Valley winds are also called as anabatic winds.

Mountain winds are also called as katabatic winds or drainage winds.

Below is the list of various Local Winds and their names in those regions:

Bora (north Adriatic coast)

Mistral (southern France)

Santa Ana (California)

Blizzards (Antarctic region)

Cape Doctor (dry south-easterly wind that blows on the South African coast in summer)

Chinook also called as "snow eater" (Rocky Mountains, a mountain range in the western North America)

Elephanta (It is a strong southerly or south-easterly wind which blows on the Malabar coast of India during the months of September and October and marks the end of the southwest monsoon.)

föhn wind or foehn wind (Central Europe)

Fremantle Doctor (afternoon sea breeze from the Indian Ocean which cools Perth, Western Australia during summer)

Punas (Andes [world's longest continental mountain range] along the western coast in South America )

Sirocco (this is a hot dust laden wind of Saharan origin blowing eastwards from Sahara across the Mediterranean)

Solano (wind of Saharan origin blowing from Sahara towards the Iberian Peninsula). Iberian Peninsula is located in the extreme southwest of Europe and includes the modern-day sovereign states of Spain, Portugal and Andorra, as well as the British Overseas Territory of Gibraltar.

Harmattan (a relatively cooler dry wind blowing over Sahara in winter season).

Loo (A local hot wind of desert origin blows towards east across the northern plain of India in summer season. This dry hot wind raises temperature significantly in the Ganga Valley up to as far as Bihar).

Cyclones and anticyclones are two special pressure and wind systems. They are also called as variable winds.

A cyclone is a system of very low pressure in the centre surrounded by increasingly high pressure outwards. In a cyclone, the winds blow in a circular manner in a clockwise direction in the southern hemisphere and in an anticlockwise direction in the northern hemisphere.

Cyclones develop in both tropical and temperate regions and accordingly they are categorised as tropical cyclones and temperate cyclones.

Tropical cyclones are very intense and cause great loss to life and property in coastal areas. They are known as cyclones in the Indian Ocean, hurricanes in the West Indies, typhoons in the China Sea and willy-willies in northwest Australia. They are also called depressions.

The winds in a cyclone blow in a circular manner and the flow of air in them is convergent. Consequently, the air rises in the central part and it results in heavy rainfall. The eye is found only in tropical cyclones.

A Tornado is a very strong tropical cyclone of a smaller size. They are specially feared in the Mississippi Valley in the USA and here they are called twisters.

The temperate cyclones develop in the mid latitude regions and the convergence of air masses with contrasting thermal characteristics gives rise to development of these cyclones. Unlike the tropical cyclones, the temperate cyclones do not have an eye.

Anticyclones are the centres of high pressure and they are the opposite of cyclones in all respects. They are centres of high pressure with gentle outward flow of air. The air circulation is clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere. The high pressure belts in the polar areas and the subtropical regions are the important anticyclonic areas. Anticyclones involve a divergent flow of air from an area of high pressure.

The direction of winds is determined by the pressure gradient and the coriollis effect.

The velocity of winds is a function of the steepness of pressure gradient and is measured with the help of an instrument called anemometer.

Winds are given various names on the basis of their velocity and a scale called Beufort Scale is followed for such classification of winds.

Scale Number Wind Velocity (kms per hour) Description of Wind

0  0-1.5 [Calm]

1 1.6-5 [Light air]

2 6-11 [Slight breeze]

3 12-19 [Gentle breeze]

4 20-29 [Moderate breeze]

5 30-39 [Fresh breeze]

6 40-50 [Strong breeze]

7 51-61 [High wind]

8 62-74 [Gale]

9 75-87 [Strong gale]

10 88-101 [Whole gale]

11 102-120 [Storm]

12 Over 120 [Hurricane]

Water occurs in three states: solid as ice (frozen), liquid as water and gaseous as water vapour. Below are the methods by which water changes it state from one to the other:

From                    To                                    Method

Vapour state       Liquid state                Condensation

Vapour state        Solid state                  Sublimation or deposition

Liquid state          Vapour state              Evaporation

Liquid state           Solid state                  Freezing

Solid state              Liquid state               Melting

Solid state               Vapour state             Sublimation

The term humidity refers to the amount of water vapour present in the air.

