Transcript Volcano - LemoineHPCScience

The volcano is named after Vulcano, an Italian island
north of Sicily.
Map of Sicily.
The Vulcano has been active for thousands
of years and the ancient Romans named their
god of fire, Vulcan, after it.
Hephaestus (Vulcan). When Zeus (the
most powerful god) discovered that man
possessed fire, he was terribly angry. He
commanded Hephaestus to make a set of
chains. Hephaestus was a god of many
skills, often referred to as the Blacksmith of
the Gods. With these chains, Zeus had
Prometheus (the god who brought fire to the
humans) tied to a great rock and left him to
be tormented by a cruel eagle.
The Romans believed that the smoke and
fire rising from the volcano came from his
forge where he and his assistants the
Cyclops were at work in his smithy
below. Hence they named the volcano after
him.
Structure of a Volcano
A volcano constitutes a vent, a pipe, a crater, and a cone.
The vent is an opening at the Earth's surface.
The pipe is a passageway in the volcano in which the magma rises
through to the surface during an eruption.
The crater is a bowl-shaped depression at the top of the volcano where
volcanic materials like, ash, lava, and other pyroclastic materials are
released.
Solidified lava, ashes, and cinder form the cone. Layers of lava, alternate
with layers of ash to build the steep sided cone higher and higher.
Volcanologists have classified volcanoes into groups based on the
shape of the volcano, the materials they are built of, and the way the
volcano erupts.
The groups are:
•Composite Volcanoes (also called strato volcanoes),
•Shield Volcanoes (also called shields),
•Cinder Cones,
•Spatter Cones, and
•Complex Volcanoes (also called compound volcanoes).
Shield Volcano
Shield volcanoes are huge in size. They are built
by many layers of runny lava flows. Lava spills out
of a central vent or group of vents. A broad
shaped, gently sloping cone is formed. This is
caused by the very fluid, basaltic lava which can't
be piled up into steep mounds.
Shield volcanoes may be produced by hot spots which lay far away
from the edges of tectonic plates. Shields also occur along the midoceanic ridge, where sea-floor spreading is in progress and along
subduction related volcanic arcs.
The eruptions of shield volcanoes are characterized by lowexplosivity lava-fountaining that forms cinder cones and spatter
cones at the vent. Famous shield volcanoes can be found for
example in Hawaii (e.g. Mauna Loa and Kilauea).
Composite Volcano
Composite volcanoes, also called strato volcanoes, are formed by
alternating layers of lava and rock fragments. This is the reason they
are called composite.
Strato-volcanoes often form impressive, snow-capped peaks which
are often exceeding 2500m in height, 1000sq.km in surface, and 400
cubic kilometers in volume.
Between eruptions they are often so quiet they seem extinct. To
witness the start of a great eruption requires luck or very careful
surveillance.
Different Shapes of Composite Volcanoes.
Strato-volcanoes are constructed along subduction
zones. Examples of composite volcanoes include Mount
Hood, Mount Rainier, Mount Shasta, Mount Fugi, Mount
Mayon, and Vesuvius.
Composite volcanoes usually erupt in an explosive way. This is usually
caused by viscous magma. When very viscous magma rises to the
surface, it usually clogs the crater pipe, and gas in the crater pipe gets
locked up. Therefore, the pressure will increase resulting in an explosive
eruption.
Although strato-volcanoes are usually large and conical, we can
distinguish different shapes of them: concave (like Agua), pyramidal
(like Stromboli), convex-concave (like Vesuvius), helmet-shaped (like
Mount Rainier), collapse caldera (like Graciosa), nested (like El Piton in
Teide), multiple summits (like Shasta), elongated along a fissure (like
Hekla).
Different Shapes of Composite Volcanoes.
A cinder cone is a steep conical hill formed above a
vent. Cinder cones are among the most common volcanic
landforms found in the world. They aren't famous as their
eruptions usually don't cause any loss of life. Cinder cones are
chiefly formed by Strombolian eruptions. The cones usually
grow up in groups and they often occur on the flanks of strato
volcanoes and shield volcanoes.
