Types of Plate Margin

Question 1

what types of margin do earthquakes and volcanoes occur at

Answer 1

constructive and destructive

Question 2

where does a constructive plate margin occur

Answer 2

where two plates are moving apart (diverging)

Question 3

how does a volcano form?

Answer 3

plates move apart, pressure is released at the margin, release of pressure causes mantle to melt, producing magma, magma is less dense than plate above, so it rises and can erupt to form a volcano

Question 4

how does an earthquake occur?

Answer 4

plates don’t move in a uniform way - some parts move faster than others, causes pressure to build up, pressure becomes too much and plate cracks, makes a fault line, causes an earthquake. Further earthquakes can occur along the fault line once created.

Question 5

what landforms occur at constructive plate margins

Answer 5

mid-ocean ridges and rift valleys

Question 6

example of an ocean ridge

Answer 6

mid-atlantic ridge

Question 7

what can form along mid-ocean ridges

Answer 7

underwater volcanoes, can build up to be above sea level e.g. iceland

Question 8

how are rift valleys formed?

Answer 8

• plates diverge beneath land, rising magma causes continental crust to bulge and fracture forming fault lines
• crust between parallel fault lines drops when plates move apart to form a rift valley
• as process continues, valley widens until it becomes a large basin that fills with sediment from the rift walls

Question 9

where does a destructive plate margin occur

Answer 9

two plates moving towards each other (converging)

Question 10

what occurs at a destructive oceanic-continental plate margin?

Answer 10

• deep sea trench
• fold mountains
• volcanoes
• earthquake

Question 11

how is an ocean trench formed?

Answer 11

• continental and oceanic crust converge, more dense oceanic crust is forced under less dense continental crust
• seafloor and lithosphere bend and form a steep v-shaped depression
• leading edge of a less-dense tectonic plate meets the leading edge off a dense plate
• denser plate moves downwards into the subduction zone

Question 12

what is an ocean trench?

Answer 12

are steep depressions in the deepest parts on the ocean where an old oceanic crust is pushed beneath either another oceanic plate or a continental plate

Question 13

what is a mid-ocean ridge

Answer 13

an elevated region with a central valley on an ocean floor at a boundary between two diverging plates where crust forms from outpouring magma

Question 14

what are the two processes concerning the formation of mid-ocean ridges

Answer 14

ridge-push and slab-pull

Question 15

explain ridge-push (mid ocean ridges)

Answer 15

occurs when the growing bulk of the ridge pushes the rest of the tectonic plate away from the ridge, often towards the subduction zone

Question 16

explain slab-pull (mid ocean ridges)

Answer 16

comes into effect in the subduction zone - is where the weights of the tectonic plate being subducted below the overlying plate dragging the rest of the plate along with it.

Question 17

what is a rift valley

Answer 17

a linear-shaped lowland between highlands or mountain ranges created by the action of a geologic fault

Question 18

what are fold mountains?

Answer 18

mountains formed from the folding of sedimentary rocks (sediment taken from rivers)

Question 19

how are fold mountains formed?

Answer 19

• two plates pushed together, at compressing boundary
• takes millions of years
• compression zone, tectonic activity forces crustal compression at the edge of crust formation
• rocks are often less stable and so more susceptible to folding
• two plates force rock upwards into a series of folds

Question 20

how do volcanoes occur at destructive plate margins

Answer 20

• oceanic crust is heated by friction and contact with upper mantle, this melts it into magma
• magma is less dense than continental crust above and so rises to the surface - creates volcanoes

Question 21

how does an earthquake occur at a destructive plate margin

Answer 21

• when one plate moves under another, it can get stuck
• this causes pressure to build up
• pressure becomes too much and so plates jerk past each other - causes earhtquake

Question 22

what occurs at a destructive oceanic-oceanic plate boundary

Answer 22

• ocean trench
• earthquakes
• volcanic eruptions
• island arcs

Question 23

processes occurring at oceanic-oceanic destructive plate margin

Answer 23

same processes occur as at continental-oceanic, two plates moving towards each other, the denser of the two will be subducted

forms ocean trench and triggers an earthquake and volcanic eruptions

Question 24

what creates an island arc

Answer 24

volcanic eruptions that take place under water

Question 25

what are island arcs

Answer 25

they are a curved chain of volcanic islands located at a destructive plate margin often with a deep ocean trench on the curved side

Question 26

how are island arcs formed

Answer 26

• 2 convergent oceanic plates meet, one denser and heavier than the other, denser plate sinks under the other
• oceanic lithosphere melts in the asthenosphere and turns into magma
• some magma may leak into the crust and bubble up to the surface of the sea bed
• when it bubbles volcanoes form at subduction zone and when they erupt they build up rock on the sea bed
• overtime enough builds up to create a volcanic island that rises above the surface - look like islands

Question 27

what happens when two continental plates meet?

Answer 27

neither is subducted so no volcanoes form, but pressure builds up so earthquakes can form.

fold mountains occur when continental crusts converge e.g. Himalayas.

Question 28

what occurs at conservative plate margins

Answer 28

only earthquakes

Question 29

when does a conservative plate margin occur

Answer 29

when two plates are moving past eachother

Question 30

how does an earthquake occur at a conservative plate margin

Answer 30

• two plates get locked together in places and pressure builds up
• causes plates to jerk past each other (or crack forming fault lines)
• releases energy as an earthquake

Question 31

example of conservative plate margin

Answer 31

pacific plate moving past the north american plate - many plates occur along this margin e.g. San Andreas fault