Physical Geography

Question 1

Climateology

1. What is a latitude?
2. What are some important latitudes?
3. What are the different latitude heat zones and what influences their temperature differences?

Answer 1

1. A latitude is the angular distance of a place north or south of the equator measured in degrees from the center of the earth.
2. As the earth is slightly flattened at the poles, the linear distance of a degree of a latitude at the pole is a little longer than that of the equator.
3. Important latitudes:
   Equator 0,
   NP 90N,
   SP 90S,
4. The Tropic of Cancer (231⁄2° N) in the northern hemisphere.
5. The Tropic of Capricorn (231⁄2° S) in the southern hemisphere.
6. The Arctic circle (661⁄2° N) in the northern hemisphere.
7. The Antarctic circle is (661⁄2° S) in the southern hemisphere.

• The mid-day sun is exactly overhead at least once a year on all latitudes in between the Tropic of Cancer and the Tropic of Capricorn. This area, therefore, receives the maximum heat and is called the torrid zone.
• The mid-day sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Cap- ricorn. The angle of the sun’s rays goes on decreasing towards the poles.
• As such, the areas bounded by the Tropic of Cancer and the Arctic circle, and the Tropic of Capricorn and the Antarctic circle, have moderate temperatures. These are, therefore, called temperate zones.
• Areas lying beyond the Arctic circle and the Antarctic circle are very cold. Here the sun does not rise much above the horizon. Therefore, its rays are always slanting. These are, therefore, called frigid zones.

Question 2

Longitude or Meridians

What are they?

What is their role?

What are important longitudes? How much time is every longitudinal move east/west?

How is the international date line drawn?

Answer 2

1. Longitude is an angular distance of a place east or west of the Prime (First) Meridian measured in degrees from the centre of the earth.
2. On the globe, longitude is shown as a series of semi-circles that run from pole to pole passing through the equator. Such lines are also called meridians.
3. It was decided in 1884 to choose the meridian which passes through the Royal Astronomical Observatory at Greenwich, near London, as the zero meridian or prime meridian.
4. All other meridians radiate eastwards and westwards of the prime meridian up to 180°.
5. Unlike the parallels of latitude, the meridians of longitude are of equal length.
6. The meridians of longitude have one very important function; they determine local time in relation to Greenwich Mean Time (GMT), which is sometimes referred to as World Time.
7. Since the earth makes one complete rotation of 360° in one day or 24 hours, it passes through 15° in one hour or 1° in 4 minutes.
8. The earth rotates from west to east, so every 15° we go eastwards, local time is advanced by 1 hour.
9. Conversely, if we go westwards by 15°, local time is retarded by 1 hour.
10. IDL is drawn zig-zag

Question 3

The earth’s rotation

1. Which direction?
2. How long to complete on rotation?
3. What is the Earth’s shape?

Answer 3

1. The spinning movement of earth is called a rotation
2. It rotates on its axis in the West to East direction
3. Earth’s axis is antipodal i.e. it passes through the centre of the earth, connecting two exactly opposite ends.
4. The earth rotates on a tilted axis i.e the rotational axis makes an angle of 23.5 with the normal, therefore a 66.5 degree with the orbital plane of the earth.
5. The earth is an oblate spheroid or geoid i.e. it is slightly flat at the poles and bulged at the equator.

Question 4

Earth’s revolutions around the sun

What is the importance?

How does it differ for NH and SH?

What are the important dates?

Answer 4

1. The earth, while rotating on its axis, also revolves around the sun i.e. the ecliptic plane. It itakes 365 and 1/4 days to complete a rotation. Every 4 years we have a leap year from the hours conserved (6hrs a year)
2. On 21st June, the Northern hemisphere is titled towards the sun and the rays of sun fall directly on the tropic of cancer, as a result summer conditions are felt. On this day in the Northern Hemisphere is the longest day and shortest night and it is the Summer solstice for the NH and winter solstice for the SH.
3. On the summer solstice, the entire arctic region falls under the area of illumination.
4. On December 22nd, the Tropic of Capricorn receives direct sunlight, and as a result, the NH experiences its longest night and shortest day signalling the start of winter. This is the winter solstice in the NH and the summer solstice in the SH.

Question 5

What is the equinox?

What is perihelion?

What is aphelion?

Answer 5

1. The equinox is on 21st March and 23rd september and it is when the sun rays fall directly on the equator, resulting in the earth experiencing equal days and nights.
2. On 23rd September it is the start of Autumn in the NH and on 21st March it is the start of Spring in the NH. This is flipped for the SH.
3. Perihelion (January) is when the earth is closest to the sun and aphelion (June) is when the earth is furthest away from the sun.

Question 6

What is the structure of the atmosphere?

Answer 6

1. Troposphere: 0-12km
2. Stratosphere: 12-50km
3. Mesosphere: 50-80km
4. Thermosphere: 80-700km
5. Exosphere: 700-10,000km

Question 7

Temperature distribution on earth

What influences the differential temperature on earth?

What role does radiation play?

What role does insolation play?

What role does conduction play?

Answer 7

1. The differential amount of sun’s energy received by various latitudinal zones on earth is the primary reason behind the occurrence of seasonal patterns of weather and climate.
2. Radiation doesn’t require a medium for heat transfer i.e. heat transfer from sun to the earth through space
3. Insolation is the amount of the sun’s energy received in the form of radiation by the earth. I.e. the angle of insolation dictates the amount. It receives it in different forms and the earth absorbs the short-wave radiations in the day and reflects out the long-wave radiations in the night.
4. Conduction is the heat transfer through molecular activity in a conduction medium. I.e. denser materials are good conductors.
5. Convection is the transfer of heat energy by actual transfer of matter.

Question 8

What are the broad categories affecting temperature distribution?

Answer 8

1. The angle of incidence/inclination of the sun’s rays/angle of insolation
2. Duration of sunshine
3. Transparency of atmosphere
4. Albedo
5. Land-sea differential
6. Prevailing winds
7. Ocean currents
8. Altitude
9. Aspects of slope
10. Earth’s distance from the sun

Question 9

What is albedo?

Answer 9

Albedo of a surface is the proportion of sunlight that the surface can reflect back into space.

Albedo of land is greater than oceans and water bodies and white, clear snow has the highest albedo (more than ice).

Question 10

What is an isotherm?

Do isotherms consider altitude?

Where are they irregular?

