Plate tectonics

Question 1

Inner core

Answer 1

Solid dense ball of metal, composed of iron and nickel Radius of 1200km
6000 degrees Celsius

Question 2

Outer core

Answer 2

Semi molten, composed of iron and nickel
Radius of 2200km
Temperatures reach 5000 degrees Celsius

Question 3

Mantle

Answer 3

The part nearest the core is quite rigid, the layer above this (the asthenosphere) is semi molten and the very top layer is rigid.
It is made up of silicate rocks, iron and magnesium.
Radius of 2900km
Average temperature of 3000 degrees Celsius

Question 4

The Crust

Answer 4

Upper most layer

Question 5

Oceanic crust

Answer 5

Dense and relatively thin (6-10km)

Composed of basalt and gabbro.

Question 6

Continental crust

Answer 6

Less dense and thicker (30-70km)

Composed of granite.

Question 7

Lithosphere

Answer 7

The rigid top part of the mantle and the crust.

Question 8

Ocean ridges

Answer 8

A landform created

Question 9

Tectonic plates

Answer 9

Huge slabs in which the lithosphere is broken up into.

Question 10

Convection Currents

Answer 10

Lower parts of the asthenosphere heat up due to the heat of the core, they become less dense and slowly rise.
As they move towards the top of the asthenosphere they cool down and slowly sink.
These circular motions create drag on the base of tectonic plates, causing them to move.

Question 11

Ridge push

Answer 11

Another theory about how tectonic plates move, also known as gravitational sliding.
At constructive boundaries, magma rises to the surface at mid-ocean ridges.
|t is very hot so heats surrounding rocks, causing them to expand and rise above the surrounding crust, forming a slope.
The new rock cools and becomes denser.
Gravity causes dense rock to move downslope and away from the margin.
This puts pressure on the plates, causing them to move apart.

Question 12

Slab pull

Answer 12

Another theory about how tectonic plates move.
At destructive boundaries, the denser crust is forced under the less dense one.
The sinking of the plate edge pulls the rest of the plate towards the boundary.

Question 13

Sea-floor spreading

Answer 13

As plates move apart, magma rises to fill the gaps created, and then cools to form new crust.
Overtime, the crust is dragged apart and more new crust forms between it.
When this happens at a plate margin under the sea the seafloor gets wider, creating mid ocean ridges.

Question 14

Constructive margins

Answer 14

Plates move apart and new crust is created.
The mantle is under pressure from the plates above so when they move, pressure is released, causing the mantle to melt, producing magma.
The magma is less dense than the plate above, and it can form a volcano.
Plates don’t move in a uniform way so pressure builds up. It eventually becomes too much so the plate cracks, making a fault line and causing an earthquake.
Once the fault line has been created, further earthquakes are likely to occur.

Question 15

Ocean ridges

Answer 15

Formed at constructive margins where diverging plates are underwater.
e.g. the Mid-Atlantic ridge. The North American and Eurasian plates are moving away from each other, it rises 2-3km above the ocean floor.

Question 16

Underwater volcanoes

Answer 16

They erupt along mid-ocean ridges and can build up to be above sea level.
e.g. Iceland was formed by the build up of underwater volcanoes along the Mid-Atlantic ridge.

Question 17

Rift Valleys

Answer 17

Formed at constructive margins where plates diverge within a continent.
Rising magma causes the continental crust to bulge and fracture.
They form when the plates keep moving apart and the crust between the parallel faults drop down.
e.g. East African Rift system - a series of rift valleys that stretch 4000km from Mozambique to the Red Sea.
It is formed by the Nubian and Somalian plates diverging.
Volcanoes can also be found here, such as Mount Kilimanjaro.

Question 18

Destructive margins: Oceanic-oceanic

Answer 18

The denser plate is subducted forming a deep sea trench.
Island arcs form when the subducted plate begings to melt; hot magma leaks out of the cracks in the crust as a series of volcanoes.
Island arcs are clusters of islands that sit in a curved line e.g. the Japanese islands.

Question 19

Destructive margins: Continental-continental

Answer 19

aka collision
Pressure builds up between the two plates, causing earthquakes.
Fold mountains also form here, e.g. the Himalayas where the Eurasian and Indian plates meet.

Question 20

Destructive margins: Oceanic-continental

Answer 20

Deep sea trench
Fold mountains
Earthquakes
Volcanoes

Question 21

Deep sea trench at an OC boundary

Answer 21

They form when the denser oceanic plate is subducted.
e.g. the Atacama trench formed when the Nazca plate was subducted by the South American plate. A 8065m deep V-shaped trench was formed 160km off the coast of Peru.

Question 22

Fold mountains at OC boundaries

Answer 22

Sediments that have accumulated on the continental crust are folded upwards along with the edge of it.

Question 23

Volcanoes at OC boundaries

Answer 23

The subducted oceanic crust melts to magma when it is heated by friction and contact with the upper mantle.
Magma is less dense so it rises to the surface to form volcanoes.

Question 24

Earthquakes at OC boundaries.

Answer 24

Caused when the two plates get stuck as one is subducted. Pressure builds up and is eventually released in the form of an earthquake.

Question 25

Conservative margins

Answer 25

2 plates sliding past each other. They can get locked together, causing pressure to build up and then released as an earthquake.
e.g. San Andreas fault. The junction between the North American and Pacific plates. Both plates are moving in a north westerly direction however the pacific plate is moving faster.

Question 26

Magma plumes

Answer 26

A vertical column of extra hot magma that rises up from the mantle. The ground above it is called a hotspot, and volcanoes form there.
The plume remains stationary overtime but the crust moves above it. Volcanic activity decreases as the crust moves away.
New volcanoes then form in the part of the crust that is now above the magma plume.
As the crust continues to move, a chain of volcanoes are formed e.g. the Hawaiian islands.
Kauai is 6 million years old and the first in the line of Hawaiian islands, ending with Hawaii itself which is 500,00 years old.