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tectonic processes and hazards - Coggle Diagram
tectonic processes and hazards
plate boundaries
CONSERVATIVE
E.G. "san andreas fault" which is between pacific & north american plates
these plates move past each other, moving at different speeds, the friction occurring causing the plates to become stuck
Pressure builds up as the plates try to move, sending out huge amounts of energy when released in the form of an earthquake
these earthquakes can be the most destructive as they occur closest to the earth's surface
UPLIFTING COLLISION
E.G. "himalayas" between the indian & eurasian plates
these are similar to 'destructive plate margins' as the magma escapes through a weakness within the rocks through a composite volcano
if 2 continental plates collide, neither will sink so the land buckles upwards to form fold mountains
CONSTRUCTIVE
E.G. "mid-atlantic ridge" between the eurasian & north american plates
here the plates move apart from on another, allowing the magma to rise up an make new land in the form of a shield volcano
the movement of the plates over the mantle can cause an earthquake
DESTRUCTIVE
E.G. "ring of fire" between the nazca & south american plates
usually involves an oceanic and a continental plate, moving towards each, causing both earthquakes and volcanoes
as the plates collide, the denser, oceanic plate is forced beneath the continental plate; the area below the surface is called the subduction zone
the pressure of the hot magma causes it to escape through the weak spots in the rock through a composite volcano
this is also a collision margin as the plate could not sink and instead would just cause an earthquake
earth's structure
inner core;
in the center of the earth being the hottest part of the earth with temps up to 5,500oC. it is solid and made up of iron and nickel
outer core;
a liquid layer surrounding the inner core also made of iron or nickel
mantle;
the thickest section of the earth at approximately 2,900km, made up of a semi-molten rock called magma
crust;
a solid, thin layer of rock, broken into tectonic plates: either continental or oceanic
continental crust
is found under large land masses or continents, generally older than oceanic crust and is less often destroyed
oceanic crust
is found underneath oceans, denser than continental crusts so can be subducted
earthquakes
are found along all types of plate margins where the friction and pressure between plates causes the ground to shake
these can cause secondary hazards such as; landslides and tsunamis
@ constructive plate margins - tend to be frequent, small and typically a low hazard risk due to geographical location
@ conservative plate margins - have a higher hazard risk due to the amount of friction between the sliding plates
@ destructive plate margins - the largest and most damaging earthquakes due to a build up of pressure leading to a sudden release of energy
volcanoes
are landforms that develop around a weakness in the earth's crust from which molten magma, volcanic rock and gases are ejected
the violence of a volcanic eruption is determined by the amount of dissolved gases in the magma and how easily the gases can escape
@ destructive plate margins - the denser oceanic plate is subducted beneath the continental plate, the pressure causing the magma to be forced upwards, causing an eruption
@ constructive plate margins - generally less explosive as there a smaller force acting on the rising magma
primary hazards
pyroclastic flows
results from the frothing of molten magma in the vent of the volcano. bubbles burst explosively to eject hot gases & pyroclastic material; glass shards, pumice, crystals, ash
tephra
is ejected material or rock fragments, often as fine as an ash, reducing visibility and affecting air travel
lava flows
are fast moving and pose a great threat to human life
volcanic gases
normally include a mix of water vapour, sulphur dioxide, hydrogen and carbon monoxide
hotspot volcanoes
are found away from the boundaries of tectonic plates and are thought to be fed by underlying mantle plumes that are unusually hot in comparison to the surrounding mantle
high pressure and temperatures at the base of the lithosphere enable melting of the rock, the molten material rising to form volcanoes at the earth's surface
the moving of plates over time can cause a chain of volcanoes, such as the Hawaiian Islands
seismic waves
are an elastic wave produced by an earthquake, measured by a seismometer and determine the amount of ground shaking recording both vertical and horizonal movements
primary or P waves
are vibrations caused by compression, spreading quickly from the fault at about 8km/sec
secondary or S waves
move more slowly at around 4km/sec, vibrating at right angles to the direction of travel
long or L waves
are surface waves with the vibration occurring in horizontal plain with a high amplitude
tsunamis
are generally a secondary hazard, initiated by undersea earthquakes, landslides, slumps and sometimes volcanic eruptions
its's characterised by long wavelengths, low amplitude & fast velocities
they grow in height as they move closer to the coastline as the water becomes shallower
it is not a single wave but a series of waves, also known as a wave train, caused by seabed displacement
there is often an escalation effect in terms of damage across each wave: the time between these waves often only being a few minutes
when there are longer periods of time between waves it often proses a greater risk as people may presume the tsunami has finished so may return to the affected area
active
subduction zones
are characterised by magmatic activity, a belt with thickened continental crust, a narrow continental shelf & active seismicity.
slab pull -
when the weight of a dense tectonic plate is subducted into the mantle
ridge push -
when gravity causes the ridge to push on the lithosphere and move tectonic plates
most tectonic plates move a few centimeters each year
