These notes provide an in depth analysis of plate tectonics, natural hazards and vulnerability. It covers content as well as case studies such as the Haiti Earthquake, Tsunamis in Japan and the Indian Ocean, and countries which suffered from a high vulnerability. It also provides some exam question...
Note- A level Geography is all about the
interaction between the physical world and
the human world. It is synoptic.
lithosphere - the solid layer from which
tectonic plates are formed
Oceanic- a thin, dense layer (6-10km
thick), which lines the ocean floors
Continental- older, thicker layer
which makes up Earth’s crust but is
less dense than the oceanic crust.
1. Mantle convection - creates convection currents
2. Slab pull - newly formed oceanic crust at mid-ocean ridges becomes denser and thicker as
it cools. This causes it to sink into the mantle under its own weight- pulling the rest of the
plate further down with it
3. Subduction- as a new crust is being created in one place, it’s being destroyed in
The crust- forms the outer shell of the Earth. There are two types of crust:
4. another.
5. Seafloor spreading- formed when magma is forced up from the asthenosphere
Paleomagnetism - study of past changes in the Earth’s magnetic field (determined from rocks,
sediment or archaeological records.)
Convergent- two plates collide - destructive
Divergent - two plates move apart - constructive
Conservative - two plates slide past each other - also known as transform margins
Destructive plate margins:
1. When oceanic plate meets continental plate
1. When oceanic plate meets oceanic plate
2. When continental plate meets continental plate
Benioff zone - the point at which one plate subducts under the other
Constructive plate margins:
Mid-ocean ridge- form submarine volcanoes which can rise above sea level creating new
islands such as Iceland.
Rift valleys - when plates move apart on continents, the crust stretches and breaks into sets
or parallel cracks (faults) The land between these faults then collapses, forming steep-sided
valleys.
Conservative plate margins:
Break in crust=fault
Large scale=transform fault e.g San Andreas fault
No crust is made or destroyed here
Associated with powerful earthquakes
, Convergent plate margins (also known as destructive plate margins) occur when two plates collide
& there are 3 types:
1. When an oceanic plate meets continental plate.
The oceanic plate is denser than the continental plate therefore when they collide,
the oceanic plate slides beneath the continental plate into the mantle and melts (this
is known as subduction).
Deep ocean trenches mark the place where the oceanic plate starts to sink beneath
the continental plate
Subduction also leads to the formation of fold mountains- as the two plates collide,
the continental plate is folded and slowly pushed up.
Friction created between the colliding plates causes earthquakes in the Benioff
zone.
Volcanic eruptions are likely to occur as magma created by melting oceanic plate
rises through the faults in continental crust to reach the surface.
2. When an oceanic plate meets oceanic plate
When 2 oceanic plates collide, the denser/faster plate is subducted beneath the
other.
The rising magma forms underwater volcanoes
These can rise above sea level to form islands which are usually found in curved
lines called island arcs.
Subduction can produce shallow/deep focus earthquakes
3. When a continental plate meets continental plate
A collision margin occurs
Both plates are of same density so neither plate is subducted
They collide and sediments are crumpled between and are forced up to form high
fold mountains (e.g. Himalayas)
Subduction can happen due to compressed sediments.
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