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Restless Earth
The lithosphere is the upper most layer
of the Earth. It is cool and brittle and
includes the top part of the mantle and
above this the crust.
The asthenosphere is a ‘lubricating’
layer beneath the lithosphere.
How do we know what the layers are
like? There are several clues:
1) Meteorites from space
2) Volcanic eruptions
3) Earthquake waves
How do the tectonic plates move?
Convection currents in the mantle move the tectonic plates a few
centimetres a year. The heat that ‘drives’ the plates is caused by
radioactive decay of uranium and thorium in the core and mantle.
Plumes are concentrated zones of heat. They bring magma to the
surface. When magma reaches the surface it is known as lava.
Pangea was a ‘super
continent’ (when all the land
masses were joined
together). This diagram
shows the position of the
continents 250 million years
ago. They are still moving
apart today!
Make sure you learn how each of the plate boundaries works and know what
sort of tectonic activity occurs at each one!
Volcanoes!
So why do people live so close to active volcanoes?
 Minerals - minerals such as tin, silver, gold, copper and even diamonds
can be found in volcanic rocks.
 Geothermal power - heat from underground is used to heat water turning
it into steam to drive turbines and produce electricity, or to heat water
supplies that are then used to provide household heating and hot water.
 Tourism – Volcanoes attract millions of visitors a year. Around the
volcano may be warm bathing lakes, hot springs, bubbling mud pools and
steam vents.
 Fertile soils – Cool lava needs hundreds of years to become weathered
and broken down before they form rich soils. When they do become soils
though, they form some of the richest ones on the planet.
 Poverty – Some people in LEDC’s are not able to move away from a
potentially dangerous volcano as they are too poor.
 Religious beliefs – e.g. the Aetas who live around Mt Pinatubo believe the
volcano is a ‘God’
Case study: Mt Pinatubo (Indonesia - LEDC)
Case Study: Sakurajima (Japan - MEDC)
Sakurajima is a stratovolcano
so is dangerous and
explosive. Why do you think
people in an MEDC such as
Sakurajima live close to it?
(write your ideas below)
What effects do volcanic eruptions have?
Social Effects
People are killed by
the explosion /
pyroclastic flows /
lahars and poisonous
gases!
Homes are destroyed
People can be injured
from harmful gases /
debris etc.
Economic Effects
Environmental Effects
Tourism can be affected
The environment can
(positively and negatively) be severely altered
e.g. forests completely
Crops can be destroyed
blown away in the blast
by lava / ash and
of the eruption
pyroclastic flows
Wildlife will not survive
Communications can be
a violent eruption
destroyed (e.g. roads /
railways)
So how can volcanic eruptions be predicted?
Are there different types of volcano?
There are three different types of volcanoes. The different types of volcanoes are: composite (or
stratovolcanoes), shield and cinder cones.
Layers, or strata, of rock and lava form the Composite or Stratovolcanoes. These volcanoes
come in a number of shapes. A composite volcano resembles a helmet. The sides of this type of
volcano are usually steep, some reaching a pointy peak at the top. This is because the lava is
viscous and so ‘plies’ up quickly forming steep layers. Sakurajim in Japan and Mt Pinatubo in
Indonesia are both good examples. Eruptions are particularly intense. As magma rises to the
eruption point, it tends to get clogged due to high viscosity. The pressure needed to force the
magma out of the volcano is huge, and the result is an explosion of both rock and lava. It is quite
dangerous to witness such an eruption up close.
Shield volcanoes are huge in size. They are built by many layers of runny lava flows (the lave
is not very viscous). Lava spills out of a central vent or group of vents. A broad shaped, gently
sloping cone is formed. This is caused by the very fluid, basaltic lava which can't be piled up
into steep mounds. Shields erupt frequently, but tend not to be highly explosive. These are
some of the best volcano eruptions to witness at a relatively close, but still safe, range, since
lava spray is uncommon. Both Mauna Loa and Kilauea in Hawaii are examples of the shield
volcano. Shields also form on the ocean floor, gradually building height through a steady stream
of magma.
Cinder cones are likewise relatively gentle in eruption. They tend to occur in mountain ranges
with other types of volcanoes. A central vent forms a volcano made up of lava fragments.