Answer 10

1. An isotherm is an imaginary line joining places having equal temperature
2. Effects of altitude are not considered when drawing isotherms.
3. Generally, Isotherms have close correspondence with the latitude parallels because the same amount of insolation is received by all the points located on the latitude.
4. Isotherms are irregular over the NH due to enhanced land ans sea contrast.
5. The thermal equator or the Inter-Tropical- Convergence Zone lies to the north of the geographical equator.
6. Due to differential heating of land and water due to ocean currents, isotherms will have sudden bends at ocean-continent boundaries.
7. Narrow isotherm spacing indicates a high thermal gradient and a wide-spacing refers to a low thermal gradient.

Question 11

What is the general temperature distribution over earth?

What about cloud cover?

What is the moderating effect aka continentality?

Does the western margin of a continent have high temperature gradients?

Are subtropics devoid of clouds?

Answer 11

1. The lowest temps occur in polar and sub-polar regions and the interiors of large continental subpolar regions.
2. Diurnal and annual range of temperatures are highest in the interiors of continents due to continentality i.e moderating effect of the seas eg: mumbai vs. delhi
3. Low temperature gradients are observed over the tropics
4. Temperature gradients are usually high over the western margins of the continents because of cold ocean currents
5. Subtropics tend to be devoid of cloud coverage due to anticyclonic circulation at the surface.

Question 12

What is the heat budget?

Answer 12

1. The heat budget refers to the give and take that takes place of isolation/incoming radiation and terrestrial outgoing radiation.

Question 13

What is the lapse rate that is witnessed as altitude increases?

Is it standard?

What is adiabatic lapse rate?

Answer 13

1. The lapse rate is the rate of change of temperature in the atmosphere with altitude.
2. Lapse rate is positive when temperature decreases and negative when temperature increases.
3. In the troposphere below the tropopause, the lapse rate is positive, however the stratosphere has a negative lapse rate - i.e. it starts warming.
4. ALR is the lapse rate with specific reference to temperature changes in relation to pressure that don’t involve an exchange of heat.

Question 14

What is a temperature inversion?

What are the ideal conditions for a temperature inversion?

What are the different kind of inversions?

What is the impact of an inversion?

Answer 14

1. Under normal conditions temperature usually decreases with an increase in altitude aka positive lapse rate, however an inversion is the reversal of this behaviour.
2. Conditions for an inversion: long nights so that outgoing radiation is greater, clear skies and cal and stable air can result in a layer of warmer air forming above a layer of cool air.
3. Intermontane, ground surface and subsidence.
4. Inversions can result in a greater trapping of pollution and dust.

Question 15

What is atmospheric pressure?

What role does it place in defining cells?

What are isobars in the atmospheric pressure context?

Answer 15

1. 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 the atmospheric pressure.
2. Atmospheric pressure varies from place to place due to differences in topography, sun’s insolation and re- lated weather and climatic factors.
3. When heated, the volume of a parcel of air increases (air expands) and hence the pressure within the air parcel falls creating a low-pressure cell (low-pressure centre).

• When cooled, the volume of the air parcel decreases (air is compressed) and hence the pressure within the air parcel increases creating a high-pressure cell (high-pressure centre).
• A combination of atmospheric pressure cells give rise to distinct pressure systems within the atmosphere.
• Distribution of continents and oceans have a marked influence over the distribution of pressure.
• In winter, the continents are cooler than the oceans and tend to develop high-pressure centres,whereas, in summer, they are relatively warmer and develop low pressure. It is just the reverse with the oceans.

4. Isobars are imaginary lines drawn to connect places having equal pressure. The spacing in this case refers to pressure gradients.

Question 16

In general, does atmospheric pressure increase or decrease with altitude?

Answer 16

It decreases with altitude.

Question 17

What are the factors that affect wind movement?

Answer 17

1. Pressure gradient force
2. Buoyant force
3. Friction
4. Coriolis force
5. Gravitational force
6. Centripetal acceleration

Question 18

What is pressure gradient force?

Answer 18

1. Pressure gradient is the difference in pressure between atmospheric pressure cells that causes the movement of air from relatively high pressure centers to relatively low pressure centers.
2. The movement of air is known as “wind” and a greater pressure differential, greater the wind speed.
3. Pressure gradients are strong when isobars are close to each other and weak when apart.
4. Wind follows the direction of the pressure gradient i.e. perpendicular to the isobars.

Question 19

What is buoyant force?

What sinks and what rises?

Answer 19

1. Atmospheric pressure cells determine whether air sinks or rises at a place.
2. The surrounding atmosphere exerts buoyant force on low-pressure cells and hence the air within a low-pressure cell rises. AKA LP rises.
3. High pressure sinks due to the density of the high-pressure cell relative to surrounding atmosphere.
4. Rising air is associated with convergence and unstable weather (cyclonic conditions) whereas the sinking (subsiding) air is associated with divergence and stable conditions (anticyclonic conditions).

Question 20

What are the broad differences between cyclones and anticyclones?

How do they differ from the northern hemisphere and southern hemisphere?

Answer 20

1. Cyclones are low pressure (rising air) systems that move anticlockwise in the NH and clockwise in the SH (due to coriolis force difference in the hemispheres)
2. Anticyclones are high pressure systems (sinking) that move clockwise in the NH and anticlockwise in the SH.

Question 21

What is frictional force?

Is it higher or lower over land?

Answer 21

1. The earth’s terrain is not uniform and there are irregularities that can act as obstacles to movement of air/wind.
2. Friction is less over the sea and high over the land.
3. At the surface due to high friction, wind direction makes sharper angles with isobars.

Question 22

VERY important: What is coriolis force?

What directions do they get deflected?

What is Farrell’s law?

Is coriolis force always in place?

What is the coriolis effect?

Answer 22

1. Due to the earth’s rotation, wind does not cross isobars at a perfect right angle, but actually get deflected in from their original path. *Visually to the right of the source in the NH and left in the SH.
2. Farrel’s law dictates that Winds in the NH get deflected to the right of their source and to the left to the source in the SH.
3. The coriolis force doesn’t seem to exist until the air is set in motion and it icnreases with wind velocity and with altitude.
4. The coriolis effect is the apparent deflection of objects moving in a straight path relative to the earth’s surface.

Question 23

Horizontal distribution of pressure

What are the 7 pressure zones/belts?

What are their latitudes?

Are pressure belts permanent in nature?

Answer 23

1. Horizontal distribution of pressure is studied by drawing isobars at constant levels by eliminating the effect of altitude on pressure.

The 7 are from N to S:

90N: High Pressure Polar Belt

60N: Sub-Polar Low Pressure Belt

30N: Sub-Tropical High Pressure Belt

0: Equatorial Low Pressure Belt i.e. Doldrums

30S: Sub-Tropical High Pressure Belt

60N: Sub-Polar Low Pressure Belt

90S: Polar High Pressure Belt

Pressure belts are not premanent in nature and they oscillate based on the angle of insolation of the sun on earth as it revolves.

