Geography

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The currently available sections include:

1. The Universe
2. The Solar System
3. The Motion of Earth
4. Latitude, Longitude and International Date Line
5. Rocks
6. Interior Structure of The Earth
7. Landforms
8. Earthquake
9. Volcanoes
10. Mountains and Plateau

Mountains and Plateau

Mountains are such highlands whose slopes are steep and the peaks are pointed. Generally, the mountains are more than 1000 mts high. The mountains whose height is less than 1000 mts, are called hills. The highest point of a mountain or a hill is called its peak. A mountain range is a system of mountains and hills having several ridges, peaks, summits and valleys, formed in a particular period and spread in a narrow belt.

Classification of Mountains

• Folded Mountains: These Mountains are the results of compressive forces, triggered by the endogenetic forces. When the rocks on (he surface of the earth are folded due to the forces generated within the earth, the resultant Himalaya Ural, Rockies, Andes, Atlas etc. examples of folded mountains.
• Block Mountains: These Mountains originate due to the forces of tension leading to the formation of rift valleys. These are also know as fault Block Mountains, as they are the result of faulting. Sierra Nevada mountain of California, USA, Vosages and Black Forest mountains of Europe.
• Accumulated Mountains: These mountain are formed due to accumulation of lava other ejected materials in the proccess of vulcanism. Fujiyama of Japan, Cotopaxi of Equador are its examples.
• Relict Mountains: When orginal mountains are eroded by the agents of gradation, they become relict mountains. Vindhyas, Aravallis, Satpura, Eastern Ghats, Western Ghats, Parasnath etc. are relict mountains.

Plateau

A plateau may be defined as that upland which has at least one side of very steep slope standing well above the neighbouring surface and whose upper part is extensive and almost flat.

Classification of Plateau

1. Intermontane Plateau: These Plateaus are surrounded by hills and mountains from all sides. For Example Tibetan plateau, Columbian plateau.
2. Piedmont Plateau: Which is surrounded by-mountain range on one side and by plain or ocean on the other side. For Example Appalachian Mountains (USA) and Patagonian plateau of South America.
3. Dome Shaped Plateau: These Plateaus are formed when the landmass is uplifted in such a manner that the middle portion is raised and the sides are rounded. Chhotanagpur plateau of Jharkhand, Ozark Plateau (USA).
4. Continental Plateau: These are very extensive Plateau and surrounded by oceanic coasts or plains. These are also called Shield. For Example Siberian shield.
5. Volcanic Plateau: These Plateau are formed due to accumulation of thick layers of bassltic laves. Deccan plateau of India and Columbian plateau of USA are the best example of this type.

Plateaus	Location
Anatolia	Turkey
Meseta	Iberian Peninsula
Chiyapas	S. Mexico
Alaska / Yukon	USA
Columbian	USA
Great Basin	USA
Colorado	USA

Volcanoes

A volcano is a vent, or opening, usually circular in form, through which gases, melted lava and fragments of rocks are ejected from the highly heated interior to the surface of the earth.
Crater: The narrow pipe, through which the magma comes out on the surface, is called Volcanic Pipe. The funnel or cup-shaped opening, at the top of the volcanic cone, is called as the Crater.
Crater Lake: When crater gets filled up with the rain-water, it forms as crater lakes for example Lonar lake in Maharashtra.
Caldera is formed due to subduction of the crater or expansion of the volcanic mouth due to successive eruptions. The largest ealdera in world is 'Aaso', which is in Japan. Lake Towa is in Indonesia which is known as super caldera.
Geyser: It is a special type of hot spring which sprouts hot water and vapour from time to time. The best examples are the Old Faithful and Exelsiar at the Yellow Stone National Park, in USA.
Fumaroles: Fumarole means such a vent throught which there is emission of gases and water vapour. Fumaroles impregnated with sulphur is called Solftara. Numerous fumaroles are found in the 'Katmai' mountains of the USA known as 'A Valley of Ten thousand Smokes' and the White Island fumarole in the Bay of Plenty, New Zealand, are also very famous.
Deccan Trapp: The basaltic lava, which comes out of the fissure voleanoes, flows slowly and gets solidified in the form of a thick shield. These layers or shields are called lava plateaux or Trapp. The best example of Trapp is the Deccan Trapp of India.
Classification on the Basis of Periodicity of Eruption :

