Download Journey to the centre Examining the crust

+
In this section you will learn about the interior of the Earth.
Journey to the centre
Continental
crust (thick)
No one has ever seen the inside of the Earth.
The deepest we have managed to get is 3.5 km
35km
in the Witwatersrand gold mine in South Africa.
Miners would have to drill another 6365 km to
reach the centre of the Earth.
What we know about the Earth's interior comes
from direct and indirect evidence. We can get
direct evidence from the Earth 's surface. Indirect
Asthenosphere
75-250km
Lower mantle
evidence, like earthquakes and material from
space, also helps us to understand the Earth.
Examining the crust
The diagram on the right shows the structure
of the Earth. The crust is the surface of the
Earth. lt is a rock layer forming the upper part
of t he lithosphere. The lithosphere is split
into tectonic plates. These plates move very
A. Geologists (scientists who study the Earth and its structure)
think the Earth has a layered structure, like an onion.
slowly, at 2-5 cm per year, on a layer called the
asthenosphere.
+ The lithosphere is the uppermost layer of the
Earth. lt is cool and britt le. lt includes the very top of
t he mantle and, above this, the crust.
There are two types of crust:
• Continental crust forms the land. This is
made mostly of granite, which is a low density
igneous rock. Continental crust is on average
30-50 km thick.
• Under the oceans is oceanic crust. This is
much thinner, usually 6-8 km thick. lt is also
denser and made of an igneous rock called
basalt.
A. Geologists collect samples of the crust and compare the two
types: polished granite from continental crust (left} and basalt from
oceanic crust (right).
Restless Earth
The asthenosphere and mantle
The movement of the tectonic plates is evidence that
there is a 'lubricating ' layer underneath the lithosphere.
This is the asthenosphere. You might think that this
layer would be a liquid. But if it was a liquid, the heavy
tectonic plates would sink into it. Geologists think the
asthenosphere is partly molten rock and partly solid
rock. it may be like very thick, dense, hot porridge!
The asthenosphere is in the top layer of the mantle.
The mantle is the largest of the Earth's layers by
volume, and is mostly solid rock. We know this
because sometimes you can see the top of the mantle
attached to an overturned piece of crust.
Earthquake waves tell us about the physical state of the
Earth. They speed up, change direction or stop when
they meet a new layer in the Earth. Some waves travel
.A. The Japanese have built a 57 000-tonne international scientific drilling
ship, the Chikyu, which will drill 7 km through the oceanic crust to reach
easily through the crust, mantle and inner core, but not
the mantle - further than anyone has ever gone before.
through the outer core. This suggests that the outer
core has a different physical state and may be liquid,
not solid.
Clues from space
At a depth of 2900 km , we can't
sample the Earth's core. Geologists
Lithosphere
- .--·
Composition
Layer
2.7
Solid
Granite
Air
temp- 900
Oceanic crust
3.3
Solid
Basalt
Air
temp- 900
Asthenosphere
3.4-4.4
Partially
molten
think that it is metal - mostly nickel
Continental
crust
and iron. Evidence for this comes from
meteorites, which are fragments of
rock and metal that fall to Earth from
Mantle
space. Most come from the asteroid
belt between Mars and Jupiter.
;-.-.--...=.....:.....,
Lower mantle
Core_ _...1 Outer core
~,;,.;;.;.;;.
Solid
900-1600
Peridotite
1600-4000
Iron and nickel
Meteorites come in several types:
• Stony meteorites, with a similar composition to
-basalt.
• Stony-iron meteorites, containing a lot of the
mineral olivine.
•
Iron meteorites, which are solid lumps of iron
and nickel.
These meteorites may be fragments of the
lithosphere, mantle and core of a shattered
planet. Iron meteorites may show that the Earth 's
core is made up of iron and nickel.
your questions
1 Draw a cross-section of the Earth. You need a large circle
divided into layers. Label the layers with details of density,
temperature and physical state.
2 What are the main differences between the lithosphere and
asthenosphere?
