Download Volcanoes - Bekah`s e

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Volcanoes
By: Bekah Richards
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Types of Volcanoes
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Composite Volcano
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Sometimes called Stratovolcanoes,
Composite volcanoes form when runny
lava escapes through a fissure and flows
a long way. Composite volcanoes are tall
cone-shaped mountains that are
typically steeply-sided, symmetrical
cones of large dimensions.
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These volcanoes are built in layers by
multiple eruptions, sometimes recurring
over hundreds of thousands of years,
sometimes over a few hundred. Andesite
magma (the most common but not the
only magma type), tends to form
composite cones. During some
eruptions, cinders, bombs and blocks
form a mountain or add height to one
that earlier volcanic eruptions had built.
During other eruptions, lava flows
cement these rocks together. Most
composite volcanoes have a crater at the
summit which contains a central vent or a
clustered group of vents.
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Cinder Cone Volcano
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Cinder cone volcanoes are the
most common kind of
volcanoes.They are steep sided
cones of basaltic fragments and
are smaller and simpler than
composite volcanoes. Streaming
gases carry liquid lava blobs
into the atmosphere that fall
back to earth around a single
vent to form the cone. The
volcano forms when ash, cinders
and bombs pile up around the
vent to form a circular or oval
cone.
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Most have a bowl-shaped crater
at the summit. The longer the
eruption, the higher the cone.
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Shield volcano
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Shield volcanoes are large volcanoes
that are built almost entirely of fluid lava
flows. It has broad sloping sides and is
usually surrounded by gently sloping
hills in a circular or fan shaped pattern,
that looks like a warrior's shield.
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The volcano is produced by the action of
the gas (steam or water vapor) with heat
from the earth's core. This action melts
rock turning it into magma. The pressure
from the heat of the gas pushes the
magma upwards till it explodes. Molten
magma shoots upward from deep below
the ocean floor and breaks through the
drifting plates to form shield volcanoes.
Lava flows gently and continuously out
of the central volcanic vent or group of
vents.
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Shield volcanoes may be produced by
hot spots which lay far away from the
edges of tectonic plates. Shields also
occur along the mid-oceanic ridge,
where sea floor spreading is in progress
and along subduction related volcanic
arcs.
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Ash Cloud: very
small solid
particles ejected
from a volcano
during an eruption
which have
intermediate axes
Vent: an opening
at the earth's
surface from
which volcanic
material, as lava,
steam, or gas, is
eliminated.
Side vent: A volcanic vent is an opening
found in the earth's crust through which
molten lava, volcanic gases and rocks
pass through onto the land surface or
into the atmosphere. The lava pours out
of fissure vents before making lava
channels that drain into the atmosphere.
Magma Chamber is a large underground pool of
liquid rock found beneath the surface of the earth.
The molten rock in such a chamber is under great
pressure, and gives enough time, that pressure can
gradually fracture the rock around it creating
outlines for the magma. If it finds a way to the
surface, then the result will be a volcanic eruption;
consequently many volcanoes are situated over
magma chambers.
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Pahoehoe Lava
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Pahoehoe lava is usually the
first kind of lava to erupt
from a volcano. The lava that
flows from Pahoehoe flows is
very, viscous, that means
that it is thin and liquid. It has
a smooth surface that dries
pretty quickly and becomes
thicker and flows more
slowly than the still hot lava
below the surface. As the
surface of the flow dries, it
turn black and becomes
crusty. The top crust is not
safe to walk on because it is
weak and can collapse.
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A’a Lave
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A'a lava flows have a rough
surface made up of broken
blocks of lava. These
broken pieces of lava are
called clinkers. It looks like
little lava spines are
sticking up from the lava as
it moves. The lava is like
paste because it is so thick
and the clinkers travel on
top of the lava flow. Below
the top layer of the lava
flow there is a core of slow
viscous lava. The clinkers
are burried by the front of
the lava flow as the lava
moves.
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Lava Pillow
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Pillow lava forms when lava
pours into the ocean. The
lava cools fast and makes a
ball. As the lava continues
to flow it forces an opening
in the crust of the pillow
and more flows out to form
another pillow shape.
Pillow lava is made from
basalt lava flows that
reaches a source of water.
Sometimes scientists find
pillow lava strings on the
land. That helps them to
know that an area of land
was under water in the
past.
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Lava Fountain
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A lava fountain is a large
amount of lava that is
thrown up into the air
when gas bubbles
expand in the melted
rock. Most lava fountains
range in height from 30
to 300 feet. Sometimes
the fountain can be as
tall as 1,500 feet
tall. Lava fountains erupt
inside lava lakes, along a
fissure, isolated vents or
from lava tubes.
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Lava Flow: A lava flow is a molten river of melted
rock. Lava flows do not come from explosive
eruptions, but they just pour out of the top of a vent
slowly. Lava flows burn and destroy everything in
their paths. How fast lava flows depends on what
the lava is made up, how steep the ground is, how
much lava is flowing from the vent, and how wide
the flow is. Basalt flows are thin enough to flow
quickly for a long distance. Lava flows made up of
andesite moves very slow and is called viscous
because it is very thick. Viscous lava flows so
slowly that lava domes can form over the mouth of
a vent.
Lava Lake:
When large amounts of lava pour into a crater a
lake of lava is made. Once the lava that has
collected in the crater has cooled and dried it is
still called a lava lake.
Lava Flow
And
Lava Lake
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Bibliography
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http://www.k12.hi.us/~kapunaha/student_projects/volc_blo
wout/shield_volcano.htm
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www.Wikipedia.com
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http://www.skybrary.aero/index.php/Volcanic_Ash
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http://library.thinkquest.org/TQ0311160/vollava.htm