Plate Techtonics

Question 1

Asthenosphere

Answer 1

A layer of softer, almost plastic-like rock which moves very slowly and carries the lithosphere on top

Question 2

Collision plate margin

Answer 2

A type of destructive margin where two continental plates moves towards each other.

Question 3

Conservative plate margins

Answer 3

When two plates slide past each other and crust is not destroyed by subduction. They are associated with powerful earthquakes but no volcanic activity

Question 4

Constructive plate margin

Answer 4

When two plates separate or diverge. They can create sea-floor spreading in oceanic areas and rift valleys in continental areas

Question 5

Continental crust

Answer 5

Thicker (35km) and older than oceanic crust. It is also less dense than the oceanic crust and is mainly composed of granite.

Question 6

Convection currents

Answer 6

Circular movements of magma driven by heat from the inner core.

Question 7

Core

Answer 7

The widest section of the Earth, where the mainly silicate rocks are in a thick, liquid state, which become denser with depth.

Question 8

Crust

Answer 8

The Earth’s outer shell, made up of oceanic crust and continental crust.

Question 9

Destructive plate margins

Answer 9

When two plates collide or converge. This can occur when an oceanic plate meets a continental plate; when an oceanic plate meets an oceanic plate; or when a continental plate meets a continental plate.

Question 10

Gravitational sliding

Answer 10

The movement of tectonic plates as a result of gravity.

Question 11

Hot spot

Answer 11

An area where radioactive decay within the Earth’s core is concentrated, generating very hot temperatures and heating the lower mantle. This creates localised thermal currents where magma plumes rise.

Question 12

Island arcs

Answer 12

Volcanoes arranged in an arc pattern in the ocean, formed when an oceanic plate subducts beneath another oceanic plate.

Question 13

Island chains

Answer 13

A line of volcanoes in the ocean formed above a hotspot.

Question 14

Lithosphere

Answer 14

The outermost solid layer of the Earth, approximately 100km thick, comprising the crust and upper mantle.

Question 15

Magma

Answer 15

Molten rock, gases and liquids from the mantle accumulating in vast chambers at great pressures deep within the lithosphere.

Question 16

Magma plume

Answer 16

A rising column of hot rock created by hot spots heating the lower mantle, creating localised thermal currents. Although usually found close to plate margins, these plumes occasionally rise within the centre of plates and then ‘burn’ through the lithosphere to create volcanic activity on the surface.

Question 17

Mantle

Answer 17

The layer of the Earth between the crust and the core, composed of mainly silicate rocks.

Question 18

Mid-ocean ridges

Answer 18

Chains of submarine mountain ridges that extend for thousands of kilometres across the ocean floor, caused by oceanic divergence.

Question 19

Oceanic crust

Answer 19

Found beneath the world’s oceans and is formed at spreading centres on oceanic ridges at constructive plate margins. It is composed of basalt and is approximately 6km thick.

Question 20

Ocean ridges

Answer 20

When oceanic plates rise at a constructive plate boundary due to upwelling magma in the mantle to form a ridge under the ocean.

Question 21

Ocean trenches

Answer 21

Long narrow depressions on the sea floor where subduction is taking place.

Question 22

Plate tectonic theory

Answer 22

The theory that explains the landforms and hazards that occur as a result of the Earth’s tectonic movement.

Question 23

Primordial heat

Answer 23

Heat left over from the Earth’s formation. This is one reason the core’s temperature can exceed 5000°C.

Question 24

Radiogenic heat

Answer 24

Radiogenic heat produced by the radioactive decay of isotopes, particularly Uranium-238, Thorium-232 and Potassium-40. This is one reason the core’s temperature can exceed 5000°c.

Question 25

Ridge push

Answer 25

The higher elevation at a mid-ocean ridge causes gravity to push the lithosphere that is further from the ridge.

Question 26

Rift valleys

Answer 26

Deep, wide valleys separated by upright blocks of land called horsts. Formed as a result of continental divergence.

E.g. East African Rift Valley

Question 27

Sea-floor spreading

Answer 27

The concept that the Atlantic sea floor is spreading outwards from the centre, with the newest rocks in the middle (for example, Iceland) and the oldest nearest to the USA and the Caribbean.

Question 28

Slab pull

Answer 28

Following subduction, the lithosphere sinks into the mantle under its own weight, helping to ‘pull’ the rest of the plate with it.

Question 29

Subduction

Answer 29

When one plate dives beneath another and is destroyed by melting.

E.g. The Andes Mountains were formed by the subduction of the Nazca Plate beneath the South American Plate.

Question 30

Transform fault

Answer 30

A fault where two plates slide past each other, often at right angles to a constructive plate boundary.

E.g. The San Andreas Fault in California

Question 31

Young fold mountains

Answer 31

Mountains that form due to the collision of continental plates, layers of rocks fold upwards, these are called nappes.

E.g. The Himalayas