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eq3 : why do the causes and impacts of tectonic activity and management of tectonic hazards vary with location?
facts about the earth’s crust
thinnest layer
made of rocks (solid)
divided in 15 tectonic plates
consists of oceanic and continental crust
facts about the earth’s mantle
semi-solid material
thickest layer
upper and lower mantle - upper is mostly solid but some melting at plate boundaries
becomes hotter and denser with depth
what is the outer core made of?
made of molten layer of iron and nickel
facts about the earth’s inner core
made of iron and nickel
densest layer
solid ball
composed mostly of iron
pressure is so high, it never melts
what is oceanic crust?
part of earth’s crust which is:
underwater
thinner (than continental)
made of basalt
denser/heavier (than continental)
newer (than continental)
what is continental crust?
part of the earth’s crust which is:
thicker (than oceanic)
made of granite
less dense/lighter (than oceanic)
older (than oceanic)
what is the lithosphere?
rigid layer, lower part of the earth’s crust and lies on top of the asthenosphere.
what is the asthenosphere?
upper part of the mantle. high temperature and pressure is low enough so rocks can flow very slowly.
what is a plate boundary/margin?
this is where two plates meet.
tectonic activity such as volcanoes and earthquakes are common along a plate margin.
types of plate boundary
constructive/divergent
destructive/convergent
transform/conservative
collision
convection currents
convection currents move circular in motion
in the lower mantle, the rock is heated by the core and rises slowly towards the crust and begins to cool.
at the asphenosphere, the rock is forced to move sideways.
as it cools, it sinks slowly to the core, then forced sideways, and is heated by the core until it rises again.
convection currents drag the plates above to move them apart.
how do constructive/divergent boundaries work?
convection currents pull apart the two plates and widen the gap between them
rising heat and reduction in pressure causes the asthenosphere to melt, forming magma
magma rises to fill the gap, which will eventually solidify, forming new land/volcanoes
e.g. Mid Atlantic Ridge - Eurasian plate moves away from North American plate
how do destructive/convergent boundaries work?
convection currents cause plates to move towards each other
when oceanic plate meets continental plate, the denser oceanic plate sinks under the less dense continental plate - this is subduction
as oceanic plate subducts, magma rises and may eventually break through earth’s surface, forming composite volcano
e.g. Andes Mountains - Nazca and South American plates move towards each other
how do conservative boundaries work?
as plates slide past, they sometimes cause friction and build up pressure →when they get past, the pressure is released, shock waves are sent to the surface
plates can move in opposite directions and similar direction, but different speeds
as crust is neither created or destroyed, there are no volcanoes but the friction causes earthquakes
what are volcanoes?
openings in the earth’s crust, or vents where lava, tephra (small rocks) and steam erupt onto the earth’s surface.
shield vs composite volcanoes
shield:
non-violent
gentle slope
wide base
lava is fluid
composite:
violent
steep slope
high with narrow base
acid lava and ash
describe the two types of lava
basic lava:
low silica content
takes longer to cool so flows over long distances
less viscous (less thick)
acid lava:
high silica content
travels only short distances
higher viscosity
what is an earthquake?
sudden and short period of intense ground shaking caused by a release of seismic energy
what is the focus of an earthquake?
where an earthquake originates deep within the earth’s crust
what is the epicentre of an earthquake?
the place on the surface of the earth directly above the focus
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