1. Active Volcanoes : These volcanoes constantly eject volcanic lavas, gases, ashes and fragmental materials. Etna and Stromboli of the Mediterranean Sea are the most significant examples of this category. Stromboli is know as the Light house of the Mediterrancean. Other volcanous of this category are - Cotopaxi of Equador (World's highers active volcano), Mt. Erebus of Antarctica (the only active volcano of the continent) and the Barren Island of the Andaman and Nicobar Islands, India.
2. Dormant Volcanoes : These volcanoes become quiet after eruptions for some time and there are no indications for future eruptions but suddenly they erupt very violently. Important examples of this category are Vesuvius in Italy; Fujiyama in Japan; Krakatao in Indonesia, and the Narcondam Island of the Andaman & Nicobar.
3. Dead or Extinct Volcanoes : These are those volcanoes which have not erupted since thousands of years and there is no indication of future eruption as well. Leading examples of this category are - Mt Kenya and Klimanjor, in Eastern part of Africa; Chimborajo in Equador; Popa in Myanmar; and Aconcagua in Andes mountains.

Two-third of the world's volcanoes are found in the coastal regions of the Pacific ocean, archipelagoes and oceanic island. Hence, the name given to this belt is the Fire Girdle of the Pacific or the Fire Ring of the Pacific.

Earthquake

An earthquake is a vibration or oscillation of the surface of the earth caused by the elasticity or the isostatic adjustment of the rocks, beneath the surface of the earth. It may be caused by human as well as natural activities. Before the earthquake waves hit a region, the amount of 'Radon' gas increases in the atmosphere of that region. Therefore, rise in the concentration ofRadon gas' over the atmosphere of a region indicates that the region is going to be hit by an earthquake. The point, below the surface of the earth, from where the seismic (earthquake) waves originate is called the 'Focus' of the earthquake. The place, perpendicularly above the focus on the surface.
The waves generated during an earthquake are called Seismic Waves, which arc classified into 3 types:

1. Primary or Longitudinal Waves. These are simply known as P-Waves. These are longitudinal waves analogous to the sound waves. These waves have the maximum velocity among the three types of seismic waves. These waves can pass through the solid as well as liquid mediums, though their velocity gets slowed down in the liquid medium.
2. Secondary or Transverse Waves. These are also called as S-Waves. These are transversal waves analogous to the light waves. These waves can travel only through the solid medium and disappear in the liquid medium. Since these waves do not pass through the core of the earth, they give an idea about the core being in liquid state.
3. Surface or Long Period Waves. These are also known as 'L' waves which originate when 'P' wave hits the surface. These waves affect only the surface of the earth. These are the most destructive and cover the longest distance among the three types of waves.

The Sismographs

The instruments sensitive to the seismic waves, which help us to measure the intensity of an earthquake are called 'Seismographs' -Different scales are used to measure the intensity of earthquakes such as

1. Rossy-Feral Scale - This scale measures the earthquakes between 1 to 11 units.
2. Mercalli Scale - It is an empirical scale. It is divided into 12 units.
3. Richter Scale - It is a mathematical (logarithmic) scale, which measures the intensity of an earthquake between 0 to 9. For each unit of increase in the Richter Scale, the amplitude of the earthquake wave increases by a factor of 10.

The lines joining the regions of same seismic intensity are called as Isoseismal Lines. The lines joining the places which experience the earthquake termors at the same time called Homoseismal Lines.

