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Unit 1 Physical Geography: The Restless Earth
Unit Lessons
•
Why is the earth’s crust so unstable?
•
What happens at plate margins?
•
How are our highest and deepest places created?
•
How do people use an area of fold mountains?
•
How and where are volcanoes created?
•
How do volcanoes affect people?
•
How can we monitor volcanoes and predict eruptions?
•
What is a supervolcano?
•
What are earthquakes and where do they occur?
•
What were the causes, effects and responses to the Kobe earthquake?
•
What were the causes, effects and responses to the Port au Prince
earthquake?
•
Why is a tsunami hazardous?
Independent study
•
An account of the uses of fold mountains and adapting to life in Livigno, The
Alps
•
A report of the eruption of Mount St Helens, USA on 18th May 1980
•
A comparison of the earthquakes in Kobe, Japan and Port au Prince, Haiti
L
What happens at plate margins?
Learning Objectives
• To know what happens at a destructive-subduction, constructive
and conservative margins
• To understand how plate margins create different types of tectonic
activity
Key terms: Subduction, ocean trench, mid-ocean ridge, volcanic islands, collision, fault,
friction
Starter
How is the structure of the earth like an apple?
Recap Questions
• Which layer do convection currents occur in?
• Which is the thinnest layer?
• What are the two types of crust? Give a difference between
them.
Distribution of plate margins and tectonic activity
• Plate margins
are unstable
parts of the
crust.
• This is where
most tectonic
activity occurs.
• The direction of
plate movement
determines the
type of plate
margin and the The Where
three types
ofmost
plate of
margin
we will look
at in
is the
the world’s
tectonic
type of tectonic
more
detail
are:
activity?
Why
is
this?
activity
1. Destructive – subduction
Remember tectonic activity means
volcanoes
2. Constructive
and3.earthquakes
Conservative
Plate Margins
• Plate margins (sometimes called boundaries) are where two
plates meet.
• Remember plates are just huge slabs of rock. But they move in
different directions.
• If they crash into each other then
it will be quite disastrous. This is
called a destructive boundary.
• If they slide past each other then
they will shake each other. This is
called a conservative boundary.
• But if they move away from each
other, then they will form new
land. This is called a constructive
boundary.
Destructive boundary
Conservative boundary
Constructive boundary
Types of plate margin
Destructive (subduction)
plate margins
Violent volcanic
eruptions
Continental plate
(North American
Plate)
Pacific Ocean
Hot liquid rock
(magma) rises
Oceanic plate (Juan
de Fuca Plate)
Oceanic plate
subducted beneath
continental plate
Earthquakes caused
by subducting plate
Mantle
Friction and heat
from mantle
melts plate
Types of plate margin
Constructive plate
margins
Over years volcanic
islands may form as
the mid-ocean ridge
breaks through the
surface of the water
(e.g. Iceland)
Magma forms
underwater
volcanoes and the
lava creates a midocean ridge (e.g.
Mid-Atlantic Ridge)
Oceanic plates are
forced apart
Rising less
dense magma
Convection currents
in mantle
Types of plate margin
Conservative plate
margins
Ocean
Pacific Plate
Crust is neither
made nor destroyed
North American
Plate
San Andreas Fault
Plates are sliding past one another, yet at different angles and different speeds. Friction
means they get caught on each other, the pressure builds and then is suddenly released
as they jolt into a new position. This is an earthquake. No volcanoes at this margin.
Exam Technique Explanation
Explanation is an important technique. It is done best using clear, ordered
sentences. Higher level explanation will include key terms and diagrams.
1.
Explain how volcanoes occur
at destructive margins? (4
marks)
The oceanic plate is subducted
beneath the continental plate,
as it is denser. As it moves into
the mantle it melts. The
magma rises and breaks
through the continental plate,
forming a violent volcanic
eruption.
Continental plate
Oceanic plate
Mantle
Plate
subducts
and melts
Volcano
Magma
rises
Exam Technique Explanation
Explanation is an important technique. It is done best using clear, ordered
sentences. Higher level explanation will include key terms and diagrams.
2.
Explain how volcanoes occur
at constructive margins? (4
marks)
Two oceanic plates are pulled
apart, magma from the mantle
rises and reaches the ocean
bed. It cools and forms
underwater volcanoes (known
as shield volcanoes). These
volcanoes may reach the
surface of the sea, becoming
volcanic islands (e.g. Iceland).
Sea
Oceanic plate
Mantle
Lava cools to form
shield volcanoes
Oceanic plate
Magma rises
and reaches
the sea bed
Exam Technique Explanation
Explanation is an important technique. It is done best using clear, ordered
sentences. Higher level explanation will include key terms and diagrams.
3.
Explain how earthquakes
occur at conservative margins?
(4 marks)
Two plates slide past one
another. Friction means they
get caught on each other, the
pressure builds and then is
suddenly released as they jolt
into a new position. This is an
earthquake.
Friction causes pressure to build
up between the plates
Plates slide past in opposite
directions.