In this video, we are going to go over plate tectonics.
Plate tectonics is the theory around the movement of the tectonic plates that make up the lithosphere,
the lithosphere is the crust and upper mantle on earth.
Underneath the lithosphere is the asthenosphere, which essentially the tectonic plates float
on, as the materials that make up the asthenosphere are made up of a non-rigid plastic rock that
is able to move.
Movement in the asthenosphere occurs through what are known as convection currents, where
hot material which is less dense moves rising up, where it cools down and becomes more dense
and then sinks creating a convection current.
It is these convection currents that drive the movement of the tectonic plates.
The Earth's outer layer is made up of a patchwork of plates.
There are two kinds of tectonic plates; continental plates and oceanic plates.
Where these plates meet are called plate boundaries; earthquakes, trenches, mountains, rifts, and
volcanoes are associated with these plate boundaries.
Depending on how these plates are moving in relation to the adjacent plate there are three
forms of plate boundaries; divergent boundaries, convergent boundaries and transform boundaries.
Divergent boundaries, also known as a constructive boundary, are when the two plates are sliding
away from each other.
When there is a divergent boundary between two continental plates a rift forms between
the two plates, this may form new ocean floor as the two plates continue to spread apart
and the ocean begins to fill it.
Where there is a divergent boundary between two oceanic plates you get mid-oceanic ridges
forming which spread from the centre creating sea-floor spreading and the creation of new
ocean basin.
Convergent boundaries, also known as destructive boundaries, are when the two plates are sliding
towards each other.
When we have convergent boundaries between a continental plate and an oceanic plate,
the oceanic plate is less dense than the continental plate so it gets pushed under the continental
plate forming a subduction zone.
Trenches are also formed at subduction zones and earthquakes are common as the subducted
pate moves down.
Where there is a convergent boundary between two oceanic plates you also get a subduction
zone, where the older more dense oceanic plate slips below the other plate, causing deep
trenches.
Magma also rises as the subducted plate moves down, this Magma forms chains of oceanic volcanoes.
These chains of oceanic volcanoes differ from those formed from hot spots such as the Hawaiian
islands.
Hot spots form volcanoes, but not because of activities going on at plate boundaries.
Hot spots are areas where the magma has broken through the lithosphere, as the crust moves
over it a chain of volcanoes are formed with one active volcano and a chain of dormant
or extinct volcano behind it, hot spots are found in the ocean and on continents.
Where there is a convergent boundary between two continental plates, which results in the
closure of an ocean basin, there is a collision called continental collision between the continental
plates, none of them gets subducted, instead, they get forced up and fold to form mountains
and mountain ranges.
Transform boundaries, also known as conservative boundaries, are when the two plates slide
past each other in opposite directions.
Tectonic plates in this situation are not formed or destroyed.
Earthquakes are common along transform boundaries as friction builds between moving plates until
the plate eventually slips past the other suddenly, causing an earthquake.
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