For any specific temperature there is a limit to the quantity of water vapour that can be held by the air. This limit is called the saturation point.

The proportion of water vapour present relative to the maximum quantity at a given temperature is called relative humidity and is expressed as percentage.

Saturation point means a relative humidity of 100 per cent.

The relative humidity can be changed either by increasing or decreasing the amount of water vapour present in the air or by changing the temperature of the air.

The term absolute humidity denotes the actual quantity of water vapour present in the air and it is defined as the weight of water vapour (grammes) in a given volume of air (cubic metre).

The term specific humidity is applied to express the ratio of weight of water vapour to the weight of moist air (including water vapour). It is stated as grammes of water vapour per kilogram of moist air.

Humidity is measured by an instrument called hygrometer.

Humidity can also be measure by an instrument called sling psychrometer.

Hygrograph is an instrument which plots a graph of relative humidity around the clock.

The column of air at any point exerts a pressure. The amount of pressure exerted by a given column of air differs according to the varying amounts of water vapour present in it. That part of barometric pressure due to water vapour alone is known as vapour pressure. The maximum vapour pressure at any temperature occurs when the air is saturated.

Vapour pressure can be measured by using dry and wet-bulb temperature in association with a set of statistical tables.

The vapour pressure is maximum at the equator (about 30 mb) and it decreases towards the poles (less than 10 mb).

The term Condensation is applied to the process of the change of the state of water from vapour to liquid. Condensation is the basis of all kinds of precipitation.

Precipitation is the fall of water from the atmosphere to the ground in any form.

The term dew point is applied to that critical temperature at which air gets fully saturated with the present amount of moisture.

Dew Point is the temperature at which the relative humidity of the concerned parcel of air will become 100 per cent without any addition of water vapour to it. Condensation usually follows if the temperature of the air falls below the dew point.

Clouds consist of very small droplets of water or minute crystals of ice, so small that can be sustained by even the slightest upward movement of air.

In order for cloud droplets to form, it is necessary that microscopic particles of dust or smoke with a high affinity for water (hygroscopic particles) are present in the air and serve as condensation nuclei.

In the absence of hygroscopic particles in the atmosphere, condensation becomes difficult even though the air may have cooled below the dew point.

Water vapour in the air that fails to condense due to lack of hygroscopic particles or any other cause in spite of the air parcel having been cooled below the dew point is called super-cooled moisture. This phenomenon is rare and generally confined to the upper parts of the tropopause.

It is possible for super-cooled moisture to have relative humidity of more than 100 per cent.

Clouds are of different types and they can be classified on the basis of their form and altitude.

On the basis of form, clouds are known as stratiform or layered types, and cumuliform or massive types.

On the basis of altitude, clouds are called cirrus (highest clouds) and alto (medium height).

The combination of two different types of clouds (viz., based on form and altitude) leads to cloud varieties such as cirrocumulus, cirrostratus, altocumulus and altostratus.

To identify a cloud from which rain or snow falls, the term "nimbo or nimbus" is appended to the cloud type, e.g., nimbostratus and cumulonimbus.

Cirrus (highest clouds) is a wispy, fibrous cloud and is associated with fair weather.

Stratus is a low dense cloud that is associated with bad weather, and it usually brings drizzle. It presents with a gray look. Fog is a very low stratus cloud.

Cumulus Clouds are massive clouds and they are also called as wool clouds.

At night, the earth surface and various objects such as leaves etc. may frequently become cooler than the air above it. This causes water vapour contained in the air to get condensed and deposited on the cooled surface. This is known as Dew.

