General Study Geo 1to8

8/11/2019 General Study Geo 1to8

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QuickReview :: Geography #1

Notes

The Sun

accounts for 99.85% of the mass of the Solar System

is 150 million km from the Earth

has a diameter of 1.4 million km

is 5 billion years old

is expected to die in another 5 billion years

temperature at the core: 15 million K

temperature at the surface: 5700 K

chemical composition: Hydrogen 82%, He lium18%, Oxygen 0.03%

Cosmic yearis the time taken by the Sun to complete one revolution around the center of thegalaxy. It is taken to be 250 million years.

Red Giantis a star that has completely burnt out its resources of Hydrogen. The star then loses

its luminous intensity and turn red in colour. The Sun is expected to become a Red Giant inabout 5 billion years.

Sunspotsare regions on the surface of the Sun that are cooler (1500 C) relative to the normal

temperature (6000 C). Sunspots cause magnetic interference on the Earth, thereby resulting in

interruptions to satellite and radio communication.

Questions

1. One AU is the average distance between1. the Earth and the Sun

2. the Earth and the Moon

3. Jupiter and the Sun

4. Pluto and the Sun2. Consider the following statements

a. Asteroids are rock debris of varying size orbiting the Sun

b. Most asteroids are small but some have diameters over 1000 km

c. The orbit of asteroids lies between orbits of Jupiter and Saturn

Which of the above are correct?

4. a, b and c

5. b and c6. a and b

7. a and c

Solar eclipse achieves totality only in limited geographical regions because
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0. the shadow of the Moon on the Earth is small compared to the cross section of the

Earth

1. the Earth is not a smooth flat surface, but instead has elevations and depressions2. the trajectory of the Moon around the Earth and the Earth around the Sun are not

perfect circles

3.

the Suns rays reach most peripheral regions of the shadow of the Moon due torefractionThe limit of mass beyond which stars suffer internal collapse is called the

0. Chandrasekhar limit

1. Eddington limit2. Hoyle limit

3. Fowler limit

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COMPOSITION OF THE SOLAR SYSTEM

THE PLANETS

1.

Mercury

1.

Closest planet to the Sun

2.

Smallest planet

3.

No satellites

2.

Venus1.

Very dense atmosphere

2.

Hottest planet (over 400 C)

3.

Large amount of greenhouse gases

3.

Earth

1.

Hydrosphere unique among rock-based planets

2.

Only planet where plate tectonics observed

4.

Mars

1.

Atmosphere made mainly of carbon dioxide

2.

Red colour comes from iron oxide

3.

Geological activity such as volcanoes as recently as 2 million years ago

5.

Jupiter1.

2.5 times the masses of all other planets combined

2.

Composed mainly of hydrogen and helium

3. Great Red Spot in atmosphere created by strong internal heat

4.

63 known satellites. Ganymede, Callisto, Io and Europa show similarities to terrestrial

planets such as volcanism and internal heating

5.

Ganymede is the largest satellite in the solar system. It is larger than mercury

6.

Has planetary ring system
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6.

Saturn

1.

Extensive ring system

2.

Rings made by small particles of water ice clumped together

3.

Rings first observed by Galileo

4.

Least dense planet in solar system

5.

60 satellites

6.

Titan is the only satellite in the solar system with a substantial atmosphere

7. Uranus

1. Orbits the sun on its side

2.

Very cold core, radiates little heat

3.

27 satellites

4.


8.

Neptune

1.

Smaller in size but more massive and more dense than Neptune

2.

13 known satellites

3.


OTHER COMPONENTS

1.

Asteroids

1.

Small objects composed of rocky and metallic minerals

2.

Small asteroids are called meteoroids

3.

Main asteroid belt occupies orbit between Mars and Jupiter

4.

Asteroid belt is sparsely populated. Spacecraft routinely pass through belt without

incident

5. Ceres is the largest body in the asteroid belt. Classified as a dwarf planet

2. Comets

1.

Small bodies composed of volatile ices

2.

Coma of a comet (tail) is observed when proximity to the sun causes the icy particlesto sublimate and ionize

3. Hale-Bopp comet was visible to the naked eye for 18 months. It was the most widely

observed and brightest comet recorded

3.

Interplanetary medium

1.

It Is the interplanetary atmosphere created by the stream of charged particles emitted

by the Sun (called solar wind)

2.

Aka Heliosphere

3.

Stretches out to 100 AU

4.

Space weather is created by geomagnetic storms on the Suns surface which disturb the

heliosphere

5. Earths magnetic field prevents solar wind from stripping away the Earths atmosphere

4.

Kuiper belt

1.

Ring of debris, similar to asteroid belt, but composed mainly of ice

2.

Present in the area beyond Neptune

3. Pluto is the largest object in the Kuiper belt


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GALACTIC CONTEXT OF THE SOLAR SYSTEM

1.

Located in the Milky Way galaxy, a spiral galaxy. Milky Way diameter 100000 light years.

Contains about 200 billion stars

2.

Solar System resides in one of the outer arms, called Orion Arm

3.

Sun lies around 25,000 light years from galactic centre. Completes one revolution every 250million years (aka Cosmic Year)

4.

Closest star is Alpha Centauri triple star system

5.

Largest star close to Sun is Sirius

6.

Closest sun-like star is Tau Ceti

7.

Closest extra-solar planet is Epsilon Eridani b, which orbits the star.r Epsilon Eridani

IMPORTANT GEOLOGICAL FEATURES IN THE SOLAR SYSTEM

1. Venus

1.

Ishtar Terra and Aphrodite Terra: two continents on Venus

2.

Maxwell Montes: highest mountain on Venus

2.

Mars

1.

Adirondack: first rock chosen to be explored by the first Mars rover Spirit in Jan 2004

2.

Gusev Crater: crater on Mars, site of landing of the Mars rover Spirit, Jan 2004

3.

Sleepy Hollow: circular, shallow depression on Gusev crater

4.

Olympus Mons: tallest volcano and mountain in the Solar System.About 3 times as tall

as Mount Everest (88000 ft)

5.

Meridiani Planum: Landing site of second Mars rover Opportunity. May indicate the

presence hot springs or liquid water in the past

3. Moon

1.

South PoleAitken basin: largest crater on the Moon, on the far side

2. Shackleton crater: Site where the Moon Impact Probe from Chandrayaan landed and

found water, Nov 2008.Located at the South Pole, where the rim gets continuous sunlight while the interior is in

perpetual shadow.

3.

Cabeus crater: Site where the LCROSS spacecraft landed and confirmed significant

presence of water, Oct 2009.

Located at the south pole

TIMELINE OF SOLAR SYSTEM EXPLORATION

1.

1957: Sputnik 1, first Earth Orbiter

2.

1961: Vostok 1, first manned Earth orbiter

3.

1966: Luna 9, first Lunar Lander4.

1969: Apollo 11, first manned lunar landing

5.

1970: Luna 17/Lunokhod 1first Lunar Rover

6.

1971: Mars 3first Mars Lander

7.

1976: Helios 2closest Solar approach

8.

1977: Voyager 2first to leave Solar System

9.

1978: International Cometary Explorerfirst comet flyby (comets Giacobini-Zinner and Halley)

10.1996: Mars Pathfinderfirst Mars Rover


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11.

2001: Genesisfirst Solar wind sample return

TIMELINE OF SOLAR SYSTEM ASTRONOMY

1.

