkages are nominal. Hence, most of the interactions are carried through the duar region along the Arunachal-Assam border.

The Eastern Hills and Mountains are having their general alignment from the north to the south direction. They are known by different local names. In the north, they are known as Patkai Bum, Naga hills, the Manipur hills and in the south as Mizo or Lushai hills. These are low hills, inhabited by numerous tribal groups practising Jhum cultivation.

The northern plains are formed by the alluvial deposits broiight by the rivers – the Indus, the Ganga and the Brahmaputra. These plains extend approximately 3,200 km from the east to the west. The average width of these plains varies between 150-300 km. The maximum depth of alluvium deposits varies between 1,000-2,000 m. From the north to the south, these can be divided into three major zones: the Bhabar, the Tarai and the alluvial plains. The alluvial plains can be further divided into the Khadar and the Bhangar.

Bhabar is a narrow belt ranging between 8-10 km parallel to the Shiwalik foothills at the break-up of the slope. As a result of this, the streams and rivers coming from the mountains deposit heavy materials of rocks and boulders, and at times, disappear in this zone. South of the Bhabar is the Tarai belt, with an approximate width of 10-20 km where most of the streams and rivers re-emerge without having any properly demarcated channel, thereby, creating marshy and swampy conditions known as the Tarai.

Northern Plains is a featureless plain with a general elevation of 50-150 m above the mean sea level. The states of Haryana and Delhi form a water divide between the Indus and the Ganga river systems.

Rising from the height of 150 m above the river plains up to an elevation of 600-900 m is the irregular triangle known as the Peninsular plateau. Delhi ridge in the northwest, (extension of Aravalis), the Rajmahal hills in the east, Gir range in the west and the Cardamom hills in the south constitute the outer extent of the Peninsular plateau. However, an extension of this is also seen in the northeast, in the form of Shillong and Karbi-Anglong plateau. The Peninsular India is made up of a series of patland plateaus such as the Hazaribagh plateau, the Palamu plateau, the Ranchi plateau, the Malwa plateau, the Coimbatore plateau and the Karnataka plateau, etc.

On the basis of the prominent relief features, the Peninsular plateau can be divided into three broad groups:

• The Deccan Plateau
• The Central Highlands
• The North-eastern Plateau.

The Deccan Plateau is bordered by the Western Ghats in the west, Eastern Ghats in the east and the Satpura, Maikal range and Mahadeo hills in the north. Western Ghats are locally known by different names such as Sahyadri in Maharashtra, Nilgiri hills in Karnataka and Tamil Nadu and Anaimalai hills and Cardamom hills in Kerala. Western Ghats are comparatively higher in elevation and more continuous than the Eastern Ghats. Their average elevation is about 1,500 m with the height increasing from north to south. ‘Anaimudi (2,695 m), the highest peak of Peninsular plateau is located on the Anaimalai hills of the Western Ghats followed by Dodabetta (2,637 m) on the Nilgiri hills.

Some of the important ranges in Eastern Ghats include the Javadi hills, the Palconda . range, the Nallamala hills, the Mahendragiri hills, etc.

The Meghalaya plateau is further sub-divided into three:

• The Garo Hills
• The Khasi Hills
• The Jaintia Hills

These are named after the tribal groups inhabiting this region. An extension of this is also seen in the Karbi Anglong hills of Assam.

To the north-west of the Aravali hills lies the Great Indian Desert. It is a land of undulating topography dotted with longitudinal dunes and barchans. This region receives low rainfall below 150 mm per year; hence, it has arid climate with low vegetation cover.

On the basis of the location and active geomorphological processes, it can be broadly divided into two:

• The western coastal plains
• The eastern coastal plains.

There are two major island groups in India – one in the Bay of Bengal and the other in the Arabian Sea. The Bay of Bengal island groups consist of about 572 islands/islets. These are situated roughly between 6°N-14°N and 92°E -94°E. The two principal groups of islets include the Ritchie’s archipelago and the Labrynth island.

Some important mountain peaks in Andaman and Nicobar islands are Saddle peak (North Andaman – 738 m), Mount Diavolo (Middle Andaman – 515 m), Mount Koyob (South Andaman – 460 m) and Mount Thuiller (Great Nicobar – 642 m). These islands are located at a distance of 280 km-480 km off the Kerala coast. The entire island group.is built of coral deposits. There are approximately 36 islands of which 11 are inhabited. Minicoy is the largest island with an area of 453 sq. km.

