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 18 th May 1980 A comparison of the earthquakes in Kobe, Japan and Port au Prince, Haiti

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 L

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. Starter

Where is the most of the world’s tectonic activity? Why is this? Remember tectonic activity means volcanoes and earthquakes 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 The three types of plate margin we will look at in more detail are: 1. Destructive – subduction 2. Constructive 3. 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 Pacific Ocean Oceanic plate (Juan de Fuca Plate) Mantle Oceanic plate subducted beneath continental plate Earthquakes caused by subducting plate Friction and heat from mantle melts plate Hot liquid rock (magma) rises Continental plate (North American Plate) Violent volcanic eruptions Destructive (subduction) plate margins

Types of plate margin Constructive plate margins Convection currents in mantle Rising less dense magma Oceanic plates are forced apart Magma forms underwater volcanoes and the lava creates a mid- ocean ridge (e.g. Mid-Atlantic Ridge) Over years volcanic islands may form as the mid-ocean ridge breaks through the surface of the water (e.g. Iceland)

Conservative plate margins Types of plate margin Ocean North American Plate Pacific 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. Crust is neither made nor destroyed

Exam Technique Explanation 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. Explanation is an important technique. It is done best using clear, ordered sentences. Higher level explanation will include key terms and diagrams. Oceanic plate Continental plate Mantle Plate subducts and melts Magma rises Volcano

Exam Technique Explanation 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). Explanation is an important technique. It is done best using clear, ordered sentences. Higher level explanation will include key terms and diagrams. Oceanic plate Mantle Magma rises and reaches the sea bed Lava cools to form shield volcanoes Sea

Exam Technique Explanation 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. Explanation is an important technique. It is done best using clear, ordered sentences. Higher level explanation will include key terms and diagrams. Friction causes pressure to build up between the plates Plates slide past in opposite directions.