Transcript Lesson 1
This term we will be looking at the power of Earth to take away life. We will be studying Yellowstone supervolcano, the ghost city of Plymouth, the killer quake that hit Haiti and the deadly Japanese tsunami. Risky World L To explain the structure of the Earth and its unstable nature To describe the location of volcanoes and earthquakes To discover the four different types of plate boundaries Where is the most risky place on Earth? Key terms: Crust, convection currents, destructive boundary, constructive boundary, conservative boundary Starter 2011 was a particularly bad year for natural disasters – from tsunamis to volcanoes. Watch the clip and think about the questions below? Do you think the world getting riskier? Why? Who is most at risk from natural disasters? Why? Discuss with your neighbour. Some interesting points Do you think the world getting riskier? Why? The world isn’t really getting any more risky, but we are growing as a race. The world population now stands at 7 billion. With more people around there is inevitably more risk. Who is most at risk from natural disasters? Why? The people most at risk are those people who live near plate boundaries. These areas are where you get most earthquakes and volcanoes. We’ll see why later… but first we need to recap the Earth’s structure. The Structure of Earth TASK Fill in your structure of the Earth sheets The Unstable Crust The crust is made of rock. But it is not a smooth, unbroken surface. The crust a cracked, broken surface like a jigsaw. Each broken piece of the crust is called a plate. The Plates Eurasian North American Pacific South American African Plate Nazca Indo Australian Plate Antarctic Remember the the arrows). TASKplates Label move your (shown plates by map. They move at the rate your finger nails grow. Why do the plates move? Crust Convection Currents Mantle The mantle is hotter nearer the outer core (about 5000 degrees Celsius) and cooler nearer the crust (about 1,300 degrees Celsius). The hotter magma is less dense, so it rises up from the outer core and moves towards the crust. When it meets the crust it cools, and falls back towards the core again. This creates giant convection currents. These currents move the plates on top. Tectonic activity This map shows where recent earthquakes and volcanoes have taken place Where Plate you find plate boundaries Like your map boundaries this shows you will plate find boundaries. tectonic What do you activity. notice about Here’s the two why… maps? Plate Boundaries • Plate boundaries (sometimes called margins) 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 one each 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. Two types of plate •There B are two types of plate to remember: oceanic plate and continental plate. Oceanic plates have oceans or seas on top of them. They are heavier and can sink into the mantle (e.g. Pacific Plate) Continental plates have large continents and land masses on top of them. They are lighter, older and cannot sink into the mantle (e.g. North American Plate) Types of plate boundary Destructive plate margin Violent volcanic eruptions Pacific Ocean Continental plate Hot liquid rock (magma) rises Oceanic plate Oceanic plate goes beneath continental plate because it is denser (heavier). Earthquakes caused by plates rubbing together Mantle Friction and heat from mantle melts plate Types of plate boundary Constructive plate margin Over years volcanic islands may form as the volcanoes break through the surface of the water (e.g. Iceland) Magma forms underwater volcanoes Oceanic plates are forced apart Rising magma Convection currents in mantle Types of plate boundary Conservative plate margin Ocean Pacific Plate Crust is neither made nor destroyed North American Plate San Andreas Fault Plates are sliding 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. Recap Questions 1. What are the 4 layers of the Earth? 2. What are the two types of plate? How are they different? 3. Why do plates move? 4. Name the 3 plate boundaries and outline what happens at each. When plates collide So this is what happens when plates collide. Count your lucky stars that we live hundreds of miles away from a plate boundary.