Plate Tectonics

Question 1

outline:
1. internal structure of earth
2. what are plate tectonics
3. why do tectonic plates move
4. what are the different types of plate boundaries

Question 2

before we start, there are 2 types of natural hazards

Answer 2

• climate- related hazard
• tectonic hazard

Question 3

1. internal structure of earth

Answer 3

• core (inner & outer, innermost layer)
• mantle (inner & outer)
• crust (outermost layer)

Question 4

core:
- solid inner core, liquid outer core
- about 3300km thick
- temperature between 3000 to 5000 degree celsius

Question 5

mantle:
- solid rock flowing under high temperature and pressure
- 2900km thick
- temperature between 800 to 3000 degree celsius

Question 6

crust:
- basalt and granite rocks
- around 70km thick

Question 7

2. What are tectonic plates?

Answer 7

• pieces of the earth’s crust that move in relation to one another
• part of the lithosphere (crust & uppermost mantle)

Question 8

3. why do plate tectonics move?

Answer 8

• continental drift theory
• convection of currents –> movement of heat within the mantle
• slab-pull force –> pulling force exerted by a dense oceanic plate plunging into the mantle due to its own weight

Question 9

slab-pull force:

Answer 9

When two plates converge, the denser oceanic crust is pulled down by gravity as it subducts beneath the less dense crust. The denser oceanic crust sinks deeper into the mantle under its own weight, pulling the rest of the plate with it, contributing to further convergence.

Question 10

4. what are the different types of plate boundaries?

Answer 10

1. divergent plate movement
2. convergent plate movement
3. transform plate movement

Question 11

1. divergent plate movement

Answer 11

• oceanic-oceanic divergence (1)
• continental-continental divergence (2)
• action of plates moving away/ apart from each other

Question 12

oceanic-oceanic plate divergence (type 1)

Answer 12

• magma rises from the mantle to fill the gap between the plates as they diverge.
• new sea-floor is formed when the lava flows out onto the seafloor as it cools, solidifies. this is known as sea-floor spreading
• this forms a mid-oceanic ridge
• newly formed rocks are closest to the middle of the ridge (youngest)
• at various points along the ridge, magma builds up overtime above the ocean to form volcanic islands (mid-atlantic ridge e.g)

Question 13

continental-continental plate divergence (type 2)

Answer 13

• can cause continents to break apart (how?)
• when plates diverge, they are stretched, causing fractures at the late boundary and the land between the 2 continental plats sinks to forma linear depression (called a rift valley) [east african rift valley]

Question 14

2. convergent plate movement

Answer 14

• oceanic-oceanic plate convergence (1)
• continental-continental convergence (2)
• oceanic-continental convergence (3)
• action of plates moving towards each other

Question 15

oceanic-oceanic plate convergence (1)

Answer 15

• the denser plate subducts beneath the less dense plate. the subducted oceanic plate causes the mantle to melt and form magma
• the magma then rises through the cracks to form volcanoes and a chain of islands overtime (marina islands e.g)

earthquakes may occur due to friction

Question 16

continental-continental plate convergence

Answer 16

• little/ no subduction occurs as both plates are too thick and bouyant
• layers of rocks on the upper part of the crust are compressed together, causing them to fold upwards/ sideways to form fold mountains (himalayas e.g)

Question 17

oceanic-continental plate convergence (3)

Answer 17

• the denser plate subducts and the oceanic trench forms at the subduction zone while fold mountains form on the continental plate
• volcanoes are also formed on the continental plate when the magma rises through the cracks to the surface