3 Exam-style question Describe the differences between
the oceanic and continental crust. (4 marks)
+
In this section you will learn how the Earth's core drives the
process of plate tectonics.
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+ In a few billion years the core
and mantle will stop convecting,
because the radioactive heat will
run out. This will shut down our
magnetic field, and life on Earth
will be destroyed by radiation
from space.
Hot rocks
Inside t he Earth it is hot. We know this
because of:
•
molten lava spew ing from active volcanoes
•
hot springs and geysers .
Heat from inside the Earth is called geot hermal
(' Earth-heat'). The heat is produced by the
The inner core is so deep and is under such huge
pressure that it stays solid. The outer core is liquid
radioactive decay of elements such as uranium
because it is under lower pressure. As heat rises
a nd thorium in the core and m antle. This ra ises
from the core, it creates convection currents in
the core 's tempe rature to over 5 000
oc.
+ Some elements are naturally unstable and
radioactive. Atoms of these elements release particles
from their nuclei and give off heat. This is called
rad ioactive decay.
Convection cell in the mantle
the liquid outer core and mantle (see below). These
vast mantle convection currents are strong enough
to move the tectonic plates on the Earth's surface.
The convection currents move about as fast as your
fingernails grow. Radioactivity in the core and mantle
is the engine of plate tectonics.
Crust
Constructive plate margin, _ _ _ ~d~~,,
where two plates are
pulled apart
-+--Yr- -----\+Vi&\\-- Convection in t he
liquid outer core
Destructive plate _ _ _J!,_.
margin, where two
t
plates are pushed
\
together
Plumes of heat
rise in the mantle;
the mantle is less
dense
Plumes
ill' Sometimes
The parts of convection
you can see the
magnetosphere.
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cells where heat moves
towards the surface are
called plumes. These
are concentrated zones
+ Did you know that
the Earth's magnetic field
sometimes 'flips', so north
becomes south and south
becomes north?
of heat. In a plume, the
mantle is less dense.
Plumes bring magma (molten rock) to
the surface. If magma breaks through
the crust, it erupts as lava in a volcano.
The northern
lights (aurora
borealis)
form when
radiation from
space hits the
magnetosphere
and lights up
the sky.
• Some plumes rise like long sheets of
heat. These form constructive plate
boundaries at the surface.
• Other plumes are like columns
of heat. These form hot spots.
Hot spots can be in the middle of
a tectonic plate, li ke Hawaii and
Yellowstone in the USA.
Magnetic field
The Earth is surrounded by a huge
invisible magnetic field called the
magnetosphere. This is a force
field. lt protects the Earth from
harmful radiation from space and
the sun (see right).
The Earth's magnetic field is made
by the outer core. As liquid iron in
the outer core flows, it works like an
electrical dynamo. This produces
the magnetic field .
, your questions
1 Why is the centre of the Earth at over 5000 °C?
2 Look at the diagram of the Earth's convection
currents. What happens to the crust at the top of one
of the convection currents in the mantle?
3 Find out why Mars is a 'dead' planet with no plate
tectonics. You might like to visit this website: http://
mars.jpl.nasa.gov/classroom/students.html
4 Each set of words below has an odd one out. For each:
a say which is the odd one out
b explain your choice.
• inner core, outer core, mantle, crust
• convection, northern lights, plume, cell, current
• lava, uranium, magma, geyser
5 Exam-style question Describe the different layers of
earth's interior. (4 marks)
+
In this section you will find out how the Earth's tectonic plates have moved
in the past, and about plate boundaries.
Pangea, the supercontinent
Scientists know that the continents were
once all joined together. They formed
a supercontinent called Pangea. The
diagram on the right shows the position
of the continents 250 million years ago.
Identical rocks and fossils dating from
this time have been found in West Africa
and eastern South America. This tells
AFRICA
us that Africa and South America were
once joined. Pangea started to split apart
about 200 million years ago. Since then,
plate tectonics has moved the continents
to the positions they are in today.