Tsunami

'Tsu-na-mi' is a Japanese word which means oncoming oceanic waves. These waves are very long and with less oscillation which originate in the oceans due to earthquakes that occur on the ocean-bed. The movement of water with the Tsunami waves is upto complete depth which makes them more caastrophic.

Landforms

Different Landforms on the earth crust are caused by both endogenetic forces and exogenectic forces

Endogenetic Forces

The forces, which the affect crust of the earth, are divided into two broad categories on the basis of their sources of origin, they are Endogenetic Forces and Exogenetic Forces. The Endogenetic Forces (Diastroph forces, volcanic eruption, Earthquak etc.) give rise to several vertical irregularities, which leads to the formation of numerous varieties of relief features on the earth surface (e.g. Plateau, mountain, plain, lakes, faults, folds etc).
Compressional Forces and Tensional Forces. Due to compressional forces, the rock strata gets folded. For example Folded Mountain Himalaya
Faults : Cracks, Fractures and Faulting are included in it. Faults are formed due to the combined effect of both the compressional and tensional forces.
Rift valley are actually formed due to displacement of crustal parts and subsidence of middle portion between two normal faults. The Dead Sea of Jordan is located in a Rift valley.
When the middle portion remains at place and the two side blocks move downwards, the Block Mountains are formed. Satpura mountains in India, Black Forest and Vosages in Germany.

Exogenetic Forces

The main function of the exogenetic forces on the surface of the earth is denudation which includes, the processes of weathering and erosion.
Weathering: The process of disintegration and decomposition of rocks, due to physical, chemical or biological factors, at their own place is known as weathering. Based on the causes, the process of weathering is classified into three types:

A. Physical or Mechanical Weathering

• Due to insolation (Temperature)
• Due to Frost action
• Due to Friction
• Due to Pressure
• Exfoliation

B. Chemical Weathering

• By oxidation
• By Carbonation
• By Hydration
• Chelation
• Hydrolysis

C. Biological Weathering

• By Plants
• By Animals
• Due to Human Activities (Anthropo Weathering).

Erosion: Large scale transportation of the weathered materials is termed as erosion

Running Water (River)

The area drained by a river and its tributaries known as River Basin Catchment Area. Differ landforms by a river are:

1. V-shaped Valley : During its youthful stage the river down-cuts (vertical erosion or valley deepening) its valley. This results into formation of V-shaped valley, which is very deep and narrow and both of its sides meet together at the valley floor. In India, indus gorge, Shipkila gorge and Dihang gorge are highly famous. Though lateral erosion is observed in the valley, down-cutting of the river is most dominant, making lateral erosion negligent. It is divided into two types on the basis of its size and shape - Gorge and Canyon. Generally Gorge is very deep and narrow valley Sometimes it is formed as a result of fast withdrawal of waterfalls. Canyon is the extended form of Gorge. Its side-walls a comparatively more vertical. The best example of Canyon in the world is the Grand Canyon on the Colorado river of USA.
2. Waterfalls and Rapids: Water falls are caused because of sudden descents or abrupt breaks in the longitudinal course of the river, A waterfall may be defined as a vertical drop water of enormous volume from a great height in the long profiles of the rivers. Niagra fall North America and Victoria fall on the Zambezi river of Africa are leading examples of waterfall. The Jog or Gersoppa falls on the Sharavati river in the state of Karnataka (India) falls from a height of 260 m. Dhuandhar fall on the Narmada river and Hundru fall (97 m) on the Subarnrekha riverare well known for their scenic beauty. Rapids are of lesser height with respect to waterfalls.
3. Alluvial cones: When rivers leave the mountains and enter the plains, their channel gradient drops substantially, resulting into drop in the load carrying capacity of the river. Consequently, load consisting of finer to coarser and big-sized materials coming from the upstream is deposited at the point of break in slope of foothill zone and thus alluvial cones are formed. When several alluvial fans get combined, it forms Bhabhar region.
4. Alluvial Fans: When river descends from the hills, it spreads the load in a vast area. This results into the formation of fan-shaped plains, called alluvial fans.
5. Meanders: While flowing through the plains, the river stream flow take several turns and makes meanders. River meandering refers to the bends of longitudinal courses of the rivers and are 'S' shaped.
6. Oxbow Lake: When the river straightens after abandoning its meandering path, then the abandoned part forms the oxbow lake.
7. Levees : The narrow belt of ridges of low height built by the deposition of sediments by the spill water of the stream on its either banks is called natural Levee or embankments. These are formed due to the deposition of the load carried by the river as it moves ahead.
8. Delta: The depositional feature of almost triangular shape at the mouth of a river debouching either in a lake or a sea, is called delta. These are formed when the river flow.-through low lying plains and consequently its load carrying capacity reduces due to decrease in its speed. It resembles the shape of the Greek-alphabet Delta.