2137 BCE: Chinese astronomers record solar eclipse

2.

2

ND

millennium BCE: Heliocentric solar system, with Sun at the centre, proposed in the Vedictexts

3.

499 CE: Aryabhata, in hisAryabhatiya, propounds heliocentric solar system of gravitation,

elliptical orbits for planets, and suggests that moon and planets shine due to reflected light

4.

500: Aryabhata accurately computes the earths circumference, solar and lunar eclipses and

length of earths revolution around the Sun

5.

620: Brahmagupta recognizes gravity as a force of attraction and describes law of gravitation

6.

628: Brahmagupta calculates motion and position of various planets

7. 1150: Bhaskara, in the Siddhanta Shiromani, calculates longitudes and latitudes

8.

1514: Copernicus states his Heliocentric theory in Commentariolus

9.

1610: Galileo Galilee discovers Callisto, Europa, Ganymede and Io, sees Saturns rings

10.

1656: Christiaan Huygens: identifies Saturns rings as rings and discovers Titan

11.

1705: Edmund Halley predicts the periodicity of Halleys Comet

12.

1755: Immanuel Kant formulates the Nebular Hypothesis of Solar System formation

13.

1930: Clyde Tombaugh discovers Pluto

14.

1946: American launch of a camera-equipped V2 rocket provides the first images of the Earth

from space

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STRUCTURE OF THE EARTH

Depth (in km)Layer

0-35Crust

35-60Uppermost part of the mantle

35-660

Upper Mantle

660-2890Lower mantle

2890-5150Outer core

5150-6360Inner core
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Crust

Depth varies from 70 km under mountains to 5 km under oceans

Thin oceanic crust is composed of dense iron, magnesium silicate rocks like basalt Thick continental crust is less dense, composed of sodium, potassium, aluminium silicate rocks

like granite

The boundary between crust and mantle is called Mohorovicic discontinuity.Signifies change

in seismic velocity and rock composition


Mantle

Schematic view of the interior of Earth. 1. continental crust - 2. oceanic crust - 3. upper

mantle - 4. lower mantle - 5. outer core - 6. inner core - A: Mohorovii discontinuity - B:

Gutenberg Discontinuity - C: Lehmann discontinuity Source: Wikipedia

Thickest layer of the earth

Composed mainly silicate rocks rich in iron and magnesium

Temperature ranges from 500 C (near the crust) to 4000 C (near the core)

Despite high heat, the mantle is primarily solid due to high pressures

The mantle is slightly ductile and can flow, although only on slow, long timescales

Motion of tectonic plates is an expression of convection in the mantle

The mantle lies exposed without any crust covering on the floor of the Atlantic Ocean near the

Caribbean Islands


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Outer core

Convection in the outer core gives rise to earths magnetic field. The mechanism of the

magnetic field is explained by the Dynamo Theory, which was proposed by Joseph Larmor in1919

Liquid in composition


Inner core

Believed to consist of an iron-nickel alloy

Hottest part of the earth. Temperature may reach that of Suns surface i.e 5700 K

Solid in composition

Compressional waves can pass through it but not shear waves

Inner core is younger than the age of the earth. Inner core: 2-4 billion years, earth: 4.5 years

Inner core is cooling slowly(about 100 C per billion years)

The inner core is too hot to hold a permanent magnetic field

It has been speculated that the inner core may rotate slightly faster than the rest of the earth

(about 0.3 to 0.5 degrees per year)


Lithosphere

Includes the crust and uppermost parts of the mantle

Constitutes the hard and rigid outer layer of the Earth

Lithosphere is broken down into tectonic plates

Is rigid and deforms through brittle failure, causing faults

Lithosphere is thought to float or move around on the Asthenosphere, creating plate tectonics


Asthenosphere

Lies below the lithosphere

Constitutes the weaker, hotter and deeper part of the upper mantle

Involved in plate movements Deforms viscously and accommodates strain through plastic deformation

Due to high temperature, rock becomes ductile, leading to convection currents

Boundary between Lithosphere and Asthenosphere is defined by a change in seismic velocity:

in asthenosphere seismic waves pass relatively slowly and hence it is called a low-velocity zone



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Discontinuities in the Earths structure

Discontinuity Depth Boundary Other notes

Mohorovicic

discontinuity

30-50 km

(continents)

7 km (ocean

floor)

crust-

mantle

Observed by abrupt change in seismic

wave velocity

Identified by Andrija Mohorovicic

(Croatia) in 1909

Gutenberg

discontinuity2900 km

Core-

mantle

Observed by difference in seismic

wave velocity

Lehmann

discontinuity220 km

Appears beneath continents but not

oceans

PLATE TECTONICS


Overview

Plate tectonics is a theory that describes large scale motions of the earths lithosphere

Proposed by Harry Hess in 1962. Builds on the concepts of continental drift, proposed by Alfred

Wegener in 1915.

Tectonic plates move because lithosphere has higher strength and lower density than the

athenosphere. Thus the lithosphere rides on the athenosphere

Tectonic plates on the earth move in relation to each other

Movement of plates is typically 50100 mm annually

Earthquakes, volcanic activity, mountain building and ocean trench formation occur along

plate boundaries Plate tectonics may exist on other terrestrial planets as well, especially Mars


Types of plate boundaries

Transform boundaries:

occur where plates slide past each other along transform faults. Eg: San Andreas Fault in

California

Divergent boundaries:occur where two plates slide apart from each other. Eg: Mid-Atlantic

Ridge, Great Rift Valley (Africa) Convergent boundaries:occur where two plates slide towards each other forming either a

subduction zone or a continental collision. Eg: Andes (South America), Japan, Himalayas

o Subduction zones:

occur where an oceanic plate is pushed underneath a continental plate. Eg ocean

trenches. The descending end of the oceanic plate melts and creates pressure on the

mantle, causing volcanoes


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o Obduction zones:

occur where the continental plate is pushed underneath the oceanic plate. However,

this is unusual as the relative densities of the plates favours subduction of the oceanic

plate

o Orogenic belts:

occur when two continental plates collide and push upward to form large mountain

ranges. Eg: Himalayas


Examples of Divergent boundaries

East African Rift (Great Rift Valley), Africa

Mid-Atlantic Ridge: separates the North and South American plates from the Eurasian and

African plates

Gakkel Ridge: a slow spreading ridge in the Arctic Ocean

East Pacific Rise: extends from the South Pacific to the Gulf of California

Carlsberg Ridge in the eastern Indian Ocean


Examples of Subduction zones

The oceanic Nazca plate being subducted under the continental South American Plate forming

the Chile-Peru Trench

The Pacific Plate being subducted under the Eurasian and Philippine Sea Plates forming the

Mariana Trench

The Philippine Sea Plate subducting under the Philippine Mobile Belt forming the Manila Trench


Examples of Orogenic belts

The belt between the Indo-Australian and Eurasian Plates giving rise to the Himalayas.This is

the most dramatic Orogenic Belt in the world

Interaction between the African and Adriatic Plates with the Eurasian Plate giving rise to the

Alps

Andes belt on the western margin of South America


Examples of Transform boundaries

The San Andreas Fault in California.This arises due to the northwards movement of the Pacific

Plate with respect to the North American Plate

Motagua Fault between the North American Plate and the Caribbean Plate

Dead Sea Transform fault which runs through the Jordan River Valley


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Major and Minor plates

Major platesMinor plates

African plateArabian plate

Antarctic plateCaribbean plate

Australian plateJuan de Fuca plate

Indian plateCocos plate

Eurasian plateNazca plate

North American plate Philippine sea plate

South American plateScotia plate

Pacific plate

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THE ATMOSPHERE OF EARTH

COMPOSITION OF THE ATMOSPHERE

Compound Distribution

Nitrogen 78%

Oxygen 21%

Argon 0.9%

Water vapour 0.4% (around 1% at the surface)

Carbon dioxide 0.03%

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STRUCTURE OF THE ATMOSPHERE

1. Troposphere


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1.

