Do you know about the salient features of the world’s physical geography? Read further to know about it.
Geography is the study of places and the relationships between people and their environments. Broadly Geography can be divided into Physical geography and Human Geography.
‘Physical geography’ is the branch of geography concerned with natural features and phenomena of the earth’s surface, such as landforms, drainage features, climates, soils, and vegetation.
‘Human Geography’ focuses on the study of people and their social groups, cultures, economies, and interactions with the environment by studying their relations from a spatiotemporal perspective.
Physical Geography includes:
- Geomorphology – It is devoted to the study of landforms, their evolution, and related processes.
- Oceanography – Oceanography is the study of the ocean’s physical, chemical, and biological characteristics, as well as the ocean’s ancient history, current state, and future.
- Climatology- It encompasses the study of the structure of the atmosphere and elements of weather and climates and climatic types and regions.
- Soil Geography – It is devoted to studying the processes of soil formation, soil types, fertility status, distribution, and use.
Geomorphology is defined as the science of description (discourse) of various forms (morphe) of the earth’s surface. Forms mean topographic features or geometric features (relief features) of the earth’s surface.
The Earth and its Evolution
The following are the theories about the origin of the earth
Origin of Earth
There are a number of hypotheses regarding the origin of the Earth. Some of them are the following:
- Nebular Hypothesis – This theory is developed by Immanuel Kant and later modified by Laplace. The hypothesis considered that the planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating.
- Binary Hypothesis – In 1900, Chamberlain and Moulton gave this theory. According to this theory, another wandering star approached the sun. As a result, the material’s cigar-shaped extension from the solar surface was separated.
- In 1950, Otto Schmidt in Russia and Carl Weizascar in Germany somewhat revised the ‘nebular hypothesis’, though differing in details. They considered that the sun was surrounded by a solar nebula containing mostly hydrogen and helium along with what may be termed dust.
- Modern Theories – Most accepted argument about the origin of the Universe is the Big Bang Theory and Edwin Hubble provided evidence that the universe is expanding. According to The Big Bang Theory, At the beginning(13.7 Billion years ago) all the matter-forming universe existed in a tiny ball (called singularity) with infinite density. This tiny ball exploded and gradually galaxies and stars were formed.
A galaxy starts to form through the accumulation of hydrogen gas in the form of a very large cloud called a Nebula. These Nebula gave rise to the formation of Stars and later small rounded objects called planetesimals. These large numbers of small bodies accrete to form fewer large bodies in the form of planets.
Evolution of Earth
The Earth was mostly in a volatile state during its primordial stage. Due to a gradual increase in density, the temperature inside has increased. As a result, the inside started getting separated depending on their densities. Through the process of differentiation that the earth-forming material got separated into different layers like the crust, mantle, and core.
Interior of the Earth
Sources to find out the interior of Earth:
- Direct source – Mining areas, Projects such as “Deep Ocean Drilling Project”, Volcanic eruption, etc.
- Indirect source – Meteors, gravitation, magnetic field, seismic activities, etc.
For instance –
Earthquake – The study of seismic waves provides a complete picture of the layered interior. All natural earthquakes take place in the lithosphere(A portion of depth up to 200 km from the surface of the earth). There are two types of body waves called P waves and S waves. P waves are similar to sound waves and can travel through gaseous, solid, and liquid materials while S waves can travel through only solid states. Hence by the study of these waves, we can understand the interior of Earth.
Hence shadow zones of P and S waves tell us that the interior of the earth has different layers with different densities.
Structure of the Earth:
The earth is made up of the following layers-
Thickness and density
1. Oceanic crust
2. Continental Crust
5 Km. and 2.7g/cm3
30 Km and 3 g/cm3
Outermost solid part or the earth. The oceanic crust is thinner as compared to the continental layer.
The oceanic crust is basaltic rock.
2900 km. and 3.4g/cm3
The upper portion of the mantle is called the asthenosphere and extends up to 400 km.
The Crust and uppermost part of the Mantle are called the lithosphere(from 10 km to 200 km).
6300 km and 13g/cm3
The earthquake wave velocities helped in understanding the existence of the core of the earth.
The core is made up of very heavy material mostly composed of nickel and iron.
Distribution of Oceans and Continents
Oceans cover around 71% of the earth’s surface and the rest is under continents. The positions of the continents and the ocean bodies, as we see them today, have not been the same in the past.
Continental drift theory
- Given by Alfred Wegener in 1912.
- All continents formed a single continental mass(PANGEA), a mega ocean(PANTHALASSA) surrounded by the same.
