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978-0-521-68059-2 - NSSC Geography Module 1
Gerhard de Klerk
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Unit 1
Plate tectonics,
earthquakes and
voIcanoes
Look at Figure 1.1 which is a photograph of Earth taken from a
satellite in space. Most of the surface of planet Earth is covered
by sea, the rest is covered by continents. Which continent can you
see in the satellite photograph? Do you think this continent will
be in the same place in a million years time?
In this unit you will discover that the continents and oceans form
the Earth’s crust which is constantly moving. This movement can
result in earthquakes and volcanoes.
This unit is divided into three sections:
Figure 1.1
The Earth from space
A
Earth’s crust on the move
B
Earthquakes
C
Volcanoes
In this unit you will learn to:
• recognise the Earth’s crust as the outer layer of planet Earth
• realise that the Earth’s crust is made up of tectonic plates
• identify tectonic plates on a world map
• explain how earthquakes happen
• investigate the Kobe earthquake of 1995
• explain how volcanoes happen
• describe three types of volcanoes
• describe the main types of intrusions and landforms
• investigate the volcanic eruption of Mount Pinatubo in 1991
• identify zones of earthquake and volcanic activity on a world map
• discuss the environmental and economic effects of earthquakes and
volcanoes on people and landscapes
• discuss strategies to manage the effects of earthquakes and
volcanic eruptions.
A
Earth’s crust on the move
Millions of years ago the Earth was a fiery ball of gas and liquid.
As it cooled, the outer parts of the Earth formed a solid layer
called the crust. But the crust is only the thin outer layer of the
Earth as you can see if you study Figure 1.2 on page 2.
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Cambridge University Press
978-0-521-68059-2 - NSSC Geography Module 1
Gerhard de Klerk
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NSSC Geography
1. The crust – thin outer layer formed of solid rocks between 6 km and 90 km
thick. This layer is the least dense.
2. The mantle – about 2 900 km thick, more dense than crust. Rocks are
in a hot, thick liquid or molten state. The molten rock has a plastic
consistency that allows it to move and flow.
3. The outer core – about 2 000 km thick, very dense but molten.
4. The inner core – 1 200 km thick, extremely hot. Thought to be
an extremely dense solid metalic ball.
Figure 1.2
The internal structure of the Earth
ACTIVITY 1
Copy and complete the table below using information from
Figure 1.2.
Layer number Name
Density
Thickness
Description
1
2
3
4
Glossary
Tectonic plates – large sections of
the Earth’s crust
Hint
The Earth is continually changing.
Although continents neared their
present locations about 50 million
years ago, they are still drifting
slowly over the planet’s surface.
Direction of
plate movement
Figure 1.3
This is what Earth probably
looked like 200 million years ago
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Scientists think that the surface of the Earth is made up of
different pieces of crust and not one continuous crust. The pieces
of crust are called tectonic plates. Most tectonic plates carry
both continents and oceans. You will find out more about tectonic
plates in the next section.
The theory of continental drift and tectonic plates
In 1912, a German meteorologist called Alfred Wegener put
forward the idea that the continents were once all joined in a
single land mass which split up over a long period of time to
form separate continents. He called the single land mass
Pangaea (“all land” in Greek), and his idea became known as the
theory of continental drift. Other scientists of the time thought
Wegener was a fool to come up with such a crazy idea!
It was only when new evidence was found in the 1950s and
1960s that Wegener was proved to be correct. For example,
scientists found identical rock types and identical fossils in
Africa and South America, which proved that these two
continents had once been joined. See if you can identify our
present continents in Pangaea in Figure 1.3.
Look at the map in Figure 1.4 which shows the main tectonic
plates into which the Earth’s crust is divided today. The plates
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Cambridge University Press
978-0-521-68059-2 - NSSC Geography Module 1
Gerhard de Klerk
Excerpt
More information
Module 1 Unit 1
3
move a few centimetres every year. The edges of the plates are
called plate boundaries. The arrows show the direction of
movement of the plates.
North
American
Plate
NORTH
AMERICA
Eurasian Plate
NT
IC
R
AT
LA
MID
Adriatic TurkishHellenic Plate
AFRICA
Pacific
Plate
SOUTH
AMERICA
South
American
Plate
MID ATLANTIC RIDGE
Nazca
Plate
Iranian
Plate
IDG
E
EUROPE
ASIA
JAPAN
Pacific
Plate
Arabian
Plate
PHILIPPINES
African
Plate
Indo-Australian
Plate
OCEANIA
Antarctic Plate
Direction of plate movement
Plate boundaries
NEW
ZEALAND
Figure 1.4
The different tectonic plates
ACTIVITY 2
Use the map in Figure 1.4 to find the answers to these
questions.
