Discuss the Degree to Which the Theory of Plate Tectonics Is Supported by the Distribution of Volcanic and Seismic Activity Across the Globe (40)

The initial theory of why the plates moved was developed by Alfred Wegner (1880-1930). In 1912 Wegener suggested that the continents were once joined as the super continent Pangaea, he then suggested that the earth’s crust was divided into 7 large plates. He said that the plates were solid and rigid and floated like rafts on the earth’s asthenosphere and they were moved around by convection currents below them. Wegner gathered much evidence to support this. Some being geological evidence in which he found coal deposits of a similar age found in the UK and North America but coal can only be formed in tropical conditions suggesting that the UK and North America must have once been next to each other and near the equator. Also evidence to support this theory is backed up by the distribution of volcanoes and earthquakes. They back up this theory because at the plate boundaries they occur on the two plates have to move, therefore backing up Wegner’s initial theory that the earth’s crust is divided up and moves around.

One process which backs up Wegner’s theory are volcanoes. This is because volcanoes occur on destructive and constructive boundaries. At a constructive boundary for a volcano to occur the two parts of continental crust are moving away from each other with then allows basaltic lava up through the crust and as the lava cools on the sea floor a volcano is formed. Then eventually over time as more lava is let out through the volcano due to its effusive eruptions a larger shield type volcano is created, for example the newly formed (1964) island of Surtsey. This process at constructive plate boundary backs up Wegner’s theory because if the two plates didn’t move apart in the first place then lava couldn’t come out through the ground therefore his theory is largely supported by the distribution of volcanoes at constructive boundaries. Also another area where volcanoes are found is at destructive plate boundaries. This is where the heavier oceanic crust sub-ducts underneath the lighter continental crust and due to the earths asthenosphere being very warm it results in a Benioff zone, an area where destructive plate is melted. Due to the Benioff zone magma is then forced upwards through the continental crust creating a very un-predictable and explosive volcano, an example of this would be when the NAZCA plate sub-ducts underneath the Brazilian shield plate. This also supports Wegner’s theory of plate movement because for a volcano to form at a destructive boundary the oceanic plate has to move underneath the continental crust which tells us that the plates do move and the distribution of volcanoes at destructive plate boundaries supports his theory.

A second process which supports Wegner’s theory of plate tectonics is earthquakes. Earthquakes support Wegner’s theory because they occur on destructive and conservative plate boundaries. This supports Wegner’s theory because for earthquakes