There are various kinds of Deltas such as :

1. Arcuate type : Delta of Nile River, Ganga- Brahmaputra Delta
2. Bird-foot type : Mississippi - Missouri Delu
3. Estuarine type : Narmada river Delta and Tap: river Delta in India.
4. Cuspate type : Ebbro delta in Spain

Sea Water

Seawater carves different landforms with the help of sea-waves, currents, tidal waves or tsunamis

1. Coastal Cliffs: Steep rocky coast rising almost vertically above seawater, is called cliff.
2. Coastal Caves: The coastal landform formed due to heavy sea-wave erosion on the coastal rocks having fissure, fracture and weak rocks.
3. Stacks: The natural arcs formed due to the coalescence of two caves are not permanent landforms. After collapsing the natural arc, the left portion projecting well above the sea-level is called stack.
4. Beach: Temporary or short-lived deposits of marine sediments, consisting of sands, shingles etc, on the .seashore are called beaches. Beaches are deposited by breaker waves between high and low tide waters. These are formed when sea is calm and winds are of low velocity.
5. Lagoons are formed when the coves or bays are almost completely enclosed by bars. Chilka Lake and Pulicat Lake on the east coast and Vembanad Lake on the west coast of India are lagoon lakes.

Glaciers

Glaciers : The moving ice mass down slope under the impact of gravity is called glacier. Snow line is generally defined as a zone between permanent and seasonal snow.
They formed on high mountains are long and narrow because they are formed in an abandoned river valley. These are known is 72 km long, is the largest of all the Indian glaciers. Different landforms carved out by glaciers are:

1. U-shaped Valley : U-shaped valleys are formed due to vertical erosion by the glaciers in the already existing river valley.
2. Hanging Valley : The valleys of tributary structure with steep walls, is formed, it is called cirque.
3. Horns : The pyramidal or triangular-faceted peak, formed due to recession and intersection of three or more cirques, is called horn. The Matterhorn Peak of Switzerland is very famous.

Wind

The wind is the most active agent of gradation in the arid and semi-arid regions where rainfall is very scanty and the ground surface is covered with loose particle of soil in the absence of both moisture and vegetation cover.
Mushroom-Rock : The rocks having broad upper part and narrow base resembling an umbrella or mushroom are called mushroom rocks. These are the result of abrasional work of wind in which the base of the rock is abraded rigorously.
Sand Dunes: The heaps or mounds of sand deposited by wind, are called sand dunes. Sand dunes keep their position changing the direction of wind. Sand dunes of crescentic shape having two horns are called Barchans. Loess: Loess plain are the extensive plains formed by the deposition of very thin soild particles brought by the wind in the outskirt of the desert region. Loess turns into very fertile soil when it gets water.
Playa: The temporary lakes created by the ephemeral streams in the bolsons, i.e. basins enclosed by hills in desert regions are called playas.

Interior Structure of The Earth

The study of the earth's interior is the subject of Geology, Since, the interior part of the earth is not visible directly, knowledge about it is gathered through indirect means. The earth as a whole has been divided into 3 broad zones - Crust, Mantle and Core.

