Category: Geography

Physical Geography

• Solar System
• Earth
  • Latitude and Longitude
  • Motions of Earth – Rotation, Revolution, Inclination of Earth Axis
  • Local and Standard Time
  • International Date Line, Calendar
  • Eclipses
• Interior of the Earth
  • Source of Information – Direct, Indirect – Earth Quakes
  • Volcanoes, crust, mantle, core etc
• Rocks
  • Rocks & landform & Soils
  • Rock Cycle – Types of Rocks – Igneous, Sedimentary, Metamorphic
• Earth Quake
  • Earth Quake and its effect
• Volcano
  • Types and Landforms
• Distribution of continents & Oceans
  • Theories and evidence
    • Continental Drift
    • Post-Drift Studies
    • Ocean Floor Configuration
    • Distribution of Earthquake and Volcanoes
      • Sea Floor Spreading
  • Forces of Drifting
  • Plate Tectonics – Plate Boundaries – Divergent, Convergent and Transform
• Landforms in India and around the world
  • River and Lakes
  • Mountains and Peaks
  • Plateaus
• Geomorphic Process
  • Endogenic Process
    • Diastrophism – Orogenic, Epierogenic, Earthquake, Plate Movement
    • Volcanism – Pacific ring of fire
  • Exogenic Forces
    • Weathering
    • Mass Movement
    • Erosion
    • Transportation & Deposition
  • Landforms and its Evolution
    • Erosional Landforms
      • Erosional landforms of groundwater
      • Erosional landforms of river
      • Erosional landforms of wind
      • Erosional landforms of sea waves
      • Erosional landforms of Glacier
    • Depositional Landforms
      • Depositional landforms of groundwater
      • Depositional landforms of river
      • Depositional landform of wind
      • Depositional landforms of sea waves
      • Depositional landforms of Glacier
  • Composition of Atmosphere
  • Structure of Atmosphere
  • solar radiation heat balance and temperature
    • solar radiation
    • Heating and cooling of atmosphere
    • Factors controlling temperature distribution
    • Distribution of temperature
    • Inversion of temperature
  • Atmospheric Circulation and Weather Systems
    • Atmospheric Pressure
    • Factors affecting speed and direction of wind

Rotation and revolution of earth

Earth has two types of Motions. They are Rotation and Revolution. Rotation is the movement of the earth on its axis. Earth takes 24 hours for one rotation around its axis. This period of rotation is known as Earthday.

Revolution is the movement of the earth around the sun in a fixed path or orbit. Earth motion around the sun in its orbit, which the earth takes 365 days which is measured as 1 year. Also, 6 Hours is ignored for convenience.

These 6 Hours are saved every year to make one day (24 Hours) and this extra day is added to the month of February. Thereby every 4th year there will be 29 days instead of 28 days. The year with 366 days is called a leap year.

The Axis of the Earth is an imaginary line, which makes an angle of 66° with its orbital plane. An Orbital Plane is a plane formed by orbit.

Effects of Motion of Earth

The earth receives sunlight from the sun. Only half side of the earth receives sunlight at one point and the other of the earth does not receive sunlight.

The side that receives sunlight is the Day, the side which does not receive Sunlight is the night. This is because of the Spherical shape of the earth.

The circle of Illumination is the circle which divides the day from night on the Sphere of Earth (Globe). This circle does not coincide with the axis.

Seasons of Earth

The season in the Earth is caused by the inclination of the earth in the same direction and revolution around the sun in an elliptical orbit. Every year is divided into Summer, winter, spring, and autumn seasons.

The change of season is because of the earth’s position around the Sun.

Summer Solstice

The Northern Hemisphere is tilted towards the sun on 21st June. The Sunrays fall directly on the Tropic of Cancer, the areas near the Tropic of Cancer receive more heat.

The regions near the Poles receive less heat are the Sun rays fall of Poles are Slanting. The North Pole which is inclined towards the Sun and the areas beyond the Arctic circle experiences continuous daylight for six months.

The Summer occurs North of the equator, as the large portion of the Northern Hemisphere is getting Sunlight. At these places, on June 21, the longest day and the shortest night occurs.

In the Southern Hemisphere, this condition is opposite, where the Southern Hemisphere has winter, where the Nights are longer than the days. The above-mentioned points are all the characteristics of Summer Solstice.

Winter Solstice

On 22nd December, the Tropic of Capricorn receives direct rays of the Sun. This is because the South Pole is tilted towards the Sun.

As the result, the rays of the Suns fall vertically at the Tropic of Capricorn which is 23° S and by this Southern Hemisphere receives more sunlight. Therefore, it is Summer in Southern Hemisphere and Winter in Northern Hemisphere.

The Days in the Southern Hemisphere is longer than the Nights. This position of the earth is called Winter Solstice. Australia is a good example for Winter Solstice, and it has Summer during December and celebrates the Christmas festival in the Summer Season.