Moving plates
Today, the Earth's lithosphere is split into
15 large tectonic plates and over 20
small ones. These are like the patches
that make up a football. The plates
move very slowly on the asthenosphere.
Where two plates meet, there is a plate
boundary. There are three types of
plate boundary, as shown on the map
opposite:
• Constructive plate boundaries formed when two plates move apart.
•
Destructive plate boundaries - formed
when two plates collide.
•
Conservative plate boundaries formed when two plates slide past
each other.
Plate boundaries are where the 'action'
is. Most earthquakes and volcanoes are
found on plate boundaries.
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pf~"'ef
+ Every year, the distance
between the UK and the
USA grows by about 2 cm.
This is because the mid·
Atlantic constructive plate
boundary creates new
oceanic crust.
Restless Earth
Pacific
Direction of plate movement
Antarctic
""""""- Constructive boundary
"""'-- Destructive boundary
- - Conservative boundary
Crust: old and new
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pfeiJ'\ef
Most continental crust is 3-4 billion years old. The
oldest oceanic crust is only 180 million years old.
Why the age difference?
New oceanic crust forms constantly at
constructive plate boundaries:
• Convection currents bring magma up from
the mantle.
• The magma is injected between the
separating plates.
• As the magma cools, it forms new
.oceanic crust.
• The plates continue to move apart, allowing
more magma to be injected.
Old oceanic crust is destroyed by subduction at
destructive plate boundaries- it is 'recycled ' by
the Earth. Continental crust was formed billions
of years ago, and has not formed since. it is less
dense than oceanic crust, so can't be subducted
and destroyed.
+ Subduction
describes oceanic crust
sinking into the mantle
at a destructive plate
boundary. As the crust
subducts, it melts back
into the mantle.
+
Look at the map of plates
and plate boundaries above.
The circle of plate boundaries
around the Pacific Ocean is
called the 'Pacific r ing of fire,
because it has many active
volcanoes.
your questions
1 Compare the map of Pangea with a modern world
map from an atlas. Describe how India has moved
since the time of Pangea.
2 Look at the map of tectonic plates.
a Which plate is the UK on?
b Name a country which is split by two plates.
c Name two plates that are moving apart.
d Name two plates that are colliding.
3 Exam-style question Explain why earth's tectonic
plates move. (6 marks)
+
In this section you will
learn which hazards
happen at different
plate boundaries.
Conservative
Tectonic hazards
Earthquakes and
volcanoes (tectonic
hazards) occur at plate
Constructive
boundaries. Different
plate boundaries produce
different tectonic hazards.
Destructive
Conservative
boundaries
As plates slide past each
other, friction between
them causes earthquakes.
These are rare but very
destructive, because they
are shallow (close to the
No volcanoes.
Iceland, on the
mid-Atlantic ridge.
The Eurasian and
North American
oceanic plates
Ipulling apart.
• Small earthquakes
up to 5.0-6.0 on
the Richter scale.
Andes mountains
in Peru and Chile.
Nazca oceanic
plate is subducted
under the South
Amencan
continental plate.
• Very destructive, up
to magnitude 9.5.
• Tsunami can form.
____
.___
Volcanoes
San Andreas fault
• Destructive
in California, USA
earthquakes up to
magnitude 8.5.
North American and
Pacific plates sliding • Small earth
past each other.
tremors almost
daily.
Himalayas. Formed
as the Indian and
Eurasian
continental plates
push into each
...... other.
Collision
zone
Earthquakes
Example
Plate
boundary
• Not very explosive
or dangerous.
• Occur in fissures
(cracks in the crust).
• Erupt basalt lava at
1200 °C.
lr •Very explosive,
destructive
volcanoes.
• Steep sided, cone
shaped.
• Erupt andestte lava
at 900-1 000
oc.
• Destructive
earthquakes, up to
magnitude 9.0.
• Landslides are
triggered.
Volcanoes are
very rare.
surface). The San Andreas
Collision zones
fault is shown below.