- Around 200 million years ago, the supercontinent broke into two large land masses s Laurasia and Gondwanaland.
- Subsequently, These landmasses continued to break into various smaller continents that exist today.
- Evidence includes The matching of continents (Jigsaw fit), Rock of the same age across the oceans, Tillite, Placer deposits etc.
- Force for drifting – Pole – fleeing force due to rotation of the earth and tidal force due to the attraction of the Sun and Moon.
- Scholars rejected this theory because they considered these forces to be totally inadequate.
Conventional Current Theory
- This theory was given by Arthur Holmes in the 1930s.
- These currents are generated due to radioactive elements causing thermal differences in the mantle portion.
- Holmes argued that there exists a system of such currents in the entire mantle portion.
- This was an attempt to provide an explanation for the issue of force.
Concept of Sea Floor spreading
Conventional current theory, mapping of the ocean floor, and the concept of Continental drift theory revealed that
- All along the mid-oceanic ridges, volcanic eruptions are common and they bring huge amounts of lava to the surface in this area.
- The rocks equidistant on either side of the crest of mid-oceanic ridges show remarkable similarities in terms of the period of formation, chemical compositions, and magnetic properties.
- Rocks closer to the mid-oceanic ridges have normal polarity and are the youngest. The age of the rocks increases as one moves away from the crest.
- The ocean rock is much younger than the continental rocks.
- The deep trenches have deep-seated earthquake occurrences while in the mid-oceanic ridge areas, the quake foci have shallow depths.
These facts and a detailed analysis of the magnetic properties of the rocks on either side of the mid-oceanic ridge led Hess (1961) to propose his hypothesis, known as the “seafloor spreading”. Hess argued that constant eruptions at the crest of oceanic ridges cause the rupture of the oceanic crust and the new lava wedges into it, pushing the oceanic crust on either side. The ocean floor thus spreads.
- Given by McKenzie and Parker and also Morgan.
- A tectonic plate (lithospheric Plate) is a massive, irregularly-shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.
- Plates move horizontally over the asthenosphere as rigid units.
- The theory of plate tectonics proposes that the earth’s lithosphere is divided into seven major and some minor plates.
- These plates have been constantly moving over the globe throughout the history of the Earth.
- It is not a continent that moves as believed by Wegener. Continents are part of a plate and what moves is the plate.
- The mobile rock beneath the rigid plates is believed to be moving in a circular manner. The heated material rises to the surface, spreads and begins to cool, and then sinks back deeper to generate what scientists call a conventional cell.
- Heat within the Earth comes from two main sources – Radioactive decay and residual heat.
Minerals and Rocks
The earth is composed of various kinds of elements. These elements are in solid form in the outer layer of the earth and in hot and molten form in the interior.
Major Elements of the Earth’s Crust:
The elements in the earth’s crust are rarely found exclusively but are usually combined with the other elements and such combinations are called Minerals. Eg. Feldspar, Quartz, etc.
A rock is an aggregate of one or more minerals. There are the following types of rocks –
An igneous rock forms out of magma and lava from the interior of the earth, also known as primary rock.
Eg. Granite, Gabbro, Basalts.
Rocks (igneous, sedimentary and metamorphic) of the earth’s surface are exposed to denudational agents and are broken up into various sizes of fragments. Such fragments are transported by different exogenous agencies and deposited. These deposits through compaction turn into rocks. This process is called lithification.
Eg. Sandstone, coal, limestone, chert, etc.
These rocks form under the action of pressure, volume, and temperature (PVT) change. Metamorphism occurs when rocks are forced down to lower levels by tectonic processes or when molten magma rising through the crust comes in contact with the crustal rocks or the underlying rocks are subjected to great amounts of pressure by overlying rocks. Metamorphism is a process by which already consolidated rocks undergo recrystallization and reorganization of materials within the original rocks.
Eg. Granite, syenite, slate schist, etc.
Rocks do not remain in their original form for long but may undergo transformation. The Rock cycle is a process through which old rocks are transformed into new ones.
The external forces are known as exogenic forces and the internal forces are known as endogenic forces these forces cause physical stresses and chemical actions on earth materials and bring about changes in the configuration of the surface of the earth are known as geomorphic processes.
Various endogenic forces include:
- Diastrophism – All the processes that move, elevate or build up portions of the earth’s crust.
Eg. Orogenic Process – Mountain building
Epeirogenic Process – Uplift or wrapping of a large part of the earth’s crust
- Volcanism– Volcanism includes the movement of molten rock onto or toward the earth’s surface and also the formation of many intrusive and extrusive volcanic forms.
