Plate Boundaries

Question 1

What is the oceanic crust?

Answer 1

• The plate that is made up of more dense rock.
• It sinks easily due to its density and is constantly created at boundaries
• It is ‘young/new rock’ and forms our ocean bed

Question 2

What is the subduction zone?

Answer 2

Where one plate is forced downwards below another plate and grinds past it causing huge amounts of friction and heat

Question 3

What is a convergent (destructive) plate boundary?

Answer 3

Where two plates are moving towards each other, one of which is continental crust and one is made of oceanic crust

Question 4

What is the continental crust?

Answer 4

• A plate that is made up of less dense rock which means it doesn’t sink
• It is very old and makes up our land surfaces

Question 5

What is a plate boundary?

Answer 5

Where two very large crustal plates meet on the earth’s surface

Question 6

What are fold mountains?

Answer 6

Large mountain ranges formed by the collision and ‘folding’ of two plates as they continually push into each other

Question 7

What is an ocean trench?

Answer 7

A particularly deep point of the ocean bed where the oceanic and continental crust have dragged each other downwards

Question 8

What the differences between the continental and oceanic crust?

Answer 8

• Continental is 70km thick, oceanic is 7km
• Oceanic is 200 million years old, continental is 3.6 billion years
• Oceanic is made of denser basalt, continental is made of granite

Question 9

What is an example of a convergent plate boundary?

Answer 9

Nazca and South American plates

Question 10

1. Convergent plate boundary

Answer 10

Denser Oceanic plate (Nazca) is forced below the continental plate

Question 11

2. Convergent plate boundary

Answer 11

Less dense Continental plate (South American plate) moves towards Oceanic plate

Question 12

3. Convergent plate boundary

Answer 12

Pressure builds up at the subduction zone - friction causes melting of oceanic plate and can cause earthquakes when friction is released

Question 13

4. Convergent plate boundary

Answer 13

Molten rock (magma) builds up in the chamber

Question 14

5. Convergent plate boundary

Answer 14

When the pressure builds up magma escapes through a composite volcano

Question 15

6. Convergent plate boundary

Answer 15

Lighter continental crust remains at the surface but crumples into fold mountains (Andes)

Question 16

What are pyroclastic flows?

Answer 16

Fast-moving currents of hot gas and rock, which reaches speeds of up to 450 mph, and temperatures of about 1000°C

Question 17

How do pyroclastic flows move?

Answer 17

They normally hug the ground and travel downhill, or spread laterally under gravity

Question 18

What is a volcanic bomb?

Answer 18

A mass of molten rock larger than 64mm, formed when a volcano ejects viscious fragments of lava during an eruption

Question 19

How do volcanic bombs move?

Answer 19

They are thrown many kilometres from an erupting vent, and become more aerodynamic further into their flight

Question 20

What do lava explosions do when erupted?

Answer 20

They can erupt during either non-explosive or explosive lava fountains and destroy everything in their path

Question 21

What are lahars?

Answer 21

They are when a snowy volcano erupts, melting the snow and ice and have the thickness of wet concrete and travel at 30 mph

Question 22

How do lahars travel?

Answer 22

Down a volcano and mixes with mud and debris from forests and communities, which turns into a “Mudslide of Death”

Question 23

What else can be formed at convergent plate boundaries?

Answer 23

Tsunamis which are caused by the sudden uplift of the oceanic plate which displaces huge amounts of water

Question 24

1. Conservative boundary

Answer 24

Earthquakes occur here because two plates are sliding past each other

Question 25

2. Conservative boundary

Answer 25

The plate can also be moving in the same direction at different speeds such as the Pacific plate which moves north at 6cm/year and the North American plate which also moves north at 2cm/year

Question 26

3. Conservative boundary

Answer 26

Plates become stuck and friction builds up

Question 27

4. Conservative boundary

Answer 27

Eventually the pressure builds up and is suddenly released into an earthquake

Question 28

5. Conservative boundary

Answer 28

No new crust is created or destroyed because the plates are not forced up or down, therefore there are no volcanoes

Question 29

When has San Francisco suffered from an earthquake?

Answer 29

1906 and 1989

Question 30

What were the impacts of the 1989 San Francisco earthquake?

Answer 30

• 63 people killed
• 3,757 people injured
• 2 mile section of freeway collapsed
• Damage cost $10 billion

Question 31

What evidence is there for collision plate boundaries?

Answer 31

• Joining up of countries, e.g. India

- Rocks folding

Question 32

1. Collision boundary

Answer 32

90 million years ago, Indian and Eurasian plate were separated by the Sea of Tethys and rivers drained land around the ocean and deposited sediment at the ocean floor

Question 33

2. Collision boundary

Answer 33

Deposition meant pressure increased and created new sedimentary rock on the ocean floor

Question 34

3. Collision boundary

Answer 34

50 million years ago, the Indian plate slammed into the Eurasian plate driven by convection currents but because they had the same density as they are both continental they rised up together

Question 35

4. Collision boundary

Answer 35

As the two plates push together, the plates get jammed and lock together due to friction and this causes sudden earthquakes

Question 36

5. Collision boundary

Answer 36

As the fold mountains are young, they are still growing and expected to grow by 5000m but erosion and weathering will limit this