Type of Volcvolcanooanoes and Volcanoes Eruption
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Type of Volcanoes and Volcanoes Eruption
Oleh :
ADITHEA GEOVANDI SURYATAMA RADINI
115120048
PROGRAM STUDI TEKNIK GEOFISIKA
FAKULTAS TEKNOLOGI MINERAL
UNIVERSITAS PEMBANGUNAN NASIONAL VETERAN
YOGYAKARTA
2012
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Volcano
A volcano is a mountain that opens downward to a pool of molten rock below
the surface of the earth. When pressure builds up, eruptions occur. Gases and rock
shoot up through the opening and spill over or fill the air with lava fragments.
Eruptions can cause lateral blasts, lava flows, hot ash flows, mudslides, avalanches,
falling ash and floods. Volcano eruptions have been known to knock down entire
forests. An erupting volcano can trigger tsunamis, flash floods, earthquakes,
mudflows and rockfalls.Volcano has a many type :
1.Fissure Volcano
Fissure volcanoes have no central crater at all. Instead, giant cracks open in
the ground and expel vast quantities of lava. This lava spreads far and wide to form
huge pools that can cover almost everything around. When these pools of lava cool
and solidify, the surface remains mostly flat. Since the source cracks are usually
buried, there is often nothing "volcano-like" to see - only a flat plain. A fissure
eruption occured at the Los Pilas volcano in Nicaragua in 1952.
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2.Cinder Cones
Cinder cones are simple volcanoes which have a bowl-shaped crater at the
summit and steep sides. They only grow to about a thousand feet, the size of a hill.
They usually are created of eruptions from a single opening, unlike a strato-volcano or
shield volcano which can erupt from many different openings. Cinder cones are
typically are made of piles of lava, not ash. During the eruption, blobs ("cinders") of
lava are blown into the air and break into small fragments that fall around the opening
of the volcano. The pile forms an oval-shaped small volcano. Famous cinder cones
include Paricutin in Mexico and the one in the middle of Crater Lake in Oregon.
3.Shield Volcanoes
Shield volcanoes can grow to be very big. In fact, the oldest continental
regions of Earth may be the remains of ancient shield volcanoes. Shield volcanoes are
tall and broad with flat, rounded shapes. They have low slopes and almost always
have large craters at their summits. The Hawaiian volcanoes exemplify the common
type of shield volcano. They are built by countless outpourings of lava that advance
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great distances from a central summit vent or group of vents. The outpourings of lava
are typically not accompanied by pyroclastic material, which make the shield
volcanoes relatively safe during eruptions. Mauna Loa, a shield volcano on the "big"
island of Hawaii, is the largest single mountain in the world, rising over 30,000 feet
above the ocean floor and reaching almost 100 miles across at its base. Other famous
shield volcanoes include Kilauea, also in Hawaii, and Olympus Mons of Mars.
4.Composite Volcanoes
The most majestic of the volcanoes are composite volcanoes, also known as
strato-volcanoes. Composite volcanoes are tall, symetrically shaped, with steep sides,
sometimes rising 10,000 feet high. They are built of alternating layers of lava flows,
volcanic ash, and cinders. Famous composite volcanoes include Mount Fuji in Japan,
Mount Shasta and Mount Lassen i California, Mount St. Helens and Mount Rainier in
Washington State, Mount Hood in Oregon, and Mount Etna in Italy.
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5.Caldera
Caldera volcanoes are the Extreme Volcanoes. This type of volcano is shaped
more like an inverse volcano. An enormous magma chamber bulges up beneath the
ground from the extremely high pressures of the trapped gases within. Ring-shaped
cracks form outward from the magma chamber toward the surface and these act as
relief valves for the magma to escape. Caldera volcanoes are the largest on earth, with
some calderas measuring from 15 to 100 kilometers wide.
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Volcanic Eruptions
The most common type of volcanic eruption occurs when magma (the term for
lava when it is below the Earth's surface) is released from a volcanic vent. Eruptions
can be effusive, where lava flows like a thick, sticky liquid, or explosive, where
fragmented lava explodes out of a vent. In explosive eruptions, the fragmented rock
may be accompanied by ash and gases; in effusive eruptions, degassing is common
but ash is usually not.
Volcanologists classify eruptions into several different types. Some are named
for particular volcanoes where the type of eruption is common; others concern the
resulting shape of the eruptive products or the place where the eruptions occur. Here
are some of the most common types of eruptions
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1. Hawaiian Eruption
In a Hawaiian eruption, fluid basaltic lava is thrown into the air in jets from a
vent or line of vents (a fissure) at the summit or on the flank of a volcano. The jets can
last for hours or even days, a phenomenon known as fire fountaining. The spatter
created by bits of hot lava falling out of the fountain can melt together and form lava
flows, or build hills called spatter cones. Lava flows may also come from vents at the
same time as fountaining occurs, or during periods where fountaining has paused.Because these flows are very fluid, they can travel miles from their source before they
cool and harden.