Examples of exogenic processes include weathering, mass movement, erosion, deposition, etc.
All the exogenic processes are covered under a term called denudation. Denudation means to strip off or to uncover. eg . Mass movements, erosion, etc.
Weathering is defined as the mechanical disintegration and chemical decomposition of rocks through the actions of various elements of weather and climate.
Types of weathering – Chemical, physical and biological weathering.
Weathering processes are responsible for breaking down the rocks into smaller fragments and preparing the way for the formation of not only regolith and soils but also erosion and mass movements.
Weathering is also important for the formation of the soils.
Mass Movements –
Mass movement is the movement of weathered materials down a slope due to gravitational forces. The movement may be gradual or sudden, depending on the gradient of the slope, the weight of the weathered debris and whether there is any lubricating moisture supplied by rain.
- Soil Creep – a slow gradual but more or less continuous movement of soil down hills.
- Soil flow or Mudflow – When the soil is completely saturated with water the individual particles are almost suspended in the water and move easily over one another and over the underlying rock.
- Landslides – The very rapid kind of movement that occurs when a large mass of soil or rock falls suddenly.
Mass movements do not come under erosion because these are aided by gravity and no geomorphic agent like running water, glaciers, wind, etc. participates in the process.
The landform is a small to medium-sized part of the surface of the Earth.
Each landform has its own physical shape, size, and materials and is a result of the action of certain geomorphic processes and agents.
The geomorphic agents(Running water, glaciers, winds, etc.) are capable of erosion and deposition.
Landforms made by Running water
There are two components of running water –
- Overland flow on the general land surface as a sheet.
- Linear flow as streams and rivers in valleys.
Most of the erosional landforms made by running water are associated with vigorous and youthful rivers flowing over steep gradients and the gentler the river channels in gradient or slope, the greater the deposition.
1. Valleys – Valleys start as small and narrow rills; the rills will gradually develop into long and wide gullies; the gullies will further deepen, widen and lengthen to give rise to valleys. Eg. V-shaped valley, canyon, etc
2. Gorge – It is a deep valley with very steep to straight sides.
3. Potholes and Plunge pools – Potholes are formed because of stream erosion aided by the abrasion of rock fragments. At the foot of waterfalls, large potholes, quite deep and wide, form, and such potholes are called plunge pools.
4. Incised or Entrenched Meanders – They are very deep wide meanders (loop-like channels) found cut in hard rocks.
5. River Terraces – They result due to vertical erosion by the stream into its own depositional floodplain.
1. Alluvial fans – When the stream moves from the higher level and breaks into a foot slope plain of a low gradient, it loses the energy needed to transport much of its load. Thus, they get dumped and spread as broad low to high cone-shaped deposits called alluvial fans.
2. Deltas – Deltas are like alluvial fans but develop along the coast.
3. Floodplains – Large-sized materials are deposited first when a stream channel breaks into a gentle slope. A riverbed made of river deposits is an active floodplain.
4. Natural levees – Natural levees are low, linear, and parallel ridges of coarse deposits along the banks of rivers. When rivers shift laterally, a series of natural levees can form.
5. Point bars – For large rivers, the sediments are deposited in a linear fashion at the depositional side of a meander.
6. Braided Channels – When selective deposition of coarser materials causes the formation of a central bar, it diverts the flow of the river towards the banks, which increases Lateral erosion. Similarly, when more and more such central bars are formed, braided channels are formed.
Note: Meanders – Meanders are loop-like channel patterns developed over the flood and delta plains. They are actually not a landform but only a type of channel pattern formed as a result of deposition.
As meanders grow into deep loops, the same may get cut off due to erosion at the inflexion point and are left as oxbow lakes.
Landforms made by Glaciers
A large mass of ice moving very slowly through a valley or spreading outward from a centre is called a glacier. The movement of glaciers is slow, unlike water flow. Erosion by glaciers is tremendous because of friction caused by the sheer weight of the ice.
1. Cirque – They are deep, long, and wide troughs or basins with very steep concave to vertically dropping high walls at their head as well as sides.
2. Horns and serrated Ridges – If three or more radiating glaciers cut headward until their cirques meet, high, sharp-pointed, and steep peaks called horns form.
3. Glacial valleys/Troughs – Very deep glacial troughs filled with seawater and making up shorelines are called fiords.
4. Others – hanging valleys, Bergschrund, etc.
The unsorted coarse and fine debris dropped by the melting glaciers is called glacial tills.