Begins at the surface and extends to between 7 km (at the poles) and 20 km (at the

equator)

2.

Temperature in the troposphere decreases with altitude i.e. the lowest parts are the

warmest

3.

The troposphere contains roughly 75% of the mass of the atmosphere and 99% of its

water vapour

4.

The lowest part of the troposphere, where friction with the Earths surface influences air

flow is called the planetary boundary layer. Usually extends from a few hundred metres

to about 2 km

5.

The tropopause is the boundary between the troposphere and the stratosphere

2. Stratosphere

Layers of the atmosphere

1.

Extends from the troposphere to about 51 km

2.

Temperature increases with height

3.

Restricts turbulence and mixing

4. Commercial airliners usually fly within the stratosphere (10 km) to optimize jet fuel

burn and to avoid atmospheric turbulence

5.

The stratopause is the boundary between the stratosphere and the mesosphere

3.

Mesosphere

1.

Extends from stratosphere to about 80 km

2.

Upon entering the earths atmosphere, most meteors burn up in the mesosphere

3.

Temperature decreases with height

4.

The mesopause, the end of the mesosphere, is the coldest place on Earth with an

average temperature of -100 C

4.

Thermosphere

1. Biggest layer of the atmosphere

2.

Extends from the mesosphere to about 500-1000 km

3.

Thermopause is a temperature boundary contained within the thermosphere
http://en.wikipedia.org/wiki/File:Atmosphere_layers-en.svg


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4.

Temperature increases up to the thermopause, then remains constant

5.

The temperature can reach 1500 C. However, despite the high temperature one would

not feel warm because the atmospheric density is too low to enable heat transfer

6.

The International Space Station orbits in the thermosphere (320380 km)

7.

The ionosphere is formed in this layer as a result of ionization caused by ultraviolet

radiation

8.

The boundary between the thermosphere and the exosphere is called exobase

5. Exosphere

1.

Uppermost layer of the atmosphere

2.

It is a transitional zone between the Earths atmosphere and interplanetary space and

does not fully fall within the atmosphere

3.

Extends to about 190,000 km. This is half the distance to the Moon, at which the

influence of solar radiation becomes greater than the Earths gravitational pull

4.

The density is so low that molecules can travel hundreds of km without colliding with

each other

5.

Composed mainly of the lightest gases such as hydrogen and some helium


OTHER LAYERS AND BOUNDARIES OF THE ATMOSPHERE

1.

Ozone layer

1.

It is contained within the stratosphere at about 1050 km above the Earths surface

2.

About 90% of the ozone layer is present in the stratosphere

3.

The ozone layer absorbs 93-99% of harmful ultraviolet light

4.

Ozone is formed when UV light strikes oxygen in the stratosphere to split the oxygen

atoms, which then reform as ozone

5. The ozone layer was discovered by the French physicists Charles Fabry and Henri

Buisson in 1913

6.

British meteorologist GMB Dobson established a worldwide network of ozone

monitoring stations between 1928 and 1958 that continues to operate today. He also

developed a spectrophotometer (called the Dobsonmeter) to measure stratospheric

oxygen from the ground. The Dobson unit, a measure of ozone density is named in his

honour

2.

Ionosphere

1.

Stretches from the thermosphere to the exosphere (100 km700 km)

2.

This is caused due to ionization by solar UV radiation

3. Responsible for radio propagation by reflecting radio waves back to the Earths

surface thereby enabling long-distance communication

4.

Plays an important part in atmospheric electricity (like lightning)

5.

Responsible for auroras3.

Homosphere and Heterosphere

1.

Homosphere is the part of the atmosphere where gases are well mixed due to

turbulence

2.

This includes the troposphere, stratosphere and mesosphere

3.

Heterosphere is the part of the atmosphere where gases are not well mixed

4.

This usually happens above the turbopause (100 km) where distance between particles

is large due to low density


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5.

This causes the atmosphere to stratify with heavier gases like oxygen and nitrogen

present in the lower layers and lighter gases like hydrogen and helium in the upper

layers

4.

Planetary boundary layer

1.

Part of the troposphere closest to the Earths surface and most influenced by it

2.

Friction with the earths surface causes turbulent diffusion

3.

Ranges from 100 m to about 2 km

5. Magnetosphere

1.

A mix of free ions and electrons from solar wind and the Earths atmosphere

2.

It is non-spherical and extends to more than 70,000 km

3.

It protects the Earth from harmful solar winds

4.

Mars is thought to have lost most of its former oceans and atmosphere to space due to

the direct impact of solar winds. Similarly Venus is thought to have lost its water due to

solar winds as well

6.

Karman line

1. Defines the boundary between the Earths atmosphere and outer space

2.

Lies at an altitude of 100 km above mean sea level

3.

At this altitude the atmosphere becomes too thin for aeronautical purposes4.

However, there is no legal demarcation between a countrys air space and outer space

7.

Van Allen Belt

1.

It is a region of energetic charged particles (plasma) around the Earth held in place by

the Earths magnetic field

2.

Extends from about 200 km to 1000 km

3.

Has important implications for space travel because it causes radiation damage to solar

cells, integrated circuits, sensors and other electronics


PHYSICAL PROPERTIES OF THE ATMOSPHERE

1. Pressure and thickness

1.

Atmospheric pressure at sea level is 1 atmosphere (around 14.7 psi)

2.

50% of atmospheric mass is below an altitude of 5.6 km

3.

90% of atmospheric mass is below 16 km

4.

99.99% of atmospheric mass is below 100 km

2.

Density and mass

1.

Atmospheric density decreases with height

2.

Density at sea level is about 1.2 kg/cu.m


OPTICAL PROPERTIES OF THE ATMOSPHERE

1.

Scattering

1.

When suns rays pass through the atmosphere, photons in light interact with the

atmosphere to produce scattering

2.

Eg: on overcast days there are no shadows because light reaching the surface is only

scattered, indirect radiation, with no direct radiation reaching the earth


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3.

Scattering is responsible for blue appearance of the sky, and for red appearance of

sunset

2.

Absorption

1.

The atmosphere absorbs radiation of different wavelengths, allowing only certain

ranges (UV to IR) to pass on to the earths surface

3. Emission

1.

The atmosphere absorbs and emits IR radiation

2.

Earth cools down faster on clear nights than on cloudy nights because clouds absorb IR

radiation from the Sun during the day and emit IR radiation towards the Earth at night

3.