Dew is more likely to occur on clear and calm nights when the radiation from the ground is rapid and the surface cools sufficiently.

Dew is not likely to occur on cloudy nights as the cooling of the surface is not complete due to the greenhouse effect of the clouds.

In winter season the cooling of the suface may cause the ground temperature to fall below the freezing point. In such a situation the moisture contained in air condenses and freezes on various objects on the ground making a thin layer of ice. This is called frost.

Frost is harmful to crops and irrigating the fields is attempted as a precaution against frost. Small and tender plants can also be protected from frost by keeping them covered at night.

Fog can be defined as a very low stratus cloud that has formed close to the ground. The visibility of fog is less than one km.

Smog is also called as smoke fog. Smog is a combination of water particles and fine particles of carbon and other substances contained in smoke.

Smog occurs in areas containing large amounts of smoke, for example industrial areas. It develops more quickly than the fog and lasts longer. Due to the presence of particles of substances like sulphur, smog gives an acid character to fog.

Mist is also a type of fog and the visibility in the case of mist is 1 km to 2 km. In case of mist water droplets occur in the lower layers of atmosphere.

Haze is formed by water particles that have condensed in the atmosphere and the visibility in this case is more than 1 km but less than 2 km.

The term precipitation refers to falling of water, snow or hail from the clouds and it results when condensation is occurring rapidly within a cloud.

Forms of Precipitation: Precipitation may occur in different forms, such as, Rainfall, sleet, snowfall and hail.

Rainfall: The most common form of precipitation is rain and it is formed when many cloud droplets coalesce into drops too large to remain suspended in the air. Rainfall occurs when the dew point of air is above the freezing point so that the condensing moisture is converted to water droplets.

Sleet: The raindrops which freeze before reaching the ground and precipitation occurs in the form of ice pellets, is called sleet.

Snowfall: Snow consists of masses of fine crystals. Snowfall occurs as a result of sublimation. The dew point of air for this to occur should be below the freezing point.

Hail: Hail consists of masses of ice with layered structure. It occurs when there are very strong updrafts in the clouds carrying raindrops up to high altitude causing them to freeze. This is common when the condensation occurs in a strong convective cell of air.

For condensation and precipitation to occur it is necessary that the air cooled to the dew point and the water vapour is converted to the liquid or solid state.

Condensation occurs when the dew point of the air is above the freezing point.

Sublimation occurs when the dew point of the air is below the freezing point.

The simplest means of cooling of air in the atmosphere is through uplift. The rising air expands due to reduced pressure of the atmosphere and its temperatures falls. This process is called adiabatic cooling.

Besides the cooling of the air, presence of condensation nuclei is also necessary for condensation to occur. These small hygroscopic particles serve as the nuclei for the formation of water droplets or ice crystal and in the absence of these particles moisture may remain in super cooled form and no condensation may take place.

Types of Precipitation: On the basis of the mechanism of uplift of air the precipitation can be convectional, orographic, cyclonic or frontal.

Convectional precipitation is as a result of convection. Convection can be defined as a vertical movement of particles of a gas or liquid. Convectional precipitation mostly occurs in equatorial and savanna regions.

Orographic precipitation is caused by landforms. It is sometimes also called mountain precipitation. This type of precipitation is caused by the air that is forced to rise up by the physical obstructions like mountains. Much of the precipitation in the northern plains of India during the southwest monsoon is due to Orographic precipitation.

When the air is caused to rise upwards due to cyclonic circulation, the resulting precipitation is said to be Cyclonic precipitation. A cyclone is an area of low pressure and air from all around flows towards this central low-pressure area. The convergent flow of air leads to uplift of air and it causes heavy precipitation. Cyclonic Precipitation occurs in both tropical and temperate regions.

Tropical cyclones cause heavy rainfall accompanied by high velocity winds. Parts of AP, Orissa and West Bengal are highly prone to such cyclones.