Cinder cones are built from lava fragments called
cinders. The lava fragments are ejected from a single vent and
accumulate around the vent when they fall back to earth.
Cinder cones grow rapidly and soon approach their maximum
size. They rarely exceed 250m in height and 500m in diameter.
The shape of a cinder cone can be modified during its
(short) life. When the position of the vent alters,
aligned, twin or secant cones develop. Nested, buried
or breached cones are formed when the power of the
eruption varies.
A great example of a cinder cone is Paricutín in
Mexico. It was born in February 20, 1943 in a corn
field and grew to 300 feet in 5 days.
Spatter Cone
When hot erupting lava contains just enough explosive gas to
prevent the formation of a lava flow, but not enough to shatter it
into small fragments the lava is torn by expanding gases into fluid
hot clots, ranging in size from 1cm to 50cm across, called spatter.
When the spatter falls back to Earth the clots weld themselves
together and solidify forming steep-sided accumulations. These
accumulations focused on an individual vent are called spatter
cones.
In fact all volcanoes could be complex volcanoes
since all of them are made up of multiple flows, ash
layers, domes, cones, etc. in varying amounts.
However, when we call a volcano a complex volcano
it is because we mean the "system" of those volcanoes
is not "simple". Caldera complexes for instance have
often got a large caldera with many subsidiary vents
and deposits, some of which could be considered
"volcanoes" in their own right.
Frankly speaking, a volcano that consists of a
complex of two or more vents is reckoned as a
compound or complex volcano.
Besides
Volcanoes, some
other features may be
found in volcanic
areas as well. These
include:
•Calderas and Crater
Lakes,
•Volcanic Plugs,
•Lava Plateaus,
•Geysers and Hot
Springs
Caldera of
Tengger in
Java,
Indonesia.
Calderas are huge bowl-shaped
craters, usually formed by
volcanic activity. Some of the
earliest geologists thought the
calderas are formed when violent
volcanic eruptions blew the tops off
the volcano. However, few calderas
are formed this way.
Calderas are formed because eruptions of huge volumes of
pyroclastic materials had left the roof of the magma chamber
unsupported, causing it to fracture and fall downwards into the
chambers. Magma is also being drained from the chamber
through fissures at depth. Collapse of the cone occurs, as it
becomes a jumble of enormous blocks, some of which sink
through the magma. This process is termed cauldron
subsidence. This process may take a long time to complete and
often happens in an extinct volcano. An example is the caldera of
Tengger in Java, Indonesia.
Crater lakes are formed when a caldera becomes filled
with water sometime after it is formed. An example is
the Crater Lake in Oregon, America. It is nine
kilometers in diameter whose floor is 600 meters in
depth, while the surrounding 6800-year-old caldera
walls rise steeply 600 meters above it.
Volcanic plugs are formed when lava solidifies in the
pipe of an extinct volcano. Over time, the volcanic cone
made up of less resistant rocks wears away, leaving
behind the solidified volcanic plug.
The Devil's Tower in Wyoming, USA is a great
example of a volcanic plug.
Lava plateaus are formed by the large
outpourings of fluid lava from long narrow openings
in the crust. During each eruption, the lava flows
out from these openings, solidifies and builds up
layer upon layer each time.
A good example would be the Columbia Plateau
in the USA.
Geysers and Hot Springs
A geyser is a hot spring that periodically erupts,
throwing water into the air. Though that sounds
simple, geysers are extremely rare.
An eruption begins when pressure on a magma
chamber forces magma up through the conduit and
out the volcano's vents. When the magma chamber
has been completely filled, the type of eruption partly
depends on the amount of gases and silica in the
magma. The amount of silica determines how sticky
(level of viscosity) the magma is and water provides
the explosive potential of steam.
AND NOW, A VIDEO ABOUT VOLCANOES IN THE
“PACIFIC RING OF FIRE”
http://www.bing.com/videos/search?q=pacific+ring+of+fire&FORM=HDRSC3#vie
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