Cinders grow quickly but tend not to exceed about 800 feet (243.84m) in height. Occasionally,
cinders form on ground with no known history of volcanic activity. In 1934, Paricutín erupted out
of a Mexican cornfield and in approximately five days, grew to 300 feet (91.44m) tall.
Tip: You will need to be able to explain
how each of the volcano types above
forms.
A comparison of two different volcanoes:
Philippines - Mt Pinatubo
Iceland - Eyjafjallajokull
Type of volcano: Composite
Type of volcano: Shield
The lava is viscous. This means that
as is solidifies the cone becomes
steep sided. It erupts with violent
force due to the viscosity of the lava
(the main vent can often get blocked).
The lava is less viscous and ‘runny’.
This means that it flows freely. It will
cover a larger surface area and as
the lava solidifies it will create a
gently sloping volcano.
Tectonic plates responsible:
The Philippines plate (oceanic)
subducted beneath the Eurasian
plate (continental). This is a
destructive plate boundary.
Tectonic plates responsible:
The Eurasian plate and the North
American plates are pulling apart.
This is a constructive plate
boundary.
Date last erupted: June 1991
Date last erupted April 2010.
Social effects:
1500 people died
50,000 people made homeless
Water contaminated
Social effects:
500 – 600 people evacuated
Roads closed / travel made difficult
People stranded around world due
to travel chaos
Schools closed in parts of Iceland
Economic effects:
Millions of pounds lost in travel
industry
Thick layer of ash erupted has made
farming impossible in parts of
Iceland
Economic effects:
200,000 buildings destroyed
Lahars devastated rice harvest
1 million farm animals died
650,000 people lost their jobs
Earthquakes!
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The focus is the point at which the earthquake starts.
The epicentre is the point directly above the focus point.
Earthquakes are measured using a seismometer.
The magnitude of an earthquake is sown on the Richter Scale.
A comparison of two different
earthquakes:
Kobe (Japan) 1995
Sichuan (China) 2008
Magnitude: 7.2
Magnitude: 8.0
Plates responsible: The
Philippine plate is subducted
beneath the Eurasian plate. This
is a destructive plate boundary.
Plates responsible: The Indian
plate and the Eurasion plate
colliding (Making the
Himalayas). This is a collision
plate boundary.
Depth of Focus point: 14km
Depth of Focus point: 19km
Location of epicentre: Awaji
Island
Location of epicentre:
Wenchuan
Deaths: 5,477
Deaths: 70,000
Injuries: 35,000
Injuries: 400,000
Buildings collapsed: over
172,000
Building collapsed: 420,000
Total damage: 10 billion yen!
Other facts: Soft ground
(unconsolidated land) made the
shaking worse.
Total damage: $75 billion
Other facts: 700 schools
collapsed! – This should not
have happened due to strict
building codes.
Japan is an MEDC whereas China has only recently become an NIC (Newly
Industrialised Country) and is still comparatively poor. How do you think their
level of development affected the way in which they prepared themselves for
earthquakes / coped with the event itself?
Restless Earth Question Checklist – make sure you can
answer these using this guide and your exercise books!
1. Draw a diagram to show the layers of the earth.
2. State two differences between oceanic and continental crust.
3. Explain why plates move.
4. Explain the term “ subduction “ when does it occur? You can draw a
diagram if you wish.
5. Why are no volcanoes found at collision boundaries?
Battle for the
Biosphere
6. Describe the main features of shield volcanoes. ( mention shape,
frequency of eruption and type of lava)
7. Describe the main features of composite volcanoes. ( mention shape,
frequency of eruption and type of lava)
8. Which type of country developed or developing is more vulnerable when
experiencing tectonic hazards? Why, use examples you have studied.
9. Compare the effects of a volcanic eruption is a developed and developing
country ? Use named examples.
10.Why are some areas of the world more likely to experience tectonic
hazards than others?
11.Why do earthquakes occur?
12.How are they measured?
13.Explain the terms, epicentre, focus, seismometer, seismograph
14.What is the differences between primary and secondary impacts of a
volcanic eruption or earthquake?
15.Why do earthquakes occur at destructive plate margins?
16.How can earthquakes and volcanoes be predicted and planned for?
17.How can buildings be protected from earthquakes?