Class 11 Geography Notes Chapter 2 Important Terms:

• Physiography: ‘Physiography’ of an area is the outcome of structure, process and the stage of development.
• Central axial range: The approximate length of the Great Himalayan range is known as the central axial range. It is 2,500 km from east to west
• Indo-Ganga-Brahmaputra Plain: It is a geological division of India that comprises the plains formed by the river Indus, the Ganga and the Brahmaputra.
• Bhabar: Bhabar is a narrow belt ranging between 8-10 km parallel to the Shiwalik foothills at the break-up of the slope. As a result of this, the streams and rivers coming from the mountains deposit heavy materials of rocks and boulders, and at times, disappear in this zone.
• Kashmir or North-western Himalayas: It comprise a series of ranges such as the Karakoram, Ladakh, Zaskar and Pir Panjal. The north-eastern part of the Kashmir Himalayas is a cold desert, which lies between the Greater Himalayas and the Karakoram ranges.
• Duns: The southernmost part of this region consists of longitudinal valleys. These are known as ‘duns’. Jammu dun and Pathankot dun are important examples.
• Tarai: South of the Bhabar is the Tarai belt, with an approximate width of 10-20 km where most of the streams and rivers re-emerge without having any properly demarcated channel, thereby, creating marshy and swampy conditions known as the Tarai.
• Bhangar: The south of Tarai is a belt consisting of old alluvial deposits which is known as the Bhangar.
• Khadar: The south of Tarai is a belt consisting of new alluvial deposits is known as Khadar.
• Dhaoladhar: The Lesser Himalayas is locally known as Dhaoladhar in Himachal Pradesh.
• Nagtibha: The Lesser Himalayas are called Nagtibha in Uttarakhand.
• Ten Degree Channel: The Andaman in the north and the Nicobar in the south are separated by a water body. It is called the Ten degree channel.
• The Peninsular Plateau: Rising from the height of 150 m above the river plains upto an elevation of 600-900 m is the irregular triangle known as the Peninsular plateau.
• The Central Highlands: They are bounded to the west by the Aravali range.
• Satpura Range: The Satpura range is formed by a series of scarped plateaus on the south, generally at an elevation varying between 600-900 m above the mean sea level.
• Barchans: The extension of the Peninsular plateau can be seen as far as Jaisalmer in the West, where it has been covered by the longitudinal sand ridges and crescent-shaped sand dunes. These are called barchans.
• Loktak: The physiography of Manipur is unique by the presence of a large lake known as ‘Loktak’.
• Molassis Basin: Mizoram is also known as the ‘Molassis basin’ which is made up of soft unconsolidated deposits.
• Kayals: Boatwaters are called kayals in Kerala.
• Karewas: Karewas are the thick deposits of glacial clay and other materials embedded with moraines.
• Dhaya: Bangal is called dhaya in Punjab.
• Bate: Khadar is called bate in Punjab.

Notes of Ch 1 India-Location| Class 11th Geography

India – Location

• India extends from Kashmir in the north to Kanniyakumari in the south and Arunachal Pradesh in the east to Gujarat in the west.

• India’s territorial limit further extends towards the sea up to 12 nautical miles (about 21.9 km) from the coast.

• The southern boundary extends up to 6°45′ N latitude in the Bay of Bengal.

• The latitudinal and longitudinal extent of India, they are roughly about 30 degrees, whereas the actual distance measured from north to south extremity is 3,214 km, and that from east to west is only 2,933 km.

• The distance between two longitudes decreases towards the poles whereas the distance between two latitudes remains the same everywhere.

• The southern part of the country lies within the tropics and the northern part lies in the sub-tropical zone or the warm temperate zone. This location is responsible for large variations in landforms, climate, soil types and natural vegetation in the country.

• From the values of longitude, it is quite visible that there is a variation of nearly 30 degrees, which causes a time difference of nearly two hours between the easternmost and the westernmost parts of our country

• A general understanding among the countries of the world to select the standard meridian in multiples of 7°30′ of longitude. That is why 82°30′ E has been selected as the ‘standard meridian’ of India. Indian Standard Time is ahead of Greenwich Mean Time by 5 hours and 30 minutes.

• There are some countries where there is more than one standard meridian due to their vast east-to-west extent. For example, the USA has seven time zones.

• India with its area of 3.28 million sq. km accounts for 2.4 percent of the world’s land surface area and stands as the seventh-largest country in the world.

Size

Indian subcontinent

• Indian subcontinent includes the countries — Pakistan, Nepal, Bhutan, Bangladesh, and India.

• The Himalayas, together with other ranges, have acted as a formidable physical barrier in the past.

• Except for a few mountain passes such as the Khyber, the Bolan, the Shipkila, the Nathula, the Bomdila, etc. it was difficult to cross it. These passes contributed towards the evolving of a unique regional identity of the Indian subcontinent.

• Peninsular part of India extends towards the Indian Ocean. This has provided the country with a coastline of 6,100 km in the mainland and 7,517 km in the entire geographical coast of the mainland plus the island groups.

• Andaman and Nicobar located in the Bay of Bengal and the Lakshadweep in the Arabian Sea.

India and its neighbours

• India is located in the south-central part of the continent of Asia, bordering the Indian ocean and its two arms extending in the form of the Bay of Bengal and the Arabian Sea.

