Transcript 1.4b
Part 1 1.4 © Oxford University Press 2009 Opportunities and risks─Is it rational to live in hazard-prone areas? What are the major landforms found at the plate boundaries? Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What landforms does internal force form at destructive plate boundaries? Use these words Magma currents toHow help you! are converge and destructive createplate compressional boundaries force. They drag formed? the plates towards each other. Towards each other © Oxford University Press 2009 Please click above for animation Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What landforms does internal force form at destructive plate boundaries? Volcanic eruption Continental crust Uppermost part of the mantle Oceanic crust Uppermost part of the mantle Asthenosphere Plate Plate What will happen when two plates collide? Compressional force Subduction zone © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What landforms does internal force form at destructive plate boundaries? Where is the destructive plate boundary? At A, B or C? How do you know? © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What landforms does internal force form at destructive plate boundaries? Destructive plate boundaries can be found at two major belts. How do you describe the distribution of the two belts? Alpine-Himalayan Belt Circum-Pacific Belt They run on land or along land margins. © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What landforms are created where plates collide? Convergence of magma currents Compressional force Continentcontinent collision: Ocean-ocean collision: Two plates with continental crusts at their edges collide Two plates with oceanic crusts at their edges collide © Oxford University Press 2009 The types of landforms depend on the nature of the colliding crusts. Ocean-continent collision: A plate with continental crust and a plate with oceanic crust at their edges collide Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What landforms does internal force form at constructive plate boundaries? Where is the constructive plate boundary? At A, B or C? How do you know? © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What landforms does internal force form at constructive plate boundaries? Constructive plate boundaries can be found in four zones. MidAtlantic zone Mid-Indian zone Antarctic zone © Oxford University Press 2009 South-east Pacific zone Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What landforms does internal force form at constructive plate boundaries? Use these words Magma toHow helpcurrents you! are diverge and create constructive tensional force. plate the They drag boundaries plates apart. formed? Drag apart © Oxford University Press 2009 Please click above for animation Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What landforms are created where plates diverge? Magma currents diverge Tensional force Mid-oceanic ridges © Oxford University Press 2009 Rift valleys Submarine volcanoes and volcanic islands Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What will happen when magma currents continue to diverge? Old oceanic ridges and submarine volcanoes are carried away from the zone of rising magma. The ocean floor is ( shrinking / expanding ) at the zone of divergence. It is called ___________________. sea-floor spreading Will the sea floor spread without limit? Why? © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What landforms does internal force form at conservative plate boundaries? Conservative plate boundaries are found where two plates ______ slide ______ past each other. San Andreas North Fault American Plate Lateral force causes _________. faulting The _____________ San Andreas Fault is located at the conservative plate boundary in California, the USA. © Oxford University Press 2009 San Andreas Fault Pacific (Credit: TomPlate Bean/Corbis) Quit Part 1 © Oxford University Press 2009 Opportunities and risks─Is it rational to live in hazard-prone areas? Quit Part 1 © Oxford University Press 2009 Opportunities and risks─Is it rational to live in hazard-prone areas? Quit Part 1 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Continent-continent collision Eruasian Plate What happens when two plates with continental crusts at their edge collide? Indo-Australian Plate © Oxford University Press 2009 Quit Part 1 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Continent-continent collision Please click above for animation © Oxford University Press 2009 Quit Part 1 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Continent-continent collision Sediment The magma ________ was currents crust deposited ofbrought theinIndo-Australian thethe coastal Indianwaters. subcontinent PlateDue subducted to the oceanic northwards beneath weight ofthe theand Eurasian overlying towards Plate sediment, theatAsian the destructive the continent. layers ofplate sediment boundary were compacted between into them. sedimentary rock. © Oxford University Press 2009 Quit Part 1 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Continent-continent collision Under When The sea the great between two compressional landmasses the plateswere reduced