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Plate tectonics

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´╗┐Helena Bonici Geography 20/06/2011 12EA2 Plate Tectonics Plate Movement Plates Separate - Divergent The Mid-Ocean Ridge and rift valleys, such as the one that runs through eastern Africa, occur along boundaries where plates are spreading apart. New oceanic crust is created as the plates separate and molten rock rises up from the mantle and fills the space. The earthquakes and the volcanic eruptions along the Mid-Ocean Ridges are a direct result of this process. Plates Collide - Convergent When two plates carrying continents collide, the continental crust buckles and rocks pile up, creating towering mountain ranges. The Himalayas were born when the Indian subcontinent smashed into Asia 45 million years ago. ...read more.


Powerful earthquakes often strike along these boundaries. The San Andreas Fault is a transform plate boundary that separates the North American Plate from the Pacific Plate. This fault system is largely responsible for the devastating earthquakes in Los Angeles and San Francisco. The surface of the Earth is broken into rigid plates. These plates are 100 to 120 kilometres thick and include the crust and a small part of the upper mantle. Many plates contain both continental and oceanic crust. The plates sit on top of a softer, more plastic layer of the mantle called the asthenosphere. All of the plates are in constant motion, some moving faster than others. They move in different directions at about five centimetres each year on average. ...read more.


The Earth?s core sets up a very strong magnetic field for planet Earth. When hot lava erupts on the ocean floor and cools it not only crystallizes, but it also becomes magnetic. This is because the magma that seeps from the Earth?s mantle has a lot of iron in it. The magnetic crystals in the cooled lava have become little magnets, all pointing in the direction of the magnetic field of the Earth. The more of these little magnetic crystals there are in a rock, the stronger the magnetic signal of the rock is. The lava erupted on the seafloor is the most magnetic because it has the smallest crystals. The crystals have no time to grow any larger because the cold, near freezing seawater at the bottom of the ocean makes the lavas cool very fast. ...read more.

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