• This maritime location of Peninsular India has provided links to its neighboring regions through the sea and air routes.

• Sri Lanka and the Maldives are the two island countries located in the Indian Ocean, which are our neighbors.

• Sri Lanka is separated from India by the Gulf of Mannar and Palk Strait.

Notes of Ch 16 Biodiversity and Conservation| Class 11th Geography

Introduction

• The basic cause for such weathering variations and resultant biodiversity is the input of solar energy and water.

• Biodiversity is a system in constant evolution, from a view point of species, as well as from view point of an individual organism

• Biodiversity is not found evenly on the earth.

• Biodiversity itself is a combination of two words, Bio (life) and diversity (variety). In simple terms, biodiversity is the number and variety of organisms found within a specified geographic region.

• It refers to the varieties of plants, animals and micro-organisms, the genes they contain and the ecosystems they form. It relates to the variability among living organisms on the earth, including the variability within and between the species and that within and between the ecosystems.

• Biodiversity can be discussed at three levels:
(i) Genetic diversity;
(ii) Species diversity;
(iii) Ecosystem diversity

Genetic Diversity

• Genes are the basic building blocks of various life forms. Genetic biodiversity refers to the variation of genes within species.

• Groups of individual organisms having certain similarities in their physical characteristics are called species.

• Human beings genetically belong to the homo sapiens group and also differ in their characteristics such as height, colour, physical appearance, etc., considerably. This is due to genetic diversity.

• This genetic diversity is essential for a healthy breeding of population of species.

Species Diversity

• This refers to the variety of species. It relates to the number of species in a defined area.

• The diversity of species can be measured through its richness, abundance and types. Some areas are more rich in species than others.

• Areas rich in species diversity are called hotspots of diversity.

Ecosystem Diversity

• The broad differences between ecosystem types and the diversity of habitats and ecological processes occurring within each ecosystem type constitute the ecosystem diversity.

• The ‘boundaries’ of communities and ecosystems are not very rigidly defined. Thus, the demarcation of ecosystem boundaries is difficult and complex.

Importance of Biodiversity

• Biodiversity has contributed in many ways to the development of human culture and, in turn, human communities have played a major role in shaping the diversity of nature at the genetic, species and ecological levels.

• Biodiversity plays the following roles: ecological, economic and scientific.

Ecological Role of Biodiversity

• Every organism, besides extracting its needs, also contributes something of useful to other organisms.

• Species capture and store energy, produce and decompose organic materials, help to cycle water and nutrients throughout the ecosystem, fix atmospheric gases and help regulate the climate. These functions are important for ecosystem function and human survival.

• The more diverse an ecosystem, better are the chances for the species to survive through adversities and attacks, and consequently, is more productive.

Economic Role of Biodiversity

• For all humans, biodiversity is an important resource in their day-to-day life.

• One important part of biodiversity is ‘crop diversity’, which is also called agro-biodiversity.

• Biodiversity is seen as a reservoir of resources to be drawn upon for the manufacture of food, pharmaceutical, and cosmetic products.

• This concept of biological resources is responsible for the deterioration of biodiversity.

• Some of the important economic commodities that biodiversity supplies to humankind are: food crops, livestock, forests, fish, medicinal resources, etc.

Scientific Role of Biodiversity

• Biodiversity is important because each species can give us some clue as to how life evolved and will continue to evolve.

• Biodiversity also helps in understanding how life functions and the role of each species in sustaining ecosystems of which we are also a species.

• The level of biodiversity is a good indicator of the state of our relationships with other living species. In fact, the concept of biodiversity is an integral part of many human cultures.

Loss of biodiversity

• Tropical regions which occupy only about one-fourth of the total area of the world, contain about three- fourth of the world human population. Over- exploitation of resources and deforestation have become rampant to fulfill the needs of large population.

• As these tropical rain forests contain 50 per cent of the species on the earth, destruction of natural habitats have proved disastrous for the entire biosphere.

• Natural calamities such as earthquakes, floods, volcanic eruptions, forest fires, droughts, etc. cause damage to the flora and fauna of the earth, bringing change the biodiversity of respective affected regions.

• Pesticides and other pollutants such as hydrocarbons and toxic heavy metals destroy the weak and sensitive species.

• Species which are not the natural inhabitants of the local habitat but are introduced into the system, are called exotic species.

• The International Union of Conservation of Nature and Natural Resources (IUCN) has classified the threatened species of plants and animals into three categories for the purpose of their conservation.

Endangered Species

• It includes those species which are in danger of extinction. The IUCN publishes information about endangered species world-wide as the Red List of threatened species.

• Red Panda — an endangered species

• Zenkeria Sebastinei — a critically endangered grass in Agasthiyamalai peak (India)

Vulnerable Species

• This includes the species which are likely to be in danger of extinction in near future if the factors threatening to their extinction continue.