Equinox

During Equinox, the direct Sun Rays fall on the equator. At this position, neither the North Pole and the south pole is tilted towards the Sun. As a result, the whole earth experiences equal days and equal nights.

This position of the earth is called the Equinox. It happens on 21st March and September 23.

On September 23, it is Spring season in the Southern Hemisphere and Autumn in the Northern Hemisphere. On March 21, it is Spring season in the Northern Hemisphere and Autumn in the Southern Hemisphere.

References

• Motion of the Earth – Ncert

Landslide

Landslide definition

A landslide is defined as the movement of a mass of rock debris down a slope. Landslides are caused by the direct influence of gravity. Landslides can be caused by rainfall, snowmelt, stream erosion, flood, earthquakes, volcanic activity, disturbance by human activities, or any combination of these factors.

Landslides cause property damage, injury, and death and adversely affect a variety of resources. For example, water supplies, fisheries, sewage disposal systems, forests, dams, and roadways can be affected.

Landslide meaning in Hindi is ‘bhooskhalan‘ (भूस्खलन).

Cause of Landslide

Landslide occurs when the gravitational and other shear stresses within a slope exceed the shear strength of the things that form the slope. This is caused naturally and is man-made. The cause of landslides in India are:

• Deforestation – Cutting and clearing of trees from the forest, slopes, mountains, hills etc are said to be one of the main causes of Landslides in India.
• Shifting Cultivation – Shifting cultivation is mostly practised in India, especially in the North and North Eastern states. This involves the clearing of trees and plants in hills. It is also an important reason behind landslides in India.
• Mining Activities – Mining involves different operations which produce large amounts of vibrations. Activities such as blasting, and grinding of underground rocks create huge vibrations that reach several hundred and beyond and pose a threat and cause the risk of landslides.
• Urbanisation – As per the latest studies, the urbanized areas are more prone to landslides caused by precipitation than the rural areas.

Types of Landslide

Landslide is classified into four types:

• Falls and Toppling
• Slides
• Flows
• Earthflow

During a Landslide

Listen for any unusual sounds that might indicate moving debris, such as trees cracking or boulders knocking together.

If you are near a river, be alert for any sudden increase or decrease in water flow and for a change from clear to muddy water. Such changes may indicate landslide activity upstream, so be prepared to move quickly.

Be alert especially when driving. Embankments along roadsides are particularly susceptible to landslides.

Disconnect the power supply in the areas of the landslide.

After the Landslide

Stay away from the slide area. There may be a danger of additional slides, Check for injured and trapped persons near the slide, without entering the direct slide area.

Direct rescuers to their locations.

Listen to local radio or television for the latest emergency information Watch for flooding, which may occur after a landslide or debris flow.

References

• https://www.mrd.gov.fj/images/Brochures/Types_of_Landslide.pdf

What is earthquake disaster management?

Earthquake

An earthquake is sudden, rapid shaking of the ground caused by the shifting of rocks beneath the earth’s surface.

Earthquakes strike suddenly without warning and can occur at any time. The impacts of earthquakes include deaths, injuries, and damage to property.

Induced Seismicity

Induced seismicity are earthquakes that are due to human activities such as extraction or injection of fluids in the subsurface(Suckale, 2010).

The causes of induced seismic activity include dam building, geothermal energy extraction, mining, hydraulic fracturing, etc.

MEASURES FOR EARTHQUAKE RISK REDUCTION

The most important measure of the reduction of risk is pre-disaster mitigation, preventive measures, preparedness will reduce the vulnerability.

This also helps in rescue and relief action rapidly after the occurrence of the earthquake.

Steps

Stay calm, do not panic.

In most cases, one can protect themselves and others by Dropping, Covering, and Hold On.

If you are in a building, sit down on the floor under a table or any other furniture, and firmly hold on to it until the earthquake has stopped.

If there is no table nearby, cover your face and head with your hands and sit on the floor in a corner of the room. Keep away from glass windows, glass doors, and things that can fall down.

Do not try to leave the building quickly; during earthquakes, people mostly die because they try to run out of the building and become trapped under ruins if the building is destroyed.

Do not go to the staircase, a balcony, or an elevator. If you are in the street, keep away from buildings; try to get into an open space and avoid power transmission lines.

If you are at home, turn off electrical equipment and gas quickly. If you are in a chemistry class or a laboratory where chemicals are stored, try to leave the room because chemicals may cause injuries.

After earthquake

First, check if you have any injuries, and then check the condition of the surrounding people. If you cannot do this, wait for the rescue team. After the earthquake when you leave the shelter, do not return for 2-3 hours because the quakes may repeat (an aftershock).

Check if there is fire; in case of a mild one try to extinguish it. Be cautious about the possibility of gas leakage and damage caused to electrical wiring.