1 Name the plates that contain the following continents:
a Africa
b Australia
c Japan
d India.
2 Find the plate boundary along the west coast of South
America.
a Name the plates on either side of this plate boundary.
b Are the plates moving apart or towards each other at this
plate boundary?
3 Find the plate boundary which passes through the Atlantic
Ocean from north to south.
a Name the plates on either side of this plate boundary.
b Are the plates moving apart or towards each other at this
plate boundary?
4 In which direction is Antarctica moving?
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978-0-521-68059-2 - NSSC Geography Module 1
Gerhard de Klerk
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NSSC Geography
Moving plates
It is difficult to believe that the hard, rigid tectonic plates that
make up the Earth’s crust are moving. But remember that, below
the crust, the mantle has a plastic consistency and can therefore
move or flow. Scientists describe the upper layer of the mantle,
immediately below the plates, as a “soft layer of slush”. The rigid
tectonic plates can drift on this slush. The energy released by this
movement triggers off earthquakes and volcanoes, especially along
plate boundaries. Section B deals with earthquakes in more detail.
B
Glossary
Earthquake – vibrations on the
Earth’s surface caused by stresses in
the crust
Earthquakes
Plate movements cause cracks or faults in the crust. The faults
produce great stresses leading to vibrations on the surface of the
Earth that we call earthquakes. The damage caused by an
earthquake can be devastating – thousands of people and animals
can be killed or injured and massive damage is done to buildings
and landscapes. Read about an earthquake that took place in
Turkey on 17 August 1999 in the article below.
Desperate families claw at rubble
Istanbul: The pre-dawn quake
which rocked much of Turkey
yesterday crushed apartment
buildings and sent millions of
people fleeing in panic into the
streets.
Terrified earthquake survivors
sought the safety of open ground
yesterday as the enormity of what
had happened became clearer in the
devastated areas they left behind:
the final toll was more than 15 500
dead and almost 25 000 injured.
Layer by layer, from thousands of
sites around western Turkey,
hundreds of bodies were removed,
many in the pyjamas and
nightgowns they were wearing when
the immense quake struck over
about 45 seconds in the cool hours
before dawn. Some bodies were
shrouded in blankets and sheets
from their beds.
As many as 10 000 people could
still be trapped in rubble around
Golcuk, a naval base about 130 km
south east of Istanbul near the
quake’s epicentre.
There was severe damage in
some areas of Izmit, some 90 km
© Cambridge University Press
east of Istanbul near the epicentre
of the quake.
Fahrettin Duman, working
alongside a mechanical digger,
struggled to pull fallen masonry
from a apartment block near his
own house in Izmit. “There are
around eight people trapped in the
staircase near the entrance, but
even with this machine we can't
reach them. There’s no sign of life,”
he said. In Izmit, medical workers
shattered pharmacy windows to get
supplies for hospitals swamped by
injured people. More than 100
sailors were dead or missing from
a nearby barracks.
Local authorities were
overwhelmed by the task of clearing
debris. “Hundreds of buildings
collapsed. We need everything –
hospitals, kitchens, tents and
ambulances,” said Nihat Ozgol,
governor of the nearby town
of Yalova.
In the Avcilar district on the
impoverished fringe of Istanbul, a
boy cried out from the cracked slabs
and splintered plaster that was once
his home, “Help me, I’m still alive!”
As rescuers – some digging with
bare hands – carted away corpses
and listened for signs of life, they
heard: “I’m here”.
A worker touched his hand. “Oh
thank you,” sobbed six-year-old
Memet Arsuglou. Soon he was free
and hugging his mother.
The edges of Istanbul, such as the
Avcilar district, revealed the
hazards of hastily built
accommodation for rural migrants to
the city. Shoddy apartment blocks
and makeshift dwellings fell to
pieces or collapsed floor upon floor.
Many nations, including the
USA, Germany, Switzerland, Iran
and Greece offered rescue
teams and equipment.
The quake measured 7,4 on
the Richter scale according to
the National Earthquake
Information Centre in Golden,
Colorado, US. Since the rescue
operation, officials are concerned
about epidemics, water shortages
and power cuts.
(adapted from articles in
Cape Times, 18 and 19 August 1999)
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Cambridge University Press
978-0-521-68059-2 - NSSC Geography Module 1
Gerhard de Klerk
Excerpt
More information
Module 1 Unit 1
5
TURKEY
IZMIT
Figure 1.5
Earthquake damage in Izmit
Figure 1.6
Turkey and the affected areas
The structure of an earthquake
Glossary
Focus (plural: foci) – the origin of
the earthquake in the Earth’s crust
Epicentre – the point on the
Earth’s surface immediately above
the focus
The point in the Earth’s crust where an earthquake begins is
called the focus. Earthquake foci are usually found along plate
boundaries, between 70 and 700 km below the Earth’s surface.