In contrast to Tropical cyclones, the temperate cyclones are less intense. The winter rains in India are caused by temperate cyclones called westerly disturbances in India.

The uplift of air may be caused due to formation of a front in an area where a cold air mass converges against a warm air mass. In such a situation the cold air lifts the warm air and it may result n condensation and precipitation. Such precipitation is called frontal precipitation. Development of such fronts often leads to formation of temperate cyclones. Hence frontal precipitation is often considered as cyclonic precipitation.

The distribution of rainfall around the world is highly uneven. Chief factors affecting distribution are: distance from the equator, distance from the sea, direction of the winds, and the presence and direction of mountains. Generally the amount of precipitation decreases moving away from the equator.

Mountains play an important role in causing rainfall, if they lie in the path and at right angle to the wind direction. The obstruction caused by the mountains causes the air to rise and this cause rainfall. On the other hand if there are no such barriers in the path of the winds, even though air may be fairly moist, no rainfall may occur.

Mountains extending in a direction parallel to the wind direction fail to cause the obstruction and this fail to cause rainfall.

The Himalayas and the Western Ghats in India cause obstruction to the winds and thus cause rainfall, the Aravallis extending in a direction parallel to the southwest monsoon blowing in from the Arabian Sea fail to cause such an obstruction and any rainfall in western parts of Rajasthan and Gujarat.

Distribution of rainfall is shown on a map with the help of isohyets, lines joining places receiving the same amount of rainfall.

The lee side (opposite side) of the mountain gets no precipitation. This is known as rain-shadow effect and the concerned area is called the rain-shadow area.

When two air masses with contrasting thermal characteristics converge in a particular region the two types of air do not mix readily and a boundary zone is produced. This zone of separation or interaction between the two air masses is called a front.

A front along which a warmer air mass rises over a layer of colder air is called as anafront. A warm front typically behaves as an anafront.

When warm air in the frontal zone is not allowed to rise over the cold air due to air subsidence at high level. Such a depressed frontal zone is called a katafront.

The Köppen climate classification scheme divides climates into five main groups, each having several types and subtypes. Each particular climate type is represented by a 2 to 4 letter symbol. Koeppen divided the world climate into five major groups and each designated by a letter code as A: Tropical Climate ; B: Dry Climate; C: Humid Mesothermal; D: Humid Mesothermal Climate ; E: Polar Climate; and H: Mountain or Highland Climate or Alpine Climate (The Alpine climates are considered to be part of group E.)

In the Koeppen climate classification, out of the major groups, four have positive moisture balances and only one the (B) group is characterized by water deficit.

A) Tropical Climate: This climate is typical of tropical areas, where the mean monthly temperature remains generally above 22 degrees C, and they do not have a perceptible winter season.

Major subtypes of A) Tropical Climate are the tropical rainforest, tropical monsoon, and the tropical savanna climates.

Tropical rainforest climate is characterized by year round precipitation, and areas experiencing this climate support dense evergreen forests of tall trees. The precipitation is generally over 250 cm and the average temperature is about 27 degrees C. The climate of the equatorial regions such as Zaire Basin and Amazonia is of this type.

Tropical monsoon climate has seasonal rainfall. Annual average temperature is 26 degrees C. Rainfall occurs in summer and it may be as high as 300 cm in favourable locations. Vegetation in this region is of deciduous type (i.e., the trees shed their leaves during the dry season). India and countries of South East Asia constitute a major area of this type of climate.

In the Tropical savanna climate, the total amount of rainfall is lesser, about 160 cm. Annual average temperatures is about 23 degrees C and the annual range is higher than the other two types of tropical climates. Vegetation is of open thorny type. Savanna type of climate is transitional between the tropical wet climates towards the equator and the dry climates towards the poles. Parts of northern Australia, savanna regions of Africa, and Venezuela are among the typical examples of the areas of this type of climate. Savannas are the areas of summer rainfall.

B. Dry Climate: This climate is characterized by a general water deficit. It has two major subtypes, tropical and subtropical deserts and the tropical and subtropical steppes.