Question 24

Equatorial Low Pressure Belt

Characteristics
Margin Features

Answer 24

1. It lies between 10N and 10S.
   2 Belt varies based on the apparent movement of the sun
2. This belt is what shifts around as the Intertropical Convergence Zone (ITCZ) giving rainfall to different parts of India.
3. It is known as the doldrums because of the calm air moving.
4. It receives highest form of insolation and, as a result, gets heated a lot, resulting in low pressure.
5. Air at the margins of low pressure region rises giving rise to clouds and turbulent weather on the margins.
6. Even with the high temps and moisture, cycolnes are not formed due to the lack of a coriolis force.

Question 25

Sub-tropical high pressure belts or Horse Latitudes

Characteristics
Margin Features

Answer 25

1. This belt extends between 35N and S.
2. This region has dynamically formed high pressure from the subsidence of air that is taking place in the air from the equatorial regions and the subpolar regions, making it a high pressure region.
3. The subsiding air is warm and dry and therefore most deserts are present here (western margins of the continents generally) and there are generally anticyclonic conditions.

Question 26

Subpolar Low Pressure Belts

Characteristics

Answer 26

1. The subpolar low pressure belts are located btween 45N and the Arctic Circle 66.5N and 45S and Antarctic Circle 66.5S.
2. These regions are formed due to coriolis force and the ascent of air as a result of convergence of westerlies from subtropical high pressure region and polar easterlies coming from polar regoins.
3. There is a high contrast between land and sea on this belt.

Question 27

Polar high pressure belt

Characteristics

Answer 27

1, They lie around the poles and are small in area and the air coming from the low pressure belt cools down at the poles and becomes cold and dry and sinking hence the high pressure in the region.

Question 28

What happens to the ITCZ in winter and summer?

Answer 28

1. The ITCZ shifts northwards or southwards based on the apparent movement of the sun i.e. angle of insolation.
2. In the NH in the summer, the northward shift of the sun causes the pressure belts to shift slightly northwards and in the winter the pressure belts shift southwards.

Question 29

What are the key prevailing winds in the regions between the pressure belts?

Answer 29

NH: (coriolis effect = deflect to right)

1. Between EQLPB and STHPB : Northeast trade winds
2. Between STHPB and SPLPB: South West Westerlies
3. Between SPLPB and PHPB: N.E. Easterlies or Polar Easterlies

SH: (coriolis effect deflects to left)

1. Between EQLPB and STHPB : Southeast trade winds
2. Between STHPB and SPLPB: North West Westerlies
3. Between SPLPB and PHPB: S.E. Easterlies or Polar Easterlies

Question 30

What are the 3 important pressure cells created by the dynamic rising and subsiding of air due to apparent movement in the sun, relative temperature etc.

Answer 30

1. Hadley Cell: The air at the equatorial low pressure belt rises because of convection currents and as the air reaches the top of the troposphere it moves towards the poles.
   - This causes an accumulation of air close to 30N and S and part of that air sinks and forms the subtropical high pressure belts. Some of the diverging wind from the subtropical high pressure belt moves back toward the equator as the tradewinds.
2. Ferrel Cell

• In the middle latitudes, the circulation is of the cold sinking air that comes from the poles and the rising warm air from the subtropical high region.
• At the surface, these winds are called westerlies.

3. Polar Cell
   - At polar latitudes the cold dense air subsides near the poles and blows toward middle latitudes known as the polar easterlies.

Question 31

Classification of winds:

What kinds?

Some important names?

Answer 31

1. Permanent/primary/Prevailing/Planetary
   - Trade winds, westerlies and polar easterlies
2. Secondary or Periodic winds
   - Seasonal winds: change direction in different season eg. monsoons in SAsia. eg. Rain on western margin of Indian continent in June as ITCZ shifts and then reverses and becomes retreating, northeast monsoon on the Eastern margin in November.
3. Local Winds
   - Blow only during particular period of the day in a small area
   - Loo, Mistral, Foehn, Bora, Chinook (keeps mountainous farm regions snow-free), Sirocco (keeps sahara dry and dusty)

Question 32

Fog

What are the kinds?
Important effects?

Answer 32

1. When the temperature of an air mass containing a large quantity of water vapour falls suddenly due to inversions, condensation takes place within itself on fine dust particles.
2. The fog is a cloud with its base near to the ground.
3. Radiation fog results from radiation, cooling of the ground and are not very thick and are in winters.
4. Advectional fog is formed by the condensation of warm air when it moves horizontally over a cold surface. These are think and persistent and occur over warm and cold water mixing zones in oceans.
5. Frontal/Precipitation fog - is produced due to convergence of warm and cold air masses where warm air is pushed under by the the heavier cold air mass.

Question 33

What are the important forms of rainfall?

Answer 33

1. Convectional rainfall
   - The air on being heated, becomes light and rises in convection currents
   - As it rises and expand and loses heat, condensation takes place and cumulous clouds are formed. When condensation is rapid, then cumulonimbus clouds are formed.
   - The process releases the latent heat of condensation which further heats the air and forces it to go up.
   - The rain is heavy but of short duration and localized. It is common in dummer over doldrums.
2. Orographic rainfall occurs when war, humid air strikes an orographic barrier (a mountain range)

• The initial momentum causes the air to rise, and as the moisture-laden air gains height, it expands because of a fall in ambient pressure and then the temperature falls through an adibiatic process.
• The condensation kicks and and once the dew point is reached, it starts raining on the windward slopes. The wind then is dry and cold and descend as katabatic wind on the leeward side while their temp rises.

3. Frontal rainfall
   - When two air masses with different temperatures meet, the turbulent conditions produce rain. I.e. in the NW Europe the cold continental air and warm oceanic air converge to produce heavey rainfall in adjacent area.
4. Cyclonic rain - is convectional rainfall on a large scale
5. Monsoonal rainfall - characterized by the seasonal reveral of winds which carry moisture especially the south-west monsoon in India.

Question 34

Tropical Cyclones

Formation
Description
Characteristics

Answer 34

1. Tropical cyclones originate over oceans in tropical areas in late summers
2. They are rapidly rotating, violent storms that feature a closed, low-pressure centre with steep pressure gradients. They also feature a closed low-level atmospheric circulation and strong winds along with a spiral arrangement of thunderstorms.
3. They form on large sea surfaces with a temperature higher than 27C and the coriolis force is what creates the vortex.
4. They are on the western margins of the oceans because warm ocean currents that flow from east to west form a thick layer of warm water.
5. Rarely on eastern margins due to the cold currents that lower the surface temperature on the eastern parts of tropical oceans.

