1. Iceland: An example of continental rifting
Iceland has a divergent plate boundary running through its middle
Iceland is located right on top of a divergent boundary. In fact, the island exists because of this feature.
As the North American and Eurasian plates were pulled apart (see map) volcanic activity occurred along the cracks and fissures (see photographs).
With many eruptions over time the island grew out of the sea!
Question: Why don’t we have islands like Iceland where ever we get an Ocean Ridge?
Answer: Scientists believe that there is a large mantle plume (an upwelling of hot mantle material) located right underneath where Iceland has formed. This would mean that more material would be erupted in the Iceland area compared with if there was just the divergent boundary without the plume underneath it.

2. Landforms and features produced at constructive(divergent) plate boundaries in oceanic areas:
Ridges
Submarine volcanoes
Transform faults
Shallow focus earthquakes

3. 1.RIDGES: Where plates move apart in oceanic areas, mid ocean ridges are produced

4. Recap: Formation of Mid-Atlantic Ridge

5. 2.Submarine(shield) volcanoes
The split in the crust provides a low pressure zone where non viscous lava can erupt to form submarine(shield shaped) volcanoes(see later notes)

6. 3.TRANSFORM FAULTS:
As new crust spreads out and moves away from the ridge at different rates, transform faults can occur at right angles to the central rift. This may be necessary , for instance, where the ocean ridge bends.

7. Can you spot transform faults?

8. Transform faults at the Mid Atlantic Ridge(MAR)
4. SHALLOW FOCUS EARTHQUAKES:
AS SECTIONS OF THE CRUST SLIDE PAST ONE ANOTHER, SHALLOW FOCUS EARTHQUAKES ARE CREATED, ORIGINATING CLOSE TO THE SURFACE ( see further notes on earthquakes)

9. RIFT VALLEYS LAKES VOLCANOES
Landforms produced at constructive(divergent) boundaries in continental regions:
RIFT VALLEYS LAKES VOLCANOES

10. Landforms produced at Constructive (divergent) margins in continental areas
1.Where plates move apart in continental areas, they produce rift valleys and eventual new areas of oceanic floor

11. Web geology animations (Diverging plates)

12. You tube clip and lecture- East African Rift valley formation
(not working at present… )

13. You tube clip using plasticine to explain...
(N.B. Arabian plate label is wrong- should be Somalian!)

14. E. Africa’s Active Rift System
The African and
‘sub plates’ (Nubian
and Somalian)
plates
are moving
away
from each other
and from the
Arabian plate…It
is a triple junction
This is an
‘ACTIVE RIFT
SYSTEM’

15. The rift is like the crust breaking on top of a loaf of bread as it comes out of the oven…yum!

16. How are rift valleys formed?
At constructive(divergent) plate boundaries in CONTINENTAL areas such as in East Africa, the brittle crust fractures as sections of it move apart due to a hot mantle plume beneath which forms a dome.
Areas of crust drop down between parallel faults to form RIFT VALLEYS.
The largest of these is the African rift valley which extends 4000km from Mozambique to the Red Sea.

18. Inward facing steep scarps

19. Gulf of Arabia Red Sea Out of Africa! Did Moses cross the ocean?
Divergent (constructive) margins
Gulf of Arabia Red Sea
Out of Africa!
Did Moses cross the ocean?

20. Here, rifting continues and new sea floor is forming between Africa on the SW side and Arabia on the NE.
The Red Sea is therefore a newly forming ocean..
50 mill years from now East Africa may detach itself from the rest of Africa!

21. VOLCANOES TOO!
The area is also associated with volcanic activity( for example the highest mountain in Africa, Kilimanjaro and Mt Kenya)

22. E.G:‘Erte Ale’ volcano , Ethiopia( with a permanent lava lake in the crater)
See Ian Stewart absailing down to the crater in ‘Power of the Planet-Volcano!’

25. And Lakes!
Lakes are often found in the valleys where the central plateau has subsided(like taking a cake out of the oven too soon!) for example Lake Victoria:

26. East African Rift Valley System
Lake Victoria

27. Earthquakes can also happen.
E.g Karonga Earthquake, S.E African Rift, North end of Lake Malawi..

28. In Summary: Constructive boundaries in oceanic areas:
KEY PROCESSES:
Sea floor spreading
Seismicity
Vulcanicity
VULCANICITY:
Non viscous,effusive
Gentle
Basaltic
Shield shaped
LANDFORMS PRODUCED:
Ocean ridges
Submarine volcanoes
Volcanic islands
SEISMICITY:
Transform faults
Shallow focus earthquakes

29. H/W
1. Go onto Weebly and make sure that all notes are complete
2. Draw a fully labelled diagram of the processes happening at a constructive (divergent) plate boundary on p.26