1. How are oceans formed?
Continents and ocean basins exist on lithospheric plates that move relative to each
Other. Between their margins, new land is always built or destroyed…

3. How are oceans formed?
New ocean basin is being made in areas such as the mid-Atlantic ridge…
These are referred to as divergent boundaries…
New crust is generated; plates pull away from each other…
Rate of spreading of plates is about 2.5 cm / year.
This would be enough for the Atlantic ocean to form over the
last million years…

4. How are oceans formed?
Iceland stands over the Mid-Atlantic ridge and has been an ideal place for study
of plate tectonics.

5. How are oceans formed?
Krafla volcano in eastern Iceland.

6. How are oceans formed?
The Atlantic ocean was formed by breakdown of Pangaea…

7. How are oceans formed? Formation of the young Atlantic, cont….
Can you think of another
area where this may be
happening today?

8. How are oceans formed?

9. Plate Tectonics
As new land is made in diverging plate boundaries, old land is “destroyed” at
convergent plate boundaries, creating trenches, mountain ranges, etc.

10. Plate Tectonics
So what happens when two plates meet at convergent boundaries?
Ex: Nazca Plate pushes into South
American Plate and is subducted.
South American Plate is lifted,
creating the Andes mountains.

11. Plate Tectonics Continental convergence zones also create
trenches that are thousands of miles long
and 8-10 kilometers deep.
Many of the earth’s active
volcanoes are also found
around these oceanic-
continental convergence zones.

12. Plate Tectonics When oceanic plates meet, one plate
will be subducted. Often, this process
results in formation of trenches:
e.g. Mariana Trench, where Pacific
and Philippines plates meet, is almost
11,000 meters deep!
These are also areas where one sees
island arcs such as the Marianas or
the Aleutian Islands…

13. Plate Tectonics When continental crusts meet, there is only
Partial subduction… Since the continental
Rocks are relatively light, the crusts tend
To buckle and push upward…. Ex: the
Himalayas

14. Plate Tectonics
Sometimes, plates slide by each other (rather than meeting head on), creating
transform boundaries…
San Andreas Fault

15. Plate Tectonics
General Review…

16. Plate Tectonics – Hot Spots
A “hot spot” can develop over a fixed
mantle plume. In these areas, magma rises
to the surface, eventually creating volcanic
islands…
This phenomenon also creates island chains
such as the Hawaiian Islands.

17. How are oceans formed?
How deep?