Greenhouse effect is directly related to emission, where certain greenhouse gases

(carbon dioxide) prevent IR radiation from the earths surface to exit back to space


WATER VAPOUR IN THE ATMOSPHERE

99.9% of water vapour is contained in the troposphere

Condensation of water vapour into liquid or ice is responsible for rain, snow etc The latent heat released during condensation is responsible for cyclones and thunderstorms

Water vapour is also a potent greenhouse gas

Water vapour is most common gas in volcanic emissions (around 60%)


CARBON DIOXDE IN THE ATMOSPHERE

It is an important greenhouse gas

Natural sources of carbon dioxide in the atmosphere include volcanic activity, combustion of

organic matter, respiration, decay of forests etc

Current carbon dioxide levels (0.0384%) are around 35% higher than the levels in 1832 The concentration of carbon dioxide is higher in the northern hemisphere because it has greater

land mass and plant mass than the southern hemisphere

Carbon dioxide concentrations peak in May(just after the end of winter in the Northern

Hemisphere) and reach a minimum in October (at the end of summer in Northern Hemisphere,

when the quantity of plants undergoing photosynthesis is greatest)

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ATMOSPHERIC ELECTRICITY

Overview

Aurora Borealis seen over Canada

The Earths surface, the atmosphere and the ionosphere combine to form a global atmospheric

electrical circuit

Free electricity is always present in the atmosphere. It is usually positive

The intensity of atmospheric electricity is usually greater in the middle of the day than in the

morning or at night. Also, it is greater in winter than in summer

Atmospheric electricity increases with altitude

The Earths surface is negatively charged, while the atmosphere is positively charged

Benjamin Franklin was the first to prove electrical phenomena of the atmosphere in 1752

Variation of atmospheric electricity

The primary cause of variation in atmospheric electricity is the thermodynamics of radiation

Atmospheric electricity is maximum in January and minimum in June

Humidity increases atmospheric electricity in the cold months but decreases it in hot months

PHENOMENA OF ATMOSPHERIC ELECTRICITY

1. Auroras

1.

Auroras are natural light displays observed in the night sky, especially in polar regions

2.

Auroras occur when the Earths magnetic field traps solar wind in the atmosphere

resulting in a collision between the solar wind and atmospheric molecules leading to

release of energy

3.

They are most prominent closer to the magnetic poles because of longer periods of

darkness and strength of the Earths magnetic field

4.

The Aurora Borealis refers to auroras in the northern hemisphere. The corresponding

auroras in the southern hemisphere are called Aurora Australis

5.

Auroras occur most often near the seasonal equinoxes: from September to October and

from March to April

6.

Auroras have maximum intensity during the intense phase of solar cycle when coronal

mass ejections increase the intensity of solar wind


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2.

Static electricity

1.

Static electricity is the build of electrical charge on the surface of objects

2.

The static charge remains on the object until it either bleeds off to the ground or is

quickly neutralized by a discharge

3.

Lightning is caused by discharge of static electricity

3. St. Elmos Fire

1.

St. Elmos Fire is a bright blue or violet glow appearing from tall, pointed objects

2.

It is a phenomenon in which plasma is created when the electric field around the object

causes ionization of air molecules

3.

Sharp objects tend to create more plasma because electrical fields are more

concentrated in areas of high curvature

4.

Lightning

1.

Lightning is an atmospheric discharge of electricity

2.

Occurs during thunderstorms, volcanic eruptions and dust storms

3.

The average lightning bolt can reach temperatures of 30,000 C (about 3 times the

temperature of the sun) and carry around 100 million V of electricity

4.

This extreme temperature compresses surrounding air and creates a supersonic shock

wave called thunder5.

In addition to light, lightning has been shown to emit radio waves, X-rays and gamma

rays

TYPES OF LIGHTNING

Lightning strikes can carry up to 100 million Volts and reach temperatures of 30,000 C

The lightning that is most commonly observed is called streak lightning. This is just the

visible part of the lightning strokethe majority of the lightning occurs inside clouds, so it is not

visible from the Earth.

1. Cloud-to-ground lightning

1.

Second most common form of lightning


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2.

b. Poses greatest threat to life and property since it strikes the ground

2.

Cloud-to-cloud lightning

1.

Lightning occurring between two clouds is called inter-cloud lightning

2.

Lightning that occurs between two areas of the same cloud that have differing electric

potential is called intra-cloud lightning

3. Ground-to-cloud lightning

1.

Lightning discharge between ground and cloud, in the upward direction

2.

Very rare

3.

Occurs when negatively charged ions from the Earths surface rise up and meet the

positive ions in the cloud

4. Heat lightning:lightning that occurs too far away for the sound of thunder to be heard

5.

Dry lightning

1.

Dry lightning is lightning that occurs without precipitation at the surface

2.

This is the most common natural cause of wildfires

3.

Occurs as a result of extreme surface temperatures when convection from the hot

surface to cooler atmosphere leads to lightning

6.

Positive lightning

1.

Occurs when positive charge is carried on the top of clouds2.

Very rare

3.

Around 10 times more powerful and longer lasting than regular negative lightning

4.

Very dangerous to life and property

5. At present, aircraft are not designed to withstand positive lightning

7. Sprite

1.

Large scale discharges occurring high above a thundercloud

2.

Occur about 80 km to 150 km above the Earths surface

3.

Reddish-orange or greenish-blue in colour

4.

May account for aircraft accidents at altitudes above thunderstorms

8.

Blue jets

1.

Occur at lower altitudes than sprites, but still above thunderclouds2.

Occur about 40 km to 80 km above surface

3.

Blue in colour

9.

Elves

1.

ELVES stands for Emissions for Light and Very low frequency Electromagnetic pulse

Sources

2.

Occur in the ionosphere, about 100 km above surface

10.Rocket-triggered lightning

1.

Lightning can be triggered by rockets carrying spools of wire into thunderstorms. When

the wire unwinds, it provides a path for lightning to conduct to the surface

2.

Lightning can also be triggered by space shuttle launches and aircraft flight

11.

Volcanically triggered lightning

1.

Extremely large volcano eruptions which eject gases and material high into the

atmosphere can trigger lightning


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LIGHTNING IN EVERYDAY LIFE

World map showing the frequency of lightning strikes. Lightning strikes most frequently in the Congo

Lightning conductor

It is a metal rod or conductor used to protect a building from lightning

It is mounted on the top of the building and connected to the ground using a wire

When strikes, it will preferentially strike the rod and be conducted harmlessly to the ground

Lightning rods are usually made from good conductors of electricity such as aluminium or

copper

Lightning protection on aircraft

On aircraft, an electrical circuit is established on the aircrafts outer surface

Aircraft made from aluminium naturally act as good conductors of electricity. When the aircraft

is made of carbon composites, a layer of conductive fibre is embedded to ensure conductivity When the aircraft is struck by lightning, current travels on the outer surface of the aircraft,

with the interior remaining unaffected

Proper shielding is provided to ensure lightning does not affect cockpit electronics, fuel tanks

and radar and other avionics

Aircraft also use static dischargers to prevent buildup of static electricity

Trees and lightning

Trees are natural conductors of lightning. They provide connection for lightning to reach the

ground. However, the outer layer of trees (bark) is not a good conductor

Trees get burnt from lightning because lightning travels on the outer surface of the tree,burning away the bark.

Usually, trees can recover from damage to the bark. However, sometimes the damage is too

severe for recovery.

