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.

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

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

Recap: Formation of Mid-Atlantic Ridge

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)

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.

Can you spot transform faults?

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)

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

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

Web geology animations (Diverging plates) http://ansatte.uit.no/webgeology/webgeology_files/english/plate%20tectonics.html

You tube clip and lecture- East African Rift valley formation https://www.youtube.com/watch?v=NsqxGHb8w6k (not working at present… ) https://www.youtube.com/watch?v=hwA7LXA-SCg https://www.youtube.com/watch?v=3jpbArY2L78

You tube clip using plasticine to explain... https://www.youtube.com/watch?v=APehiE08YVk&noredirect=1 (N.B. Arabian plate label is wrong- should be Somalian!)

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’

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

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.

Inward facing steep scarps

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?

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!

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

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!’...........

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:

East African Rift Valley System Lake Victoria

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

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

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