San
Francisco
Key
e
major earthquake
location and date
0
200 km
+
USA
""o~
Los Angeles
"0,:
Pacific Ocean
N
+ Collision
zones are a type
of destructive
boundary. They form
mountain ranges
like the Himalayas
(see right). Two
continental plates of
low-density granite
collide, pushing
up mountains.
Earthquakes happen
on faults (huge
cracks in the crust) in
collision zones.
Mountain range
~
Asthenosphere
.A. A conservative p late boundary
.A. A collision zone boundary
Constructive boundaries
Destructive boundaries
As plates move apart, magma rises up through
As the plates push together (see the diagram
the gap, as the diagram below shows. The magma
below), oceanic plate is subducted. As it sinks,
is basalt and is very hot and runny. lt forms lava
it melts and makes magma called andesite (after
flows and shallow sided volcanoes.
the Andes). Sea water is dragged down with the
oceanic plate. This makes the magma less dense
Earthquakes are caused
so it rises through the continental crust. The water
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by friction as the
plates tear apart.
erupts as steam making volcanoes very explosive.
+
These earthquakes
are small. They don 't
cause much damage.
Every year there are
about 100 000 earthquakes
strong enough to be felt.
The largest earthquake
recorded was a magnitude
9.5 in Chile in 1960.
Sinking oceanic plate can stick to the continental
plate. Pressure builds up against the friction . When
the plates finally snap apart, a lot of energy is
released as an earthquake. These earthquakes can
+ Tectonic
hazards are
natural events
that affect people
and property.
be devastating, especially if they are shallow.
Constructive plate
boundary
Destructive plate
boundary
~--Lava
erupts
forming volcanoes
Plates spread
apart
Convection currents
from mantle bring
magma towards
the surface
Magma is forced up
between the plates.
When this cools new
oceanic plate forms
I
Dense oceanic
plate is subducted
under the less
dense continental
plate
The oceanic plate melts --..:....;,.A Earthquakes
back into the mantle
your questions
1 Which type of plate boundary is most dangerous for
humans to live on?
2 Match the words below into pairs:
constructive fault
collision zone fissures
landslides
explosive destructive
conservative
Write a brief explanation of your pairs.
3 Look at the diagram of the San Andreas fault. The
two plates can 'lock', stopping them from sliding.
Why do you think this is?
4 Exam-style question Compare the physical
features and tectonic hazards of constructive and
destructive plate boundaries. (6 marks}
+
In this section you will examine the impact of volcanoes on
developed countries.
Destructive power
The most devastating volcanoes are the most
Ash and gas column
explosive ones. The Volcanic Explosivity Index
(VEl) measures destructive power on a scale
from 1 to 8. Mount St Helens, which erupted in
May 1980, measured 4. Modern humans have
never experienced an eruption measuring 8.
Ash fall builds up on roofs,
causing buildings to collapse , .
Volcanoes produce many hazards. Some are
Lava bombs can kill
people close to the crater
from the primary effects of the volcano,
whereas others are secondary. Some benefit the
Pyrocla~st~ic:_f~lo~w"!:::.=====:::::
Pyroclastic flows
are deadly clouds
of hot ash and
gas that sweep
along at 200 km/h
_j
areas affected, whereas others cause problems.
Sakurajima, Japan
Lahar (volcanic
mudslide) occurs
when rain or snow
Japan is on a destructive plate boundary
where the Pacific plate is subducted beneath
the Eurasian plate, causing active volcanoes.
One, Sakurajima (below) , has erupted since the
.A. Volcanic hazards
1950s, sometimes 200 times a year. Ash and
lava have buried buildings and
destructive
plate
boundary
--.......
plate
movement
KYUSHU ISLAND
7000 people live at the
base of the volcano.
Hot springs and lava flows are
a popular tourist attraction; the
area is a national park.
The 1914 lava flow
joined the island
to the mainland.
<
~
Restless Earth
Lava lake
farmland, poisonous gases have caused alerts in local
towns and brought acid rain, killing plants.
