Plate Margins

Question 1

describe convection currents

Answer 1

• lower parts of the asthenosphere heat up, become less dense and slowly rise
• when they move to the top, they cool down, become more dense and slowly sink
• these circular movements create drag on the base of the tectonic plates and cause them to move

Question 2

describe slab pulls

Answer 2

• at destructive plate margins, denser crust is forced under the less dense crust
• the sinking of the plate edge pulls the rest of the plate towards the boundary

Question 3

describe ridge push

Answer 3

• at constructive plate margins, magma rises to the surface and forms new crust
• heats the surrounding rocks and expand causing a slope
• the new crust cools and becomes denser, denser rock moves downslope
• this puts pressure on the tectonic plates causing them to move apart

Question 4

describe sea-floor spreading

Answer 4

• tectonic plates diverge, magma rises up and then cools to form a new crust
• the new crust is dragged apart and new crust forms between it
• when this happens at the plate margin, the sea floor gets wider

Question 5

what are mid-ocean ridges?

Answer 5

oceanic divergence forms chains of submarine mountain ridges and regular breaks called transform faults
these faults occur at right angles to the plate boundary and they widen at different rates

Question 6

what are rift valleys?

Answer 6

continental divergence forms massive rift valleys which is when the lithosphere stretches causing to fracture into parallel faults
the land between these faults collapses into deep valleys

Question 7

what is a constructive plate margin?

Answer 7

this occurs when two plates are moving apart or diverging

Question 8

what is a destructive plate margin?

Answer 8

this occurs when two plates are moving towards each other or converging

Question 9

example of a OP meeting a CP

Answer 9

pacific coast of south america

Question 10

example of a OP meeting an OP

Answer 10

mariana trench in the western pacific

Question 11

example of a CP meeting a CP

Answer 11

the himalayas

Question 12

what happens when a OP meets a CP?

Answer 12

the more dense oceanic crust is forced under the less dense continental crust so is subducted

Question 13

what are formed at an OP-CP margin?

Answer 13

deep ocean trenches e.g. peru-chile trench
fold mountains e.g. the andes
volcanoes
earthquakes

Question 14

what happens when an OP meets an OP?

Answer 14

the denser of the two plates will subduct under each other which forms a deep sea trench, volcanoes and earthquakes

Question 15

what happens when a CP meets a CP?

Answer 15

neither plate subducts so there aren’t any volcanoes but pressure cause earthquakes and fold mountains form

Question 16

what is a conservative plate margin?

Answer 16

this occurs when two plates are moving past each other

Question 17

what happens at conservative plate margins?

Answer 17

the plates get locked together and pressure builds up which causes earthquakes

Question 18

what are magma plumes?

Answer 18

this is a vertical column of extra-hot magma that rises up from the mantle

Question 19

what happens at magma plumes?

Answer 19

volcanoes form above magma plumes and remains stationary but the crust moves it, new volcanoes form in the new part of the crust and create a chain of volcanoes

Question 20

what are island arcs?

Answer 20

during subduction, the descending begins to melt and becomes less dense, it then rises towards the surface and creates volcanoes