The point on the Earth’s surface immediately above the focus is
called the epicentre.
The earthquake is caused by seismic waves, called P and
S waves, which pass through the Earth’s crust from the focus to
the surface. When they reach the surface these waves become
L waves which cause the most damage and this damage is
concentrated at the epicentre.
Find these structural features in Figure 1.7
epicentre
L waves
Earth‘s
crust
P and S waves
focus
Figure 1.7
Structure of an earthquake
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978-0-521-68059-2 - NSSC Geography Module 1
Gerhard de Klerk
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NSSC Geography
Tsunamis are huge sea waves caused by earthquakes in the sea
floor. Following the earthquake, water spreads out in all
directions travelling at speeds up to 800 km/h. If a tsunami
reaches a coastline it can present as a wall of water between
10 and 30 metres high which can flood whole towns and cities and
drown thousands of people.
The Richter scale
The Richter scale measures the size of the seismic waves and
their speed of travel to classify the magnitude of the earthquake.
The scale extends from 1 to 9. Each step in the scale represents
a magnitude ten times greater than the previous step.
For example, a magnitude of 4 is ten times greater than a
magnitude of 3. The following examples give you some idea of the
damage caused by earthquakes measured at numbers on
the Richter scale:
Less than 2,6 We do not usually feel this.
2,5–5,4 We can feel this, but very little damage is done.
5,5–6 Cars and houses shake. Windows crack.
6,1–6,6 Old buildings or poorly built buildings may
collapse. Some damage to houses.
7–7,9 Major earthquakes. Huge damage to buildings,
roads, railways, powerlines.
Over 8 Total destruction.
ACTIVITY 3
Answer the following questions which are based on the article
on page 4. You will need to refer to the background information
on earthquakes as well.
1 a Give the date and time when the Turkish
earthquake occurred.
b How long did the earthquake last?
c Do you think the time at which the earthquake
occurred could have led to a higher death toll?
Explain your answer.
2 a Where was the epicentre of the earthquake?
b Why was the damage worst at, or near, the epicentre?
3 a What caused most of the deaths and injuries in
this earthquake?
b How could there have been less damage and fewer deaths?
Give evidence from the article.
4 a What magnitude was this earthquake?
b Describe the scale used to measure the earthquake.
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978-0-521-68059-2 - NSSC Geography Module 1
Gerhard de Klerk
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Module 1 Unit 1
7
5
Find Turkey on the map in Figure 1.6. Is Turkey situated
on or near a plate boundary? If so, name the plates on the
other sides of the boundary.
6
Why would the earthquake cause water shortages and
power cuts?
7 a What is an epidemic?
b What types of epidemic do you think the officials were
referring to?
8 a Turkey has suffered many earthquakes in the past. In
view of this do you think the authorities were prepared for
this earthquake? Give evidence from the case study to
support your answer.
b Suggest ways in which Turkey could avoid such heavy loss
of life and damage in future earthquakes.
Earthquake zones
Look at the map in Figure 1.8 which shows the main earthquake
zones of the world.
ASIA
NORTH
AMERICA
ITALY
EUROPE TURKEY
HIMALAYA
JAPAN
GREECE
AFRICA
PHILIPPINES
Equator
SOUTH
AMERICA
OCEANIA
NEW
ZEALAND
KEY
Earthquake activity
Figure 1.8
The main earthquake zones of the world
The distribution of earthquakes
Earthquakes occur in zones or belts. The most important earthquake
belt is around the Pacific Ocean. It follows the west coasts of the North
and South Americas, the Aleutian Islands, Japan, the Philippines and
New Zealand. From Indonesia, a belt stretches westward through
the Himalaya Mountains in India to the Mediterranean Sea, along
Turkey, Greece and Italy. Another belt stretches down East Africa and
is known as the East African Rift Valley.
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NSSC Geography
ACTIVITY 4
Compare the map in Figure 1.8 with the map of tectonic
plates in Figure 1.4 and answer the questions.
1 Describe any similarities you notice between the plate
boundaries and the earthquake zones.
2 Explain these similarities.
3 Look at the table of major earthquakes.
Year
Place
Estimated deaths
1960
Morocco
1976
China
1978
Iran
15 000
1985
Mexico
10 000
1995
Japan
12 000
500 000
5 400
Table 1
a Find each place on the maps in Figures 1.4 and 1.8.
For each earthquake, name the plates on either side
of the plate boundary.
b List the factors which could have led to the different
numbers of deaths in each of these earthquakes.
