Unit 1 Physical Geography: The Restless Earth

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Unit 1 Physical Geography The Restless Earth

• Unit Lessons
• Why is the earths 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

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What happens at plate margins?
L

• 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
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How is the structure of the earth like an apple?
Starter

• 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.

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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 type of tectonic
  activity

Where is the most of the worlds tectonic
activity? Why is this? Remember tectonic activity
means volcanoes and earthquakes
The three types of plate margin we will look at
in more detail are 1. Destructive subduction
2. Constructive3. Conservative
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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.

Destructive boundary

• 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.

Conservative boundary
Constructive boundary
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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)
Friction and heat from mantle melts plate
Oceanic plate subducted beneath continental plate
Earthquakes caused by subducting plate
Mantle
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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 mid-ocean ridge (e.g. Mid-Atlantic
Ridge)
Oceanic plates are forced apart
Convection currents in mantle
Rising less dense magma
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Types of plate margin
Conservative plate margins
Crust is neither made nor destroyed
Ocean
North American Plate
San Andreas Fault
Pacific Plate
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.
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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.

• 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
Volcano
Oceanic plate
Plate subducts and melts
Magma rises
Mantle
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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
Lava cools to form shield volcanoes
Oceanic plate
Oceanic plate
Magma risesand reachesthe sea bed
Mantle
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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.