Volcanic eruptions can be predicted - scientists can say
Layers of ash from
pyroclastic flows
Side vent
when a volcano will erupt. They can then warn people
to take shelter or evacuate. The diagram below shows
how Sakurajima is monitored and also the evacuation
procedure there.
~ Lava pi pe
Japan is a developed country. lt can afford to spend
money on monitoring, protection and evacuation . When
Magma
chamber
Sakurajima does erupt, it will probably not cause many
deaths. Homes, crops and industries will be destroyed,
but most people have insurance and the Government
~
Stratovolcano (or composite cone volcano)
will help to repair the damage. In developed countries,
tectonic hazards damage property (economic costs) but
cause less harm to people (social costs).
Aircraft are used to
measure the amount
of gas the volcano
gives off
_,..;
seismometers. These
r earthquakes which
as magma rises
so scientists can predict
an eruption
Tiltmeters detect
when the volcano
swells up as it
fills with magma
Concrete lahar
channels divert
dangerous
'""'-__,_ m udflows
Boreholes measure
water temperature
as magma
heats it up
~ ~
Hot springs /
are monitored
Concrete shelters
protect against
volcanic bombs
and ash
Evacuation
clearly sign
posted; regular
evacuation drills
your questions
1 Copy and complete the following table to show the
effects of Sakurajima:
Benefits
Problems
Primary effects
Secondary effects
2 Make a table like the one on the right:
IProtection
.6. Two men take cover in a lava bomb shelter during
an eruption of Sakurajima (in the background).
+ Primary effects- caused instantly by the
eruption. These are directly linked to the volcano
e.g. lava, acid rain, gases and earthquakes.
+ Secondary effects - in the hours, days,
and weeks after the eruption. These are often
caused by the volcano e.g. disease, food and
water shortages.
IPrediction
Use it to list methods used to protect people from
Sakurajima, and how scientists predict an eruption.
3 Exam-style question Using examples, explain how
volcanic eruptions can be predicted. (4 marks)
+
In this section you will learn how volcanoes can have devastating
consequences for people in the developing world.
At risk
In the developing world , people are at greater
risk from tectonic hazards than those in
developed countries:
•
They often live in risky locations, because
there is nowhere else to live.
•
They can't afford safe, well-built houses, so
buildings often collapse.
•
They don't have insurance.
•
Their governments don't have the money and
•
resources to provide aid.
Communications are poor, so warning and
evacuation may not happen.
Most volcanic eruptions with high death tolls are
& Lava destroyed 40% of Goma, covered half the airport and
destroyed 45 schools. Water and electricity supplies were also cut off
by the lava.
in the developing world.
Mount Nyiragongo
In January 2002, a fast flowing river of
basalt lava, 1OOOkm wide, poured out of
Mount Nyiragongo and into the city of Goma
(see photo). 100 people died, mostly from
poisonous gas and getting trapped in lava. A
number of social impacts also resulted:
• 12 500 homes were destroyed by lava flows
and earthquakes - and as the eruption was
predicted, 400 000 people were evacuated.
Many people had to move to overcrowded
refugee camps.
• Disruption to the mains water supplies
caused concern for the spread of diseases.
Many economic impacts also resulted:
• Poisonous gases caused acid rain which
affected farmland and cattle - many farmers
lost income.
1 Magma rising from the mantle
2 Convection currents pull the two plates apart
3 The valley has formed as some of the crust has
sunk downwards
Mt Sakurajima,
Japan
• Due to poverty, most people could not
afford to rebuild their homes.
Within days, people began returning to
Goma. Over 120 000 were homeless.
This was a crisis and people needed
help quickly. With little clean water, food
and shelter, diseases like cholera could
spread. The United Nations and Oxfam
began a relief effort to help.
• The United Nations sent in 260 tonnes
of food in the first week. Families got 26
kg of rations.
• In the UK, a TV appeal asked people
to give money to help.
• Governments around the world gave
$35 million to get aid to the refugees.
• Emergency measles vaccinations
were carried out by the World Health
Organisation.
