Savanna Biome

The savanna biome is usually associated with the tropical wet-dry climate of Africa and South America.

Local Winds

Local winds are driven by local effects.

Sea and land breezes are simple examples of how uneven heating and cooling of the air can set up thermal circulations and create local winds.

A similar situation creates mountain and valley winds.

Often these winds are moderate and just part of the local environment. But some local winds are more dangerous.

If you’re from Southern California, you’re probably familiar with the Santa Ana, a fierce, searing wind that often drives raging wildfire into foothill. It blows from the interior desert region of Southern California across coastal mountain ranges to reach the Pacific coast. It warms as it descends, and it is often funneled through local mountain gaps and across canyon floors with great force.

Other local winds include the chinook, a warm and dry local wind that results when air passes over a mountain range and descends on the lee side. It is known for rapidly evaporating and melting snow.

The mistral of the Rhône Valley in southern France i…

Demographic Transition Theory

Demographic Transition Theory in its original form was propounded by Warren Thompson and Frank Wallace Notestein.

The theory postulates of a special pattern of demographic transformation high fertility and high mortality to low fertility and low mortality, when society progresses from a dominantly rural, agrarian and illiterate society to a predominantly urban, industrial and literate society.

These changes occur in stages which are collectively known as a Demographic Cycle. Demographic transition theory can be used to describe and predict the future population of an area.
Stages of Demographic Transition:

Stages of Economic Growth by Rostow

Walt Whitman Rostow, propounded his theory of economic growth dealing with the stages of economic growth. He made an effort to correlate the process of economic growth to the growth of population and common social and political features of the growth process.

According to Rostow, the economic growth occurs in five basic stages, of varying length. In chronological order they are:
The traditional society,The preconditions for take-off,The take-off,The drive to maturity, andThe age of high mass consumption.Stages of Economic Growth:

Population Pyramid

The age-sex structure of a population refers to the number of females and males in different age groups. A population pyramid is used to show the age-sex structure of the population. The shape of the population pyramid reflects the characteristics of the population. The left side shows the percentage of males while the right side shows the percentage of women in each age group.
1. Expanding Population Pyramid: The countries that are characterized by high birth rate and high death rate, typical of the first stage of demographic transition, shall have a very broad base, which narrows down rapidly giving a concave shape to the sides of the triangle.Birth rates were high and families were large, partly because people did not think of limiting them and partly because a large family was of an advantage.In working-class families, all the children could contribute to the family income. However, death rates were also very high because epidemic diseases such as bubonic plague, cholera, and typhoi…

Under Population

Concept of under population is just the opposite of overpopulation. Under Population occurs when the population of an area is too small for full utilization of its resources.

The condition of under population may also appear when the resources of an area can support a larger than the existing population without lowering the standard of living or without creating any type of unemployment.

Over Population

According to S.D. Maurya, An excess of population in an area in relation to the available resources and technology denotes overpopulation. This situation occurs when the number of people exceeds that of the optimum population and the standard of living tends to decline. The result of over population maybe underemployment, unemployment, low per capita income, low standard of living, etc.

According to R.C. Chandana, ‘When the carrying capacity of an area is exceeded by its population the area is said to be overpopulated because the area has more population than what it can comfortably support’.

Over population takes place generally when the rate of population growth is much higher than that of the development of resources in an area.

Malthus Theory of Population

The British economist and demographer Thomas Robert Malthus undoubtedly was the first scholar two propound a population theory based on scientific and natural law. His book on the principles of population growth was published in 1798. Malthus traveled various West European countries and collected many important data in support of his population theory. Thus, the Malthus theory of Population was based on his experience and observations.

His motive was definitely humanitarian, as he was always thinking and trying about the welfare of humanity.
Assumptions of the Theory: While formulating his population theory, Malthus assumed the following postulates:
Food is necessary to the existence of human being and the population is necessarily limited by the means of subsistence.The passion between the two opposite sexes is necessary and will remain nearly in this present stage.Law of diminishing return applies to agriculture. Having assumed these postulates, Malthus stated that the power of popul…

Optimum Population

The optimum population is an economic concept which denotes a balanced population-resource relationship in an area.

According to Preston Cloud, optimum population is the one that lies within limits, large enough to realize the potentialities of human creativity to achieve a life of high quality for all the inhabitants indefinitely, but not so large as to threaten dilution of quality or the potential to achieve it or the wise management of the ecosystem.

