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1: The Planet Earth
lllLearning Objectives
In this chapter you will learn about:
1 The Earth’s Layers
2 The Plates
3 Earthquakes
4 Volcanoes
The Earth’s Layers
The earth consists of three layers:
1 The crust
2 The mantle
3 The core
Crust
The mantle
The mantle:
l Is a very hot layer
l Comprises rocks in a molten or
semi-molten state
The core
The core:
l Is the centre of the earth
l Is the hottest of all the layers
l Comprises iron and nickel
Core
Fig 1.1 A section through earth
The crust
The crust:
l Is the outer layer
l Comprises solid rock
l Has a very thin layer
l Contains the earth’s plates
Mantle
The Plates
There are seven major plates:
1 Eurasian Plate
2 Indian Plate
3 African Plate
4 American Plate
5 Nazca Plate
6 Pacific Plate
7 Australian Plate
The plates carry the continents and the
oceans. The plates are constantly moving.
The process is called continental drift.
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JUNIOR CERTIFICATE GEOGRAPHY – HIGHER LEVEL
Iceland
EURASIAN
PL ATE
ies
Rock
Alps
AMERICAN
PL ATE
PACIFIC
PL ATE
Mi
d-
At
Fig 1.2 Major plates
and plate boundaries
INDIAN
PL ATE
Plate boundary
Plate movement
l
Earthquakes produce shock waves.
A seismograph measures shock waves.
The Richter Scale records the size
of the shock waves.
l Large sea waves which occur due to
earthquake activity under the sea are
called tsunamis, e.g. SE Asia, 2004.
When plates collide fold mountains
form, e.g. the Rockies.
l When plates separate volcanoes
occur, e.g. Mt Etna.
l When plates slide past each other
earthquakes happen, e.g. the San
Andreas Fault.
l
l
Earthquakes
The effects of earthquakes
Earthquakes occur when plates slide past
each other.
1 Loss of life, e.g. the Afghanistan
earthquake in 1998 killed over
4,000 people.
2 Collapse of buildings and bridges
which hinders transport and the
movement of people and goods.
These must be rebuilt at huge
expense to the government and
insurance companies.
3 Damage to gas mains and electricity
pylons can cause fires.
The place within the crust where the earthquake occurs is the focus. The point on the
surface above the focus is the epicentre.
Fault
Tremors
Epicentre
Major
damage
Focus
Tremors
Fig 1.3 Effects of an earthquake
2
e
Ridg
tic
lan
AUSTRALIAN
PL ATE
Andes
NAZCA
PL ATE
AFRICAN
PL ATE
Undamaged
Minor
damage
Earthquake prevention
1 Construct earthquake proof buildings.
2 Construct buildings on stable ground.
3 Study seismic records to attempt to
predict where earthquakes are likely
to occur.
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CHAPTER 1
Volcanoes
When two plates separate, the magma
under the earth’s crust reaches the surface,
cools and hardens to form lava.
Sometimes the lava forces its way upwards
through a vent forming a volcanic mountain.
coast of America have felt the effects of
devastating earthquakes. The world’s
active volcanoes are found in the Pacific
Ring of Fire. They include:
l Mt St Helens
l Mt Fujiyama
l Mt Pinatubo
l Krakatoa
l Aconcagua
Crater
Lava flow
Mt St Helens
Mt Fujiyama
Layer of cinders
Layer of ash
Mt Pinatubo
Vent
Krakatoa
Aconcagua
Active volcanoes
Zone of active volcanoes
Fig 1.5 Active volcanoes
Magma chamber
Fig 1.4 A volcano
The Mid Atlantic Ridge
Beneath the Atlantic Ocean the North
American Plate is separating from the
Eurasian Plate. Magma fills the gap
between the two plates. The magma then
cools and hardens forming a chain of
mountains called the Mid Atlantic Ridge.
Some of these mountains are so high that
they rise above sea level as islands, e.g.
Iceland and the Azores.
The Pacific Ring of Fire
On the edge of the Pacific Ocean some of
the world’s plates separate and collide.
Consequently, it is here that most earthquakes and volcanoes occur. San
Francisco and Los Angeles on the west
Types of volcanoes
1 Active: the volcano erupts frequently,
e.g. Mt Etna.
2 Dormant: the volcano has not
erupted for a long time, e.g. Mt St
Helens.
3 Extinct: the volcano has not erupted
in recent times, e.g. Slemish Mt,
Co. Antrim.
l
l
l
l
l
Points to note
Focus
Epicentre
Richter scale
Mid Atlantic Ridge
Pacific Ring of Fire
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JUNIOR CERTIFICATE GEOGRAPHY – HIGHER LEVEL
As a re
Advantages of volcanoes
When plates collide mountains, called Fold
1 untains
Fertile soils,
e.g. formed.
the slopesThe
of Mt
Mo
ar,,,e
Rocky
Vesuvius
Mounta ins are Fold Mountains. They were
2 Precious
minerals,
e.g.
form
ed due stones
to theand
collision
betw
eengold,
the
silver,
lead
and
copper.
The
copper
Pacific and North American Plates. The
ores ofthe
thelsBeara
Peninsula
Co.also
Himalayas,
and the
Pyreneesinare
Kerry
are
volcanic
in
origin
Fold Mountains.
sliding plates create friction between
Disadvantages of volcanoes
themselves leading to a build up of
1 pressure.
Loss of life,
e.g. they
the eruption
When
do slide of
past each
Krakatoa
in
1883
resulted
in
other the pressure is reduced. Thehuge
ground
seavibrate
waves drowning
40,000
may
giving rise to
an earthquake.
people. The Peruvian earthquake in
1970 killed
peoplealong the
Earthquakes
are50,000
very common
2 Damage to property, e.g. the eruption
3 Building materials, e.g. granite which
of Mt Vesuvius in AD 79 buried
Pompeii and Herculaneum
formed
beneath
the
surface
is
used
in
Often plates slide past each other. The
3 The eruption of Mt Pinatubo in the
buildings
Philipines in 1991 had major effects
4 Hot springs (geysers) generate
on the environment:
electricity, e.g. Iceland and New
l The cloud of gas, ash and dust
Zealand
blocked out the sun’s rays and
5 Tourism, e.g. Mt Vesuvius and Mt
resulted in a drop of several degrees
Etna in Italy attract tourists every
year
in global temperatures
l Millions of tons of sulphur dioxide
were released into the atmosphere.
This pollution will form acid rain in
the future with a harmful effect on
flora and fauna
Key Words
The Earth’s Layers
l The crust
l The mantle
l The core
The Plates
l Continental drift
l Fold mountains
Earthquakes
l Focus
l Epicentre
4
l
l
l
l
Shock waves
Seismograph
Richter Scale
Tsunamis
Volcanoes
l Magma
l Lava
l The Mid Atlantic Ridge
l The Pacific Ring of Fire
l Advantages of volcanoes
l Disadvantages of volcanoes
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CHAPTER 1
Questions
1
The map shows some crustal plates and their boundaries.
Choose the correct answer in each of the statements below:
(a) The shaded area labelled ‘X–Y’ is The Pacific Ring of Fire/The Zone of Ice and Fire.
(b) The plate labelled ‘Z’ is The Nazca Plate/The Pacific Plate.
(c) The mountains labelled ‘M’ are The Andes/Rockies. (3)
(JC Geography, 2005, Section 1, 1)
2
Examine the diagram which shows how an earthquake happens. (3)
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