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What is a Volcano?
A volcano is an opening, or rupture in a planet's
surface or crust, which allows hot magma, volcanic
ash and gases to escape from below the surface.
How are volcanoes formed?
A volcano is formed when plates hit each other.One of the plates goes under the other. This is
where the earth heats and melts the rock into
magma and gases. This can happen as deep
as 100 miles below the earth
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vent
cone
magma chamber
conduit
The volcano includes thesurrounding cone oferupted material.
the vent is the openingfrom which lava flows.Dust, ash, and rockparticles can also bethrown out of the vent!
Parts of the Volcano
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The power of Volcanoes!
Volcanoes can be heard 5000 km away and
can affect people in the range of 50 km.
Volcanoes are powerful enough to destroy an
island and produce 40 m waves when it eruptsand kill 36000 by the wave going 16km in
land.
Many active volcanoes lie under water.
The lava of the volcano can reach 1,250C.
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Volcanoes around the world!
There are more than 1500 potential activevolcanoes around the world.
There are currently no active volcanoes in
Australia but there was one huge eruption 4600
years ago. In South Australia Mt Gambier was the volcano
which erupted 4600 years ago.
Mt St Helens in the USA was dormant for 123
years until it erupted violently in 1980, lowing400 metres off its top and killing 57 people.
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How do volcanoes work?
Pressure from gases in the mantle squeezes the molten rockupwards. The surface of the Earth can swell until it cannot
take any more pressure and then It then explodes with lava.
Hot, molten rock (magma) is buoyant (has a lower
density than the surrounding rocks) and will rise upthrough the crust to erupt on the surface.
When magma reaches the surface it depends on how
easily it flows (viscosity) and the amount of gas
(H2O, CO2, S) it has in it as to how it erupts.Large amounts of gas and a high viscosity (sticky)
magma will form an explosive eruption!
Small amounts of gas and (or) low viscosity (runny)
magma will form an effusive eruption
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Magma is a mixture of molten rockwhich is found under the earth.
What comes out of the volcano when it
erupts is called lava.
Lava is made up of magma and gasessuch as hydrogen sulphide and steam.
Lava flows down the volcano at speeds
of less than 10 km/h and will later cool
to form solid rock.
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Types of Volcanoes!
Explosive Volcanoes Explosive volcanoes are the volcanoes that
when they erupt produce more ash than
lava. When explosive volcanoes erupt they
produce a large area of gas that is
exploded into the atmosphere along with
pieces of extremely hot rocks. The sudden
cooling produces these hot rocks and
shattering of molten rock as it loses its
dissolved gases.
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Explosive Volcanoes Explosive volcanoes have a liquid that lookslike lava, but it is the melted rock of the
volcano.
When an explosive volcano erupts there wont
be any time to evacuate. So volcanologists
constantly watch these volcanoes for signs of
eruption, to have time to evacuate any humanlife from the area.
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Non Explosive volcanoesNon-explosive volcanoes are the volcanoesthat when they erupt lava pours out of the
opening and flows down the mountainside.
When a non-explosive volcano erupts, it
erupts in fountains from the summit or as
curtains of fire from large fissures which split
the volcano's sides.
Non-explosive volcanoes are usually foundclose to oceans or seas, because when a non-
explosive volcano erupts its lava usually flows
into an ocean or the sea.
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Composite volcanoes Composite volcanoes, sometimes known as strato volcanoes,
are steep sided cones formed from layers of ash and lava flows.
Composite volcanoes can rise over 8000 feet.
Examples of composite volcanoes include Mount Fuji (Japan),
Mount St Helens (USA) and Mount Pinatubo (Philippines).
When composite volcanoes erupt they are explosive
Shield volcanoes Shield volcanoes have gently sloping sides and are
formed from layers of lava.
Eruptions are typically non-explosive. Shield volcanoes produce fast flowing fluid [lava]
that can flow for many miles.
Examples of shield volcanoes include the Hawaiian
volcanoes. Although these eruptions destroy
property, death or injury to humans rarely occurs.
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Dome
Dome volcanoes have much steeper sides than shield volcanoes.
This is because the lava is thick and sticky. It cannot flow very far before it cools and hardens. An example is
Puy de Dome in the Auvergne region of France which last
erupted over 1 million years ago.
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Such as:
The Earths moon
Mercury Venus
Mars
Io (A moon of Jupiter).
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A small video clip
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