1. Marines – Moraines are long ridges of deposits of glacial till.
Deposits are at the end of a glacier – Terminal moraines
Deposits on both sides – Lateral moraines.
2. Eskers – Eskers are meandering ridges of sediment that form in water channels beneath or within the glacier ice. The floors of these channels can be rock, sediment, or ice.
3. Outwash plain – assorted roughly stratified deposits.
4. Drumlins – Drumlins are smooth oval shaped ridge-like features composed mainly of glacial till along with some masses of gravel and sand.
Landforms made by Groundwater
The water under the ground flows horizontally through the bedding planes, joints or through the materials themselves. It is this downward and horizontal movement of water that causes the rocks to erode.
Any limestone or dolomite region showing typical landforms produced by the action of groundwater through the process of solution and deposition is called Karst topography.
1. Sinkhole – an opening more or less circular at the top and funnel-shaped towards the bottom.
2. Doline – Some sinkholes collapse due to the presence of some caves or hollows beneath them and become bigger sinkholes.
3. Uvalas – When several sinkholes join together to form a valley of sinks, they are called valley sinks or Uvalas.
4. Lapies – the irregular grooves and ridges formed when most of the surfaces of limestone are eaten by the solution process.
1. Stalactites – It is a deposit of calcium carbonate (such as calcite) resembling an icicle hanging from the roof or sides of a cave.
2. It rises up from the floor of the caves.
The Stalagmites and stalactites eventually fuse to give rise to columns and pillars of different diameters.
Landforms made by waves and currents
Most of the changes along the coasts are accomplished by waves. When waves break, the water is thrown with great force onto the shore, and simultaneously, there is a great churning of sediments on the sea bottom.
High Rocky Coasts – Along these coasts, the river appears to have been drowned with a highly irregular coastline. Shores do not show any depositional landforms initially. Erosion features dominate.
Low Sedimentary Coasts – Along these coasts the rivers appear to extend their length by building coastal plains and details. Depositional features dominate.
Cliffs, Terraces, Caves, and Stacks –
Cliffs are common on the high rocky coasts.
At the foot of such cliffs, there may be flat or gently sloping platforms covered by rock debris derived from the sea cliff behind.
Such platforms occurring at an elevation above the average height of waves is called wave-cut terrace.
Sometimes, waves create hollows and these hollows get widened and deepened to form Sea Caves.
Sea stacks are nothing but the isolated standing rocks in the sea which were once a part of the cliff.
Bar, Barrier, and spit –
A ridge of sand and shingle formed in the sea in the off-shore zone (from the position of low tide waterline to seaward) lying approximately parallel to the coast is called an off-shore bar.
An off-shore bar that is exposed due to the further addition of sand is termed a barrier bar.
Sometimes such barrier bars get keyed up to one end of the bay when they are called spits.
A lagoon is formed when barrier bars and spits form at the mouth of a bay and block it.
Others – Dunes, Beaches, etc.
Landforms made by winds
Winds, particularly in hot deserts, cause deflation, abrasion, and impact. Deflation means the lifting and removal of dust and smaller particles from the surface of rocks.
The impact is a sheer force of momentum which occurs when sand is blown into or against a rock surface.
Abrasion is the physical process of rubbing, scouring or scraping whereby particles of rock (usually microscopic) are eroded away by friction.
Climatology is the scientific study of climate and how it changes over time is defined as the average weather conditions over time. In climatology, we study topics like- Atmosphere, Heat budget, Jet streams, cyclones, precipitation, etc.
The atmosphere can be studied as follows:
Composition of the Atmosphere –
The atmosphere is composed of gasses, water vapour, and dust particles.
Details of gasses in the lower atmosphere –
Carbon Dioxide is meteorologically a very important gas as it is transparent to the incoming solar radiation but opaque to the outgoing terrestrial radiation and reflects back some part of it towards the earth’s surface.(Greenhouse effect).
Structure of the Atmosphere
The structure of the atmosphere is as follows
- The lowermost layer of the atmosphere.
- Its average height is 13 km and extends roughly to a height of 8 km near the poles and about 18 km at the equator.
- This is the most important layer for all biological activity.
- It extends up to a height of 50 km. It contains a high concentration of ozone (O3) in relation to other parts of the atmosphere
- Weather-related incidents do not take place in this layer. The air blows horizontally here. Therefore this layer is considered ideal for flying aircraft.
- It contains a high concentration of ozone (O3) in relation to other parts of the atmosphere.
- It is the third layer of the atmosphere spreading over the stratosphere.