EXCEPTION: During El Nino, strong hurricanes occur on the eastern pacific due to a weak walker cell (accumulation of warm waters)

Question 35

What are jetstreams?

Which jetstreams are permanent?

Answer 35

1. The coriolis force acting on a body increases with its velocity. Winds in the upper atmosphere are free from frictional effect and are controlled by the pressure gradient and coriolis force.
2. When isobars are straight and there is no friction, the pressure gradient force is balanced by the coriolis force and the win as a result blows parallel to the isobar i.e. deflection is at a maximum. This win is geostrophic win and a Jet stream is a kind of geostrophic win.
3. Polar jet and subtropical jet are permanent jet streams that breeze through the upper troposphere for most part of the year.

Question 36

What is a temperate cyclone?
Characteristics
Important Points
Formation
What role do fronts play?

Answer 36

1. Cyclonic systems developing in the mid and high latitudes beyond tropics are temperate cyclones.
2. Unlike tropical cyclones that experience a convective cyclogensis of a thermal origin, the temperate cyclones occur due to frontal cyclogensis with a dynamic origin i.e. interaction of air masses influenced by coriolis force.
3. Front is a three-dimensional boundary zone formed between two converging air masses with different physical properties (temperature, humidity, density).
4. The two air masses don’t merge readily due to the effect of the converging atmospheric circulation, different physical properties, relatively low diffusion coefficient and a low thermal conductivity.

• Frontogenesis involves convergence of two distinct air masses.
• Frontolysis involves overriding of one of the air masses by another.
• In northern hemisphere frontogenesis (convergence of air masses) happens in anti-clockwise direction
and southern hemisphere, clockwise direction.

Types of fronts: Stationary, Cold, Warm, Occluded.

Question 37

What is El Nino?

What is its relation to India?

Answer 37

1. In a normal year, a surface low-pressure develops in the regions of Northern Australia and Indonesia and a high-pressure system over peru.
2. As a result, the trade winds over the pacific move strongly from east to west.
3. Easterly flow of trade winds carried warm surface waters westward bringing convective storms to Indonesia and coastal Australia. Along the coast of peru, the cold bottom nbutrient rich water wells up to the surface to replace the water that is pulled to the west.
4. However, in El Nino the air pressure drops over large areas of the central pacific and coast of South America. The normal low pressure system is replaced by a weak high in western pacific, and this causes trade winds to be reduced. This allows the equatorial counter current (west to east) bringing drought to western pacific and rains to the equatorial coast of south america.

El Nino is inversely related to Indian monsoons and it impacts India’s agraian economy as it tends to lower the production of summer crops such as sugarcane, cotton and oilseeds.

Question 38

Oceanography

What are the major ocean relief features?
What are their characteristics?

Answer 38

1. the continental shelf

• gently sloping seaward extension of the continental plate.
• Shallow seas and gulfs are found along the continental shelf
• Shelf will end in a steep slope called the shelf break
• Formed due to submergence of a continent part and a relative rise in sea level.
• 20% of the world’s petroleum and gas comes from shelves, as does marine food.

2. the continental slope
   - gradient of the slope varies between 2-5 degree
   - It connects the continental shelf and the ocean basin
   - the depth of the slope region varies between 200-3000m
   - Its end indicates the end of the continents-
   - Canyons and trenches are observed in this regoin.
3. the continental rise
   - The slope gradually loses steepness and the rise becomes virtually flat
4. the Deep Sea Plain or the abyssal plain.
   - Deep sean planes are gently sloping and cover 40% of the ocean floor.

Question 39

What are minor ocean relief features?

Answer 39

1. Ridges (along a divergent boundary)
2. Abyssal Hills (submerged volcanic mountains), Seamounts and gyuots.
3. Trenches (along a convergent boundary)
4. Canyons (an erosional landform)
5. Island arcs (formed due to volanism along the convergent boundary)
6. Atolls and coral reefs.

Question 40

What is a marginal sea?

What is its importance?

Answer 40

In oceanography, a marginal sea is a sea partially enclosed by islands, archipelagos, or peninsulas.

Some of the major marginal seas include the Arabian Sea, Baltic Sea, Bay of Bengal, Bering Sea, Black Sea, Gulf of California, Gulf of Mexico, Mediterranean Sea, Red Sea, and all four of the Siberian Seas
(Barents, Kara, Laptev, and East Siberian).

The primary differences between marginal seas and open oceans are associated with depth and proximity to landmasses.

Marginal seas, which are generally shallower than open oceans, are more influenced by human activities, river runoff, climate, and water circulation.

Marginal seas are very susceptible to pollution and can experience algal bloom and, oil drilling and have 90% of the world’s fisheries.

Question 41

What are bays, gulfs and straits, Isthmus?

Answer 41

1. Bays are a small body of water that is set off from a larger body of water where the land curves inward. It is a water body surrounded on three sides by land and fourth towards the open ocean. The mouth is wide - bay. Narrow - fuld.
2. A gulf is a large body of water generally with a narrow mouth. Persian gulf is important with respect to world energy as petroleum is transferred through it. Gulf of Mexico is the biggest.
3. A strait is a narrow passageway of water between continents, islands or between two large bodies of water. Strait of Gibraltar is very important as is the Strait of Bosphorous that connects the Black sea and the Sea of Marmara. The Strait of Hormuz is also important.
4. An Isthmus is a narrow strip of land connecting two larger land masses.

Question 42

Ocean movements

What are ocean currents?

What are factors that influence their movement?

What are the types of ocean currents?

Answer 42

1. Movements in oceans are categorized as waves, tides and currents.
2. Horizontal currents arise due to friction between wind and water.
3. Coriolis force and differences in water level gradient play a major role.
4. Ocean currents are like river flow in oceans as they represent a regular volume of water in a definite path and direction.
5. They are influnced by primary forces such as heating by solar energy, wind, gravity and coriolis force and secondary forces such as temperature difference and salinity difference.
6. Ocean currents can be surface currents or deep water currents. Surface currents consitute about 10% of the water movement in oceans whereas deep water make up for 90%.
7. Further, ocean currents can be cold currents or warm currents. i.e. cold currents occur when cold water at poles sinks and moves toward the equator as subsurface flow and warm currents that travel out from the equator along the surface flowing towards the poles to replace the cold water leaving.

Question 43

Where do warm currents and cold currents tend to generally flow in relation to the margin of continents in the different hemispheres?