• Survival of these species is not assured as their population has reduced greatly

Rare Species

• Population of these species is very small in the world; they are confined to limited areas or thinly scattered over a wider area.

Conservation of biodiversity

• Biodiversity is important for human existence. All forms of life are so closely interlinked that disturbance in one gives rise to imbalance in the others.

• There is an urgent need to educate people to adopt environment-friendly practices and reorient their activities in such a way that our development is harmonious with other life forms and is sustainable.

• There is an increasing consciousness of the fact that such conservation with sustainable use is possible only with the involvement and cooperation of local communities and individuals. For this, the development of institutional structures at local levels is necessary.

• The critical problem is not merely the conservation of species nor the habitat but the continuation of process of conservation.

• The Government of India along with 155 other nations have signed the Convention of Biodiversity at the Earth Summit held at Rio de Janeiro, Brazil in June 1992.

• The world conservation strategy has suggested the following steps for biodiversity conservation:

→ Efforts should be made to preserve the species that are endangered.
→ Prevention of extinction requires proper planning and management.
→ Varieties of food crops, forage plants, timber trees, livestock, animals and their wild relatives should be preserved;
→ Each country should identify habitats of wild relatives and ensure their protection.
→ Habitats where species feed, breed, rest and nurse their young should be safeguarded and protected.
→ International trade in wild plants and animals be regulated.

• To protect, preserve and propagate the variety of species within natural boundaries, the Government of India passed the Wild Life (Protection) Act, 1972, under which national parks and sanctuaries were established and biosphere reserves declared.

• There are some countries which are situated in the tropical region, they possess a large number of the world’s species diversity. They are called mega diversity centres.

• There are 12 such countries, namely Mexico, Columbia, Ecuador, Peru, Brazil, emocratic Republic of Congo, Madagascar, China, India, Malaysia, Indonesia and Australia in which these centres are located.

• Hotspots are defined according to their vegetation. Plants are important because these determine the primary productivity of an ecosystem.

• Most, but not all, of the hotspots rely on species-rich ecosystems for food, firewood, cropland, and income from timber. In Madagascar, for example, about 85 per cent of the plants and animals are found nowhere else in the world.

• Other hotspots in wealthy countries are facing different types of pressures. The islands of Hawaii have many unique plants and animals that are threatened by introduced species and land development.

Notes of Ch 15 Life on the Earth| Class 11th Geography

Introduction

• The biosphere includes all the living components of the earth. It consists of all plants and animals, including all the micro-organisms that live on the planet earth and their interactions with the surrounding environment.

• Most of the organisms exist on the lithosphere and/or the hydrosphere as well as in the atmosphere. There are also many organisms that move freely from one realm to the other.

• Life on the earth is found almost everywhere. Living organisms are found from the poles to the equator, from the bottom of the sea to several km in the air, from freezing waters to dry valleys, from under the sea to underground water lying below the earth’s surface.

Ecology

• Ecology is the study of the earth as a ‘household’, of plants, human beings, animals and micro-organisms. They all live together as interdependent components.

• Ecological Systems: The interactions of a particular group of organisms with abiotic factors within a particular habitat resulting in clearly defined energy flows and material cycles on land, water and air.

Ecological adaptation

• Different types of ecosystems exist with varying ranges of environmental conditions where various plants and animal species have got adapted through evolution.

Types of Ecosystems

• Terrestrial ecosystem- can be further be classified into ‘biomes’.

• A biome can be defined as the total assemblage of plant and animal species interacting within specific conditions. These include rainfall, temperature, humidity and soil conditions. Some of the major biomes of the world are: forest, grassland, desert and tundra biomes.

• Aquatic ecosystems- can be classed as marine and freshwater ecosystems. Marine ecosystem includes the oceans, estuaries and coral reefs. Freshwater ecosystem includes lakes, ponds, streams, marshes and bogs

Structure and Functions of Ecosystems

• The structure of an ecosystem involves a description of the available plant and animal species.

• From a structural point of view, all ecosystems consist of:
→ Abiotic
→ Biotic factors.

• Abiotic factors include rainfall, temperature, sunlight, atmospheric humidity, soil conditions, inorganic substances (carbon dioxide, water, nitrogen, calcium, phosphorus, potassium, etc.).

• Biotic factors include the producers, the consumers (primary, secondary, tertiary) and the decomposers.

• Producers include all the green plants, which manufacture their own food through photosynthesis.

• The primary consumers include herbivorous animals like deer, goats, mice and all plant-eating animals. The carnivores include all the flesh-eating animals like snakes, tigers and lions.

• Certain carnivores that feed also on carnivores are known as top carnivores like hawks and mongooses.

• Decomposers are those that feed on dead organisms (for example, scavengers like vultures and crows), and further breaking down of the dead matter by other decomposing agents like bacteria and various micro- organisms.

