plate tectonics Flashcards
structure of the earth
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
difference between continental and oceanic crust
continental crust is thicker but less dense- 30-70km thick
oceanic: thinner but more dense- 6-10km thick
explain the convection currents theory
- 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
explain slab pull
- 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
explain ridge push( gravitational pull)
- 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
sea floor spreading
- when gravitational sliding occurs at plate margins under the sea the sea floor gets wider
- sea floor spreading creates mid ocean ridges
name the 9 tectonic plates
pacific nazca north american south american african eurasion indo australian philippine antartic
name the 3 types of plate margins with examples
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
characteristics/processes associated with constructive plate margins
shield volcanoes - Eyjafjallajokull
shallow focused earthquakes
ocean ridges
rift valleys
how are ocean ridges formed
- 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
example of an ocean ridges
Iceland was formed by the build up of volcanoes along the mid Atlantic ridge
how are rift valleys formed
- 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
example of a rift valley
-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
characteristics/processes associated with destructive plate margins
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
how are deep sea trenches formed
- 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
examples of deep sea trenches
peru-chile trench in the pacific ocean
how are fold mountains formed
- formed when an oceanic and continental plate or two continental plates collide
- sediment accumulated on the crust are folded up when the plates collide
examples of fold mountains
Himalayan mountain
how are volcanoes formed at destructive plate margins
- 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
how are island arcs formed
they are formed when the magma created by one plate subducting under another rises along the fault line
example of island arcs
the Mariana cluster islands
characteristics/processes associated with conservative margins
earthquakes occur here
how do earthquakes occur at conservative plate margins
- two plates get locked together
- the pressure builds causing the plates to jerk past each other
- the release of energy causes an earthquake
examples of earthquakes at conservative plate margins
the pacific plate is moving past the North American plate
-San Andreas Fault in California
what are magma plumes
- 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
example of magma plume chain islands
Hawaiian islands