4 Study the map (Figure 1.9) below and answer
the questions.
Equator
KEY
Earthquake belts
Figure 1.9
Earthquake belts
a Describe the distribution of earthquake belts.
b Briefly explain why earthquakes are more likely to
occur in these areas.
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Gerhard de Klerk
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Module 1 Unit 1
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Case study: The Kobe earthquake
The congested old centre
of the city was one big bonfire
yesterday morning. Thousands of
homes were shown to be at risk
not just of collapse, but of
catching alight.
All big Japanese cities have
thousands of wooden buildings
which are natural firetraps. Some
are old, others were built in the
last 20 to 30 years.
The rescue services found
themselves unable to cope with
the sheer size of the operation.
One group of people were
imprisoned in their homes,
trapped and waiting for rescuers
for more than 14 hours after
the earthquake.
The only light in the centre of
Kobe yesterday came not from
electricity but from 129 separate
fires. Where fires died out it was
because there was nothing left
to burn.
JAPAN
Kobe. Wall of fire 300
– 500m wide. 77 000
residents evacuated to
temporary rescue
centres.
05:45 local time. An
earthquake centred under
the Island of Awajishima
measures 7.2 on the
Richter scale, killing 4 500
and injuring 6 334. It was
the worst earthquake in
Japan since 1946 when
3 769 people were killed in
central Japan.
Ashiya
Kobe
Kyoto
Osaka
Island of
Awajishima
e
scal m
30 k
Sea of Japan
Kyoto
Kobe
Tokyo
Nearly 10 000
houses, buildings
and other
structures were
destroyed or
partially damaged
Osaka
Pacific Ocean
Awajishima
Japan
Source: British: Geological Survey
Trench
Thrust zone
Ocean
floor
Eurasian
plate
CHINA
PHILIPPINES
Pacific plate
Figure 1.10
Earthquake damage in Japan
ACTIVITY 5
Figure 1.10
Eurasian
plate
Earthquake Pacific
damage
in Japan
plate
Upper mantle
1
INDONESIA
Philippines plate
PAPUA NEW GUINEA
Figure 1.10 contains information about a major
earthquake that affected an area in Japan, especially
the city of Kobe, in January 1995.
a
b
c
d
e
What is an earthquake?
What is a plate?
Using Figure 1.10, explain why plate movements off
the east coast of Japan sometimes cause earthquakes.
Give three reasons why this earthquake caused such
a great loss of life and property.
What can be done to reduce the effects of earthquakes
in areas where they are likely to occur?
In Section C you will examine another natural event which is
caused by plate movements: volcanoes.
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Gerhard de Klerk
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NSSC Geography
C
Glossary
Magma – molten rock from the
mantle within the Earth’s crust
Lava – molten rock which erupts
onto the Earth’s surface
Volcano – a landform built up of
lava, ash and cinders ejected from a
vent in the surface of the Earth
Volcanoes
When a crack or fault appears in the Earth’s crust, molten rock
called magma, forces its way from the mantle up the fault and
erupts on the surface of the Earth to form a volcano. When the
magma reaches the surface of the Earth it is called lava. Besides
lava, some volcanoes eject steam, ash, dust and poisonous gases,
such as sulphur.
Where are the world’s active volcanoes?
Volcanic eruptions are most common along plate boundaries
where movement and cracking occurs.
Look at Figure 1.11 which is a map showing the world’s
active volcanoes.
ICELAND
Mount St Helens
1980
NORTH
AMERICA
Surtsey
1963
Montserrat
1995
Mauna Loa
1984
Nevada del Ruiz
1985
Cotopaxi
1904
Vesuvius
EUROPE AD 79
Unzen
1792
1991
ASIA
Pinatubo
1991
Etna
1669
1998
AFRICA
Kamchatka
Peninsula
JAPAN
PHILIPPINES
Equator
Krakatoa
1883
Tambora
1815
SOUTH
AMERICA
OCEANIA
KEY
Volcano activity
Volcano belts
Historic volcanoes
Tristan da Cunha
1961
Ruapehu
1995
NEW
ZEALAND
Figure 1.11
The world’s active volcanoes
The distribution of volcanoes
Three-quarters of the Earth’s 550 historically active volcanoes lie
along a belt called the “Ring of Fire”, which runs along the edge of
the Pacific Ocean. The zone stretches from Antarctica through
New Zealand, the Philippines, Japan, the Kamchatka Peninsula
in Russia, the Aleutian Islands, Alaska and along the west coast
of Northern South America. From Indonesia a branch stretches
westward to Italy, the Azores and the West Indies. The
mid-Atlantic ridge, stretching from Iceland in the north to the
island Tristan da Cunha in the south, is also characterised by a
number of volcanoes.
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