Tectonics

Question 1

How thick do continental crusts tend to be?

Answer 1

70km

Question 2

How thick do oceanic crusts tend to be?

Answer 2

5-10km

Question 3

What are the different layers of the earth?

Answer 3

• The crust; oceanic and continental
• The lithosphere; 7 plates broken at diff. sections which float on the asthenosphere
• The asthenosphere; made of plastic
• The mesosphere; the mantle
• The outer core
• The inner core; made of iron nickel

Question 4

Where does earths internal heat come from?

Answer 4

• Primordial heat left over from earths formation

- Radiogenic heat produced by radioactive decay of isostopes

Question 5

How hot is the earths core?

Answer 5

Around 5000 degrees C

Question 6

What is paleomagnetism?

Answer 6

This is about the magnetism of rocks. Iron particles of lava erupted on the ocean floor are aligned w/ earths magnetic field. The lava solidifies and gives a permanent record of earths polarity at the time of the eruption.
Scientists can use this to see when an eruption was.

Question 7

What is sea floor spreading?

Answer 7

The process by which molten material adds new oceanic crust to the ocean floor. Hot magma rises to the surface creating spreading ridges. A new crust is formed and the existing crust is pushed out of the way.
It shows the alternating polarity of rocks in the ocean.

Question 8

What is the rate of spreading and what does it confirm?

Answer 8

Rate of spreading is around 5cm a year and confirms studies of Earth’s magnetic field in rocks. Every 400,000 years the Earth’s magnetic field switches polarity; magnetic north and south switch.

Question 9

What is ridge push?

Answer 9

Also known as gravitational sliding, it is when hot magma rises to the surface and creates spreading ridges. A new crust is formed and the old one pushed out of the way.
(sea floor spreading)

Question 10

What are the different plate boundaries?

Answer 10

• Destructive
• Conservative
• Constructive

Question 11

What is a destructive plate boundary also known as?

Answer 11

A convergent plate boundary.

Question 12

What is constructive plate boundary also know as?

Answer 12

A divergent plate boundary.

Question 13

What is a convergent boundary and what landforms/hazards are found on it?

Answer 13

A convergent boundary is when 2 plates collide. It can happen between oceanic plates and continental plates.

• Deep sea trench
• Fold mountains
• Volcanoes
• Earthquakes
• Island arcs

Question 14

How are deep sea trenches formed?

Answer 14

When a continental and oceanic crust or 2 oceanic crusts collide and the oceanic crust, being heavier and more dense, is subducted beneath the continental.
An example is the Peru-Chile trench in the Pacific ocean

Question 15

How are fold mountains formed?

Answer 15

When an oceanic and continental crust or 2 continental crusts collide. Sediment accumulated along the continental crust is folded upwards along the edge of the crust forming a fold mountain.

Question 16

How do convergent boundaries form volcanoes?

Answer 16

When an oceanic and continental crust collide and the oceanic plate is subducted, it melts creating more magma in the mantle and an increase of pressure. The magma is less dense than the continental crust above so it will rise to form volcanoes. These are often very explosive eruptions.

Question 17

How do convergent plate boundaries cause earthquakes?

Answer 17

When an oceanic plate becomes stuck whilst being subducted under an oceanic plate, pressure builds up. The pressure is often released via a violent earthquake.

Question 18

How are island arcs formed?

Answer 18

When 2 oceanic plates converge and the crust along the subduction zone is pushed up forming a chain of islands. Usually volcanic. E.g. Marianna Islands.

Question 19

What is a conservative plate boundary?

Answer 19

When 2 plates are moving past each other. They can be moving in diff. directions or the same direction at diff. speeds. They stuck and pressure builds up which results in an earthquake.
E.g. San Andreas fault

Question 20

What is a divergent plate boundary and what landforms/hazards can be found along it?

Answer 20

This can occur w/ continental or oceanic crust. It involves the 2 plates being pulled apart.

• Ocean ridges
• Rift valley
• Shield volcanoes

Question 21

How are ocean ridges formed?

Answer 21

When 2 oceanic plates move apart and the space is filled w/ basaltic lava upwelling from below and hardening to form a ridge.
There can be volcanic activity forming shield volcanoes where the magma slowly flows out of the ridge. These can sometimes reach above the ocean surface.

Question 22

How are rift valleys formed?

Answer 22

When continental crust moves apart, the crust between the parallel faults drops down.

Question 23

What are magma plumes?

Answer 23

Radioactive decay within the earths core generates v. hot temperatures and if the decay is concentrated hot spots will firm around the core. These hot spots heat the lower mantle creating currents localised thermal currents where the magma rises vertically.
These can occasionally rise within the centre of plates and burn thro the lithosphere creating volcanic activity on the surface. The hot spot remains stationary but the overlying plate can move resulting in the formation of a chain of volcanoes.