Plate boundaries - Destructive plate margins

Question 1

What is the asthenosphere?

Answer 1

A semi-molten zone of rock underlying the earth’s crust.

Question 2

What is a conservative boundary?

Answer 2

A boundary between plates where movement is parallel to the plate margin and the plates slide past each other.

Question 3

What is a constructive boundary?

Answer 3

A boundary between plates where the plates are diverging or moving apart.

Question 4

What is a destructive boundary?

Answer 4

A boundary between plates where the plates are converging (moving towards one another).

Question 5

What is the lithosphere?

Answer 5

The crust of the earth, around 80-90km thick.

Question 6

What is magma?

Answer 6

Molten material which rises beneath the earth’s surface when hotspots, in the asthenosphere, generate convection currents.

Question 7

What are tectonic plates?

Answer 7

Rigid, less dense slabs of rock floating on the asthenosphere.

Question 8

What is a hotspot?

Answer 8

An area within the Earth’s crust with an unusually high temperature.

Question 9

What is a magma plume?

Answer 9

An upwelling of abnormally hot rock within the earth’s mantle.

Question 10

What are the three different types of destructive plate margins?

Answer 10

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

Question 11

What happens at a Continental - oceanic collision zone? Why?

Answer 11

1. When the two plates meet, the more dense oceanic plate subducts beneath the less dense continental crust
2. A deep oceanic trench is formed at the subduction zone
3. The oceanic plate melts into magma in the subduction zone.
4. Above the subduction zone, a volcanic chain is created by convection currents.

Question 12

What specific hazards are caused at a Continental - Oceanic (destructive) subduction zones?

Answer 12

• Earthquakes (pressure builds as magma volume increases causing friction and this pressure is released)
• Volcanic eruptions - viscous magma with volatile content
• Ground deformation

Question 13

What landforms can be created at a Continental - Oceanic subduction zones?

Answer 13

• Fold mountains
• Composite and caldera volcanoes (formed from andesitic magma)
• Deep ocean trench

Question 14

Give an example of a landform and hazard at a Continental - Destructive subduction zone.

Answer 14

1. Volcano Chaiten was formed from the converging movement of the South American plate and the Nazca plate.
2. Andes fold mountains
3. Peru Chile ocean trench

Question 15

What happens at an Oceanic - Oceanic subduction zone? Why?

Answer 15

1. Convection currents in the lithosphere causes the two oceanic plates to converge.
2. The denser section of the crust is forced to subduct (denser oceanic plate). A deep ocean trench is formed when the plate subducts.
3. The oceanic plate melts, forming andesitic magma in the subduction zone, the benioff zone forms.
4. This magma rises through the asthenosphere to form composite volcanoes which form an island arc.

Question 16

What specific hazards occur at an Oceanic - Oceanic subduction zone?

Answer 16

• Explosive earthquakes (benioff zone)
• Volcanic eruptions (viscous magma with volatile content)
• Ground deformation

Question 17

What landforms are created at an Oceanic - Oceanic subduction zone?

Answer 17

• Trench
• Composite and caldera volcanoes
• Island arc
• Back arc basin

Question 18

What happens at a Continental - Continental collision zone?

Answer 18

1. When the two continental plates converge (due to slab pull), with similar densities, neither plate is subducted so compressional forces fold the sediments upwards.
2. Thrust faults also push sea - floor sediment upwards when the plates collide.
3. This sediment forms fold mountains which are uplifted by a plate.

Question 19

What is a key aspect of a Continental - Continental collision zone?

Answer 19

There is no active volcanism or deep focus earthquakes since the subducting slab (often oceanic) is detached when the two plates collide.

Question 20

What is orogenesis?

Answer 20

The process of mountain building due to plate tectonics.

Question 21

What landforms are formed at at a continental - continental (destructive)
subduction zone?

Answer 21

1.Fold mountains
2. Fault scarps

Question 22

Give an example of landforms created at an oceanic-oceanic (destructive) subduction zone.

Answer 22

1. Indonesian Island Arc
2. Hunga Tonga