- It extends up to a height of 80 km.
- The ionosphere is located between 80 to 400 km above the mesopause.
- Radio waves transmitted from the earth are reflected back to the earth by this layer and due to this, radio broadcasting has become possible.
- The temperature here starts increasing with height.
The uppermost layer of the atmosphere is called the Exosphere.
Solar Radiation and Heat Budget
The earth’s surface receives most of its energy in short wavelengths and incoming solar radiation is called insolation.
The amount and intensity of insolation vary during the day, in a season, and in a year.
The earth after being heated itself becomes a radiating body and it radiates energy to the atmosphere in the long waveform. This energy heats up the atmosphere from below. This process is known as terrestrial radiation.
The long wave radiation is absorbed by atmospheric gasses, particularly by carbon dioxide and other greenhouse gasses. Thus, the atmosphere is indirectly heated by the earth’s radiation.
The earth as a whole does not accumulate or lose heat. It maintains its temperature. This can happen only if the amount of heat received in the form of insolation equals the amount lost by the earth through terrestrial radiation. This balance between the insolation and the terrestrial radiation is termed the heat budget or heat balance of the earth.
The albedo of the Earth can be defined as a measure of how much light that hits a surface is reflected back without being absorbed.
The interaction of insolation with the atmosphere and the earth’s surface creates heat which is measured in the terms of temperature.
Factors controlling temperature distribution
- Distance from the sea
- Air mass and ocean currents
Inversion of temperature
When the temperature decreases with an increase in elevation are called the normal lapse rate. At times, the situation is reserved and the normal lapse rate is inverted. It is called inversion of temperature. Eg. Sea breeze, land breeze, Fog, etc.
The weight of a column of air contained in a unit area from the mean sea level to the top of the atmosphere is called atmospheric pressure.
In the lower atmosphere, the pressure decreases rapidly with height.
Force affecting the velocity and direction of the wind
The air in motion is called wind. The wind blows from high pressure to low pressure. Forces – Gravitational force, Friction force, Pressure Gradient force, Coriolis Force.
The force exerted by the rotation of the earth is known as the Coriolis force.
The wind circulation around a low pressure is called cyclonic circulation. Around high pressure, it is called anticyclonic circulation.
General Circulation of the atmosphere
It depends on the –
- Latitudinal variation of atmospheric heating
- The emergence of pressure belts
- The migration of belts following the apparent path of the sun
- The distribution of continents and oceans
- The rotation of the earth
The pattern of the movement of the planetary winds is called the general circulation of the atmosphere.
- The air at the Inter-Tropical Convergence Zone (ITCZ), which lies near the equator, rises due to the heating caused by the reflected radiation from the surface thus creating low pressure.
- The winds from the tropics (i.e. region around the Tropic of Cancer and Capricorn) flow from their positions towards this low-pressure area. As the air from the tropics reaches the convergence zone it begins to rise because of heating. It reaches an altitude of 14 km and then starts to move towards the poles thus creating the upper air circulation or upper atmospheric circulation.
- While travelling towards the poles, as the air of the upper air circulation gets cold and dense, there is accumulation around 30° N and S latitudes. Some part of the cold air sinks towards the ground creating a subtropical high.
- As it reaches the surface, the wind again starts moving towards the ITCZ near the equator and becomes known as easterlies. This cycle of air circulation in between the Equator and the Tropics is known as the Hadley Cell.
- The cycle of the air in between the mid-latitudes (i.e. around the tropics) and the poles is known as the mid-latitude cell or Ferrel cell. In this case, the rising warmer air) is coming from the subtropical high and the sinking cool air is coming from the poles. Such winds near the surface are known as
- The cycle of air circulation in-between the poles and the mid-latitudes is known as the Polar cell.
When the air remains over a homogenous area for a sufficiently long time, it acquires the characteristics of the area.
The air masses are classified according to the source regions-
- Warm tropical and subtropical oceans
- The subtropical hot deserts
- The relatively cold high-latitude oceans
- The very cold snow-covered continents in the Arctic and Antarctica
- Maritime tropical
- Continental tropical
- Maritime polar
- Continental polar
- Continental arctic
When two different air masses meet, the boundary zone between them is called Fronts by the process of frontogenesis.
Types of fronts –
Temperate cyclones are also known as Extra-tropical cyclones where the term “Extra-tropical” signifies that this type of cyclone generally occurs outside the tropics with a latitude range between 30° and 60°. They are low-pressure systems with associated cold fronts, warm fronts, and occluded fronts. These cyclones are formed along the polar front. In the beginning, the front is stationary. These cyclones move from west to east.
