Constructive margins

Question 1

What happens at a constructive margin?

Answer 1

plates diverge from one another due to opposing convection cell currents. New crust is continually made here so they are young rocks.

Question 2

RIFT VALLEYS

Answer 2

= occur when two continental plates are moving apart.

• as the plates diverge, crust is subject to high pressures causing fracturing and faulting.
• sections of crust between the parallel fault lines sink down.
• the lithosphere was been thinned by tension, resulting in rising magma escaping the surface as volcanoes e.g. Mt Kilimanjaro.

Question 3

RIFT VALLEYS (example)

Answer 3

EAST AFRICAN RIFT VALLEY

• Eastern Africa. North East African plate is moving away from the main plate that is heading North.
• valley consists of 2 parallel rifts that extend for 4000km form Mozambique to the Red Sea.
• lake Tanganyika occurred on the valley floor.

Question 4

OCEAN RIDGES

Answer 4

= the longest continuous uplifted features on the Earth’s surface. (60,000km)

• in some parts can rise 3,000 m above sea level
• depend on rate at which plates move apart
• 10mm/yr leads to a wide ridge at 50km wide, 3,000m deep rift.
• 90mm/yr leads to a smooth crest and no ridge

Question 5

OCEAN RIDGES (volcano example)

Answer 5

SURTSEY (1963)

• submarine volcanoes occur along the ridge. they sometimes rise above sea level after successive eruptions.
• gentle sides due to basaltic lava
• eruptions frequent but gentle

Question 6

OCEAN RIDGES (earthquake formation)

Answer 6

=as new crust forms and spreads, transform faults occur at right angles to plate boundary. spreading plates on either side of faults move at differing rates.
- friction leads to shallow focus earthquakes.