force, getting theinsedimentary size closer andtogether, finally rock neitherup disappeared. folded of and the continental rose up to form crusts ___________________, offold bothmountains plates could subduct called thesince Himalayas. both of them are thick and light. © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 2 Ocean-ocean collision North American Plate When the North American Plate collides with the Pacific Plate, do they create fold mountains? Pacific Plate © Oxford University Press 2009 Quit Part 1 2 Opportunities and risks─Is it rational to live in hazard-prone areas? Ocean-ocean collision How does the denser The submarine volcanoes appear to the Aleutian During the subduction, whatparallel will Pacific Plate move Trench. happen inside the asthenophere whenmay the magma Some of and them above the sea level to become on therise earth’s surface? currents ________________. They finally develop into a chain of volcanic islandsconverge? __________________. volcanic island arc Pacific Ocean Magma rises through cracks Sedimentary rock Volcanic island arc (Aleutian Islands) is folded up Ocean trench (Aleutian Trench) Sediment and Pacific Plate North American Plate sedimentary rock Subducted plate Magma currents converge melts into magma Asthenosphere © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 2. Ocean-Ocean Collision The Philippine Plate collides with the Eurasian Plate Volcanic arc Volcanic island Volcano The Eurasian Plate The Philippine Plate Mantle © Oxford University Press 2009 Quit Part 1 2 Opportunities and risks─Is it rational to live in hazard-prone areas? Ocean-ocean collision Aleutian Islands Kuril Islands Ryukyu Islands Watch a video clip of the formation of Surtsey, a volcanic island in southern Iceland Please click to browse online Marianas Islands Distribution of ocean trenches and volcanic island arcs © Oxford University Press 2009 Quit Part 1 3 Opportunities and risks─Is it rational to live in hazard-prone areas? Ocean-continent collision Nazca Plate © Oxford University Press 2009 What happens when the South American Plate collides with the Nazca Plate? South American Plate Quit Part 1 3 Opportunities and risks─Is it rational to live in hazard-prone areas? Ocean-continent collision Fold mountain The Andes (____________) Reverse faults ________ Volcanoes ____________ Pacific Ocean Ocean trench Peru-Chile Trench Sedimentary rock (________________) Earthquake ____________ _____________ force Compressional Nazca Plate Denser plate _________ subducts and melts into magma Asthenosphere © Oxford University Press 2009 South American Plate Magma rises through cracks Magma currents converge Quit Part 1 3 Opportunities and risks─Is it rational to live in hazard-prone areas? Ocean-continent collision Other example What landform can we find at the destructive plate boundary between the North American Plate and the Juan de Fuca Plate? Fold mountain (The Rockies) © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Aleutian Islands The Aleutian Islands consist of five island groups. This photo shows three of the five island groups from space. The Aleutian Islands (Credit: NASA) © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Mid-oceanic ridges Cracks produced. Mid-oceanic ridge Magma rises from the (Mid-Atlantic Ridge) asthenosphere Atlantic Ocean North Eurasian Plate American Plate Magma A fissure running along the Mid-Atlantic currents Ridge in Almannagjá, Iceland diverge Asthenosphere (Credit: Ng Kim Hung) © Oxford University Press 2009 When the two plates diverge, magma rises from the asthenosphere through the cracks between them, and pushes the plates up at the edges of the crack. Magma cools, solidifies and forms a mid-oceanic ridge. The ridge formed from the divergence of the North American Plate and the Eurasian Plate is called the Mid-Atlantic Ridge It is __________________. the longest in the world. Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Mid-oceanic ridges Mid-Atlantic Ridge What is happening there? © Oxford University Press 2009 The Mid-Atlantic Ridge is not a smooth continuous line since the constructive plate boundary there is broken. Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Mid-oceanic ridges Section II Section I A © Oxford University Press 2009 B The divergence of magma currents drives the two sections, I and II, to spread in the same direction. Between A and B, the movement of plates at both sides is in opposite directions. This part is called a transform fault. Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Rift valleys © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Submarine volcanoes and volcanic islands East Pacific Ridge Cracks develop under tensional force Submarine volcanoes Magma currents diverge Volcanic island (Easter Island) Asthenosphere Formation of an volcanic island along the East Pacific Ridge © Oxford University Press 2009 The divergence of magma currents forms cracks, which extend into the asthenosphere. The pressure of magma is released. Vulcanicity occurs and forms __________ submarine __________. volcanoes When these volcanoes rise above the sea level after repeated eruptions, they form _________ volcanic _________. islands Quit