Answer 43

1. Cold currents are usually found on the west coast of the continents (because of clockwise flow in northern hemisphere and anti-clockwise flow in southern hemisphere) in the low and middle latitudes (true in both hemispheres) and on the east coast in the higher latitudes in the Northern Hemisphere.
2. Warm currents are usually observed on the east coast of continents in the low and middle latitudes (true in both hemispheres). In the northern hemisphere, they are found on the west coasts of continents in high lat- itudes.

Question 44

What are the 7 important pacific ocean currents?

Hint: You essentially have a clockwise movement in the Northern Hemisphere looking at the pacific ocean.

Answer 44

1. Kuroshio current - warm
   - The north equatorial current turns northward off the Philippines to form the kuroshio current
   - It flows in the subtropical high pressure belt and its northern part gets influenced by the westerlies.
2. The Oyashio/Okhotsk - cold
   - Flows across the east coast of the Kamchatka peninsula to merge with the warm waters of kuroshio and this convergence of the cold and warm water makes this zone one of the richest fishing grounds.
3. The North Pacific Current - warm
   - From the south east coast of Japan, under the influence of the westerlies, the Kuroshio current turns eastward and moves as the North Pacific current reaching the west coast of N. America and then bifurcates into two.
4. Alaska current – warm
   • The northern branch of North-Pacific current flows anti-clockwise along the coast of British Columbia and Alaska and is known as the Alaska current.
   • The water of this current is relatively warm as compared to the surrounding waters in this zone.
5. Californian current – cold
   • The southern branch of the North-Pacific current moves as a cold current along the west coast of USA and is known as the Californian current.
   • The Californian current joins the north equatorial current to complete the circuit.
6. East Australian current – warm
   • Following the pattern in the northern hemisphere, the south equatorial current flows from east to west and turns southwards as the East Australian current.
   • It then meets the South Pacific current near Tasmania which flows from west to east.
7. Peru current or Humboldt Current – cold
   • Reaching the south-western coast of South America, South Pacific current turns northward as the Peru cur- rent. It is a cold current, which finally feeds the south equatorial current, thus completing the great circuit.
   • The zone where Peru Cold current meets the warm equatorial ocean waters is an important fishing zone.

Question 45

What are the important Atlantic Ocean currents in the Northern Hemisphere?

Answer 45

Equatorial Atlantic Ocean Currents – warm
• Under the influence of prevailing trade winds (easterly trade winds), the north equatorial current and the south equatorial current start from the eastern Atlantic (west coast of Africa), moving from east to west.

• This raises the level of western Atlantic (north of the Brazil bulge) ocean by few centimetres.

• And this creates a counter-equatorial current which flows between the north equatorial current and the
south equatorial current in west-east direction.

Antilles current – warm

• The south equatorial current bifurcates into two branches near Cape de Sao Roque (Brazil).
• Part of the current enters the Caribbean Sea along with north equatorial current into the Mexican Gulf, while the remainder passes along the eastern side of the West Indies as the Antilles current.
• There is a rise in water level in the Mexican Gulf because of large amounts of water brought by the Missis-sippi River and branches of north and south equatorial currents. Gulf Stream and North Atlantic Drift – warm
• Antilles current creates a current that flows out through the Strait of Florida as Florida current, which mixes with Antilles current from the south.
• This combined current moves along the east coast of USA and is known as the Florida current up to the Cape Hatteras and as the Gulf Stream beyond that.
• Near the Grand Banks, the Gulf Stream mixes with cold Labrador and East Greenland currents and flows eastward across the Atlantic as the North Atlantic Drift.
• Here, westerly movement of North Atlantic Drift is due to the influence of westerlies.

Norwegian current – warm
• The North Atlantic Current breaks up into two branches on reaching the eastern part of the ocean.

• The main current, continuing as the North Atlantic Drift, reaches the British Isles from where it flows along the coast of Norway as the Norwegian current and enters the Arctic Ocean.

• Norwegian current is very important as it keeps ocean to the north of Norway partly free from ice and
also moderates the extremes of climate.

• The southerly branch flows between Spain and Azores as the cold Canary current.
• This current finally joins the north equatorial current completing the circuit in the North Atlantic.
• The Sargasso Sea, lying within this circuit, is full of large quantities of seaweed and is an important geo-graphical feature. A sea with no land borders.

Question 46

What are the important currents in the South Atlantic sector?

Answer 46

Brazil current – warm
• In the South Atlantic Ocean, the south equatorial current, flowing from east to west, splits into two branch- es near Cape de Sao Roque (Brazil).

• The northern branch joins the north equatorial current (a part of it flows in Antilles Current and other into Gulf of Mexico), whereas the southern branch turns southward and flows along the South American coast as the warm Brazil current.
• The south-flowing Brazil current swings eastward at about latitude 35°S (due to westerlies) to join the West Wind Drift flowing from west to east.
• A small branch of West Wind Drift splits and flows between Argentinian coast and Falkland Islands, and this current is called as Falkland cold current.
• It mixes with warm Brazil current at the southern tip of Brazil.

Benguela current – cold current
• A branch of the South Atlantic splits at the southern tip of Africa and flows along the west coast of South Africa as the cold Benguela current, which joins the south equatorial current to complete the circuit.

Question 47

What are the important Indian Ocean currents?

How does it change in the winter and in the summer?

Answer 47

1. Winter Circulation

• The north-east monsoons drive the water along the coast of Bay of Bengal to circulate in an anti- clockwise direction.
• Similarly, the water along the coast of Arabian Sea also circulate in an anti-clockwise circulation.

2. Summer circulation

• In summer, due to the effects of the strong south-west monsoon and the absence of the north-east trades, a strong current flow from west to east, which completely obliterates the north equatorial current.
• Hence, there is no counter-equatorial current as well.
• Thus, the circulation of water in the northern part of the ocean is clockwise during this season.

Question 48

What are the direct and indirect effects of ocean currents?

Answer 48

1. Desert formation - cold currents on the western margins of tropical and subtropical continents
2. Rains - warm currents bring rain to coastal areas and even interiors eg. british isles rain
3. moderating effect - i.e. warm norwegian current helps keep parts of norway ice free and canay cold current brings cooling effect to Spain.
4. Fishing - mixing of cold and warm currents bring rich fishing conditions. I.e. Grandbanks in newfoundland, canada and northeastern coast of Japan as well.
5. The pile up of warm waters in the tropics can cause tropical cyclone conditions.
6. The currents help with navigation.

Question 49

What are the factors that affect the temperature distribution of oceans?

