The whole of plate tectonics

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  • Created by: Ruth Butt
  • Created on: 05-05-14 14:01
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Ruth Butt 13SM
Volcanic Activity:
There are intrusive volcanic features which occur beneath the earth's surface and extrusive features
which occur on the earth's surface where there are major types (e.g. volcanic eruptions) and minor
types (e.g. geysers and springs).
Once magma erupts onto the earth's surface, it's called lava and there are 3 types of lava:
1. BASALTIC LAVA which is produced at constructive margins (when plates move apart from
each other, e.g. Eurasian and North American plates) which has low viscosity and silica
content, and has high temperatures of over 950c.
2. ANDESITIC LAVA is found at destructive margins (where plates move towards each other,
e.g. Nazca and South American plates), has medium viscosity and silica content, and
temperatures of between 750-950c.
3. RHYOLITIC LAVA is also found at destructive margins, has the highest viscosity and silica
content, and the lowest temperature of less than 750c.
Volcanic eruptions with BASALTIC LAVA flows are frequent, erupt for long periods of time, but aren't
violent and do flow easily. ANDESITIC and RHYOLITIC LAVAS have a higher viscosity and lava and
gases cannot escape as easily. This causes pressure to build up and blockages to form until cleared by
a violent, short-lived, occasional eruption.
DOME: Also known as a strato/composite volcano, they often occur at destructive margins, and have
steep sides due to producing Andesitic and Rhyolitic lava with high viscosity.
CALDERA: These are very wide, large
volcanoes which occur at destructive margins
and produce Andesitic and Rhyolitic lava. The
central part of the volcano has collapsed as the
magma chamber below has emptied. There
are layers of ash, lava and cinder with a wide,
circular crater several metres across.
Intrusive features:

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Ruth Butt 13SM
1. HOT SPRINGS- This is where groundwater emerges at the surface close to an area of volcanic
activity. They have a high mineral content due to dissolved solids, and are popular with
tourists, e.g. the Rio Hondo in Argentina.
2. GEYSERS- When groundwater is heated above boiling point due to magma, so water and
steam are ejected at high speeds. The water becomes pressured, forcing its way through
cracks in rocks till the hot water and steam spray out from a vent.…read more

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Ruth Butt 13SM
Triggered by underwater earthquakes, the movement of the seabed causes large amounts of water
to be DISPLACED which produces large waves. The greater the seabed movement, the more water is
displaced and the bigger the wave.
Volcanic eruptions and landslides can also cause tsunamis. They can travel for 100's of km's in deep
water which results in mass destruction, and a high death toll as little can be done to protect the land.…read more

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Ruth Butt 13SM
eruption when citizens don't wish to leave their beloved homes, and believe an earthquake isn't
realistically likely to happen.
Finally, when predicting tsunamis, we rely on earthquake detection systems to allow for
evacuation, however this is reliant on good communication systems, and so if people don't
receive the message they won't evacuate.
Earthquakes- Buildings can be built to withstand earthquakes, e.g. by reinforced concrete or
special foundations which absorb seismic waves.…read more

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Ruth Butt 13SM
The more people in an area the more are at risk of the effects of a disaster. There is a higher risk in
densely populated cities where collapsing buildings poses a risk to life. Evacuating large numbers of
people can be difficult as roads become blocked and trapped.
When in the day is happens can have an effect on the severity of its impacts. If it occurs at night, more
are inside and are likely to be crushed by collapsed buildings.…read more


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