How does the theory of plate tectonics help to explain the world distribution of earthquake and volcanic zones? The Earth’s crust is made up of seven major plates and several smaller plates. These plates drift on top of the mantle. When two plates meet, they can either be constructive, destructive or conservative. At a conservative plate margin, one plate moves past another. As the plates are not smooth, great amounts of tension build up and earthquakes are made when the tension is released and the plate moves.
An example of a conservative plate margin is the San Andreas Fault. The North American plate moves South West at 5cm a year, whereas the Pacific plate moves North West at just 1cm a year. At a destructive plate margin, plates move towards each other. When an oceanic crust meets a continental crust, the denser oceanic crust is forced under the continental plate and melts due to friction and high pressure in the subduction zone. The pressure builds up and is released suddenly, creating earthquakes.
Subsequently, the continental plate is crumpled by the pressure and fold mountains are formed. An example of a fold mountain is the Andes. When two oceanic plates converge, one is usually subducted under another and a deep oceanic trench is formed. The Marianas Trench, for example, is a deep ocean trench created as a result of the Phillipine plate subducting under the Pacific plate. When two continental plates meet, neither is subducted, instead they are pushed upwards.
The collision of the Eurasian plate and the Indian plate pushed up the Himalayas. At a constructive plate margin, plates pull apart from each other. In this case, new land is formed between the diverging plates. An example of this plate margin is the North American plate moving westward, pulling away from the Eurasian plate moving eastward, and creating the Mid-Atlantic Ridge. The Hawaiian islands are evidence of the plate tectonic theory of hot spots.
To the west and to the north of Hawaii is a sting of smaller islands and submerged volcanoes. Geologists believe that a huge column of upwelling lava, a. k. a. a plume, lies at a fixed position under the Pacific Plate. The ocean floor moves over this hotspot, and the upwelling lava creates a steady succession of new volcanoes that migrate along the plate. Kilauea is still rumbling because the island has yet to move off this hotspot.
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