Answer 49

1. Insolation: The average daily duration of insolation and its intensity.
2. Heat loss: The loss of energy by reflection, scattering, evaporation and radiation.
3. Albedo: The albedo of the sea (depending on the angle of sun rays).
4. The physical characteristics of the sea surface: Boiling point of the sea water is increased in the case of
   higher salinity and vice versa (if Salinity is increased➔Boiling point will increase➔Evaporation will
   decrease).
5. The presence of submarine ridges and sills: Temperature is affected due to lesser mixing of waters on the
   opposite sides of the ridges or sills (e.g. subsurface layers in Mediterranean Sea).
6. The shape of the ocean (enclosed seas): enclosed seas in the low latitudes record relatively higher temperature than the open seas (due to less mixing and higher overall insolation); whereas the enclosed seas in the high latitudes have lower temperature than the open seas.

• E.g. Mediterranean Sea records higher temperature than the longitudinally extensive Gulf of California.

7. Local weather conditions such as cyclones.
8. Unequal distribution of land and water: The oceans in the northern hemisphere receive more heat due to their contact with larger extent of land than the oceans in the southern hemisphere.
9. Prevalent winds generate horizontal and sometimes vertical ocean currents: The winds blowing from the land towards the oceans (off-shore winds: moving away from the shore) drive warm surface water away from the coast resulting in the upwelling of cold water from below (this happens near Peruvian Coast during normal years).
   • Contrary to this, the onshore winds (winds flowing from oceans into continents) pile up warm water near the coast, and this raises the temperature (this happens near the Peruvian coast during El Nino event).
10. Ocean currents: Warm ocean currents raise the temperature in cold areas while the cold currents decrease the temperature in warm ocean areas.

Question 50

What is photic zone and aphotic zone?

What is thermocline and pycnocline?

Answer 50

1. Photic or euphotic zone extends from the upper surface to ~200 m. The photic zone receives adequate solar insolation.
2. Aphotic zone extends from 200 m to the ocean bottom; this zone does not receive adequate sunrays.
3. The thermocline is the boundary region where there is a rapid decrease in temperature as we go deeper into the ocean.
4. Pycnocline is a boundary separating two liquid layers of different densities. Pycnocline exists in oceans at a depth of 100-1000 m because of large density difference between surface waters and deep ocean water. Pycnocline effectively prevents vertical currents except in polar regions.

Question 51

Ocean Salinity

Factors Affecting
Horizontal Distribution
Vertical Distribution

Answer 51

Salinity is the term used to define the total content of dissolved salts in seawater.

I t is calculated as the amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater.

It is usually expressed as parts per thousand or ppt.

Factors affecting:

1. The salinity of water in the surface layer of oceans depend mainly on evaporation and precipitation.
2. Surface salinity is greatly influenced in coastal regions by the freshwater flow from rivers, and in polar regions by the processes of freezing and thawing of ice.
3. Wind also influences salinity of an area by transferring water to other areas.
4. The ocean currents contribute to the salinity variations.
5. Salinity, temperature and density of water are interrelated. Hence, any change in the temperature or density influences the salinity of an area.

Normal open ocean salinity ranges from 33 to 37 ppt and the regions with high salinity often coincide with high pressure cells aka hardly any rain and subsiding dry winds cause evaporation.

• Lake Van in Turkey (330 ppt)
• Dead Sea (238 ppt)
• Great Salt Lake, Utah (220 ppt)

With depth, the salinity also varies, but this variation again is subject to latitudinal difference. The decrease is also influenced by cold and warm currents.

In high latitudes, salinity increases with depth. In the middle latitudes, it increases up to 35 metres and then it decreases. At the equator, sub-surface salinity is lower.

As with thermocline, in water there is the halocline after which salinity sharply increases.

Question 52

What are the ideal conditions for coral growth?

What is coral bleaching?

Answer 52

1. Stable climatic conditions
2. Perpetually warm waters
3. Not too much salinity but not freshwater either
4. Abundant plankton is key i.e. supply of oxygen and microscopic marine food
5. No pollution
6. Coral Bleaching is when, without algae, the coral loses its major source of food, affecting the symbiotic relationship, turning it white and susceptible to disease.

Question 53

What are the kind of resources from the oceans?

Answer 53

1. Terragic

2. Pelagic

Question 54

Geomorphology

How are earthquake waves produced?

Answer 54

1. The abrupt release of energy along a fault (sharp break in the crustal layer) causes earthquake waves.
2. The pressure on the rock layers builds up over a period and overcomes the frictional force resulting in a sudden movement generating shockwaves (seismic waves) that travel in all directions.
3. The point where the energy is released is called the focus or the hypocentre of an earthquake.
4. The point on the surface directly above the focus is called epicentre.
5. An instrument called ‘seismograph’ records the waves reaching the surface.

Question 55

What are the types of seismic waves?

What is the difference between p-waves and s-waves?

What are L-waves?

What are rayleigh waves?

Answer 55

The seismic waves/earthquake waves are of two types, body waves and surface waves.

Within body waves there are P waves and S waves:

1. The P-waves or primary waves (longitudinal in nature ― wave propagation is similar to sound waves).
2. The S-waves or secondary waves (transverse in nature ― wave propagation is similar to ripples on the
   surface of the water).
3. Secondary waves (secondary ➔ they are recorded second on the seismograph) or S-waves are also called as transverse waves or shear waves or distortional waves.
4. They are analogous to water ripples or light waves.
5. Transverse waves or shear waves mean that the direction of vibrations of the particles in the medium is perpendicular to the direction of propagation of the wave. Hence, they create troughs and crests in the
   material through which they pass (they distort the medium).
6. S-waves arrive at the surface after the P-waves.
7. These waves are of high frequency and possess slightly higher destructive power compared to P-waves.
8. The trembling on the earth’s surface caused due to these waves is from side to side (horizontal).
9. S-waves cannot pass through fluids (liquids and gases) as fluids do not support shear stresses.
10. The body waves interact with the surface rocks and generate new set of waves called surface waves (long or L-waves). These waves move only along the surface.
11. Surface Waves are also called long period waves because of their long wavelength
12. They are low-frequency transverse waves (shear waves).
13. They develop in the immediate neighbourhood of the epicentre and affect only the surface of the earth and die out at smaller depth.
14. A Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean. It is the most destructive in its shaking and damage potential.

Question 56

Map the the interior structure of the earth from surface to core. What are the mechanical layers and what are the chemical layers?

