This document summarizes the three types of plate boundaries: 1) When an oceanic plate meets a continental plate, the oceanic plate is subducted beneath the continental plate. This can form deep trenches and volcanic island arcs. 2) When two oceanic plates meet, one plate subducts beneath the other, forming ocean trenches and island arcs offshore. 3) When two continental plates meet, they are forced upwards to form fold mountains rather than subducting. This leads to earthquakes but no volcanic activity. Mountain ranges like the Himalayas and Andes are examples of this type of plate boundary.

1. By Natasha Ann Morrison.. 

2. 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 continental
plate
Oceanic plate moves towards another oceanic
plate
Continental plate moves towards another
continental plate
•Oceanic plate moves towards a continental
plate
Oceanic plate moves towards another oceanic
plate

3. What happens when an oceanic
plate and a continental plate meet?
Oceanic crust is denser than
continental crust. Therefore,
when the two plates meet, the
oceanic plate is forced beneath
the continental plate. This is
called Subduction.

4. Deep Trench!
On the surface, where the 2 meet,
a deep trench can be formed.

5. Example
Off the Western coast of South
America, the Nazca plate is being
forced underneath the South
American Plate.
This has led to the formation of the
Peru-Chile Trench. It is 8065m
below sea level at its deepest point
and is roughly 3700m long.

6. Peru-Chile Trench

7. As the oceanic plate descends , heat is
generated by the friction of the two
plates meeting. This causes the oceanic
plate to melt and turn back into magma
in an area of the subduction zone known
as the Benioff zone. The magma rises
through 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.

8. Example
The West Indies in the Carribean are an
example 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.

9. Sediment that has accumulated on
the continental shelf on the margin
of the land mass are deformed by
folding and faulting.

10. Folding is when rock is bent by pressure and
heat, forcing the shape of it to be altered.

11. Extreme stress and pressure can
sometimes cause the rocks to shear along a
plane of weakness creating a fault.

12. 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 are
7000km long and 700km wide, reaching an
average height of 4000m

13. The Andes

14. Another feature which is common
at this fault is an earthquake. This
is caused by the increase in
pressure along the line of the
subducting plate.

15. What happens when an oceanic plate
meets an oceanic plate?
When oceanic plates meet, one is forced
underneath the other and the processes
of subduction begin. Because two
oceanic plates are meeting, this plate
boundary always occurs offshore.
Ocean Trenches and Island Arcs
are the features associated at this
type of boundary.

16. Example
On the Western side of the Pacific
ocean, the Pacific plate is being
subducted underneath the smaller
Philippine Plate. A very deep trench has
been formed, known as Mariana’s trench
and an island arc has also been formed.
This island arc consists of volcanic
islands including Guam and the
Marianas, which have been formed by
upwelling magma from the Benioff zone.

18. What happens when a continental
plate meets a continental plate?
When two continental plates meet,
not much subduction happens,
because they have lower densities
than the layers of the Earth beneath
them. Instead, as the plates move
towards each other, their edges and
the sediments between them are
forced upwards to form fold
mountains.

19. 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.

20. 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. The
highest mountain on the planet, Mount
Everest (at 8848m), belongs to this
mountain range. The Himilayas are
350km wide and 3000km long.

21. The Himalayas

22. Thank You for watching Tasha’s
presentation..!