Volcanic Case

The plate tectonics theory was put forward by Alfred Wegener suggesting that the continents were at one point all conjoined in one supercontinent known as Pangaea. He then suggested that Pangaea had drifted apart through the movement of plates to give us the current position of continents we have today. Wegener's theory was linked to a variety of evidence, however it took further research and evidence for this to become a leading theory. This means that although volcanic and seismic events help to prove the plate tectonics theory valid, there is also a range of other factors involved.

Vulcanicity is the surface presence of Magma within the Earth's crust. Whereas seismicity is where the build up of pressure in the crust is released. Both volcanic and seismic activty when plotted on a map can be seen to follow certain patterns and it is this distribution that helps explain the plate theory. The distributions of earthquake events are found in broad, uneven belts around plate margins and it is the movement of the plates that cause the seismic events. Most of these earthquakes occur along destructive margins, where the heavier oceanic crust descends underneath continental crust. A build up of pressure here, where no subduction takes place for a space of time, eventually leads to a large slippage of the oceanic plate causing shockwaves to rip through the surrounding area, an example of this is the 1995 earthquake in Kobe, Japan where the plate slipped over 1m. Earthquakes are also common however at conservative margins, where plates slip past each other and the build up of friction can cause seismic activity regularly. The San Andreas fault for example in California is a conservative margin and the fault lines show where the crust has failed, the slippages of plates here caused the 1989 San Francisco earthquake. These seismic events thus prove that the plate tectonics theory is valid as the movement of plates is ongoing, as well as land being created and destroyed and the effects of this can be seen through the earthquakes observed on the earth's surface today.

Volcanic events and their distribution also shows tell tale signs of the presence of plates and are often found at destructive plate margins, where in many cases the oceanic crust is forced below the continental crust,