Tropical cyclones are violent storms that originate over oceans in tropical areas and move over coastal areas and move over to the coastal areas bringing about large-scale destruction caused by violent winds, very heavy rainfall and storm surges.
- Large sea surface with a temperature higher than 270 C
- Presence of the Coriolis force
- Small variations in the vertical wind speed
- A pre-existing weak-low-pressure area or low-level cyclonic circulation
- Upper divergence above the sea level system
A mature tropical cyclone is characterized by the strong spirally circulating wind around the centre, called the Eye.
The Cyclone creates storm surges and they inundate the coastal lowlands. The storm peters out on the land.
According to World Meteorological Organisation (WMO), “a strong narrow current concentrated along a quasi-horizontal axis in the upper troposphere or the stratosphere characterized by strong vertical and lateral wind shear and featuring one or more velocity maxima is called the jet stream.”
Water in The Atmosphere
The following are the properties of water in the atmosphere.
Evaporation and Condensation
- The water vapour in the air is known as humidity and the actual amount of water vapour present in the atmosphere is known as the absolute humidity. The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as relative humidity.
- The amount of water vapour in the atmosphere is added or withdrawn due to evaporation and condensation respectively. Evaporation is the process by which water is transformed from liquid to a gaseous state. The transformation of water vapour into water is called condensation.
- Dew- When the moisture is deposited in the form of water droplets on cooler surfaces of solid objects (rather than nuclei in the air above the surface) such as stones, grass blades and plant leaves, it is known as dew.
- Frost – Frost forms on cold surfaces when condensation takes place below the freezing point (00C), i.e. the dew point is at or below the freezing point.
- Fog – When the temperature of an air mass containing a large quantity of water vapour falls. All of a sudden, condensation takes place within itself on fine dust particles. So, the fog is a cloud with its base at or very near the ground.
A cloud is a mass of water drops or ice crystals suspended in the atmosphere. Clouds form when water condenses in the sky. The condensation lets us see the water vapour. There are many different types of clouds – Cirrus, Cumulus, Stratus, Nimbus, etc.
A combination of these four basic types of clouds can be again divided into three types:
- High clouds- Cirrus, cirrostratus etc.
- Middle clouds – Altostratus, altocumulus; etc
- Low clouds – Stratocumulus and nimbostratus.
The process of continuous condensation in free air helps the condensed particles to grow in size. When the resistance of the air fails to hold them against the force of gravity, they fall onto the earth’s surface. So after the condensation of water vapour, the release of moisture is known as precipitation.
Sleet is frozen raindrops and refrozen melted snow water. When a layer of air with a temperature above freezing point overlies a sub-freezing layer near the ground, precipitation takes place in the form of sleet. Raindrops, which leave the warmer air, encounter the colder air below.
Types of Rainfall
The following are the various types of rainfalls:
The air getting heated becomes light and rises in convection currents.
As the air rises, it expands and drops the temperature and subsequently, condensation takes place and cumulus clouds are formed.
This type of rainfall generally takes place in the equatorial regions and internal parts of the continents, predominantly in the northern hemisphere.
When the saturated air mass comes across a mountain, it is forced to ascend and as it rises, it expands; the temperature falls, and the moisture is condensed. The chief characteristic of this sort of rain is that the windward slopes receive greater rainfall.
The area situated on the leeward side, which gets less rainfall is known as the rain-shadow area. It is also known as the relief rain.
Cyclonic activity causes cyclonic rain and it occurs along the fronts of the cyclone. As the warm air rises, it cools, and the moisture present in it condenses to form clouds. This rain falls gradually for a few hours to a few days.
World Climate and Climate Change
The world climate is classified based on the scheme developed by V. Koeppen. He identified a close relationship between the distribution of vegetation and climate.
Climate change refers to long-term shifts in temperatures and weather patterns.
Oceanography is a scientific discipline concerned with all aspects of the world’s oceans and seas, including their physical and chemical properties, their origin and geologic framework, and the life forms that inhabit the marine environment.
In Oceanography, we learn about Hydrological cycles, Currents, waves, tides, marine life such as coral life, major and minor relief features, etc.
Water can be used and reused. Water undergoes a cycle from the ocean to land and land to ocean. The hydrological cycle is the circulation of water within the earth’s Hydrosphere in different forms.
Relief of Ocean Floor
The floors of the oceans are rugged with the world’s largest mountain ranges, deepest trenches and the largest plains.
The oceanic part can be divided into – Pacific, Atlantic, Indian and Arctic.
