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The Earth’s Shifting Crust

Chapter 11. The Earth’s Shifting Crust. The Quaking Earth. Earth’s surface is constantly moving An earthquake happens somewhere on Earth about every three minutes An Earthquake is a sudden release of energy that occurs when rocks shift in the Earth’s crust

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The Earth’s Shifting Crust

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  1. Chapter 11 The Earth’s Shifting Crust

  2. The Quaking Earth • Earth’s surface is constantly moving • An earthquake happens somewhere on Earth about every three minutes • An Earthquake is a sudden release of energy that occurs when rocks shift in the Earth’s crust • A Fault is a line of weakness in the rocks of the Earth’s crust

  3. The Quaking Earth (cont.) • In Canada, the greatest earthquake danger is in British Columbia • BC is a region that is crossed by many faults

  4. What causes Earthquake? • They occur when the Earth’s plates grind past one another • The jagged rocks of the crust become locked together and only snap free when the pressure to move builds up • A tsunami is cause when the earthquake shakes the ocean floor • Sometimes a tsunami can cause more damage than the earthquake

  5. Locating and Measuring Earthquakes • Seismographs are used to measure the beat of the Earth • The pen on the seismograph jumps as it records the shock waves created by an earthquake • The epicentre is the point below the Earth’s surface where energy is released as pieces of rock move to new positions along a fault

  6. Locating and Measuring Earthquakes (cont.) • To pinpoint the epicentre • Scientists calculate how far the shock waves travelled to reach three nearby seismograph stations • Next they draw circles of this radius • Find the point where they all meet

  7. Locating and Measuring Earthquakes (cont.) • Richter scale is used to measure the intensity of the earthquake • Richter scale is based on a 10 point system • Scale of 5 is one tenth as strong as 6

  8. Understanding the Movements of the Earth • Surface of the Earth is constantly changing • Fold mountains heave upwards, volcanoes erupt, earthquakes shatter solid rock and faults open in the Earth’s crust • Many mountains, volcanoes, earthquakes, and faults occur around the edges of the Pacific Ocean and in a band across Asia and Europe

  9. Continental Drift • A theory developed by Alfred Wegener • To explain the landform pattern of Earth • Theory suggests that land masses move slowly over the Earth’s surface • Does not explain what causes them to move • Not accepted by scientist because they believed the Earth was solid right through to the centre

  10. Plate Tectonics • Convection currents is when the plates on the Earth’s crust are slowly dragged together, apart, or sideways by the rolling motions of molten rock in the mantle • The mantle is the semi-liquid layer that lies just beneath the crust • Plate tectonics theory suggests that this plate movement creates landform pattern both on land and beneath the ocean

  11. Plate Tectonics and Landform Pattern • The ocean floor is not flat • It contains long, narrow trenches, and mountains • There are as mountains under the ocean as above the ocean on land • Oceans are shallowest in the middle and deepest around the edges • The above things occur when the Earth’s plates move together or apart

  12. When Plates move Apart • Two plates of the Earth’s curst are moving apart in the middle of he Atlantic Ocean at an average rate of about 3 cm per year • The molten rock that pours through the gap has built underwater mountain chain that circles the Earth • Along the ridge new volcanic islands emerge

  13. When Plates move Together • Around the edges of the Pacific Ocean are deep ocean trenches • Ocean trenches are long, narrow, and deep grooves in the ocean floor formed when an oceanic plate has been pulled under a continental plate • The whole range of landform building activity occur here: fold mountains, volcanoes, earthquakes, and faults

  14. When Plates move Together (cont.) • The edges of the Pacific Ocean are the most active regions on Earth • Fold mountains are created as the ocean floor slowly buckles and bends upwards • Deep trenches form as the ocean plate is hauled under the continent • The ocean plate grinds and lock against the underside of the continent, causing regular earthquakes • The earthquakes shatter the crust, causing faults and cracks • The ocean plate melts as it is dragged into the mantle and molten rock moves up through the fault which results in the Pacific Ring of Fire

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