Types of plate margin Flashcards
When does a constructive margin occur?
1) A constructive margin occurs where two plates are moving APART (diverging).
2) The mantle is under pressure from the plates above. When they move apart, the pressure is released at the margin.
3) The release of pressure causes the mantle to melt, producing magma.
4) The magma is less dense than the plate above, so it rises and can erupt to form a VOLCANO.
5) The plates don’t move at a similar pace- some parts move faster than others. This causes pressure to build up. When the pressure becomes too much the plate cracks, making a fault line and causing an earthquake. Once his fault lines are made, further earthquakes can occur.
What is an Ocean ridge? (constructive margin creation)
1) Where diverging plates are underwater, an ocean ridge forms. For example, the Mid-Atlantic Ridge is where the Eurasian plate and North American plate are moving apart.
2) Underwater volcanoes erupt along mid-ocean ridges and they can build up to be above sea level. For example, Iceland has been formed by the build-up of underwater volcanoes along the Mid-Atlantic Ridge.
What is a Rift Valley?
(constructive margin creation)
1) Where plates diverge beneath the land, rising magma causes the continental crust to bulge and fracture, forming fault lines.
2) As the plates keep moving apart, the crust between the parallel faults drops down to form a rift valley. For example, the East African Rift System is a series of rift valleys that stretches from Mozambique to the Red Sea- about 4000km. It formed because the Nubian and Somalian plates are diverging. Some parts of the system are hundreds of meters deep and thousands of meters wide.
3) Volcanoes are found around rift valleys. For example, Mount Kilimanjaro and Mount Kenya are volcanoes in East African Rift System..
When does a destructive margin occur?
A destructive margin occurs when two plates are moving toward each other (converging).
What happens at these margins depends on the types of plates converging:
-Oceanic-Continental
-Oceanic-Oceanic
-Continental-Continental
What is an Oceanic-continental convergent boundary?
1) Where oceanic crust and continental crust converge, the more dense oceanic crust if forced under the less continental crust (it subducted) This forms a DEEP SEA TRENCH ( a very deep trench in the sea) e.g. Peru- Chile trench in the pacific ocean.
2) FOLD MOUNTAINS also form where the plates meet. they’re made up of sediments that has accumulated on the continental crust, which is folded upwards along the edge of the continental crust.
3) The oceanic crust is heated by friction and contact with the upper mantle, which melts into magma.
4) The magma is less dense than the continental crust above and will rise back to the surface to form volcanoes.
5) As one plate moves under the other they can get stuck. This causes pressure to build up. When the pressure becomes too much the plates jerk past each other, causing an earthquake.
What is an Oceanic-Oceanic convergent boundary?
1) Most of the same processes occur when two plates of oceanic crust are moving toward each other- the denser of the two will be subducted, forming a DEEP SEA TRENCH and triggering EARTHQUAKES and VOLCANIC ERUPTIONS.
2) Volcanic eruption that takes place underwater (e.g. when two plates of oceanic crust converge) creates ISLAND ARCS- clusters of islands that sit in a curved line, e.g. the Mariana Island.
What is a Continental-continental convergent boundary?
1) Where two plates of continental crust move towards each other, neither is subducted so there aren’t any volcanoes- but the pressure that builds up between them can cause EARTHQUAKES.
2) FOLD MOUNTAINS form when continental crusts converge. E.g. the Himalayas were created in this way.
How can magma plumes form volcanoes away from plate margins?
Most volcanic activity occurs at late margins, but there are some areas of intense volcanic activity that arent near any plate margins. These are caused by magma plumes:
1) A magma plume is a vertical column of extra hot magma that rises up from the mantle.
2) Volcanes form above magma plumes.
3) The magma plume remains stationary over time, but the crust moves above it.
4) Volcanic activity in the part of the crust that was above the magma plume decreases as it moves away.
5) New volcanoes form in the part of the crust that is now above the magma plume.
6) As the crust continues to move, a chain of volcanoes is formed.