Divisions of The Ocean Floors –
- The Continental shelf – It is the shallowest part of the ocean showing an average gradient of 1° or even less. The shelf typically ends at a very steep slope, called the shelf break. The continental shelves are covered with variable thicknesses of sediments brought down by rivers, glaciers, and wind, from the land and distributed by waves and currents. Massive sedimentary deposits received over a long time by the continental shelves become the source of fossil fuels.
- The continental Slope – The continental slope connects the continental shelf and the ocean basins.
- The deep sea Plain- Deep sea plains are gently sloping areas of the ocean basins. These are the flattest and smoothest regions of the world.
- The oceanic Deep- These areas are the deepest parts of the oceans. The trenches are relatively steep-sided, narrow basins.
The various other relief features are:
- Mid oceanic Ridge – It is composed of two chains of mountains separated by a large depression. Eg. Atlantic Ridge
- Seamount – It is a mountain with pointed summits, rising from the seafloor that does not reach the surface of the ocean. Seamounts are volcanic in origin.
- Guyots – It is a flat-topped seamount. They show evidence of gradual subsidence through stages to become flat-topped submerged mountains.
- Atolls – These are low islands found in the tropical oceans consisting of coral reefs surrounding a central depression. It may be a part of the sea (lagoon), or sometimes form enclosing a body of fresh, brackish, or highly saline water.
The temperature of Ocean Waters
Factors Affecting –
- Unequal distribution of land and water
- Prevailing wind
- Ocean currents
- The salinity of oceanic water
Horizontal and vertical Distribution of Temperature –
- Temperature decreases with the increased depth.
- The boundary region( 100-400 m), from where there is a rapid decrease in temperature, is called the thermocline.
- Below the thermocline, the Temperature changes very slightly.
- The average temperature of surface water is about 270
- It gradually decreases from the equator towards the poles.
- The oceans in the northern hemisphere record relatively higher temperatures than in the southern hemisphere.
Salinity in the Ocean Water
The total content of dissolved salts in seawater is termed Salinity.
A salinity of 24.7 %0 has been regarded as the upper limit to fix ‘brackish water’
Factors affecting Oceanic salinity –
- Depend upon evaporation and precipitation.
- Influenced by freshwater flow from rivers in coastal regions.
- Ocean currents
Horizontal and vertical distribution of salinity
- The salinity of a normal open sea – is between 33 to 37.
- In estuaries and the Arctic sea, it fluctuates between 0 to 35.
- In the hot and dry regions where the evaporation of water is high, it may reach 70.
- In landlocked countries such as the Red sea, it is recorded 41 due to higher evaporation.
- In the Indian Ocean the average salinity –
- Salinity at the surface decreases by freshwater input or increases by loss of water to evaporation and Ice.
- Salinity in the depth is very much fixed as there is no water added or lost.
- Salinity generally increases with an increase in depth.
- There is a distinct zone called Halocline, in this zone, there is a sharp increase in salinity.
Movements of Ocean Water
The movements of ocean water can be horizontal or vertical. The horizontal motion of oceanic water refers to the ocean currents and waves while vertical motion refers to tides.
Waves are formed by energy passing through water, resulting in it moving in a circular motion. Water particles travel only in a small circle as a wave passes. The Wind causes waves to travel in the ocean and the energy is released on coastlines. When the depth of water is less than half the wavelength of the wave, the wave breaks.
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 faraway places, possibly from another hemisphere.
Waves travel because the wind pushes the water body in its course while gravity pulls the crests of the waves downward.
Ocean currents are rivers in the oceans and represent a regular volume of water in a definite path and direction. The strength of the Current refers to the speed of the current.
Forces that influence currents –
- Heating by solar energy
- Coriolis force
- The difference in water density
Types of Ocean current
- Surface currents – constitute about 10% of all the water in the ocean. These waters are the upper 400m of the ocean. They can be divided into –
- Cold currents – bring cold water into warm water areas. They are usually found on the west coast of the continents in low and middle latitudes. Eg. Peruvian current, Labrador current etc
- Warm Currents – Bring warm water into cold water areas and are usually observed on the east coast of constituents in the low and middle latitudes. Eg. Brazilian Current, Agulhas Current etc.
- Deep Water currents – make up the other 90% of the ocean Water.
The periodical rise and fall of the sea level once or twice a day, mainly due to the attraction of the sun and moon,is called a tide.
- The gravitational pull of the sun and moon
- Centrifugal force
The tide-generating force is the difference between these two forces – The gravitational attraction of the moon and the centrifugal force.