Be careful while opening wardrobe doors to take necessary items. Use only lanterns; do not use an oil lamp or a candle. Listen to the radio to receive information about the earthquake.

Fundamentals of Geomagnetism

The Magnetic field of the earth is also called Geomagnetism. The strength of the Earth’s magnetic field changes from place to place and its value is in order of 10^-5 T.

The scientific reason for the earth magnetic field is still not satisfactory. Earlier is was the large bar magnet is present along the axis of rotation of earth deep inside the earth. But it is scientifically correct.

Also by theory of Dynamo effect, it was though that magnetic field is arised by the electrical current generated by convective motion of metallic fluids consisting of iron and nickel in molten form.

The magnetic field of lines shows that the magnetic dipole located at the centre of the earth. But the axis of the dipole does not coincide with the axis of rotation of earth as it is tilted to 11.3°.

The place of the north magnetic pole is at a latitude of 79.74° N and a longitude of 71.8° W, a location in northern Canada. The magnetic south pole is at 79.74° S, 108.22° E in Antarctica.

The pole near the geographic north of the earth is the North Magnetic Pole and similarly the pole near the geographic south pole is called South Magnetic Pole.

There is some confusion in the nomenclature of the poles this is because if one looks at the magnetic field lines of the earth, the field lines go into the earth at the north magnetic pole (Nm) and come out from the south magnetic pole (Sm).

This convention comes as the magnetic north was the direction to which the north pole of a magnetic needle-pointed and the north pole of a magnet was so named as it was the north-seeking pole and practically, the north magnetic pole behaves like the south pole of a bar magnet inside the earth and vice versa.

Magnetic declination in surveying

When a point is taken into account on the earth’s surface. At such a point, the direction of the line of the longitude circle judges the geographical north-south direction.

The line of longitude towards the pole being the direction of true north. The vertical plane containing the line of the longitude circle and also the axis of rotation of the earth is termed the Geographic Meridian.

Similarly, the Magnetic meridian of an area is the vertical place which passes through the imaginary line connecting the magnetic north and the south poles and this plane would cross the surface of the earth in a longitude sort of a circle.

A magnetic needle, which is free to swing horizontally, would then lie in the magnetic meridian and also the north pole of the needle would point towards the magnetic north pole.

Since the line joining the magnetic poles is titled with relevance to the geographic axis of the earth, the magnetic meridian at a point makes angle with the geographic meridian.

This, then, is the angle between the true geographic north and the north shown by a compass needle. This angle is called the magnetic declination or simply declination.

The declination is larger at higher latitudes and smaller close to the equator. The declination in India is little, it is at Delhi with 0°41′ E and 0°58′ W at Mumbai. Thus, in each of these places, a magnetic needle shows the true north quite accurately.

There is an added amount of interest. If a magnetic needle is perfectly balanced about a horizontal axis so that it can swing in a plane of the magnetic meridian, the needle would make an angle with the horizontal and is known as the angle of dip or inclination.

The Great Indian Desert lies to the Northwest of the Aravali hills and is a land of undulating topography dotted with longitudinal dunes and barchans.

Region of the Great Indian Desert that the Thar Desert receives low rainfall below 150mm per year.

Due to the low rainfall, this region has an arid climate with low vegetation cover.

It is because of these Physical characteristics, that this is also called Marusthali, which is a region in the west that is a very dry part.

This region extends over 62,000 sq. km, north of the Luni river.

It is believed that this region during the Mesozoic era, was under the sea and this belief is made strong by the pieces of evidence found at the wood fossils park at Aakal, marine deposits around Brahmsar, near Jaisalmer.

These wood fossils were as old as 180 million years.

Marusthali desert

The great Indian desert is called Marusthali.

The underlying rock structure of the desert is an extension of the Peninsular plateau but still because of the extremely arid conditions, its surface features have been carved by physical weathering and wind action.

The desert lands feature found here are mushroom rocks, shifting dunes, and an oasis which is mostly in its southern part.

Based on the orientation, the desert can be divided into the northern part is sloping towards Sindh, and the south towards the Rann of Kachchh.

The south half of Marusthali forms a never-ending bowl, framed by flat-topped hills of sand, rocks, and limestone.

The north part has ridden closely packed with coarse sand.

The rivers mostly in this region are ephemeral(lasting for a very short time). The Luni river flowing in the southern part of the desert has some importance.

The Low precipitation and high evaporation make this region a water deficit.

There are some streams that suddenly disappear after some distance and which show the existence of inland drainage by joining a lake or playa.

The lakes and the playas have brackish water which is an important source of obtaining salt.

In this region, the soil is mostly loamy.

The crops grown in this region were attacked frequently by locust invasion.

Occupation in Marusthali

Livestock raising and irrigated farming. The crops grown here are Cereal grains, chickpeas, cotton, sugarcane, groundnuts, and oilseeds. Also, Lignite and gypsum are mined here.