The Crust

The Average thickness of this upper most layer of the earth is about 30 km. The average density of the upper crust is 2.8 and that of the lower crust is 3.0. This difference in density is believed to be due to the pressure. This discontinuity in density between upper crust and lower crust is known as 'conrad discontinuity'. Silica and Allumunium are the main constituent elements of the crust. Therefore, it is also know as the SIAL.

The Mantle

At the lower end of the crust the speed of the seismic waves increases suddenly and reaches upto 7.9 to 8.1 km/sec. This results into a discontinuity between the upper mantle and the lower crust, which shows a change in the density of the rocks. This discontinuity was discovered in 1909 by a Russian scientist A. Mohorvicie, therefore, it is named after him as 'Mono-discontinuity'. The mantle extends UPPER MANTLE" upto a depth of about 2900 km from the Moho-discontinuity,. Silica and Magnesium are the major constitutiing elements of this layer, hence it is also called SIMA.
Between 100 km to 200 km depth of the upper mantle, the velocity of the seismic waves is slowed down to 7.8 km/sec. Therefore, this zone is is known as the 'Zone of Low Velocity'. The discontinuity in density between upper mantle and lower mantle is known as Repetti discontinuity.

The Core

At the lower end of the lower mantle the velocity of the P waves suddenly increases to 13.6 km/sec. This shows as sudden change in the density of the rocks resulting into a type of discontinuity, known as 'Weicher Gutenber Dscontinuity'. It is divided into two parts Outer core and inner core. S waves cannot penetrate into the outer core. The density of the core is more than the double of the density of the mantle. In the inner core where the density is at its maximum, the velocity of the P waves is 11.23 km/sec because of its relatively liquid or semiliquid state due to excessive temperature but because of too much pressure it is in semi-liquid or plastic state. It's main constituens are nickel and iron, so it is also known as NIFE.

Rocks

Rocks are made up of individual solid substance called minerals. A rock as any natural mass of mineral matter that makes up the earth's crust. On the basis of the formation, rocks are classified into :

1. Igneous Rocks
2. Sedimentary Rocks
3. Metamorphic Rocks

Igneous Rocks

These rocks are formed by cooling, solidification and crystallization of hot and molten magma found below the earth crust. These are granular and crystalline rocks. These are also known as 'Primary or Ba'sic Rocks' because of the fact that these rocks were first to be formed and supply raw material for other types of rocks to be formed. No layering is found in these rocks and fossils are also not found. Nearly 90% of the crust is made up of igneous rocks. For example Granite Basalt Dolerite and Magetite

Sedimentary Rocks

Rocks formed on the surface of the earth due to the erosion and depositon of igneous and metamorphi rocks are known as sedimentary rocks. Sedimentary rocks are found over about 75% area of the crust, but they contribute only 5% in the formation of the crust. These rocks contain fossils. On the basis of the nature of the sediments, sedimentary rocks are classified into :

• Mechanically formed sedimentary rocks, such as : Sandstones, Conglomerates, Clay rocks, Shale and Loess.
• Organically formed sedimentary rocks, such as : Limestones, Coal and Peat.
• Chemically formed rocks, such as : Chalk rocks, Gypsum and Salt rock.

Metamorphic Rocks

Metamorphic rocks are formed due to complete alternation in the appearance and constitution of pre-exising rocks due to change in mineral composition and texture through temperature and pressuer. These are the hardest rocks and do not contain fossils.

Metamorphic rocks formed through the sedimentary rocks. (Meta - Sedimentary of Para - Metamorphic Rocks.)

• Slate from Shale
• Marble from Limestone
• Quartzite from chalk & dolomite

Metamorphic rocks formed through the Igneous rocks. (Meta - Igneous or Ortho-Meta morphic rocks)

• Gneisses from Granites
• Amphibolite from Basalt
• Schist from Basalt

Metamorphic rocks formed by the further metamorphosis of metamorphic rocks.

• Phyllite from Slate
• Schist from Phyllite
• Serpentine from Gabbro