Oak and elm are two trees most frequently struck by lightning. Teak provides the best

conducting connection for lightning

By attracting lightning towards them, trees prevent damage to nearby buildings. However, for

the same reason, it is not safe to seek shelter under trees during lightning
http://en.wikipedia.org/wiki/File:Global_lightning_strikes.png


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Shelter from lightning

To get shelter from lightning, there needs to be an electrical connection through the exterior

surface on to the ground. The connection must ensure that people do not get in contact with

the electricity

Best lightning shelters: houses, buildings, closed-roof cars, closed-cabin boats etc

Worst lightning shelters: trees, tents, open barns, open-roof cars, open boats etc

It is unsafe to use radios, cellphones etc during lightning strikes

MEASUREMENT OF ATMOSPHERIC ELECTRICITY

1.

Electrometer

1.

Simple instrument for measuring atmospheric electricity at ground surface

2.

Developed in 1700s by Alessandro Volta

3.

Consists of a glass jar with a pointed metal rod, whose lower end is attached to two

straws. Electricity in the atmosphere cause the two straws to recede from each other,

the amount of divergence indicating the intensity of electricity

2.

Weather balloons

1.

A balloon which carries instruments aloft to send back information regarding

temperature, humidity etc

2.

The device that does the actual measuring is called radiosonde

3.

The radiosonde is an inexpensive device, and it is lost when the life of the balloon

expires

3.

Lightning rocket

1.

It is a device that measures electrostatic and ionic charge in the atmosphere

2.

Consists of a rocket launcher which is in communication with the detection device on

the ground

3. This system controls the time and location of a lightning strike

4.

Uses solid (cesium salts) or liquid (calcium chloride) propellants to produce exhaustgases that act as a conducting pathway between the clouds and the ground


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WIND

Causes of wind

Wind is caused by differences in pressure

It always flows from high pressure to low pressure

The two major driving factors of large scale atmospheric circulation are

o Heating difference between the equator and the poles

o

Rotation of the planet, which leads to air being deflected according to the Corioliseffect. Coriolis effect is the apparent deflection of moving objects when viewed from a

rotating reference frame

Near the Earths surface, friction causes wind to be slowerthan it otherwise would be

Away from the surface, large scale winds tend to approach a state of equilibrium called

Geostropic Balance

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Measurement of wind


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A rock formation in Bolivia, sculpted by wind erosion

Wind direction is reported based on the direction from which it originates. Eg: a northerly wind

blows from the north to the south Wind direction is observed using weather vanes(atop buildings) and windsocks (at airports)

Wind speed is measured using anemometers

Weather balloons and RADAR/LIDAR can also be used for measuring wind speed and direction

Sustained winds are usually observed 10 m from the surface of the Earth

Globally, wind speeds are reported over a 10 minute average. India reports winds over a 3

minute average


Wind categorization on the Beaufort scale

Beaufort scaleWind speed

(knots)

General termTerminology of IMD

(covers north Indian Ocean)

06 027 Breeze Depression

7 28-33 Gale Deep depression

89 3447 Strong gale Cyclonic storm

1011 4863 Storm Severe cyclonic storm

1216 64120 Hurricane Very severe cyclonic storm

17 > 120 Hurricane Super cyclonic storm


AEOLIAN PROCESSES

Aeolian process refers to the action of wind in shaping the surface of the Earth.

1.

Wind erosion
http://en.wikipedia.org/wiki/File:Saltation-mechanics.gif


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1.

Wind erodes the earth by deflation and abrasion. Deflation is the removal of fine,

loosely grained particles while abrasion is the wearing down of surfaces by grinding

action

2.

Regions that experience intense and sustained erosion are calleddeflation zones

3.

Desert rocks that have been exposed to wind for long periods of time exhibit a dark

shiny stain called desert varnish

4.

Blowoutsare hollows formed by the removal of particles by wind

2. Wind transport

Suspension, saltation and creep

1.

Particles are transported by wind through the processes of suspension, saltation and

creep

2.

Suspension is the holding of small particles in the atmosphere due to upward currents

in air.Dust and haze are examples of suspension.

3.

Saltation is the movement of particles in jumps and skips by lifting up slightly from the

surface. Examples of saltation include sand drift over deserts, soil blowing over fields.

4.

Creep is the slow downward progression of rock and soil down a low grade slope.Creep is responsible for the rounded shape of hillsides

5.

Other wind transport phenomena include dust storms and dust devils. Covered in detail

below.

3. Wind deposition

1.

Wind-deposited bodes occur as sand sheets, ripples and dunes

2. Sand sheets are flat, gently undulating surfaces of sand.They form about 40% of

Aeolian deposition surfaces.

3. Wind blowing on a sand surface also causes ripples,which form into crests and

troughs. In ripples, the coarsest materials collect on the crests

4.

Sand dunes are hills of sandsimilar to ripples, except that they are larger and have the

coarsest materials on the troughs


ROLE OF WIND IN NATURE

1.

Desert dust migration

1.

Dust from deserts is carried across huge distances over to other continents

2.

Example: dust from the Sahara desert blows via the Caribbean to North America
http://en.wikipedia.org/wiki/File:Saltation-mechanics.gif


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3.

Desert dust migration can affect rainfall patterns

4.

It also causes the sky to change colour from blue to white

2.

Effect on plants

1.

The dispersal of seeds through wind is called anemochory

2.

Examples of seeds that disperse through wind: dandelions, maples, weeds

3.

Wind also limits tree growth. The tree line is often lower in coasts and isolated

mountains because high winds reduce tree growth

4.

Wind also causes soil erosion leading to uprooting of trees

3. Effect on animals

1.

Cattle and sheep are prone to wind chill when high wind speeds render their protective

covering inffective

2.

For penguins, their flippers and feet are susceptible as well

3.

Bird migration and insect return tend to flow with wind patterns


WIND IN OUTER SPACE

1.

Planetary wind

1.

The loss of gas from a planet to outer space is called planetary wind

2.

This happens when light elements such as hydrogen move up to the exobase (limit of

atmosphere), and then reach escape velocity to escape to outer space

3.

The planet Venus is said to have its atmosphere due to planetary wind

2.

Solar wind

1.

Solar wind is a stream of charged particles (plasma) ejected from the sun

2.

This plasma is ejected from the upper atmosphere of the sun at up to 400 km/s

3.

Solar wind creates the heliosphere, a vast bubble in interstellar medium

4.

Planets require large magnetic fields to reduce the ionization of their upper atmosphere

by solar wind. Mars is said to have lost its atmosphere due to solar wind

5.

The surfaces of Venus and the Moon are bombarded directly by solar wind, resulting inhigh radiation levels


GEOLOGICAL PHENOMENA CAUSED BY WIND

1.

Sand dunes

1.

Sand dunes are hills of sand built by wind

2.

Dunes are usually longer on the windward side and shorter on the leeward side

3.

Sand dunes can form in dry inland regions and also in coastal areas and underwater as

well

4.

Dunes can move over tens of metres due to the consistent action of strong wind.Through saltation, wind picks up particles from the windward side and deposits it on the

leeward side, gradually moving the dune

5. The tallest sand dunes in the world are found in the Namib Desert

2. Erg

1. An Erg is a large area of desert covered with wind-swept sand with little or no

vegetative cover

2.

In essence, ergs are large dune fields


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3.

Ergs are mainly found in Africa, central and western Asia and central Australia

4.