Types of Tides
The height of rising water varies appreciably depending upon the position of the sun and moon with respect to the earth.
- Spring tides – When the sun, the moon and the Earth are in a straight line – Tide will be higher.
They occur twice a month, one during the full period and another during the new moon period.
- Neap tides- Sun and moon are perpendicular to each other.
The forces of the sun and moon tend to counter one another.
Tide will be low.
Tidal flows are of great importance in navigation. These tides are also helpful in desilting the sediments and in removing polluted water from river estuaries.
Islands and Coral Reefs
An island is a piece of land surrounded on the sides by water.
Types of Islands
- Continental Islands – These islands were formerly part of the mainland and are now detached from the continent. They may be separated by a shallow lagoon or a deep channel.
Eg. Madagascar, Formosa etc
- Oceanic Islands – These islands are normally small and are located in the midst of oceans.
- Mauna Loa in Hawaii, Volcanic islands such as the Canary islands
They are very tiny creatures with the ability to secrete calcium carbonate within their cells has given rise to a particular type of landform.
Favourable conditions corals survive –
- Water Temperature – Not below 200C
- Area – Tropical and subtropical zones
- Shallow water area
- Saltish and free from sediment water
There are different types of coral reefs such as Fringing Reefs, Barrier Reefs and Atolls.
Soil is a dynamic medium in which many chemical, physical and biological activities going on constantly. Soil can be defined as – a collection of natural bodies on the earth’s surface containing living matter and supporting or capable of supporting plants.
Process of Soil Formation
- A precondition for soil formation is weathering. It is a weathering mantle which is the basic input for soil to form.
- The weathered material or transported deposits are colonized by bacteria and other inferior plants.
- The dead remains of organisms and plants help in humus accumulation.
- Minor grasses and ferns may grow in starting and later big plants and trees.
- Plants’ roots penetrate down, burrowing animals bring up particles, and the mass of material becomes porous and sponge-like with a capacity to retain water and to permit the passage of air and finally a mature soil.
Soil forming factors
- Parent material – a passive control factor and soil formation depend upon the texture and structure.
- Topography – a passive control factor. The amount of exposure of a surface covered by parent materials to sunlight etc. depends on topography.
- Climate – an active control factor. Factors such as precipitation, moisture in the soil, temperature, etc. play a major role in soil formation.
- Biological Activity – The vegetative cover and organisms that occupy the parent materials from the beginning and also at later stages help in adding organic matter and moisture retention, nitrogen etc
- Time – The length of time the soil-forming processes operate, determines the maturation of soils and profile development.
Salient features of the world’s physical geography: Examples
The world’s physical geography is characterized by a wide diversity of landforms, climates, and ecosystems. Some of the most salient features of the world geography include:
- Oceans and seas: The Earth is mostly covered by water, with the Pacific Ocean being the largest. There are five main oceans on Earth: the Atlantic Ocean, the Indian Ocean, the Southern Ocean, the Arctic Ocean, and the Pacific Ocean. These oceans are connected by a network of smaller seas, straits, and channels.
- Continents: The Earth’s land is divided into seven continents: Africa, Antarctica, Asia, Europe, North America, Australia, and South America.
- Mountains: Some of the world’s most iconic mountain ranges include the Himalayas, the Andes, the Rockies, the Alps, and the Karakoram.
- Plateaus and uplands: Major plateaus include the Tibetan Plateau and the Deccan Plateau.
- Plains and lowlands: Major lowlands include the Amazon River Basin, the Ganges-Brahmaputra Delta, the Mississippi River Valley, and the European Lowlands.
- Deserts: Major deserts include the Sahara, the Arabian Desert, the Gobi Desert, and the Atacama Desert.
- Rainforests: The world’s largest rainforests are found in the Amazon and Congo Basins, as well as in Indonesia and Malaysia.
- Oceans currents and winds: The ocean currents and winds are major drivers of the Earth’s climate, helping to distribute heat and moisture around the globe.
- Rivers and lakes: Some of the world’s longest rivers include the Nile, the Amazon, the Yangtze, and the Mississippi. Some of the largest lakes include the Caspian Sea, Lake Superior, and Lake Victoria.
- Glaciers and ice caps: Some of the world’s most iconic glaciers and ice caps include those in Antarctica, Greenland, and the Canadian Arctic.
The study of physical Geography is essential for the sufficient allocation of natural resources on the earth. It is essential for enabling human resolution as per the adjacent conditions and to be improved in order to protect our planet earth.
Article written by -Ankit Sharma