Key points

Answer 56

Mechanical:

• lithosphere, asthenosphere, mesospheric mantle, outer core and inner core

Chemical
- oceanic crust (basaltic) continental crust (grantic), upper mantle, lower mantle, outer core and inner core.

1. The crust is the outermost layer and the crust + the upper mantle are a part of the lithosphere.
2. The continental crust is composed of lighter (felsic) sodium potassium aluminium silicate rocks, like granite.
3. The oceanic crust, on the other hand, is composed of dense (mafic) iron magnesium silicate igneous rocks, like basalt.
4. The aesthenosphere is below the lithosphere and is highly vicous, mechanically weak and it is the main source of magma.

Question 57

Stages and kinds of rocks

What are they?

Where do they form?

What is intrusive and extrusive rock?

Further describe the difference between felsic and mafic.

Answer 57

1. Rock can be broadly be categorized into igneous, sedimentary and metamorhpic rock.
2. Igenous rock is when magma from a volcano cools down rapidly. It is a primary/basic rock form from which all other rocks are derived
3. Acidic lava becomes felsic rock and basic lava becomes mafic rock - both of which are igneous rocks.

Intrusive rock can be hypabyssal i.e. dolorie, pigmatyte, magnetite. Extrusive rock is outside.

Question 58

Describe the earth’s magnetic field

What is the self-sustaining loop?

What is the form of movement in the field?

What is geomagnetic reversal?

Answer 58

1. Earth’s magnetic field is generated in the earth’s outer core.
2. Lower pressure than the inner core means the metal in the outer core is fluid.
3. The temperature of the outer core ranges from 4400 °C in the outer regions to 6000 °C near the inner core.
4. This flow of liquid iron generates electric currents, which in turn produce magnetic fields.
5. Charged metals passing through these fields go on to create electric currents of their own, and so the cycle continues. This self-sustaining loop is known as the geodynamo.
6. The spiral movement of the charged particles caused by the Coriolis force means that separate magnetic fields created are roughly aligned in the same direction, their combined effect adding up to produce one vast magnetic field of the planet.
7. A geomagnetic reversal or a reversal in earth’s magnetic field is a change in a planet’s magnetic field such that the positions of magnetic north and magnetic south are interchanged.

Question 59

What is the difference between endogenic and exogenic geomorphic movements?

What are slow, gradual and sudden movements?

What is the significance of weathering?

Answer 59

1. Endogenic movements are ultimately driven by the earth’s internal heat. They are internal movements that take place say due to convectional currents that are created due to temp and pressure differences amongst various layers of the earth. Further coriolis effect can affect where the currents travel.
2. Diastrohpic endogenic movements are slow deformations to the earth’s crust whereas sudden movements are earthquakes, volacanoes etc.
3. Diastrophic movements are further classified into epeirogenic movements (continent forming ― sub-
   sidence, upliftment) and orogenic movements (mountain building ― folding, faulting).
4. Exogenic movements take place on the surface and refer to weathering and erosion usually that can take place physically, chemically, biologically.

Weathering is the first step in the formation of soil from rocks.
• Weathering weakens soil and rocks and makes it easy to exploit natural resources.
• Weathering leads to natural soil enrichment.
• Weathering leads to mineral enrichment of certain ores by leaching unwanted minerals leaving behind the valuable ones.

Question 60

What are the 5 proposed theories to understand tectonic processes?

Quick points about each.

Answer 60

1. Continental Drift Theory (CDT)
   - Continental drift refers to the movement of the continents relative to each other. Pangea+Panthallasa
2. Polar wandering (similar to Continental Drift Theory)
   - Polar wandering is the relative movement of the earth’s crust and upper mantle with respect to the rotational poles of the earth.
3. Seafloor Spreading Theory (SFST)
   - Seafloor spreading describes the movement of oceanic plates relative to one another.
4. Plate Tectonics (PT)
   • Plate tectonics is the movement of lithospheric plates relative to each other.
5. Convection Current Theory (CCT)
   • Convection current theory forms the basis of SFST and PT. It explains the force behind plate movements.

Question 61

Plate tectonics has proved to be the leading theory to explain tectonic processes leading to the earth’s current disposition, what is the significance of the theory?

What are the 3 ways in which plates can interact with each other in this theory?

Answer 61

1, Almost all major landforms formed are due to plate tectonics.

2. New minerals are thrown up from the core with the magmatic eruptions.
3. Economically valuable minerals like copper and uranium are found near the plate boundaries.
4. From present knowledge of crustal plate movement, the shape of landmasses in future can be predicted.
5. For instance, if the present trends continue, North and South America will separate. A piece of land will separate from the east coast of Africa. Australia will move closer to Asia.

Three ways of plate interaction:

Divergence forming divergent Edge or the Constructive Edge: leads to mid-ocean ridges. Basaltic magma shoots up and divergent edges are sites of earth crust formation.

Convergence forming convergent edge or destructive edge: In this kind of interaction, two lithospheric plates collide against each other. The zone of collision may undergo crumpling and folding, and folded mountains may emerge (orogenic collision). Himalayan Boundary Fault is one such example.

• When one of the plates is an oceanic plate, it gets embedded in the softer asthenosphere of the continental plate, and as a result, trenches are formed at the zone of subduction.

Transcurrent Edge or Conservative Edge or Transform Edge: In this kind of interaction, two plates slide past against each other, and there is no creation or destruction of landform but only deformation of the existing landform.
- In oceans, transform faults are the planes of separation generally perpendicular to the mid-oceanic ridges.
- San Andreas Fault (Silicon Valley lies dangerously close to the faultline) along the western coast of USA is
the best example for a transcurrent edge on continents.

Question 62

What does ocean-ocean convergence result in?

What is the Mariana Trench?

Answer 62

It has led to the formation of Japanese Island Arc, Indonesian Archipelago, Philippine Island Arc and Caribbean Islands.

1. In Ocean-Ocean Convergence, a denser oceanic plate subducts below a less dense oceanic plate forming a trench along the boundary.
2. The Mariana Trench or Marianas Trench, the deepest trench, is located in the western Pacific Ocean.
   - The Mariana Trench is formed due to the subduction of the Pacific Plate below the Mariana Plate.
   - The maximum known depth is between 10,994 & 11,034 metres in its floor known as the Challenger Deep.

Question 63

What is oceanic and continental convergence?

What is a cordillera?

What about continent-continent convergence?