Ergs have been found on Venus, Mars and Titan as well

3.

Loess

The rich fertile soil of the Loess plateau has been the mainstay of Chinese agriculture forcenturies

1.

Loess is a sediment formed by the accumulation of wind-blown silt, sand and clay,

loosely cemented by calcium carbonate

2.

Loess deposits often occur in very thick layers, sometimes more than 100 m thick.It

occurs as a blanket deposit covering areas of hundreds of square km

3.

Loess is highly prone to erosion

4.

Loess can occur from glacial or non-glacial soils. Example of glacial loess: Mississippi

Valley, USA. Example of non-glacial loess: Shanxi, China

5.

Loess tend to develop into highly fertile soils

4. Wind waves

1.

Wind waves are surface waves that occur in oceans, lakes etc due to the action of wind2.

Wind waves can range from ripples to more than 30 m in height

3.

A wind wave system generated by local winds in called wind sea. Wind wave system not

generated by local winds is called swell

4.

Factors that influence the formation of waves include: wind speed, distance of open

water, time duration and water depth

5.

Tsunamis and tides are specific types of waves caused not by wind, but by geological

effects. They have longer wavelength than wind waves

6.

Waves can be measured using buoys that record the motion of the water surface

7.

A breaking wave is one whose one can no longer support its top causing it to collapse

8.

There are three main types of waves

1.

Spilling or rolling waves: Safest waves for surfing.Most common type of wavesfound at shores.

2. Plunging or dumping waves: preferred by experienced surfers.Found where

there is a sudden rise in ocean floor like a sandbar

3. Surging waves: very dangerous for surfing.Tend to form on steep shorelines,

where the depth results in waves not breaking as they approach the shore



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GEOGRAPHICAL FEATURES SHAPED BY WIND

FeatureLocation Wind effect Notes

Mississippi River

Alluvial Valley South-central USA Glacial loess

Loess plateauShanxi, Northern China

Non-glacialloess

Thickest loess in the world (335

m)

Most erodible soil on earth

Selima sand sheetEgypt, Sudan

Wind

depositionLargest sand sheet

Namib desert sand

dunes Namibia, AngolaWind

deposition

Oldest desert in the world (55

million years)

Paha Iowa, USA Sand dunes

Badain Jaran desert Inner Mongolia (China,Mongolia)

Sand dunesTallest stationary sand dunes in

the world (500 m)

Great dune of PilatFrance Sand dune Largest sand dune in Europe

MerhebUAE Sand dune Used for motor sports

Kelso dunesUSA Sand dune

Cerro BlancoSechura Desert, Peru Sand dune Highest sand dune in the world


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WIND CIRCULATION

Overview

The global circulation patterns of wind on Earth

Winds that blow predominantly from a single direction over a particular point on the Earths

surface are called Prevailing Winds

The general trends in wind direction are called dominant winds

In general regional winds can be divided into two groups

o Global windslike easterlies, westerlies

o Local windslike land breeze, sea breeze

Prevailing winds greatly influence climate patterns such as rainfall gradients, where the

windward side of mountains have high rainfall while leeward side experience desert conditions

Wind roseis a graphic plotting tool that is used to describe the speed and direction of wind at a

particular location

Insects drift along prevailing winds, while birds are able to fly independent of them

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Distribution of prevailing winds

In general, easterly winds flow at low and high altitudesi.e. near the tropics and the poles

Westerly winds flow at the mid-latitudes
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Directly under the subtropical ridge i.e. close to the equator, winds are lighter in intensity. These

subtropical regions are called the doldrums, or horse latitudes

The strongest winds are usually in the mid-latitudes,where cold air from the Artic meets warm

air from the tropics

Most of the earths deserts are found near the subtropical ridge,with high pressure leading to

low humidity


GLOBAL WINDS

Trade Winds

o Trade winds are the prevailing easterly winds that blow across the tropics

o They blow from the northeast in the northern hemisphere and from the southeast in the

southern hemisphere

o Trade winds act as the steering for tropical storms that form in the Atlantic, Pacific

and south Indian Oceans.These storms make landfall in North America, Southeast Asia

and India, respectivelyo Trade winds steer African desert dust across the Atlantic Ocean towards North

America(esp. the Caribbean and Florida)

o The weaker a trade wind becomes, the more rainfall it brings

o Trade winds are stronger in winter than summer

o The one region of the Earth where trade winds are absent is the north Indian Ocean

Westerlies

o Westerlies are the prevailing winds in the mid-latitudes i.e. between 35 and 65

degrees latitude

o They blow from high pressure areas in the horse latitudes towards the poles

o Westerlies blow from the southwest in the northern hemisphere and from the

northwest in the southern hemisphere

o

Westerlies are instrumental in carrying warm equatorial winds towards the western

coasts of continents

o They are responsible for carrying desert dust from the Gobi Desert into North America

o They are stronger in winter than in summer, and over regions that have less land to

interrupt their flow. They are stronger in the Southern Hemisphere because of the vast

ocean expanses uninterrupted by land mass

o Westerlies are strongest in the Roaring Forties i.e. between 40 and 50 degrees latitude

Polar Easterlies

o Polar easterlies are the prevailing winds that blow at the north and south poles

o They are cold and dry winds

o They blow from high pressure areas near the poles towards low pressure areas within

the mid-latitudeso They blow from the east to the west

o Polar easterlies are often weak and irregular

o They are also called Polar Hadley Cells, named after George Hadley who discovered

them in 1753



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LOCAL WINDS

Notable local winds

1. Sea and land Breeze1.

Sea and land breezes are caused by the temperature differential between the sea and

coastal areas

2.

Sea breeze occurs when the land gets heated during the day creating a low pressure,

and cool air from the sea rushes in

3.

Land breeze occurs when the land cools off rapidly at night causing low pressure over

the sea, and warm air flows from the land to the sea

4.

Sea breeze occurs during the day while land breeze occurs at night

2. Mountain winds

1.

In elevated surfaces heating of the ground exceeds heating of surrounding air, thereby

changing wind circulation

2.

Hills and valleys significantly distort airflow by acting as physical barriers. This is known

as barrier jet

3.

Jagged terrain results in unpredictable flow patterns and turbulence

4.

Passes in the mountain range experience lower pressure resulting in high wind speeds

and erratic and turbulent air currents

5.