According to S.D. Maurya, the optimum population is the population size (the number of people) that in relation to given economic, social or military goals, produces the maximum return.

According to R.C. Chandana, the term optimum population may be defined as a density of population which with the given resources and skills, produces the maximum (greatest) economic welfare (usually the maximum income per capita) or allows the highest standard of living.

The concept of optimum population is concerned with the high quality of life. The …

Population Problems of Developing Countries

More than 80% population of the world lies in developing countries. The list of developing countries is very long. It includes all the countries of Asia (except only Japan), Africa, Latin America and some countries of Southern Europe.

The level of economic, social and technological development in these countries is, however, low and very low which has been affecting the agriculture efficiency and productivity of industrial development. In this article, we will discuss various population problems in these developing countries.

Most of the Asian countries like China, India, Pakistan, Bangladesh, Sri Lanka, Myanmar, Indonesia, Thailand, Malaysia, Philippines, and Nepal, are overpopulated and have a high growth rate. On the contrary, there are many countries which are treated as underpopulated.

They are underdeveloped because their population is relatively small and inadequate to utilize their abundant natural resources. Such countries are Brazil, Columbia, Peru, Argentina, etc. in Latin…


Wave-like bands are formed in the crustal rocks due to tangential compressive force resulting from horizontal movement caused by the endogenetic force originating deep within the earth. Such bands are called 'Folds' wherein some parts are bent up and some parts are bent down.

Different Components of a Fold:The up folded rock strata in the arch-like form are called 'anticlines'.While the down folded structure forming through-like feature is called 'syncline'.The inclination of rock beds to the horizontal plane is termed as 'dip'.The strike of an inclined bed is the direction of any horizontal line along a bedding plane. The direction of dip is always at the right angle to the strike.Types of Folds:
The nature of folds depends on several factors e.g. the nature of rocks, the nature and intensity of compressive forces, duration of the operation of compressive forces, etc.

The elasticity of rocks largely affects the nature and the magnitude of the folding p…


Faults are the fractured surface in the Earth's crust.

During the formation of a fault, the vertical displacement of a rock block may occur up to several 100 meters and horizontally the rock blocks may be displaced up to several kilometers.

A fault represents weaker zones of the earth where crustal movements become operative for a longer duration.
Different Components of a Fault:Fault Plane is that plane along which the rock blocks are displaced by tensional and compressional forces acting vertically and horizontally to form a fault. It plane may be vertical, inclined, horizontal, curved or of any other form.The Dip is the slope of a fault.Upthrown Block represents the uppermost block of a fault.Downthrown Block is the lowermost block of a fault.Hanging wall represents the upper wall of a fault.The Footwall is the lower wall of a fault.Fault Scrap is the cliffs that represent the edge of a vertically displaced block.Types of Faults:
Faults can be generalized into four principal typ…

Drainage Systems

Drainage system refers to the origin and development of streams through time. The examples of drainage systems are consequent, subsequent, and antecedent and superimposed streams, etc.

The origin and subsequent evolution of any drainage system in a region are determined and controlled by two main factors:
The nature of the initial surface and slope andThe geological structures (e.g. folds, faults)Types of Drainage Systems: Drainage systems are divided into two broad categories based on the adjustment of the streams to the initial surface and geological structures e.g. (1) Sequent Drainage Systems, and (2) Insequent Drainage Systems.
Sequent Drainage Systems: In this drainage system, streams follow the regional slope and are well adjusted to the geological structures e.g. consequent and subsequent streams.

(1) Consequent Streams are the first stream to be originated in a particular region, and many streams remain consequent throughout their evolutionary development.

These streams have th…


The coast is the shore of sea or ocean. When we use the word ‘coasts’ or ‘coastlines’, we’re referring to the zone in which coastal processes operate, or have a strong influence. The coastline includes the shallow water zone in which waves perform their work as well as beaches and cliffs shaped by waves.
Types of Coasts or Coastlines: Despite the great variety of coastal features, coastlines may be divided into two basic types e.g. Coastlines of Emergence and Coastlines of Submergence.
(1.) Coastlines of Emergence: These coastlines are formed due to the upliftment of the land or a fall in the sea level.

Uplifted Lowland Coast: The uplift of part of the continental shelf produces, a smooth gently sloping coastal lowlands.The offshore waters are shallow with lagoons, salt marshes, and mudflats.Ports that were once located on the coast become inland towns.Example: south-eastern U.S.A., Western Finland, eastern Sweden and parts of coastal Argentina, south of the Rio de la Plata.Emergent Upla…

Theory of Isostasy

In this article, we will discuss the views of Airy and Pratt on the theory of Isostasy.