The tropical and subtropical deserts have a temperature of about 38 degrees C with an annual range of about 25 degrees C. The average rainfall is about 25 cm to 40 cm. The typical areas of the tropical desert type of climate are the Sahara, Atacama, Thar, Arabian and Kalahari deserts and also a vast area in Australia. Most of the tropical deserts occupy the western margins of the continents near the tropics. The subtropical deserts are usually in the interiors of the continents. The tropical deserts are also called the hot deserts.

The tropical and subtropical steppes are areas of comparatively lower temperature and slightly more precipitation compared to the tropical and subtropical deserts type of climate. Annual average temperature is about 21 degrees C. Temperate grasses are the chief vegetation of these regions. American Prairies and Eurasian Steppes are the major areas of these grasslands. These regions are ideally suited for the cultivation of grain crops such as wheat.

C) Humid Mesothermal Climate: This climate is subdivided into three main types, the Mediterranean type, China type and West European type.

Mediterranean type of climate is typical of western coastal areas of the continents between 30 degrees and 45 degrees latitude in both the hemispheres. The annual average temperature is about 16 degrees C. Annual rainfall is 40 to 60 cm and occurs in winters while the summers are dry. Olives, grapevine and the citrus family fruits are the chief products of these regions. Areas around the Mediterranean Sea, central region of Chile, southern tip of South Africa and south western part of Australia are the chief regions of this climate.

The China type of climate is characterized by warm summers and cool winters. The average temperature is about 19 degrees C and rainfall about 120 cm. This type climate is experienced in the eastern parts of the continents in approximately the same latitudes in which the Mediterranean climate is found. The major areas of this type of climate are in China, Argentina, southeastern USA and the eastern coastal regions of Australia.

The typical area of the West European type of climate is the coastal region of Western Europe. This type of regions extends Europe, parts of North America, South America and eastern coastal region of Australia. Average annual temperature is about 10 degrees C.

D) Humid Micro-thermal Climate is also known as taiga type of climate, named after the type of forests growing there. This type of climate is experienced in two large belts, on each in North America and Eurasia. Most of the Siberian region and the high latitude areas of USA and Canada have this climate. Vegetation is of Coniferous type. These forests are important source for the softwoods and the fur bearing animals.

E) Polar Climate is also known as Tundra type of climate and it is experienced in the polar areas. This is characterized by severe winters and even summers are cold. These regions are known for blizzards, high velocity winds carrying ice particles with them. These regions are called the cold deserts and they occupy the areas of Arctic margins of North America and Eurasia and the Antarctic continent.

H) The Highlands Climate or Mountain climate or Alpines climate is experienced in the mountainous regions of the Himalayas, Tibetan Plateau, Rockies, Andes and the Alps. This type of climate is similar to E) Polar Climate.

The continuous movement of water in the biosphere is called the Hydrological cycle.

Water is added to the atmosphere through evaporation from the rivers, oceans, lakes, land surface and soils and through transpiration by plants.

On an average, oceans account for 97.2; atmosphere contains only about 0.001 per cent; the ice caps and glaciers account for about 2.15 per cent; ground water accounts for about 0.635 per cent of the total water available on the earth.

The ice caps are the largest reservoirs of fresh water on earth.

Precipitation is the most important source of fresh water on the earth.

The process of water entering the rocks of the earth is called percolation. The rate of percolation is a function of the porosity and permeability of the rocks.

Porosity refers to the presence of pores in the rocks while permeability refers to the capacity of the rock to allow water to move from upper parts to the lower parts.

For being permeable, a rock should not only have pores, the pores should be inter-connected also.

The water percolating and thus occurring in the rocks of the earth is called the ground water.

The water present in rocks since their time of formation is called connate water.

The ground water moves down under gravity till an impermeable rock bed. On reaching such a rock layer, the water starts saturating the pore spaces above this level.