Answer 63

1. The concept of Continent-Ocean Convergence is important to understand the formation of the Rockies, the Andes and other similar fold mountain systems.
2. Continent-Ocean Convergence is also called Cordilleran Convergence because this kind of convergence gives rise to extensive mountain systems.
3. A cordillera is an extensive chain of mountains or mountain ranges. Some mountain chains in North Ameri- ca and South America are called cordilleras.
4. Continent-Ocean Convergence is similar to ocean-ocean convergence. One important difference is that in continent-ocean convergence mountains are formed instead of islands.
5. In continent-continent convergence there is similar density so there is no subsidence, leading to collision and the creation of a single large continental mass joined by a mountain range eg. Himalayas, Alps, Urals, Appalachians, Atlas Mountains.

Question 64

What are the different kind of mountains?

Answer 64

Original or Tectonic mountains

1. Original or Tectonic mountains are the product of tectonic forces.

The tectonic mountains may be categorized into:

1. fold mountains (the Himalayas, the Rockies, the Andes),
2. block mountains (Vosges mountains in France, the Black Forest in Germany, Vindhya and Satpura in India) and
3. volcanic mountains (Cascade Range in the USA, Mount Kenya, Mount Kilimanjaro, Mount Fuji-yama).

Question 65

Volcanic Landforms

How are they divided?

What is plutonic rock? What is igenous rock?

Answer 65

1. Volcanic landforms are divided into extrusive and intrusive landforms based on whether magma cools within the crust or above the crust.
2. Rocks formed by cooling of magma within the crust are called Plutonic rocks.
3. Rocks formed by cooling of lava above the surface are called Igneous rocks.
4. In general, the term ‘Igneous rocks’ is used to refer all rocks of volcanic origin.

Question 66

What are the causes of volcanism?

What are the types of lava?

Answer 66

1. There is a huge temperature difference between the inner layers and the outer layers of the earth due to the differential amount of radioactivity.
2. This temperature difference gives rise to convectional currents in the mantle.
3. The convection currents in the mantle create convergent and divergent boundaries (weak zones).
4. At the divergent boundary, molten, semi-molten and sometimes gaseous material appears on earth at the first available opportunity.
5. The earthquakes here may expose fault zones through which magma may escape (fissure type volcano).
6. At the convergent boundary, the subduction of denser plate creates magma at high pressure which will escape to the surface in the form of violent eruptions.

Lava can be acidic or basic. Acidic lava has more silica, is highly viscous and generally results in more explosive volcanoes whereas basic lava is less viscous and has quieter explosions. Eg. A cone would be an extrusive acidic felsic extrusive igneous landform wheras a dome would be a basic mafic extrusive igneous landform.

Question 67

What are some intrusive igneous volcanic structures?

List from furthest away from neck of volcano to closer

Answer 67

1. Batholith - dome like structure formed due to slow coolin
2. Stock - similar to batholith
3. Lapolith - saucer shape structure formed due to cooling magma
4. Sheet - horizontal accumulation of magma in the shape of horizontal layers
5. Phacolith - wave-like
6. Laccolith - mushroom, concave towards core and convex towards earth

7, Dike - 100s of KM and a vertical accumulation.

Question 68

What are the most visible extrusive volcanic landforms, especially with regards to where the explosive activity takes place?

Answer 68

1. Conical Vent and Fissure Vent
2. Fissure vent
   • A fissure vent (volcanic fissure) is a narrow, linear volcanic vent through which lava erupts, usually without any explosive activity.

• The vent is often a few meters wide and may be many kilometres long.
• Fissure vents are common in basaltic volcanism (shield type volcanoes). Hawaiian ones for example.

3. Conical vent

• A conical vent is a narrow cylindrical vent through which magma flows out violently.
• Conical vents are common in andesitic volcanism (composite or stratovolcano).

4. Mid-Ocean Ridges - basaltic lava leading to seafloor spreading
5. Caldera - when the magma chamber empties and the volcanic material above the chamber collapses into it, leading to a cauldron like appearance. You can have crater lakes there.
6. Lava Dome
7. Cinder Cone

Question 69

What are some important rock-forming minerals?

Answer 69

1. Feldspar:
   - Half the crust is composed of feldspar. It has a light colour, and its main constituents are silicon, oxygen, sodium, potassium, calcium, aluminium. It is used for ceramics and gloss making.
2. Quartz:
   - It has two elements, silicon and oxygen. It has a hexagonal crystalline structure. It is uncleaved, white or colourless. It cracks like glass and is present in sand and granite. It is used in the manufacture of radio and radar.
3. Bauxite: A hydrous oxide of aluminium, it is the ore of aluminium. It is non-crystalline and occurs in small pellets.
4. Cinnabar (mercury sulphide): Mercury is derived from it. It has a brownish colour.
5. Dolomite: A double carbonate of calcium and magnesium. It is used in cement and iron and steel indus- tries. It is white.
6. Gypsum: It is hydrous calcium sulphate and is used in cement, fertiliser and chemical industries.
7. Haematite: It is a red ore of iron.
8. Magnetite: It is the black ore (or iron oxide) of iron.
9. Amphibole: It forms about 7 per cent of the earth’s crust and consists mainly of aluminium, calcium, silica, iron.

Question 70

Describe the rock cycle?

Answer 70

The rock cycle is a continuous process through which old rocks are transformed into new ones.

1. Igneous rocks are primary rocks, and other rocks form from these rocks.
2. Igneous rocks can be changed into sedimentary or metamorphic rocks.
3. The fragments derived out of igneous and metamorphic rocks form into sedimentary rocks.
4. Sedimentary and igneous rocks themselves can turn into metamorphic rocks.
5. The crustal rocks (igneous, metamorphic and sedimentary) may be carried down into the mantle (interior of the earth) through subduction process and the same meltdown and turn into molten magma, the source for igneous rocks.

Question 71

What is India’s exposure to earthquakes?

What are some of the different kinds of earthquakes?

Answer 71

1. Plate tectonic convergence (Slipping of land along the faultline along convergent, divergent and transform boundaries cause earth- quakes.)

• Reverse faults (convergent boundary) are associated with the most powerful earthquakes, megathrust earthquakes, including almost all of those of magnitude 8 or more.

2. Volcanic (caused by the consequent release of elastic strain energy both by tec- tonic faults and the movement of magma in volcanoes.)
3. Human (drilling etc.)
4. Reservoir-induced seismicity (water filled in reservoir adds pressure that stresses existing faults and leads to fractures)

Question 72

What is India’s exposure to earthquakes?

Answer 72

1. the latest seismic zone map prepared by the National Disaster Management Authority reveals that nearly 59% of India’s land area is prone to moderate or severe earthquakes.
2. This earthquake zoning map divides India into five different zones of earthquake intensity and highlights the location that falls under them.
3. The NE region, and Gujarat are zone 4 with the highest risk.