Different relief features of varying magnitudes e.g. mountains, plateaus plains, lakes, seas, and oceans, faults, and rift valleys, etc. standing on the earth's surface are probably balanced by certain definite principle, otherwise, this would have not been maintained in their present form.

Whenever this balance is disturbed, there start violent earth movement and tectonic events. Thus, isostasy simply means "mechanical stability between the upstanding parts and low-lying basins on a rotating Earth."

The word isostasy derived from the German word 'isostasios' (meaning thereby 'in equipoise'), was first proposed by American geologist Clarence Edward Dutton.

According to Dutton, the upstanding parts of the earth must be compensated by lighter rock material from beneath so that the crustal reliefs should remain in mechanical stability.
Discovery of the Concept: The concep…

Seafloor Spreading

Harry Hammond Hess propounded in his theory of seafloor spreading that the mid-oceanic ridges were situated on the rising thermal convection currents coming out from the mantle. The oceanic crust moves in opposite directions from mid-oceanic ridges.

These molten lavas cool down and solidify to form new crust along the trailing ends of divergent plates. Thus, there is continuous creation of new crust along the mid-oceanic ridges and the expanding crusts (plates) are destroyed along the ocean trenches.

What is Geography?

In very simple words "Geography is the description of the earth". Eratosthenes, a 3rd century BC Greek scholar coined the term geography (from "geo" meaning "the earth" and "graphe" meaning "the description"). Thus, the literal meaning of geography is to describe the earth.

Geography is concerned with the study of nature and human interaction. The geographical phenomenon both the physical and human are not static but highly dynamic. They change over time as a result of the interactive process between ever-changing earth and untiring and ever-active human beings.

Human is an integral part of nature and nature has the imprints of human. Nature has influenced different aspects of human life. Its imprints can be noticed on food, clothing, shelter, and occupation.

The present society has passed the stage of primitive society, which were directly dependent on their immediate physical environment for sustenance.

Present society has modified …

Plate Tectonics

The rigid lithospheric slabs are called plates. The study of the whole mechanism of evolution nature and motions of plates, deformation within plates and interactions of plate margins with each other is collectively called as plate tectonics. Plate tectonic theory, a significant scientific advancement of the decade 1960’s is based on two major scientific concepts e.g. (1) the continental drift theory and (2) the concept of seafloor spreading.

The rigid lithospheric plates floating over the underlying plastic asthenosphere. A plate includes not only continents but oceans as well, hence, there are oceanic and continental plates.

There are seven major plates, an equal number of intermediate-sized plates and perhaps a dozen smaller plates are recognized. Many of the smaller plates are remnants of once larger plates that are not being subducted.

The major plates are as follows:
Antarctica and the surrounding oceanic plateNorth American (with western Atlantic floor separated from the South …

Interior of the Earth

The interior of the Earth is divided into different layers and in many ways such as based on chemical composition or mechanical properties. Chemically, Earth's interior is divided into the crust, mantle, and core. Mechanically, it can be divided into lithosphere, asthenosphere, mesosphere, and barysphere.
Source of Information: Most of our knowledge about the interior of the earth is largely based on indirect evidence. Yet, a part of the information is obtained through direct observations.
Direct Sources:Mining,Deep ocean drilling, and volcanic eruptions are some examples of direct sources.
During the process of mining and drilling at different depths; rocks and minerals are extracted which gives information about the crust.We also know through the mining activities and various deep drilling projects; that the temperature and density increase with the increasing depth.Volcanic eruption suggests that there is at least such a layer below the earth’s surface which is in the liquid stat…

Inversion of Temperature

Inversion of temperature occurs when warm air lies over cold air. Normally, temperature decreases with increasing altitude in the troposphere at an average rate of 6.5 °C per 100 meters but sometimes this normal trend of decrease of temperature with increasing heights is reversed under special circumstances i.e. temperature increases upward up to a few kilometers from the Earth's surface. Thus, warm air layer lies over the cold air layer. This phenomenon is called temperature inversion.
Types of Temperature Inversion: Inversion of temperature occurs in several conditions. Sometimes, it occurs at the ground surface while sometimes, it occurs at a greater height. Thus, temperature inversion classified into the surface and upper-air inversion based on relative heights from the Earth's surface
(1.) Surface Inversion: The inversion of temperature that occurs at ground levels.

