PLATE BONDARIES

Divergent Plate Boundary

At a divergent boundary a new crust will be created as two plates pull away from each. It may cause the ocean to grow wider. Iceland is a prime example of a divergent boundary as the Mid Atlantic Ridge is located here between the North American and Eurasian plates. The North American plate is moving westward and the Eurasian eastward as a result new crust is created on both sides of the boundary. The new crust creates a rift along the boundary which means that at some point in the future Iceland will seperate and the water of the Atlantic will sill the widening gap between the two plates.

Convergent Boundaries

Here crust is destroyed as on plate slides underneath another, and is then reused in the interior of the Earth as. The area where one plate goes beneath another is known as a subduction zone and at these sites mountains and volcanoes can often be found.

Oceanic-Oceanic Convergence

At an oceanic-oceanic convergence one plate is normally subducted under another forming a deep oceanic trench. They can also result in the formation of underwater volcanoes, the debris and lava from these volcanoes will build up over millions of years until a submarine volcano rises above sea level to become an island volcano. Theses usually create a string of volcanoes called island arcs which have been formed in the same way. 

Oceanic- Continental Convergence

When the oceanic plate pushes in to the continental plate it is subducted causing the continental plate to lift upwards and form a mountain range. The oceanic plate will sink in to the subduction trench but the deepest part of the subducting plate begins to break in to smaller pieces which become locked for long periods of time. These can then suddenly move due to the increased pressure and cause a large earthquake which may cause an uplift of the land, sometimes by as much as a few meters. 

Continental - Continental Convergence 

The boundary where two continents meet head on, neither will become subducted because of the light weight of the continental rock. The crust will instead be pushed upwards or sideways under the pressure. A prime example of a continental-continental convergence is the Asia and Eurasia collision 50 million years ago where the Eurasia plate crumples upwards and overrode the Indian Plate, this lead to the slow formation of the Himalayas and the Tibetan Plateau. 

Transform Fault Boundaries 

Transform boundaries occur when two plates are moving past each other horizontally, these are usually found along the bottom of the ocean floor. The San Andreas fault in California is a transform fault line which occurs on land, it connects the East Pacific Rise with the South Gorda Explorer Ridge. The fault is approximately 1, 300km long and in places it is tens of kilometers wide, the Pacific plate has been moving past the North American plate for almost 10 million years at an average rate of 5 cm/ yr.  

To teach the different types of plate tectonics I thought that it would first be useful to use a world map to locate the seven main plates which make up the crust. Then we could identify the features which occur along the plate boundaries and possibly match these to the specific types of boundaries.