Two types of food-chains

• Grazing food-chain, the first level starts with plants as producers and ends with carnivores as consumers at the last level, with the herbivores being at the intermediate level. There is a loss of energy at each level which may be through respiration, excretion or decomposition. The levels involved in a food- chain range between three to five and energy is lost at each level.

• A detritus food-chain is based on autotrophs energy capture initiated by grazing animals and involves the decomposition or breaking down of organic wastes and dead matter derived from the grazing food-chain.

Types of Biomes

• There are five major biomes
(i) Forest
(ii) Desert
(iii) Grassland
(iv) Aquatic
(v) Altitudinal biomes

Forests

Subtypes:
A. Tropical
1. Equatorial
2. Deciduous
B. Temperate
C. Boreal

Regions:
A. 1. 10° N-S A
2. 10° – 25° N-S
B. Eastern North America, N.E. Asia, Western and Central Europe
C. Broad belt of Eurasia and North America (parts of Siberia, Alaska, Canada and Scandinavia)

Climatic Characteristics:
A. 1. Temp. 20- 25C, evenly distributed
2. Temp. 25- 30°C, Rainfall, ave. ann. 1,000mm, seasonal
B. Temp. 20-30°
C. Rainfall evenly distributed 7501,500mm, Welldefined seasons and distinct winter.
D. Short moist moderately warm summers and long cold dry winter; very low temperatures. Precipitation mostly snowfall 400 -1,000 mm

Soil:
A. 1. Acidic, poor in nutrients
2. Rich in Nutrients
B. Fertile, enriched with decaying litter
C. Acidic and poor in nutrients, thin soil cover

Flora and Fauna:
A. Multi-layered canopy tall and large trees.
A2. Less dense, trees of medium height;many varieties coexist. Insects,bats, birds and mammals are common species in both.
B. Moderately dense broad leaved trees. With less diversity of plant species. Oak, Beach, Maple etc. are some common species. Squirrels, rabbits, skunks, birds, black bears, mountain lions etc.

C. Evergreen conifers like pine, fur and spruce etc. Wood peckers, hawks, bears, wolves, deer, hares and bats are common animals.

Desert

Subtypes:

A. Hot and Dry desert

B. Semi arid desert

C. Coastal desert

D. Cold desert

Regions:

A. Sahara, Kalahari, Marusthali, Rub-el-Khali

B. Marginal areas of hot deserts

C. Atacama

D. Tundra climatic regions

Climatic Characteristics:

A. Temp. 20 – 45°C.

B. 21 – 38°C.

C. 15 – 35°C.

D. 2 – 25°C A-D Rainfall is less than 50 mm

Soil:
Rich in nutrients with little or no organic matter

Flora and Fauna:
A-C. Scanty vegetation; few large mammals, insects, reptiles and birds
D. Rabbits, rats, Antelopes and ground squirrels

Grassland

Subtypes:
A. Tropical Savannah
B. Temperate Steppe

Regions:
A. Large areas of Africa, Australia, South America and India
B. Parts of Eurasia and North America

Climatic Characteristics:
A. Warm hot climates, Rainfall 500-1,250 mm
B. Hot summers and cold winter. Rainfall 500 900 mm

Soil:
A. Porous with thin layer of humus.
B. Thin flocculated soil, rich in bases

Flora and Fauna:
A. Grasses; trees and large shrubs absent; giraffes zebras, buffalos, leopards, hyenas, elephants, mice, moles, snakes and worms etc., are common animals
B. Grasses; occasional trees such as cotton​woods, oaks and willows; gazelles, zebras, rhin-oceros, wild horses, lions, varieties of birds, worms, snakes etc., are common animal

Aquatic

Subtypes:
A. Freshwater
B. Marine

Regions:
A. Lakes, streams, rivers and wetlands
B. Oceans, coral reefs, lagoons and estuaries

Climatic Characteristics:
A-B Temperatures vary widely with cooler air temperatures and high humidity

Soil:
A. Water, swamps and marshes
B. Water, tidal swamps and marshes

Flora and Fauna: Algal and other aquatic and marine plant communities with varieties of water dwelling animals.

Altitudinal

Regions:
Slopes of high mountain ranges like the Himalayas, the Andes and the Rockies

Climatic Characteristics:
Temperature and precipitation vary depending upon latitudinal zone

Soil:
Regolith over slopes

Flora and Fauna:
Deciduous to tundra vegetation varying according to altitude

Biogeochemical Cycles

• The sun is the basic source of energy on which all life depends. This energy initiates life processes in the biosphere through photosynthesis, the main source of food and energy for green plants.

• Out of the total solar insolation that reaches the earth’s surface, only a very small fraction (0.1 per cent) is fixed in photosynthesis.

• Life on earth consists of a great variety of living organisms. These living organisms exist and survive in a diversity of associations. Such survival involves the presence of systemic flows such as flows of energy, water and nutrients.

