Tectonic plate boundaries

Question 1

What is a constructive (divergent) plate boundary?

Answer 1

When two plates move apart from one another e.g mid atlantic ridge (Europe moving away from N America)

Question 2

What are the processes that take place at a constructive plate boundary?

Answer 2

• Ridge-push
• Seafloor spreading (forming new ocean crust)
• rifting
• Volcanic and seismic activity

Question 3

What are the landforms associated with constructive plate boundaries?

Answer 3

• Volcanoes (effusive, less viscous lava)
• Earthquakes (due to faults displaces ridges causing a release of pressure/energy)
• Mid oceanic ridges
• Rift valley
• formation of new oceanic crust
• Black smokers (hydrothermal vents/superheated jets of water that emerge on the ocean floor containing metal sulphides)
• graben (down faulted section of a rift valley)
• pillow lava

Question 4

what is a mid ocean ridge?

Answer 4

• boundary between 2 diverging oceanic plates
• 2 parallel chains of submarine mountains separated by a graben
• offset/broken into segments in places by transform faults which displace the ridge

Question 5

What is pillow lava and how is it formed?

Answer 5

formed at divergent plate boundaries, are caused by magma rising directly onto the sea bed which then rapidly cools forming rounded mounds of magma called pillow lavas

Question 6

What is a rift valley and how is it formed?

Answer 6

• A valley formed by down faulting between parallel faults e.g East african rift valley
• can be submarine or formed on land
• Formed on a divergent plate boundary
• formed due to magma rising causing overlying rocks to dome, this places the lithosphere under great stress which eventually fractures along parallel faults
• For rifting to occur on land the continental crust must be considerably thin
• This also causes a centre block to drop in between the ridge forming a graben (a flat/sunken valley floor)
• As the process continues the valley widens and can becomes a large basin that can fill with sediment
• rift valleys can also sink below sea level e.g forming the Red Sea

Question 7

What is a destructive (convergent) plate boundary?

Answer 7

When a oceanic plate and a continental plate move towards each other and the oceanic plate gets sub-ducted under the continental plate as it is more dense

Question 8

What processes occur at a (convergent) plate boundary?

Answer 8

• slab-pull
• subduction
• volcanic/seismic activity

Question 9

What are the landforms associated with destructive plate boundaries?

Answer 9

• Ocean trenches
• volcanoes
• Earthquakes
• fold mountains

Question 10

What is and how is an ocean trench formed?

Answer 10

• formed due to the subduction of the oceanic plate, which causes a deepening of the ocean
• long,narrow depression
• asymmetric, steeper side facing towards continental plate
• 6,000 -11,000m
• marks the zone of subduction, where oceanic crust descends into the asthenophere
• as it descends the leading edge of the continental plate is buckled forming an ocean trench