Plate Margins- Content

Question 1

Why are the youngest rocks found at constructive plate margins?

Answer 1

Because new crust is being formed as magma rises from the asthenosphere to fill the gap where the plates are moving apart, and this solidifies to form new, dense basaltic rock.

Question 2

What are formed when plates move apart in oceanic areas?

Answer 2

Mid oceanic ridges

Question 3

What are formed when plates move apart in continental areas?

Answer 3

Rift valleys

Question 4

What are the dimensions that mid oceanic ridges can reach?

Answer 4

Total length 60,000km

3000km above the ocean floor

Question 5

What cut across mid oceanic ridges?

Answer 5

Transform faults

Question 6

What do transform faults at constructive margins lead to?

Answer 6

They lead to frictional stress building up and shallow focus earthquakes being released

Question 7

How are oceanic ridges formed?

Answer 7

When two plates pull apart there is a weaker zone in the crust and an increase in heat near the surface. The expanded crust forms a ridge. The central part of the ridge collapses and subsides into the crust below.

Question 8

How are submarine volcanoes formed?

Answer 8

Where the crust splits there is a lower pressure zone where more liquid lava erupts to form submarine volcanoes

Question 9

How are rift valleys formed?

Answer 9

Rift valleys are formed when the lithosphere stretches causing it to fracture into sets of parallel faults. The land between these faults collapses into deep wide valleys separated by blocks of land called horsts.

Question 10

What is an example of a Rift Valley?

Answer 10

The Great African Rift Valley which extends 4000km from Mozambique to Red Sea down the eastern side of a Africa.

Question 11

What happens if the stretching of continental plate continues?

Answer 11

If the stretching of the plate continues, the thinned basalt and continental rocks will drop below sea level and lead to the formation of a new ocean.

Question 12

What are the three types of destructive margin?

Answer 12

1. Oceanic towards continental
2. Oceanic towards oceanic
3. Continental towards continental

Question 13

What are the two types of constructive margin?

Answer 13

• in oceanic areas e.g. Mid Atlantic Ridge

- in continental areas e.g. Great African Rift Valley

Question 14

Why is new crust formed at constructive plate margins?

Answer 14

The gap created by the separating plates is being filled by magma rising from the asthenosphere and this solidifies to form new basaltic rock

Question 15

What are the maximum dimensions of a mid oceanic ridge?

Answer 15

• total length 60,000km

- rise 3000km above ocean floor

Question 16

What do transform faults lead to?

Answer 16

Transform faults lead to frictional stress building up and it is released in shallow focus earthquakes

Question 17

How are rift valleys formed?

Answer 17

When the lithosphere stretches and fractures into sets of parallel faults. The land between these faults collapses into deep, wide valleys which are separated by upright blocks of land called horsts

Question 18

What is an example of a Rift Valley?

Answer 18

The Great African Rift Valley which runs 4000km down the eastern side of Africa from Mozambique to the Red Sea

Question 19

What happens if the stretching of a continental plate continues?

Answer 19

The thinned basalt and continental rocks will eventually drop below sea level, leading to the formation of a new ocean

Question 20

What are the three types of destructive margins?

Answer 20

• oceanic towards continental
• oceanic towards oceanic
• continental towards continental

Question 21

What are formed at oceanic/continental destructive?

Answer 21

Deep trenches such as the Peru Chile trench which is more than 8km deep

Question 22

What can happen along the edge of the continental plate at oceanic/continental margins?

Answer 22

Sediments can be uplifted to form fold mountains such as the Andes along the a Pacific side of South America

Question 23

How do earthquakes occur at continental/oceanic destructive margins?

Answer 23

Further friction with the continental plate builds up and can be released causing major earthquakes

Question 24

What is the Benioff zone?

Answer 24

The place where the oceanic plate subducting beneath the continental plate starts to be melted into magma due to a build up of heat and pressure

Question 25

What happens to the magma from the melted subducting oceanic plate?

Answer 25

It is less dense than the surrounding asthenosphere so the molten material rises in plumes of magma. When it reaches the surface, volcanoes are formed

Question 26

What are the volcanoes at oceanic/continental plate margins like?

Answer 26

The lava has a viscous nature so it flows less easily which means it creates composite volcanoes, which are very explosive.

Question 27

What happens if at destructive plate margins the eruptions take place off shore?

Answer 27

If the eruptions take place offshore, it can form a line of volcanic islands known as an island arc e.g. West Indies

Question 28

What is an example of oceanic/oceanic destructive?

Answer 28

The western side of the Pacific Ocean where the Pacific plate is being sub ducted beneath the smaller Philippine plate to form the Marianas trench

Question 29

What three things occur at continental/continental destructive margins?

Answer 29

1. Sediment is forced up into fold mountains
2. The friction can trigger shallow focus earthquakes
3. Material is also forced downwards to form deep mountain roots

Question 30

What are examples of continental/continental destructive margins?

Answer 30

• where the African plate is being forced northwards into the Eurasian plate, forming the Alps
• where the Indo-Australian plate is being forced into the Eurasian plate to form the Himalayas, where there is high levels of earthquakes

Question 31

What occurs at conservative plate margins?

Answer 31

• stress is created between the plate edges which results in shallow focus earthquakes e.g. San Francisco 1906

Question 32

An example of a conservative plate margin

Answer 32

The San Andreas fault system