In a developing country, the main
problem is poverty. Most people fled
from the lava with nothing. lt was months
before many could start building new
homes. By June 2002, however, some
roads had been cleared of lava and the
water supply repaired .
Future threats
Mount Nyiragongo was active again in
2005. lt could erupt at any time. There
is also volcanic activity under Lake Kivu.
Gases like carbon dioxide and sulfur
djoxide rise through the Earth into the
lake. They get trapped in mud on the
lake bottom. An earthquake could shake
these gases free. In 1986 this happened
to volcanic Lake Nyos in Cameroon, also
in Africa. 1700 people suffocated from
breathing in too much carbon dioxide.
Mt Nyiragongo,
DRC
Volcano
type
Steep-sided
stratovolcano (or
composite cone)
over 1000 meters
high
Stratovolcano over
3400 metres, high
but not as steep as
Mt Sakurajima
Magma
type
Andesite. High
gas conten t, high
viscosity.
Basalt. Low gas
content, very low
viscosity.
Explosivity
VE14-5
VE11
Hazards
Lava flows , volcanic
bombs, pyroclast ic
flows, ash fall.
Erupts aim ost
continually, but with
major eruptions
once every 200-300
years.
Lava flows and gas
emissions. Contains
a lava lake within its
crater, which can
drain causing huge,
fast moving lava
flows.
+ Social impacts are the impacts upon people.
+ Economic impacts are the impacts upon the wealth of
an area.
+ Refugees are people who are forced to move due to
nat ural hazards or war.
+ Aid is help. lt can be short-term such as food given in
emergency, or long-term such as training in health care.
+ A relief effort is like aid. lt is help given by organisations
or count ries to help those facing an emergency.
your questions
1 Explain in your own words what we mean by aid and
relief effort.
2 a Draw an identical table to that for Question 1 on
page 17, and complete it to show the effects of
Mount Nyiragongo.
b Which volcano seems to have the greatest effects Nyiragongo or Sakurajima? Explain your answer.
3 How successful was the relief effort in helping people
affected by Mount Nyiragongo's eruption?
4 Why do you think people still live around Mount
Nyiragongo and Lake Kivu?
5 Exam-style question Using a named example, explain
the economic and social impacts of a volcanic eruption.
(6 marks)
+
In this section you will learn how earthquakes
are measured and about their awesome power.
Why is the ground
shaking?
Earthquakes can't be predicted.
They start without warning
and can be catastrophic. An
earthquake is a sudden release
of energy. it's a bit like bending
a pencil until it suddenly snaps.
Underground, tectonic plates
try to push past each other
The shaking is worse on the surface
if the focus is shallow
Earthquake
waves travel
out in all
directions
Huge
devastation
en
Q)
.::s:.
ell
.r:::
en
Lots of
devastation
and deaths
"'0
c
:::>
e
Ol
.r:::
Damage
begins,
but deaths
are rare
(.)
:.c
~
0
+-'
+-'
c
Q)
earth's surface
above the
focus
+-'
X
w
The earthquake starts at the focus
- building up pressure. The
pressure is suddenly released
IKey
along faults (cracks in the crust),
sending out a huge pulse of
energy. This travels out in all
directions as earthquake waves
A magnitude 6.0 earthquake is 10 times
more powerful than a magnitude 5.0.
how much the ground shakes - is
its magnitude. A seismometer
measures this using the Richter
scale (see right) or Moment
magnitude scale.
Port-au-Prince, Haiti
On 12 January 201 0, a
magnitude 7.0 earthquake
struck Haiti. This was
very similar in size to the
1995, magnitude 7.2 Kobe
earthquake in Japan. However,
the earthquakes had very
different causes and effects.
& The shallower the focus, the more
destructive the earthquake tends to be.
The epicentre experiences the most shaking.
Port-au-Prince, Haiti 2010
Kobe, Japan 1995
•
The power of an earthquake -
I
Magnitude
& The Richter scale is a logarithmic scale.
(see the diagram on the far right).
