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Preview of Volcanoes

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Volcanism is the eruption of magma onto the surface of the Earth. It is an endogenous process caused
by the movement of plate tectonics. Magma under the crust is under very great pressure.
When folding and faulting occur, cracks or fractures appear. These are lines of weakness. When
these lines of weakness develop downward in the crust and reach the magma, they will release the
pressure in the magma. This allows magma to rise up along the lines of weakness and intrude into the
crust. Some magma may even reach the Earth's surface.
Molten rock beneath the surface is referred to as magma, but once on the surface it is called
Magma at high temperature and pressure exploit any weaknesses in the crust and may even
erupt on the surface as lava.
Volcanoes are openings in the earth's crust through which lava, ash and gas erupt.
Volcanic activity is classified as Intrusive or Extrusive depending on whether the magma breaks
the surface or not.
Extrusive igneous rocks are formed by the crystallisation /partial melting of
magma within the crust and mantle.
o Takes place ON the Earth's surface.
o Basalt is a common extrusive igneous rock.
o The major form of this activity is volcanic eruption of lava and other materials.
The type of volcanic feature is determined by the nature of the material ejected and the type of
eruption. Material ejected from an eruption may be Gaseous, Solid or Liquid:
Gaseous emission:
o Gaseous emissions are dominated by superheated steam ­ but also Carbon
Monoxide, Hydrogen, Sulphide, Sulphur Dioxide and Chlorine. These
gases are highly dangerous.
o Gases are released from magma through unstable elements reaching such high
concentrations in the base magma that they evaporate.
Solids emission:
o Includes ash, dust and glassy cinders.
o Dormant volcanoes contain shattered remains of solidified lava that
previously plugged the vent of the dormant volcano.
Liquid emission:
o Includes lava bombs known as Tephra or Pyroclasts, which solidify in mid-air i.e.
o Tephra in its finest form of hair-like trails is called lapilli.
o Also include Surface lavas ­ acidic or basic ­ flowing from vents and

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Types of lava
Basaltic (Basic) lava:
Erupts primarily from shield volcanoes, fissure systems, scoria cones, and spatter cones.
Most common at along spreading ridges (constructive margins).
Dominated by Iron and Manganese and low in silica content (48% - 52%).
Eruption is fluid and free-flowing - high water contents.
Temperature of eruption over 950 degrees ­ frequent eruptions that last long period of
time.…read more

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Types of eruptions
Icelandic Basaltic Lava flows gently from fissures
Hawaiian Basaltic Lava flows gently from central
Strombolian Basaltic Frequent, explosive eruptions
of tephra and steam.
Occasional, short lava flows.
Vulcanian Basaltic, andesitic and rhyolitic Less frequent, but more violent
eruption of gases, ash and
Vesuvian Basaltic, andesitic and rhyolitic Following long periods of
inactivity, very violent gas
explosions blast as high into
the sky.
Peleean Andesitic and rhyolitic Very violent eruptions of nuees
ardentes.…read more

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Eruption: gentle, persistent (A'a flow) - creates extensive lava Plateaus.
o Has a long, linear vent ­ fairly flat surface.
Lava Plateaux
A wide area of solidified lava that can be up to 1km thick covering large
surface areas. They are multi layered because of repeated lava flows and
occur where lava (basaltic with low viscosity, lower silica content and low
explosive) pours out of long fissures rather than a central vent, covering
much larger areas with thick layers of magma i.e.…read more

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Minor extrusive feature
o An intermittent turbulent discharge of superheated water
ejected and accompanied by a vapour phase/hot springs
where the water erupts i.e. The Strokkur Geyser in
Iceland & Old Faithful in Yellowstone National Park
o Formed in areas of intense volcanic activity.
o Water heated at depth in the crust by magma chambers
(probably solid intrusive rocks) channelling their way
through cracks in rocks and escaping through vents,
erupting on the surface as steam and hot water.…read more

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Intrusive Volcanic Feature
INTRUSIVE volcanic features occur due to lava being intruded into the lithosphere or rock, they cool
and solidify into rocks and are later exposed at the land surface as erosion and weathering DENUDES
the land downwards. The majority of volcanic features are actually intrusive, most volcanic materials
never actually make it to the earth's surface in their molten state.
o Forms when magma solidifies in vertical intrusions (cracks).…read more

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Larger-scale intrusive landform, massive in size and depth formed deep below the
o Forms when large masses of magma cool and solidify. As the
magma cools slowly, large crystals are formed in the rock (e.g.
o Batholiths are often dome-shaped and exposed by later
erosion. This is the case on Dartmoor and on the Isle of Arran.
o Batholiths can be several hundreds of km in diameter.…read more

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What are Fold Mountains?
Fold Mountains are formed along plate boundaries.
Over millions of years, thick sediments were deposited in huge depressions called geosynclines.
Rivers carried sediments and deposited them into the depressions. The sediments were
compressed into solid sedimentary rocks such as sandstone and limestone.
The plates moved together, forcing the rocks to fold upwards into Fold Mountains.
There are found at DESTRUCTIVE MARGINS (e.g. the Andes Mountains) and at COLLISION
MARGINS (e.g. the Himalayas).…read more

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It's not possible to prevent earthquakes and volcanic eruptions. However, careful management of
these hazards can minimise the damage that they cause. Prediction is the most important aspect of
this, as this gives people time to evacuate the area and make preparations for the event.
Predicting and preparing for volcanoes
Unfortunately volcanic eruptions cannot be prevented.
Managing hazards such as earthquakes and volcanoes can be done by:
prediction and preparation.…read more

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Funds need to be available to deal with the emergency and a good communication
system needs to be in place.
Preventing an eruption
Currently, it is impossible to prevent a volcanic eruption, but it is possible to keep damage to a
minimum. In 1973, citizens of Iceland poured cold water onto flowing lava to slow it down, an act
that helped save the fishing port of Heimaey. In Sicily, on Mount Etna, engineers blasted holes in
the hard crust covering a lava flow using explosives.…read more


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