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Plate Tectonics

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Jai Mehta 11AY 1) 2) a) Plates "float" or move very slowly (a few mm per year) on the molten material of the mantle. Convection currents in the mantle cause this movement. b) Plates meet at plate boundaries or margins. c) Plates that move apart are known as diverging and are constructive, as new features are formed e.g. submarine volcanoes in the Mid Atlantic plate margin. d) Plates that move towards each other are converging and destructive - Fold Mountains, earthquakes, and volcanoes are common. e) Plates which move sideways against each other are conservative margins - material isn't gained or lost, volcanoes are rare and earthquakes are common e.g. San Andreas Fault. f) Pangaea was a single landmass; made up of all the present continents, believed to have existed between 300 and 200 million years ago the rest of the Earth was covered by the Panthalassa Ocean. Pangaea split into two landmasses Laurasia in the north and Gondwanaland in the south, which subsequently broke up into several continents. These then moved slowly to their present positions, due to plate tectonics. Jai Mehta 11AY 3) ...read more.


Since the plates on either side of a transform boundary are just sliding past each other and not tearing or crunching each other nothing happens to the land. Instead, transform boundaries are marked in some places by linear valleys along the boundary where rock has been ground up by the sliding. In other places, transform boundaries are marked by features like streambeds that have been split in half and the two halves have moved in opposite directions. The most famous transform boundary in the world is the San Andreas Fault, shown in the drawing above. The slice of California to the west of the fault is slowly moving north relative to the rest of California. Since motion along the fault is sideways and not vertical, Los Angeles will not crack off and fall into the ocean, as popularly thought, but it will simply creep towards San Francisco at about 6 centimeters per year. In about ten million years, the two cities will be side by side! Although transform boundaries are not marked by spectacular surface features, their sliding motion causes lots of earthquakes. The strongest and most famous earthquake along the San Andreas Fault hit San Francisco in 1906. ...read more.


The crash formed the Andes Mountains, the long string of volcanoes along the mountain crest, and the deep trench off the coast in the Pacific Ocean. Jai Mehta 11AY Destructive collision boundaries, these are places where two continental plates collide causing fold mountains, earthquakes, and volcanoes. Millions of people live in and visit the beautiful mountain ranges being built by plate collisions. For example, the Rockies in North America, the Alps in Europe, the Pontic Mountains in Turkey, the Zagros Mountains in Iran, and the Himalayas in central Asia these were formed by plate collisions. Each year, earthquakes and volcanic eruptions in those mountains kill thousands of people. Occasionally, big eruptions or earthquakes kill large numbers of people. In 1883 an eruption of Krakatau volcano in Indonesia killed 37,000 people. In 1983 an eruption caused mudslide on Nevada del Ruiz in Columbia and it killed 25,000 people. In 1976, an earthquake in Tangshan, China killed an astounding 750,000 people. On the other hand, earthquakes and volcanoes occurring in areas where few people live and therefore harm no one. If we choose to live near destructive collision boundaries, we can build buildings that can resist earthquakes, and we can evacuate areas around volcanoes when they threaten to erupt. 1 ...read more.

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