These conditions are dangerous to ascending and descending airplanes


MONSOON WINDS

Overview

Monsoons are defined as seasonal reversing winds accompanied by seasonal changes

in precipitation

The major monsoon systems of the world are the West African and Asia-Australian

monsoon systems

The origin of monsoons about 15-20 million years ago has been linked to the uplift of

the Tibetan Plateau after the collision of India and Asia 50 million years ago


Cause of monsoons
http://en.wikipedia.org/wiki/File:Map_local_winds.png


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Monsoons are caused by the larger amplitude of seasonal land temperature cycle

compared to that of nearby oceans. This temperature differential arises because air

over land warms faster and reaches higher temperature than the air over nearby ocean

The hot air over land tends to rise creating a low pressure

This creates a steady wind blowing from the ocean towards land, bringing moist air from

the oceans

In winter the land cools off quickly creating a high pressure that blows wind from land to

sea

In essence, monsoons are similar to sea and land breezes, except that they occur on a

much larger scale


The Southwest Monsoon

The Southwest monsoon in India. It brings about 80% of India's annual rainfall

The southwest monsoon occurs from June to September

The southwest monsoon is caused by rapid heating of the Thar desert and north-central India in

summer, creating a low pressure that is filled by moisture laden winds from the Indian Ocean

The Himalayas prevent the wind from blowing towards Central Asia and redirect them inwards

to cause rainfall

The Arabian Sea branch of the southwest monsoon brings rainfall to the Malabar coast andcentral India

The Bay of Bengal branch of the southwest monsoon picks up additional moisture in the Bay of

Bengal and arrives at the eastern Himalayas, and then turns west towards the Indo-Gangetic

plains

Mawsynram in Shillong is the wettest place on Earth with about 12,000 mm of rainfall

annually

The traditional start date of the southwest monsoon is June 01
http://en.wikipedia.org/wiki/File:India_southwest_summer_monsoon_onset_map_en.svg


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The southwest monsoon accounts for 80% of rainfall in India


The Northeast Monsoon

The northeast monsoon occurs October to December in India Around September, northern India begins to cool rapidly creating a high pressure zone

This brings dry cold winds from the Himalayas towards the Deccan and into the Indian Ocean

While travelling towards the Indian Ocean, the wind picks up moisture in the Bay of Bengal and

pours it over southern peninsular India

The northeast monsoon accounts for 50-60% of rainfall in Tamil Nadu


JET STREAMS

Overview

The polar and subtropical jet streams

Jet streams are fast, narrow air currents in the atmosphere

Jet streams are usually located near the tropopause (transition between troposphere and

stratosphere)

The main jet streams are westerly winds, flowing from the west to the east

Jet streams are used for weather forecasting and aviation. It is hypothesised that they could be

used as an energy source as well

Jet streams have been observed in the atmosphere of Jupiter as well


Cause of jet streams

Jet streams are caused by a combination of atmospheric heating and the rotation of the earth

They form near boundaries of adjacent air masses with significant differences in temperature


Occurrence of jet streams
http://en.wikipedia.org/wiki/Jet_stream


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The strongest jet streams are the polar jets (23,000-39,000 ft) and the somewhat weaker

subtropical jets (33,000-52,000 ft)

Other weaker jets also exist, especially over central USA

There is one polar jet stream and one subtropical jet stream each in the northern and southern

hemispheres

The northern hemisphere polar jet is situated over the northern latitudes of North America,

Europe and Asia, while the southern polar jet always circles Antarctica

The northern and southern hemisphere jet streams have been found to be drifting towards the

poles at a rate of 2.1 km per year

Jet streams are typically a few hundred miles wide and about 3 miles thick vertically

Wind speeds usually exceed 92 km/h, although speeds of over 398 km/h have been observed


Jet streams and aviation

Jet streams are often as the preferred flight plans for commercial airliners

Flying with the jet streams decreases travel time and reduced fuel consumption Conversely, flying against jet streams can add to travel time and increase fuel consumption. For

this reason, flight plans use circuitous routes to avoid flying against jet streams

Commercial use of jet streams began in 1952 on the Tokyo-Honolulu route cutting travel time

from 18 hours to 11.5 hours


A FEW NOTEWORTHY LOCAL WINDS

Wind Location Description

CalimaSahara to Canary Islands

(west African coast)Carries dust from the Sahara

Chinook Rocky mountains Warm, dry westerly winds

Elephanta Malabar coastSouth easterly wind

Marks end of southwest monsoon

Noreaster North east USA Strong storm winds from the northeast

Norwester East coast of New Zealand Warm dry winds

Santa Ana

windsSouthern California

Strong, extremely dry winds

Responsible for frequent wildfires

Sirocco North Africa, Europe

Strong winds from the Sahara that cause dusty dry

conditions in north Africa and cold wet conditions in

Europe


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Reaches hurricane speeds, can last hours to days

Shamal Persian GulfStrong Northwesterly wind

Causes large sandstorms in Iraq


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ROCKS

Overview

Rocks are naturally occurring solid aggregates of minerals or mineraloids (a mineral-like

substance that does not exhibit crystallinity)

The Earths outer solid layer, the lithosphere, is made of rocks

Rocks are generally classified into three types

o Igneous rocks

o Sedimentary rocks

o Metamorphic rocks

The structure and composition of rocks change over time, causing one type of rock to be

reclassified as another

The study of rocks is called petrology

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IGNEOUS ROCKS

Overview

Igneous rocks are rocks which form from the cooling and solidification of magma

They are the results of volcanic processes


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The magma can be derived from melts of pre-existing rocks in either the crust or mantle.

Typically, rocks melt under conditions of extremely high temperatures, low pressures or changes

in composition

Igneous rocks can be of two types:

o Intrusive (plutonic) rocks

o Extrusive (volcanic) rocks

Igneous rocks make up about 90% of the Earths crust.However, they are hidden from the

surface by a thin layer of sedimentary and metamorphic rocks

Igneous rocks can be seen at mid ocean ridges, areas of volcanism and intra-plate hotspots

They are crystalline and impervious

They are resistant to erosion and weathering

Geological significance of igneous rocks

Crystallisation of magma leading to igneous rocks

Since igneous rocks come from the mantle, the minerals and chemistry of igneous rocks give

information about the composition of the mantle

Their features are characteristic of a particular tectonic environment, allowing reconstitution of

tectonic conditions

They host important mineral deposits such as uranium, tungsten, tin, chromium, platinum

Mineralogical composition of igneous rocks

Felsic rock: highest content of silicon with predominance of quartz and feldspar. These rocks are

usually light coloured and have low density

Mafic rock: lesser content of silicon, predominance of mafic minerals (manganese and iron).

These rocks are usually dark coloured and have higher density than felsic rocks

Ultramafic rocks: lowest silicon content, with more than 90% of mafic minerals

Felsic Mafic Ultramafic

Intrusive Granite Gabbro Peridotite

Extrusive Rhyolite Basalt Komatite
http://en.wikipedia.org/wiki/File:Fractional_crystallization.svg


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Intrusive igneous rocks (plutonic rocks)

Intrusive igneous rocks are formed from magma that cools and solidifies within the crust

These rocks are coarse-grained. Mineral grains in these rocks can be identified by the naked eye

The central cores of most mountain ranges are made of intrusive rocks (usually granite). Theselarge formations of intrusive rocks are called batholiths

Examples of intrusive igneous rocks include granite and diorite

Extrusive igneous rocks (volcanic rocks)

Extrusive igneous rocks are formed at the surface, from magma released into the surface from

volcanic eruptions

Extrusive rocks cool and solidify quicker than intrusive

Extrusive rocks are fine grained in nature

Examples of extrusive rocks include basalt and rhyolite

Large Igneous Province (LIP)

The Deccan Traps in the Western Ghats

Large Igneous Provinces are extremely large accumulations of igneous rocks (both intrusive and

extrusive)

They refer to igneous rocks extending over 100,000 sq km, that formed in a short geological

time scale of a few million years or less

LIPs usually consist of basalt and rhyolite rocks When created, LIPs often have an area of few million sq km and volume on the order of a million

cubic km. Majority of the LIPs volume is emplaced in less than a million years.

