plate tectonics

Question 1

structure of the earth

Answer 1

inner core: solid iron and nickel- 6000 degrees Celsius

outer core: semi molten iron and nickel

mantle: semi molten 1000-3500 degrees Celsius
asthenosphere: rigid layer of mantle below lithosphere
crust: rock
lithosphere: top layer of mantle and crust which is split into tectonic plates

Question 2

difference between continental and oceanic crust

Answer 2

continental crust is thicker but less dense- 30-70km thick

oceanic: thinner but more dense- 6-10km thick

Question 3

explain the convection currents theory

Answer 3

• earths mantle is hottest close to the core
• this causes lower parts of the asthenosphere to heat up become less dense and slowly rise
• as they move towards the top of the asthenosphere the cool and sink
• the circular movements are called convection currents
• this causes drag on the base of the tectonic plates causing them to move

Question 4

explain slab pull

Answer 4

• 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 5

explain ridge push( gravitational pull)

Answer 5

• at constructive plate margins magma rise to the surface to form new crust forming a slope
• as the crust cools and becomes more dense gravity causes it to move downslope away form the plate margin
• this puts pressure on the tectonic plates causing them to move apart

Question 6

sea floor spreading

Answer 6

• when gravitational sliding occurs at plate margins under the sea the sea floor gets wider
• sea floor spreading creates mid ocean ridges

Question 7

name the 9 tectonic plates

Answer 7

pacific 
nazca
north american
south american
african
eurasion
indo australian
philippine
antartic

Question 8

name the 3 types of plate margins with examples

Answer 8

constructive: when two plates move apart
e. g. North American(east) and Eurasian(west) - Iceland

destructive: when two plates move towards each other
e. g. Eurasian (west) and Pacific (east) - Japan

conservative: when two plates move against each
other at different speeds and/or directions
e.g. Pacific and North American - San Andreas Fault

Question 9

characteristics/processes associated with constructive plate margins

Answer 9

shield volcanoes - Eyjafjallajokull
shallow focused earthquakes
ocean ridges
rift valleys

Question 10

how are ocean ridges formed

Answer 10

• they form at constructive margins underwater
• when the plates move apart magma rises to create ne crust
• as the crust cools and becomes more dense gravity pulls it down away from the margin
• this creates a slope/ridge
• underwater volcanoes erupt along the ridges and can build up to be at sea level

Question 11

example of an ocean ridges

Answer 11

Iceland was formed by the build up of volcanoes along the mid Atlantic ridge

Question 12

how are rift valleys formed

Answer 12

• when plates at constructive margins move apart rising magma causes bulges and fractures creating faults lines
• as the plates continue to move the crust between the parallel fault lines falls creating rift valleys
• the large mounts of land on either side of a rift valley are called horsts

Question 13

example of a rift valley

Answer 13

-east African rift valley: series of rift valleys from Mozambique to the red sea that is 400km long
it was created by diverging of the Nubian and Somalian plates

Question 14

characteristics/processes associated with destructive plate margins

Answer 14

composite volcanoes - Mnt St Helens
OvO: shallow intermediate deep focused earthquakes
CvO: intermediate deep focused earthquakes
CvC: shallow focus earthquakes

deep sea trenches
fold mountains
island arcs

Question 15

how are deep sea trenches formed

Answer 15

• typically occur when a oceanic plate is submerged under a continental plate or a less dense oceanic plates
• this point is called the subduction zone
• the gap created is the trench

Question 16

examples of deep sea trenches

Answer 16

peru-chile trench in the pacific ocean

Question 17

how are fold mountains formed

Answer 17

• formed when an oceanic and continental plate or two continental plates collide
• sediment accumulated on the crust are folded up when the plates collide

Question 18

examples of fold mountains

Answer 18

Himalayan mountain

Question 19

how are volcanoes formed at destructive plate margins

Answer 19

• when the oceanic plate subducts it melts into the mantle

- the magma is less dense than the continental plate so it will rise back up as a volcano

Question 20

how are island arcs formed

Answer 20

they are formed when the magma created by one plate subducting under another rises along the fault line

Question 21

example of island arcs

Answer 21

the Mariana cluster islands

Question 22

characteristics/processes associated with conservative margins

Answer 22

earthquakes occur here

Question 23

how do earthquakes occur at conservative plate margins

Answer 23

• two plates get locked together
• the pressure builds causing the plates to jerk past each other
• the release of energy causes an earthquake

Question 24

examples of earthquakes at conservative plate margins

Answer 24

the pacific plate is moving past the North American plate

-San Andreas Fault in California

Question 25

what are magma plumes

Answer 25

• stationary vertical columns of magma rising from the mantle that form volcanoes
• as the crust moves over the plume the previous volcano becomes less active and a new one is created
• as this continuous a chain of volcanoes is created
• when the volcanoes become dormant islands are creates

this doesn’t occur at plate margins

Question 26

example of magma plume chain islands

Answer 26

Hawaiian islands