The Zone of rocks in which the pore space is completely filled by water is called the zone of saturation. The uppermost surface of this zone of saturation is called the water table.

The rocks of the earth that contain water are called aquifers. Some of the rocks of the earth are non porous and they do not contain any water. Such rocks are called aquicludes.

A spring is formed were the water table intersects the ground.

Mineral springs are those that contain large amount of minerals in dissolved form. A large number of such mineral springs occur in Kumaon Himalayas in Uttarakhand and Himachal Pradesh.

Manikaran region of Himachal Pradesh has a large number of hot springs.

A geyser is a periodic jet of hot water and stream. Geysers are another variant of hot springs.

The most well known among geysers is the Old Faithful in the Yellowstone National Park in Wyoming, USA which erupts every 65 minutes.

Artesian wells form another important source of ground water in many areas. In an artesian well the water rises to the surface on its own under the hydrostatic pressure and no power is needed to draw water from it. The areas where the artesian well can be dug are called artesian basins. Artesian Basin of Australia is the most well known area for artesian wells.

Hydrosphere is the name given to the mass of water that covers about 71 per cent of the earth's surface. Oceans are the largest single constituent unit of hydrosphere. The world ocean contains more than 97 per cent of the total water on the earth. The study of various aspects of the oceans is called oceanography.

Five oceans of the world are Pacific, Atlantic, Indian, Arctic and Southern ocean.

The Pacific is the largest among all the oceans and it covers about one third of the total area of the globe. It is the deepest ocean also.

The Atlantic Ocean is the second largest ocean and due to numerous indentations, it has the longest coastline. It resembles the letter 'S' in shape. It has large number of marginal seas and bays and the Mediterranean Sea is a large marginal sea of this ocean.

The Indian Ocean is the third major ocean. Due to this ocean's limited extension into the Northern Hemisphere it is called as half an ocean. This is the only ocean in the world that is named after a country.

The Arctic Ocean is the northernmost ocean and the north pole of the earth is situated in this ocean. Often Arctic Ocean is considered as a marginal sea of the Atlantic Ocean. The Arctic Ocean is also connected to the Pacific Ocean through the Bering Strait.

The Southern Ocean extends wholly in the southern hemisphere and it surrounds the Antarctica.

The Oceans are included among the first order landforms on the earth's surface and occupy the deepest areas on earth.

On the basis of the surface configuration, the ocean floors can be divided into four major units and they are Continental Shelf, Continental Slope, Continental Rise and the Abyssal Plain or the Deep Sea Plain.

The Continental Shelf is the coastal part of the ocean which is generally not very deep and the slope of the bottom is very gentle, the gradient being less than 1 degree. The continental shelves occupy about 7 per cent of the total ocean area. Coral reefs are generally found on this part.The Continental Slope is the outermost part of the true ocean basin and extends seawards from the Continental shelf. The Continental Slope has a gradient ranging between 2 degrees and 5 degrees.

The boundary between the continental shelf and the continental slope if called the andesite line. The line is named after the andesite rock which is a volcanic rock forming the bottom of the seas and oceans and usually not occurring on the continents.

At the foot of the continental slope is found an area slightly rising due to the accumulation of the debris transported over the continental slope. This part of the ocean floor having a rough convex slope is called the continental rise.

The continental slope is rich in minerals found in the sedimentary rocks. Some of the oil deposits of the oceanic areas occur in this zone.

The Abyssal Plain or the Deep Sea Plain is the deepest and the most extensive part of the ocean floor and it accounts for the largest proportion of total areas of the oceans. It is the site for deep-sea fishing, and extraction of oil and gas and other minerals.

The parts of the Abyssal Plain are occupied by raised ridges or submarine mountains and by the very deep trenches or the canyons. Indian Ocean has the famous 90 E ridge.

The volcanic peaks which remain under water are called sea mounts.

Flat topped peaks in the ocean are called guyots. The Pacific Ocean is specifically known for guyots.