LIPs are postulated to arise from hotspots of linear chains of volcanoes

LIPs are often linked to mass extinction events. This is said to arise from the enormous

quantities of sulphuric acid released into the atmosphere, the subsequent global cooling and

absorption of oceanic oxygen.
http://en.wikipedia.org/wiki/Deccan_Traps


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The Deccan Traps, one of the largest volcanic features on Earth, is an example of a Large

Igneous Province. The Traps consist of multiple layers of basalt, more than 2 km thick and cover

an area over 500,000 sq km, and were formed as a result of volcanic eruptions in the Western

Ghats about 66 million years ago. It is believed that the enormous volcanic eruptions led to

global cooling of around 2C, and were instrumental in the mass extinction of non-avian

dinosaurs.

SEDIMENTARY ROCKS

Overview

Sedimentary rock is the type of rock formed sedimentation of material.This sedimentation can

occur on the Earths surface or within bodies of water

Sedimentary rocks form the thin outermost layer of the earths crust, making up about 5% of

the total volume of the crust

Sedimentary rocks are deposited in strata called bedding

Coal is a sedimentary rock

Examples of sedimentary rocks include shale, sandstone, limestone


Geological significance of sedimentary rocks

Sedimentary rocks are the only rocks that contain fossils

Study of sedimentary rocks provides information about subsurface, which is important in civil

engineering for construction of roads, bridges etc

Sedimentary rocks are also important sources of natural resources like fossil fuels, water, ores

etc The study of sedimentary rock strata serves as the main source of scientific knowledge about

the Earths geological history

Sedimentary rocks are the only rocks that contain fossils.Sedimentary rocks contains fossils

because, unlike igneous and metamorphic rocks, they form at temperatures and pressures that

do not destroy fossils

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Composition of sedimentary rocks

Most sedimentary rocks contain either quartz or calcite

Unlike igneous and metamorphic rocks, sedimentary rocks do not contain multiple major

minerals

Carbonate rocks contain carbonate minerals like calcite, aragonite or dolomite

Siliclastic rocks contain silica-bearing minerals like quartz

Clastic sedimentary rocks

Clastic rocks are composed of fragments, called clasts, of pre-existing rocks

Clastic sedimentary rocks are those that are formed from rocks that have been broken down

due to weathering, which are then transported and deposited elsewhere

Clastic sedimentary rocks come in various grain sizes. They range from fine clay in shales, to

sand in sandstone and gravel, cobbles and boulder size fragments in conglomerates and breccias

Conglomerates are clastic sedimentary rocks with rounded fragments, while breccias consist of

clasts with angular fragments. Both conglomerates and breccias contain clasts larger than sand

(> 2 mm)

Examples include shale, sandstone, siltstone


Organic sedimentary rocks

Organic sedimentary rocks contain materials generated by living organisms

They usually contain carbonate minerals generated by these organisms

Examples include corals, chalk, coal and oil shale


Chemical sedimentary rocks

Chemical sedimentary rocks are formed from minerals in solution that become oversaturated

They usually occur as a result of evaporation

Examples include limestone, barite, gypsum


METAMORPHIC ROCKS

Overview

Metamorphic rocks form as a result of transformation of an existing rock, in a process called

metamorphism. The existing rock is calledprotolith

Metamorphic rocks are formed when theprotolithsare subject to extreme temperatures and

pressures

They form from tectonic process, intrusion of magma, or simply by being deep beneath the

earths surface (being subject to high temperatures and pressures of rock layers above)

Much of the lower continental crust is metamorphic


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Examples of metamorphic rocks include gneiss, slate, marble

Composition of metamorphic rocks

Metamorphic rocks are composed of metamorphic minerals

Metamorphic minerals are those that form only at high temperatures and pressures.Theseinclude sillimanite, kyanite, andalusite, staurolite and garnet (all of which are silicates)

Metamorphic rocks also contain smaller amounts of micas, feldspars and quartz. However,

these are not products of metamorphism, and are instead leftovers from theprotoliths


Contact metamorphic rocks

Contact metamorphic rocks are those that form when magma is injected into surrounding rock

The cooling magma leads to igneous rocks, and around this is a zone called contact

metamorphism aureolewhere metamorphic rocks are formed

The extreme temperatures cause sandstones to metamorphise into quartz, limestone intomarble and shale into cordierite

Igneous rocks are harder to transform than sedimentary rocks since they form at even greater

temperatures


Regional metamorphic rocks

Regional metamorphic rocks are those that form due to metamorphism over a wide area

Regional metamorphism tends to make rocks foliated

Regional metamorphic rocks tend to form at great depths simply under the temperature and

pressures of upper layers of rock Continental crusts are examples of regional metamorphic rocks


IMPORTANT ROCK TYPES

Rock Classification Composition Notes

BasaltIgneousextrusive

volcanicFeldspar, pyroxene

Present on moon, Mars, Venus

Basalt rocks sustain microbial life

Fine texture

GraniteIgneous (intrusive,

felsic)Quartz, feldspar

Coarse texture

Massive, hard and tough

Exhibit radioactivity (uranium)


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Shale Sedimentary (clastic) ClayContain organic matter

Contains multiple thin layers

Limestone SedimentaryCalcite (calcium

carbonate)

Used in quicklime, mortar, cement, concrete

Soluble in water

Host of most cave systems

Sandstone Sedimentary Quartz, feldspar

Common building material

Porous, allows water percolation

Host of water aquifers and petroleumreservoirs

Slate Metamorphic Clay, volcanic ash

Used to make roofing, flooring

It is an electrical insulator, used forswitchboards

Can host even microscopic amounts of

fossils

Gneiss Metamorphic Garnet, biotite

Marble Metamorphic

Calcite

(calciumcarbonate)

Comes from metamorphism of limestone

Pure white marble comes from pure

limestone

Colours, swirls, veins come from mineralimpurities

Important source of calcium carbonate,used in toothpaste, paint

Quartzite Metamorphic Quartz

Comes from metamorphism of sandstone

Used as a decorative stone

Used for railway ballast


IMPORTANT ROCK FORMATIONS/STRUCTURES

For a full list of rock formations see here

For a list of fascinating rock formations, see here
http://en.wikipedia.org/wiki/List_of_rock_formationshttp://en.wikipedia.org/wiki/List_of_rock_formationshttp://www.oddee.com/item_96838.aspxhttp://www.oddee.com/item_96838.aspxhttp://www.oddee.com/item_96838.aspxhttp://en.wikipedia.org/wiki/List_of_rock_formations


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Formation/structure Location Classification Notes

Deccan TrapsDeccan Plateau,

India

Large Igneous

Province (LIP)

One of the largest volcanic

features on earth

Siberian Traps Siberia, Russia LIP One of the largest known volcanicevents (250 million years ago)

Acasta Gneiss Quebec, Canada MetamorphicOldest known rock in the world

(4.28 billion years)

Devils Tower Wyoming, USA IgneousMonolithic rock that rises 1200

feet above surrounding terrain

Blue Lias England Limestone and shale Rich in dinosaur fossils

Red Fort Delhi Sandstone

Hawa Mahal Jaipur Sandstone

Mahabalipuram

sculpturesMahabalipuram Granite

Mount Augustus Western AustraliaSandstone and

conglomerateLargest monolith in the world

Savandurga Karnataka Gneiss and granite Largest monolith in India

Sphinx Egypt Limestone

Oldest known monumental

sculpture

Largest monolith statue in world

Phobos monolith Mars Igneous


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Documents

General Study Geo 1to8