Magnitude
\ Plate movement
•
•
Magnitude - 7.2 (soft ground also made the
shaking worse)
Focus - 16km deep on a fault
Epicentre - 20km from Kobe (population
1.5 million)
•
•
•
Magnitude - 7.0
Focus - 13km deep on a conservative
plate boundary
Epicentre - 25km from Port-au-Prince
(population 2.5 million)
Primary effects:
• 5000 people died and 26 000 were injured.
The population density is very high and
people were still in bed when it struck at
5:46am.
• Bridges and roads collapsed, train lines
were damaged - disrupting transport and
communication links.
• £1 00 billion of damage was caused to
roads, houses, factories and infrastructure
(gas, electric, water and sewage pipes).
Pr imary effect s:
• 316 000 people died and a further
300 000 were injured.
• Many houses were poorly built and
collapsed instantly. 1 million people were
made homeless.
• The port, communication links and
major roads were damaged beyond
repair. Rubble from collapsed buildings
blocked road and rail links.
Secondary effects:
• Many fires broke out throughout the city,
triggered by broken gas pipes, resulting in
further deaths.
• Businesses were affected for many weeks
due to disruption caused by rebuilding.
• Homelessness, disrupted schooling,
unemployment and increased stress
problems lasted for many months as the
authorities struggled to cope with the scale
of the damage caused.
Secondary effects:
• The water supply system was destroyed
- a cholera disease outbreak killed ove
8000 people.
• The port was destroyed - making it
hard to get aid to the area.
• Haiti 's important clothing factories were
damaged. These provided over 60% of
Haiti's exports. 1 in 5 jobs were lost.
• 1 year after the earthquake, 1 million
people remained displaced - many still
living in refugee camps.
Restless Earth
Long-term planning
Tsunami
Earthquakes beneath the sea bed can generate
The secret of survival is long-term planning.
tsunami (see below). Tsunami are waves that travel
Japan is a developed country, so it can afford
at up to 900 km/ h, with wavelengths of over
t o do this. There is a 70 % probability (chance)
200 km. In the open ocean wave height is less than
of a magnitude 7.2 earthquake hitting Toyko in
1m, but as the waves approach the coast they
the next 30 years. lt could kill 7000 and injure
slow down, bunch up and wave height increases
160 000. There is no way of predicting when
up to 30m. When tsunami hit, they cause a very
it might happen.
powerful flood, pushing several kilometres inland
•
Every year Japan has earthquake drills.
destroying homes, bridges and infrastructure.
•
Emergency services practise rescuing people.
Warning systems in the ocean can detect tsunami
•
People keep emergency kits at home
and set off sirens and alarms but this is only useful
containing water, food , a torch and radio.
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if the epicentre is some distance from the coast.
None of the countries affected by the 2004 Asian
A damper in the roof
acts like a pendulum,
red ucing building
sway
Cross bracing stops
floors collapsing
Shock absorbers
bui lt into cross
braces
tsunami received any warning because there was
no warning system in the Indian Ocean.
Tsunami w aves
. - spread out in---all directions
Tsunami waves slow d own and
w avelength drops, but wave
height increases dramatically
Wat er forced upward
~ . . . . .- seabed jolts upward
\
\
\fFault
\
\
\ , Earthquake focus
A strong steel frame
which is also flexible,
stops cracking
ryou-rquestions
·
Strong double
glazed windows
stop broken glass
showering down
Very deep
--:-"-- foundations, to
prevent collapse
.A Many buildings in Japan are earthquake proof like this
one. They can withstand a major earthquake. Gas supplies
automatically shut off, reducing the risk of fire.
t·r~..~,-~
~
•
\
Sea bed
becomes
s hallower
c loser to
coast
:
1 Earthquake damage is reduced as you move away
from the epicentre. Why is this?
2 a Draw a large version of the Richter scale diagram
b Use a website, like Wikipedia, to find a list of
earthquakes since 2000. Mark their magnitudes
and death tolls on your diagram.
c Is there a link between magnitude and death toll?
3 Using the diagram above, list and number the
stages in the formation of a tsunami.
