Tectonic activity and hazards glossary-Edexcel A2 unit 4 option


So this is a glossary on every key word you need to know for the unit 4 exam.

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Key words glossary unit 4: tectonic activity and hazards
Key word Definition
Areal extent This is the volume of the area that is affected; this depends
on the magnitude and type.
Ash falls Very disruptive; they can damage buildings and plants.
Asthenosphere Second layer of the crust.
Basaltic magma (mafic) Low silica content and high content of Fe and Mg.
Batholith Large masses of intrusive rock that may cause doming to the
surface as they are forming. Heat transferred from the
magma causes metamorphic rock.
E.g. Sierra Nevada batholith, California USA.
E.g. Chilean coastal batholith
Benioff zone A zone of earthquakes that is produced by the interaction of
the oceanic crustal plate with a continental plate.
Block mountains This occurs when stress is extensional and the crust is
thinned. There are two types lifted and tilted.
Calderas This is a steep depression and there are three types:
crater-lake caldera, basaltic caldera and resurgent-caldera.
E.g. Yellowstone
Cinder cones The volcanic shape is straight sides with steep slopes, the
composition is tephra occasionally andesitic and the plate
boundary is a hot spot.
E.g. El Jorullo, Mexico.
Collision plate boundary Two continental plates collide and are crushed against each
other. They are pushed upwards to form new mountains.
Composite volcanoes/stratovolcanoes They are composed of lava and ash with a small summit
E.g. Mount Mayon, Philippines.
Continental drift This was published by Alfred Wegner (1912); it explained that
300 million years ago there was a single continent (Pangea).
This further split into Laurasia and Gondwanaland.
Convection currents This is the movement of magma in the asthenosphere; this
causes the movement of plates (plate tectonics). It is caused
by radioactive decay in the core of the Earth.
Convergent plate boundary The oceanic crust is denser than continental crust and so
when they converge the oceanic plate is subducted in the
asthenosphere beneath the continental plate. This melts
approximately 100km below the surface. The melted surface
(the oceanic crust) is less dense (now) and so it rises through
weaknesses in faults and plate boundaries. It can cool
forming intrusive (molten into cracks or between layers of
rocks) igneous rocks, e.g. granite. Or it may form a violent
volcanic eruption. Earthquakes are also common at the
Benioff zone where the plates get locked due to the pressure
and break away after the release. It was known as the
destructive plate boundary.
Disaster-loss-recovery-cycle This is a continual event because of the socio-economic
factors. It becomes chronic as it becomes more difficult for
the area to cope. Human factors are likely to increase the
chance of death because of the lack of preparation, aid and
political instability.
E.g. Haiti.
E.g. Philippines.
Divergent plate boundary Pressure from the rising magma leads to a doming of the
surface and the formation of a ridge. As the plates move
apart, faults are produced in which magma can rise through.
Rising magma cools and solidifies producing new crust:
within the existing crust or following a volcanic eruption.
Dome volcanoes This is very steep sided and this is because acid lava
solidifies very quickly when exposed to air.
E.g. Chaiten caldera, Michinmakiida volcano, Chilli.

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Key words glossary unit 4: tectonic activity and hazards
Duration This is one of the factors of a hazard profile; the time taken
for the tectonic event to happen.
Dykes Cut across the bedding planes of the rock. Magma forms
cracks and weaknesses. It cools and solidifies before
reaching the surface. Forms linear ridges when exposed.
E.g.. Mt Calanna, Mt Etna, Italy.
Extrusive igneous activity This is the production of different landforms created by
material outpouring from the Earth's crust.…read more

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Key words glossary unit 4: tectonic activity and hazards
Katmalan eruptions There are massive ash flows; this is with explosive tephra,
hot springs and fumaroles.
Laccolith Magma cools between layers. It is smaller than a batholith.
E.g. Pine Valley mountains, Utah, USA.
Lahar This is when melt water flows it mixes with loose soil and ash
forming a lahar.
Landslides Movement of masses of rock, Earth or debris down a slope.
Slope failure can occur because of an earthquake or heavy
rain.…read more

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Key words glossary unit 4: tectonic activity and hazards
Sills Formed parallel to bedding planes. Cracks run horizontally. It
provides a line of weakness where the magma flows. As it
cools, the magma contracts providing cracks in the rocks.
E.g. Palisades Sill, New York New Jersey, USA.
E.g. Whin Sill, UK.
Solfatara This is created when gas (mainly sulphur dioxide) escapes
onto the surface.
E.g. Solfatara volcano, Italy.…read more


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