• Balance of the chemical elements is maintained by a cyclic passage through the tissues of plants and animals. The cycle starts by absorbing the chemical elements by the organism and is returned to the air, water and soil through decomposition.

• These cycles are largely energised by solar insolation. These cyclic movements of chemical elements of the biosphere between the organism and the environment are referred to as biogeochemical cycles.

• There are two types of biogeochemical cycles : the gaseous and the sedimentary cycle. In the gaseous cycle, the main reservoir of nutrients is the atmosphere and the ocean.

• In the sedimentary cycle, the main reservoir is the soil and the sedimentary and other rocks of the earth’s crust.

The Water Cycle

• All living organisms, the atmosphere and the lithosphere maintain between them a circulation of water in solid, liquid or gaseous form referred to as the water or hydrologic cycle.

The Carbon Cycle

• Carbon basic elements of all living organisms.

• The carbon cycle is mainly the conversion of carbon dioxide. This conversion is initiated by the fixation of carbon dioxide from the atmosphere through photosynthesis.

• Such conversion results in the production of carbohydrate, glucose that may be converted to other organic compounds such as sucrose, starch, cellulose, etc. Here, some of the carbohydrates are utilised directly by the plant itself.

• During this process, more carbon dioxide is generated and is released through its leaves or roots during the day. The remaining carbohydrates not being utilised by the plant become part of the plant tissue. Plant tissues are either being eaten by the herbivorous animals or get decomposed by the micro- organisms.

• The herbivores convert some of the consumed carbohydrates into carbon dioxide for release into the air through respiration.

• The micro-organisms decompose the remaining carbohydrates after the animal dies. The carbohydrates that are decomposed by the micro-organisms then get oxidised into carbon.

The Oxygen Cycle

• Oxygen is the main by-product of photosynthesis. It is involved in the oxidation of carbohydrates with the release of energy, carbon dioxide and water.

• The cycling of oxygen is a highly complex process. Oxygen occurs in a number of chemical forms and combinations. It combines with nitrogen to form nitrates and with many other minerals and elements to form various oxides such as the iron oxide, aluminium oxide and others.

• Much of oxygen is produced from the decomposition of water molecules by sunlight during photosynthesis and is released in the atmosphere through transpiration and respiration processes of plants.

The Nitrogen Cycle

• Nitrogen is a major constituent of the atmosphere comprising about seventy-nine per cent of the atmospheric gases.

• It is also an essential constituent of different organic compounds such as the amino acids, nucleic acids, proteins, vitamins and pigments.

• Only a few types of organisms like certain species of soil bacteria and blue green algae are capable of utilising it directly in its gaseous form.

• Generally, nitrogen is usable only after it is fixed. Ninety per cent of fixed nitrogen is biological.

• The principal source of free nitrogen is the action of soil micro-organisms and associated plant roots on atmospheric nitrogen found in pore spaces of the soil.

• Nitrogen can also be fixed in the atmosphere by lightning and cosmic radiation. In the oceans, some marine animals can fix it.

• After atmospheric nitrogen has been fixed into an available form, green plants can assimilate it.

• Herbivorous animals feeding on plants, in turn, consume some of it.

• Dead plants and animals, excretion of nitrogenous wastes are converted into nitrites by the action of bacteria present in the soil.

• Some bacteria can even convert nitrites into nitrates that can be used again by green plants. There are still other types of bacteria capable of converting nitrates into free nitrogen, a process known as denitrification.

Other Mineral Cycles

Phosphorus, sulphur, calcium and potassium

• They usually occur as salts dissolved in soil water or lakes, streams and seas.

• Mineral salts come directly from the earth’s crust by weathering where the soluble salts enter the water cycle, eventually reaching the sea.

• Other salts are returned to the earth’s surface through sedimentation, and after weathering, they again enter the cycle.

• All living organisms fulfill their mineral requirements from mineral solutions in their environments. Other animals receive their mineral needs from the plants and animals they consume.

• After the death of living organisms, the minerals are returned to the soil and water through decomposition and flow.

Ecological Balance

• Ecological balance is a state of dynamic equilibrium within a community of organisms in a habitat or ecosystem. It can happen when the diversity of the living organisms remains relatively stable.

• Gradual changes do take place but that happens only through natural succession. It can also be explained as a stable balance in the numbers of each species in an ecosystem. This occurs through competition and cooperation between different organisms where population remains stable.

• This balance is brought about by the fact that certain species compete with one another determined by the environment in which they grow. This balance is also attained by the fact that some species depend on others for their food and sustenance.

• Such accounts are encountered in vast grasslands where the herbivorous animals (deer, zebras, buffaloes, etc.) are found in plenty. On the other hand, the carnivorous animals (tigers, lions, etc.) that are not usually in large numbers, hunt and feed on the herbivores, thereby controlling their population.

• In the plants, any disturbance in the native forests such as clearing the forest for shifting cultivation usually brings about a change in the species distribution.