4 a Classify earthquake impacts in Japan into social
and economic.
b Which are greater? Explain your answer.
5 Exam-style question Using named examples,
compare the social and economic impacts of two
earthquakes. (6 marks)
+
In this section you will find out about the impacts of earthquakes
on developing countries, and how people respond to them.
Death and destruction
Earthquakes in the developing world often have very high death tolls compared to volcanoes.
Destructive earthquakes happen regularly, as the table shows.
Location
Sendai, Japan
I
Kashmir, Pakistan
Aceh, Indonesia
-'·"llf'
201 1
15 800
2005
1186 000
2004
280 000
Bam, Iran
Magnitude
Key facts
9.0
The tsunami (secondary effect) caused the most of the
deaths. The economic costs were over $200 billion.--...;;::::::::::..:..o;;;;;;;;;O
andslides (secondary
l One third of the deaths were due to Ibuilt
colla sed schools.
7.6
effect). Many children died in poorly
9.3
Most of the deaths were caused by a tsunami (secondary
effect) that hit 14 countries around the Indian Ocean.
6.6
Many people were trapped when their poorly built, mud
brick homes collapsed in the densely populated city.
Earthquake in Sichuan
Sichuan is a province in central
Many of the areas hit were poor
and rural.
ASIA
D
China. On 12 May 2008 it was hit by
a magnitude 8.0 earthquake. There
Key
Q
was no warning. The social impacts
were devastating:
• 70 000 people died
• 375 000 people injured
INDIAN
OCEAN
Epicentre
N
' - Collision zone
o
500 km
t~
' - Direction of
plate movem ent
(
Beijing•
Mountainous region
• 5 million homeless
The economic impacts were large
too. Over 1 million people lost their
job because their workplace was
destroyed. The rebuilding costs
Shanghai~
""' eChengdu
Wenchuan- .f
Linqiong•
\ Sichuan
were estimated at $75 billion. Many
landslides occurred (a secondary
province
effect), some of which dammed rivers
creating dangerous 'quake lakes'
which can burst, causing flooding.
There were up to 200 large
aftershocks. On 27 May a
magnitude 6.0 aftershock caused
420 000 buildings to collapse.
the Himalayas. Earthquakes are
common in this collision zone.
Restless Earth
+ Aftershocks
often occur as
the fault 'settles'
into its new
position. They
can injure or kill
rescuers. In the
developing world,
aftershocks often
destroy buildings
that were
weakened by the
first earthquake.
Local responses
Heavy rain, landslides and aftershocks
made the rescue effort difficult:
• The Prime Minister, Wen Jiabao, flew to
the area very soon after the earthquake.
• 50 000 soldiers were sent to help dig for
survivors.
• Helicopters were used to reach the most
isolated areas.
• Chinese people donated $1.5 billion in
aid.
International responses
China quickly asked the rest of the world
to help:
• Some countries sent money.
The UK gave $2 million.
• Finland sent 8000 six-person tents, and
Indonesia sent 8 tonnes of medicines.
Cross-braced wood
• Rescue teams flew in from Russia,
Hong Kong, South Korea and
Singapore.
Building for the future?
The Sichuan earthquake caused over
700 schools to collapse. China has strict
building rules, so schools should have
withstood the shaking. Even in a poorer
developing country, buildings can be
made cheaply to withstand earthquakes.
The diagram on the right shows how.
Concrete ring ties the
walls to the foundations
Simple steel rod
foundations
Walls made of mud
and straw packed
between wooden
slats
your questions
1 Explain why the Sichuan earthquake happened.
Remember to include plate names and boundary
types in your answer.
2 a Make a list of all the effects of the Sichuan
earthquake.
b Use two colours to circle social effects (effects on
3 Look back on the effects of the two volcanoes and
two earthquakes you have studied.
a Compare impacts each had on people and
property.
b Explain the differences.
4 Exam-style question Explain why earthquakes
people) and economic effects (effects to do with
happen on destructive plate margins. You may draw a
money).
diagram to help with your answer. (4 marks)