The proportion of dissolved salts to pure water is called salinity. Chlorine is the most abundant element causing salinity in sea water and Sodium Chloride is the most abundant compound. Besides sodium chloride, the ocean water contains sulphates and chlorides of calcium, magnesium and potassium also.

The average salinity of the oceans is taken as 34.5 per 1000. This means that on an average one kg of sea water contains 34.5 grammes of salt.

Proportion of different salts in Sea Water

Salt                                                                        Proportion in Total Salts

Sodium Chloride                                                27.213

Magnesium Chloride                                          3.807

Magnesium Sulphate                                         1.658

Potassium Sulphate                                           0.863

Calcium Sulphate                                                0.123

Magnesium Bromide                                          0.076

Dead Sea and Lake Van are the water bodies with the highest salinity levels.

There are three kinds of motions in the oceans and they are tides, waves, and currents.

Tides imply a rhythmic rise and fall of water in the oceans under the gravitational pull of the moon and the sun. Tides do not imply transport of water from one region to the other.

Waves are caused due to the friction with the winds or some other reason. In the case of a wave also, there is no actual movement of water from one place to another. In case of a wave the water moves vertically as the wave passes.

The currents represent the third type of movement in ocean waters. The currents in the oceans, unlike the waves and tides involve actual transportation of water from one part of the oceans to the other. Currents are defined as movement of ocean water in well-defined directions.

The density of ocean water is a function of the salinity and temperature. There is a direct relationship between density and salinity but the relationship between density and temperature is an inverse one.

The density of ocean waters increases with increasing salinity but decreases with increasing temperature.

The ocean currents are classified as warm and cold currents. If the water moving in the form of a current is warmer than the normal temperature of the latitude, it is called a warm current. Conversely, if the temperature of the water moving in the form of a current is lower than the normal temperature of the latitude, it is called a cold current.

Currents from moving from lower latitudes to higher latitudes are warm, while those flowing from higher latitudes to the lower latitudes are cold currents.

Currents have a tendency to circulate waters in a clockwise direction in the northern hemisphere and in anticlockwise direction in the southern hemisphere.

The Agulhas current in the Indian Ocean is an example of a major warm current.

A strait is a narrow stretch of water that connects two larger bodies of water. At the same time, it separates two neighbouring land masses. Strait of Gibraltar connects the Atlantic Ocean with the Mediterranean Sea and separates Spain in Europe from northern Morocco in Africa.

An Isthmus is a narrow stretch of land connecting two large land masses and thus this narrow stretch separates two water bodies. The Isthmus of Panama connects North and South America and separates the Atlantic Ocean from the Pacific Ocean.

A lake is defined as a large inland body of water. Generally the water in lakes is stagnant. Lakes are formed in a number of ways like the erosional and depositional activity by rivers, glaciers, wind and waves.

Playa lakes are formed in deserts due to flowing in of rainwater into local depressions sometimes carved by wind erosion. Ex: Lake Chad in Africa and Sambhar in Rajasthan.

Lagoon lakes are produced due to erosional and depositional action of waves in the coastal regions. Ex: Lake Chilka in Orissa and Lake Pulicat in Tamil Nadu.

Craters of volcanoes also form lakes and they are called crater lakes or volcanic lakes. Ex: Lake Lonar in Maharashtra and some of the lakes in Siberia.

Some lakes are remnants of ancient ocean and sea areas. Ex: Caspian Sea.

Lakes are either fresh water of salt water lakes.

Most of the lakes receiving a continuous inflow of fresh water through rivers or glaciers are fresh water lakes. Lake Wular in Kashmir valley and the Great Lakes of North America are all fresh water lakes.

Lakes situated in the deserts where the rate of evaporation of very high, receive limited inflow of water and are salty. Such lakes are called Salt Lakes. The Great Salt Lake of USA, Lake Van in Turkey, Dead Sea, and the lakes of Rajasthan.