This type of plate boundary can also be called a Convergent Plate Boundary.They can occur in one of 3 different situations:Oceanic plate moves towards a continentalplateOceanic plate moves towards another oceanicplateContinental plate moves towards anothercontinental plate•Oceanic plate moves towards a continentalplateOceanic plate moves towards another oceanicplate
What happens when an oceanic plate and a continental plate meet? Oceanic crust is denser than continental crust. Therefore, when the two plates meet, theoceanic plate is forced beneath the continental plate. This is called Subduction.
Deep Trench!On the surface, where the 2 meet, a deep trench can be formed.
Example Off the Western coast of SouthAmerica, the Nazca plate is being forced underneath the South American Plate.This has led to the formation of the Peru-Chile Trench. It is 8065mbelow sea level at its deepest point and is roughly 3700m long.
As the oceanic plate descends , heat is generated by the friction of the twoplates meeting. This causes the oceanic plate to melt and turn back into magmain an area of the subduction zone known as the Benioff zone. The magma risesthrough the gaps in the continental plate and can form a volcano if it reaches the Earth’s surface. If the eruptions take place offshore, a line of volcanic islands can be formed called an island arc.
Example The West Indies in the Carribean are anexample of an island arc. They outline the Northern and Eastern edges of the Carribean Sea. The area consists of the Antilles, Bahamas and the Lucayan Archipelago.
Sediment that has accumulated onthe continental shelf on the margin of the land mass are deformed by folding and faulting.
Folding is when rock is bent by pressure and heat, forcing the shape of it to be altered.
Extreme stress and pressure cansometimes cause the rocks to shear along a plane of weakness creating a fault.
These sediments can be uplifted to form fold mountains. An example of this these are the Andes along the pacific side of South America. The Andes are the worlds longest continental mountain range. They are7000km long and 700km wide, reaching an average height of 4000m
Another feature which is commonat this fault is an earthquake. This is caused by the increase in pressure along the line of the subducting plate.
What happens when an oceanic plate meets an oceanic plate? When oceanic plates meet, one is forcedunderneath the other and the processes of subduction begin. Because twooceanic plates are meeting, this plate boundary always occurs offshore. Ocean Trenches and Island Arcs are the features associated at this type of boundary.
Example On the Western side of the Pacific ocean, the Pacific plate is being subducted underneath the smallerPhilippine Plate. A very deep trench hasbeen formed, known as Mariana’s trenchand an island arc has also been formed. This island arc consists of volcanic islands including Guam and the Marianas, which have been formed byupwelling magma from the Benioff zone.
What happens when a continental plate meets a continental plate? When two continental plates meet, not much subduction happens, because they have lower densitiesthan the layers of the Earth beneath them. Instead, as the plates movetowards each other, their edges and the sediments between them are forced upwards to form fold mountains.
As there is little subduction, there is no volcanic activity, but earthquakes are common.Material and sediment can also be forced downwards to form deep mountain roots.
Example The Indo-Australian plate is being forced northwards into the Eurasian plate. What was once the Sea of Tethys has had sediments forced upwards into it in large overfolds to form the Himalayas in Asia. Thehighest mountain on the planet, Mount Everest (at 8848m), belongs to this mountain range. The Himilayas are 350km wide and 3000km long.