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plate tectonic theory

By Tkmax100 Nov 03, 2014 1107 Words
“Evaluate how plate tectonics theory helps our understanding of the distribution of seismic and volcanic events” (40 marks) The theory of plate tectonics was first introduced by Alfred Wegener in 1912. He observed the continents an could see they interlock like a jig saw puzzle, for example the West African Coastline fits snugly into the South American coastline, he suggested that at one point in time there was only one giant continent called “Pangea”. Later evidence was found that proved this theory as the fossil remains of a dinosaur, the Mesosaurous was found along the coast of Brazil as well as along the coastline of Gabon, also fossilised pollen species and rock sediments were both found along these coastlines. This further demonstrated that Wegener’s theory was accurate. Wegener’s ideas were proved further right and built upon our understanding of tectonic activities. Sea floor spreading was discovered showing that rock is being created and destroyed, this lead us to believe that plates and plate boundaries existed. The mid-Atlantic ridge is a constructive plate boundary where by the Eurasian and North American plates are moving apart, this allows magma to rise creating new plate material. This has created the island of Iceland which in itself has rift valleys which are evidence so support the plates are moving apart. Carbon dating has helped prove this theory as the crust nearer to the UK is much older than the crust along the mid-Atlantic ridge. Paleomagnetism is where metallic elements in the crust are aligned in opposing layers. Every couple 1000 years the earth’s polarity flips, this means that every time the metallic elements align themselves in the opposite direction. In the case of constructive plate boundary plate tectonic theory has helped our understanding as we can now determine that at constructive pate boundaries fissure volcanoes are more common here, therefore suggesting the nature of a potential eruption may not be as destructive as a composite volcano. Muchseismic activity and volcanic activity can be found along the Pacific Ring of Fire. Running close by parallel to these boundaries were very deep ocean trenches eg the Marianas Trench, which were the deepest parts of the ocean. Scientists realised that the ocean trenches showed that some plates are subducted. Here an oceanic plate which is denser would subductunder a continental plate; the plate would liquefy inside the mantle creating a pool of magma which would rise through the cracks in the rock forming a volcano. This addition to the plate tectonic theory explained why volcanoes are more or less always found along plate boundaries which are destructive, due to rising magma and destructive, due to plate melting. However plate boundaries are different. Many earthquakes are distributed along the Eurasian/Indo-Australian plate boundary where there are no volcanoes. There are very high mountains here such as the Himalayas. The theory of plate tectonics explains that oceanic plates, because they are denser, always subduct continental plates. Here two continental plates meet – so scientists developed a theory that Fold Mountains were created. The two plates converge; neither subducts the other as they are of similar density, they both push each other up due to the force acting on them by convection currents, creating fold mountains. Pressure builds and eventually the plates fault upwards, breaking and adding to the creation of the Fold Mountains. The build-up of pressure and sudden faulting explained why so many earthquakes occurred along this boundary, such as in Bam, Iran in 2003. The earthquakes found along destructive plate boundaries such as the Japan earthquake in 2011 were caused by a similar build-up of pressure, because the subducting (Pacific) plate would ‘stick’ to the subducted (Eurasian) plate, pulling it down and then eventually all of this energy would be released propelling the plate upwards creating an earthquake. The volcanoes of Hawaii and Yellowstone are found in the middle of plates. These areas are called hot spots. Hot spots are formed by magma plumes in the mantle which melts the crust at a particular point forming a volcano. The magma plume is stationary and the crust moves over it. This creates a series of volcanoes as can be seen by the many islands in Hawaii. The plume creates a volcano, the crust moves by convection current so the plume would no longer build a volcano there and would start a new one alongside. The old volcano would be eroded by marine erosion until it went under the sea. So hot spots helped to prove plate movement and therefore the theory of plate tectonics. However this has proved how unpredictable volcanic events can be as we would presume they occur on plate boundaries nonetheless we can see that volcanic activity can occur in many different places All the evidence, sea floor spreading, hot spots and subduction proves the plates move. The theory behind this was later developed: those convection currents in the mantle drove movement and slab pull at subduction zones drag the plate across the fairly liquid mantle. This theory proves that there is a general correlation between earthquakes/volcanoes locations and their proximity to a plate boundary. However they onlyexplain where tectonic events generally occur, not specifically plate tectonic theory cannot tell us where along a boundary an earthquake will occur just that an earthquake will occur somewhere along that boundary, also the effects of an earthquake can be felt far away from a boundary. The Boxing Day tsunami in 2004 affected the Maldives which are located on separate plates. Also seismic waves travel and can be felt over a wide area. A very important point to note is that plate tectonic helps the understanding of the educated, particularly in the West. People in LEDCs with poor education will be unaware of plate tectonic theory and many of these are religious, so they will say tectonic events are from god and so plate tectonic theory does not help that understanding because they are not privy to it. In conclusion the recent development of plate tectonics theory has greatly helped our understanding of the distribution of seismic events. We now understand that plates are continually moving and earthquakes and volcanoes are found along these boundaries. Exceptions to this rule such as Hawaii also help prove tectonic theory due to their unique creation. Whilst this has helped our understanding we also recognise the fact those in LEDCs with poor access to education are unaware of plate tectonic theory so the theory will not yet have helped their understanding and may have an effect if such a seismic event was to occur, they would be inadequate services to deal with these situations

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