(A) Radiation Inversion or Ground Surface Inversion, also called as Non-Advectional Inversion because it occur…

Continental Drift Theory

The idea of lateral movement of continents or continental drift was put forward in 1912 by Alfred Wegener in a book ‘The Origin of Continents and Oceans’. The continental drift theory of Wegener ‘grew out of the need for explaining the major variations of climate in the past’.

According to A. Wegener, The climatic changes which have occurred on the globe may be explained in two ways.
If the continents remained stationary at their place throughout geological history of the earth, the climatic zones might have shifted from one region to another and thus a particular region might have experienced varying climatic conditions from time to time.If the climatic zones remained stationary, the landmasses might have been displaced and drifted. Wegener opted for the second alternative as he rejected the view of the permanence of continents and ocean basins.

According to Wegener, the Earth is made of SIAL, SIMA, and NIFE. SIAL, comprising the continents, is floating over SIMA, which is the upper …

Strato Volcanoes and Shield Volcanoes

Volcanic eruptions can be explosive or quiet. The nature of the eruption depends on the type of magma involved. There are two main types of igneous rocks— felsic and mafic—and each type builds a distinctive form of volcano—a strato volcano or shield volcano.

Strato Volcanoes Felsic lavas (rhyolite and andesite) are very thick and gummy, resisting flow. So, felsic lava doesn’t usually flow very far from the volcano’s event, building up steep slopes.

When the volcano erupts, ejected particles of different sizes, known collectively as tephra, fall on the area surrounding the crater, creating a cone shape.

The sluggish streams of felsic lava and layers of tephra produce a stratovolcano.

Its tall cone steepens toward the summit, where you find the crater—a bowl-shaped depression.

The crater is the principal volcano vent. Felsic lavas from stratovolcanoes hold large amounts of gas under high pressure, so they can produce explosive eruptions.

Sometimes the volcanic explosion is so violent t…

Dust Storms

Strong, turbulent winds blowing over barren surfaces can lift great quantities of fine dust into the air, forming a dense, high cloud called a dust storm.

Coastal Foredunes

Landward of beaches, there is often a narrow belt of dunes guarding the coastline. These coastal foredunes are irregularly shaped hills and depressions.

They are normally covered by beach grass with a few other species of plants that can survive the severe environment.

Composition of the Atmosphere

The Earth is surrounded by air—a mixture of various gases that reaches up to a height of many kilometers. This envelope of air makes up our atmosphere.

It is held in place by the Earth’s gravity. Almost all the atmosphere (97 percent) lies within 30 km of the Earth’s surface.

The upper limit of the atmosphere is at a height of approximately 10,000 km above the Earth’s surface—a distance that is nearly as large as Earth’s diameter.

The proportion of gases in dry air is highly uniform up to an altitude of about 80 km (50 mi). About 99 percent of pure, dry air is nitrogen (about 78 percent by volume) and oxygen (about 21 percent).

These two main component gases of the lower atmosphere are perfectly mixed, so pure, dry air behaves as if it is a single gas with very definite physical properties.

Nitrogen gas is a molecule consisting of two nitrogen atoms (N2 ). It does not easily react with other substances. Soil bacteria do take up very small amounts of nitrogen, which can be used by pla…

Stream Erosion

Streams erode in various ways, depending on the nature of the channel materials and the tools with which the current is armed.

The flowing water drags on the bed and banks and also forces particles to hit the bed and banks.

These actions easily erode alluvial materials, such as gravel, sand, silt, and clay.

This form of erosion is called hydraulic action, and it can excavate enormous quantities in a short time when river flow is high.

As the banks are undermined, large masses of alluvium slump into the river, where the particles are quickly separated and become part of the stream’s load.

Urban Heat Island

Air temperatures in the central region of a city are typically several degrees warmer than those of the surrounding suburbs and countryside.


Situated in southern Africa, Zimbabwe achieved independence from the UK in 1980. President Robert Mugabe, in power since then, has become increasingly authoritarian.


Bordered to the south by the Zambezi River, Zambia lies at the heart of southern Africa. In 1991, it made a peaceful transition from single-party rule to multiparty democracy.


Located in southern Arabia, Yemen was formerly two countries: the People’s Democratic Republic of Yemen (south and east) and the Yemen Arab Republic (northwest) were united in 1990.