• This change is due to competition where the secondary forest species such as grasses, bamboos or pines overtakes the native species changing the original forest structure. This is called succession.

Notes of Ch 14 Movements of Ocean Water| Class 11th Geography

Introduction

• The horizontal motion refers to the ocean currents and waves. The vertical motion refers to tides.

Ocean currents are the continuous flow of huge amount of water in a definite direction while the waves are the horizontal motion of water.

• Water moves ahead from one place to another through ocean currents while the water in the waves does not move, but the wave trains move ahead.

• The vertical motion refers to the rise and fall of water in the oceans and seas. Due to attraction of the sun and the moon, the ocean water is raised up and falls down twice a day. The upwelling of cold water from subsurface and the sinking of surface water are also forms of vertical motion of ocean water.

Waves

• Waves are actually the energy, not the water as such, which moves across the ocean surface.

• Water particles only travel in a small circle as a wave passes. Wind provides energy to the waves.

• Wind causes waves to travel in the ocean and the energy is released on shorelines.

• The motion of the surface water seldom affects the stagnant deep bottom water of the oceans. As a wave approaches the beach, it slows down. This is due to the friction occurring between the dynamic water and the sea floor.

• When the depth of water is less than half the wavelength of the wave, the wave breaks.

• The largest waves are found in the open oceans. Waves continue to grow larger as they move and absorb energy from the wind.

• When a breeze of two knots or less blows over calm water, small ripples form and grow as the wind speed increases until white caps appear in the breaking waves.

• A wave’s size and shape reveal its origin. Steep waves are fairly young ones and are probably formed by local wind.

• Slow and steady waves originate from far away places, possibly from another hemisphere.

• The maximum wave height is determined by the strength of the wind, i.e. how long it blows and the area over which it blows in a single direction.

• Waves travel because wind pushes the water body in its course while gravity pulls the crests of the waves downward. The falling water pushes the former troughs upward, and the wave moves to a new position

Characteristics of Waves

• Wave crest and trough: The highest and lowest points of a wave are called the crest and trough respectively.

• Wave height: It is the vertical distance from the bottom of a trough to the top of a crest of a wave.

• Wave amplitude: It is one-half of the wave height.

• Wave period: It is merely the time interval between two successive wave crests or troughs as they pass a fixed point.

• Wavelength: It is the horizontal distance between two successive crests.

• Wave speed: It is the rate at which the wave moves through the water, and is measured in knots.

Tides

• The periodical rise and fall of the sea level, once or twice a day, mainly due to the attraction of the sun and the moon, is called a tide.

• Movement of water caused by meteorological effects (winds and atmospheric pressure changes)are called surges. Surges are not regular like tides.

• The moon’s gravitational pull to a great extent and to a lesser extent the sun’s gravitational pull, are the major causes for the occurrence of tides.

• Another factor is centrifugal force, which is the force that acts to counter balance the gravity.

• Together, the gravitational pull and the centrifugal force are responsible for creating the two major tidal bulges on the earth. On the side of the earth facing the moon, a tidal bulge occurs while on the opposite side though the gravitational attraction of the moon is less as it is farther away, the centrifugal force causes tidal bulge on the other side.

• The tidal bulges on wide continental shelves, have greater height. When tidal bulges hit the mid-oceanic islands they become low. The shape of bays and estuaries along a coastline can also magnify the intensity of tides. Funnel-shaped bays greatly change tidal magnitudes.

• When the tide is channelled between islands or into bays and estuaries they are called tidal currents.
Tides of Bay of Fundy, Canada The highest tides in the world occur in the Bay of Fundy in Nova Scotia, Canada. The tidal bulge is 15 – 16 m

Types of Tides

Tides based on Frequency

• Semi-diurnal tide : The most common tidal pattern, featuring two high tides and two low tides each day. The successive high or low tides are approximately of the same height.

• Diurnal tide : There is only one high tide and one low tide during each day. The successive high and low tides are approximately of the same height.

• Mixed tide : Tides having variations in height are known as mixed tides. These tides generally occur along the west coast of North America and on many islands of the Pacific Ocean.

Tides based on the Sun, Moon and the Earth Positions

• The height of rising water (high tide) varies appreciably depending upon the position of sun and moon with respect to the earth. Spring tides and neap tides come under this category:

• Spring tides: The position of both the sun and the moon in relation to the earth has direct bearing on tide height.

• When the sun, the moon and the earth are in a straight line, the height of the tide will be higher.

• These are called spring tides and they occur twice a month, one on full moon period and another during new moon period.

• Neap tides: Normally, there is a seven day interval between the spring tides and neap tides.

• At this time the sun and moon are at right angles to each other and the forces of the sun and moon tend to counteract one another.

• The Moon’s attraction, though more than twice as strong as the sun’s, is diminished by the counteracting force of the sun’s gravitational pull.

• Once in a month, when the moon’s orbit is closest to the earth (perigee), unusually high and low tides occur. During this time the tidal range is greater than normal. Two weeks later, when the moon is farthest from earth (apogee), the moon’s gravitational force is limited and the tidal ranges are less than their average height.

• The time between the high tide and low tide, when the water level is falling, is called the ebb. The time between the low tide and high tide, when the tide is rising, is called the flow or flood.

Importance of Tides

• Since tides are caused by the earth-moon-sun positions which are known accurately, the tides can be predicted well in advance.

• This helps the navigators and fishermen plan their activities. Tidal flows are of great importance in navigation.

• Tidal heights are very important, especially harbours near rivers and within estuaries having shallow ‘bars’ at the entrance, which prevent ships and boats from entering into the harbour.

• Tides are also helpful indesilting the sediments and in removing polluted water from river estuaries.

• Tides are used to generate electrical power (in Canada, France, Russia, and China).

• A 3 MW tidal power project at Durgaduani in Sunderbans of West Bengal is under way.

Ocean Currents

• Ocean currents are like river flow in oceans. They represent a regular volume of water in a definite path and direction.

• Ocean currents are influenced by two types of forces namely:
(i) primary forces that initiate the movement of water;
(ii) secondary forces that influence the currents to flow.

• The primary forces that influence the currents are:
(i) heating by solar energy;
(ii) wind;
(iii) gravity;
(iv) Coriolis force.

• Heating by solar energy causes the water to expand. That is why, near the equator the ocean water is about 8 cm higher in level than in the middle latitudes. This causes a very slight gradient and water tends to flow down the slope.

• Wind blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water surface affects the movement of the water body in its course.

• Gravity tends to pull the water down the pile and create gradient variation.

• The Coriolis force intervenes and causes the water to move to the right in the northern hemisphere and to the left in the southern hemisphere. These large accumulations of water and the flow around them are called Gyres.

• Differences in water density affect vertical mobility of ocean currents

Characteristics of Ocean Currents

• Currents are referred to by their “drift”.

• Usually, the currents are strongest near the surface and may attain speeds over five knots. At depths, currents are generally slow with speeds less than 0.5 knots.

• The speed of a current as its “drift.” Drift is measured in terms of knots. The strength of a current refers to the speed of the current.

Types of Ocean Currents

• The ocean currents may be classified based on their depth as:

(i) Surface currents

(ii) Deep water currents

• Surface currents constitute about 10 per cent of all the water in the ocean, these waters are the upper 400 m of the ocean; deep water currents make up the other 90 per cent of the ocean water.

• These waters move around the ocean basins due to variations in the density and gravity.

• Ocean currents can also be classified based on temperature as:

(i) Cold currents

(ii) Warm currents

• Cold currents bring cold water into warm water areas. These currents are usually found on the west coast of the continents in the low and middle latitudes (true in both hemispheres) and on the east coast in the higher latitudes in the Northern Hemisphere.

• Warm currents bring warm water into cold water areas and are usually observed on the east coast of continents in the low and middle latitudes (true in both hemispheres). In the northern hemisphere they are found on the west coasts of continents in high latitudes.

Major Ocean Currents

• Major ocean currents are greatly influenced by the stresses exerted by the prevailing winds and Coriolis force.

• The oceanic circulation pattern roughly corresponds to the earth’s atmospheric circulation pattern.

• The air circulation over the oceans in the middle latitudes is mainly anticyclonic (more pronounced in the southern hemisphere than in the northern hemisphere).

• In regions of pronounced monsoonal flow, the monsoon winds influence the current movements.

• Due to the coriolis force, the warm currents from low latitudes tend to move to the right in the northern hemisphere and to their left in the southern hemisphere.

• The oceanic circulation transports heat from one latitude belt to another in a manner similar to the heat transported by the general circulation of the atmosphere.

• The cold waters of the Arctic and Antarctic circles move towards warmer water in tropical and equatorial regions, while the warm waters of the lower latitudes move pole wards.

Effects of Ocean Currents

• Ocean currents have a number of direct and indirect influences on human activities.

• West coasts of the continents in tropical and subtropical latitudes (except close to the equator) are bordered by cool waters.

• The best fishing grounds of the world exist mainly in these mixing zones.

• There is fog, but generally the areas are arid.

• The mixing of warm and cold currents help to replenish the oxygen and favor the growth of planktons, the primary food for fish population.

• They are characterized by cool summers and relatively mild winters with a narrow annual range of temperatures.

• West coasts of the continents in the middle and higher latitudes are bordered by warm waters which cause a distinct marine climate.

• Warm currents flow parallel to the east coasts of the continents in tropical and subtropical latitudes. This results in warm and rainy climates.

• These areas lie in the western margins of the subtropical anti-cyclones.

• Their average temperatures are relatively low with a narrow diurnal and annual ranges.