Hawaiian eruptions get their names from the Kilauea volcano on the Big
Island of Hawaii, which is famous for producing spectacular fire fountains. Two
excellent examples of these are the 1969-1974 Mauna Ulu eruption on the volcano's
flank, and the 1959 eruption of the Kilauea Iki Crater at the summit of Kilauea. In
both of these eruptions, lava fountains reached heights of well over a thousand feet.
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2. Strombolian Eruption
Strombolian eruptions are distinct bursts of fluid lava (usually basalt or
basaltic andesite) from the mouth of a magma-filled summit conduit. The explosions
usually occur every few minutes at regular or irregular intervals. The explosions of
lava, which can reach heights of hundreds of meters, are caused by the bursting of
large bubbles of gas, which travel upward in the magma-filled conduit until they reach
the open air.
his kind of eruption can create a variety of forms of eruptive products: spatter,
or hardened globs of glassy lava; scoria, which are hardened chunks of bubbly lava;
lava bombs, or chunks of lava a few cm to a few m in size; ash; and small lava flows
(which form when hot spatter melts together and flows downslope). Products of an
explosive eruption are often collectively called tephra.
Strombolian eruptions are often associated with small lava lakes, which can
build up in the conduits of volcanoes. They are one of the least violent of the
explosive eruptions, although they can still be very dangerous if bombs or lava flows
reach inhabited areas. Strombolian eruptions are named for the volcano that makes up
the Italian island of Stromboli, which has several erupting summit vents. These
eruptions are particularly spectacular at night, when the lava glows brightly.
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3. Vulcanian Eruption
A Vulcanian eruption is a short, violent, relatively small explosion of viscous
magma (usually andesite, dacite, or rhyolite). This type of eruption results from thefragmentation and explosion of a plug of lava in a volcanic conduit, or from the
rupture of a lava dome (viscous lava that piles up over a vent). Vulcanian eruptions
create powerful explosions in which material can travel faster than 350 meters per
second (800 mph) and rise several kilometers into the air. They produce tephra, ash
clouds, and pyroclastic density currents (clouds of hot ash, gas and rock that flow
almost like fluids).
Vulcanian eruptions may be repetitive and go on for days, months, or years, or
they may precede even larger explosive eruptions. They are named for the
Italian island of Vulcano, where a small volcano that experienced this type of
explosive eruption was thought to be the vent above the forge of the Roman smith god
Vulcan.
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4. Plinian Eruption
The largest and most violent of all the types of volcanic eruptions are Plinian
eruptions. They are caused by the fragmentation of gassy magma, and are usually
associated with very viscous magmas (dacite and rhyolite). They release enormous
amounts of energy and create eruption columns of gas and ash that can rise up to 50
km (35 miles) high at speeds of hundreds of meters per second. Ash from an eruption
column can drift or be blown hundreds or thousands of miles away from the volcano.
The eruption columns are usually shaped like a mushroom (similar to a nuclear
explosion) or an Italian pine tree.
Plinian eruptions are extremely destructive, and can even obliterate the entire
top of a mountain, as occurred at Mount St. Helens in 1980. They can produce falls of
ash, scoria and lava bombs miles from the volcano, and pyroclastic density currents
that raze forests, strip soil from bedrock and obliterate anything in their paths. These
eruptions are often climactic, and a volcano with a magma chamber emptied by a
large Plinian eruption may subsequently enter a period of inactivity.
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5. Lava Domes
Lava domes form when very viscous, rubbly lava (usually andesite, dacite or
rhyolite) is squeezed out of a vent without exploding. The lava piles up into a dome,
which may grow by inflating from the inside or by squeezing out lobes of lava
(something like toothpaste coming out of a tube). These lava lobes can be short and
blobby, long and thin, or even form spikes that rise tens of meters into the air before
they fall over.
Lava domes are not just passive piles of rock; they can sometimes collapse
and form pyroclastic density currents, extrude lava flows, or experience small and
large explosive eruptions (which may even destroy the domes!) A dome-building
eruption may go on for months or years, but they are usually repetitive (meaning that
a volcano will build and destroy several domes before the eruption ceases).
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6. Surtseyan Eruption
Surtseyan eruptions are a kind of hydromagmatic eruption, where magma or
lava interacts explosively with water. In most cases, Surtseyan eruptions occur when
an undersea volcano has finally grown large enough to break the water's surface;because water expands when it turns to steam, water that comes into contact with hot
lava explodes and creates plumes of ash, steam and scoria.
The classic example of a Surtseyan eruption was the volcanic island of
Surtsey, which erupted off the south coast of Iceland between 1963 and 1965.
Hydromagmatic activity built up several square kilometers of tephra over the first
several months of the eruption; eventually, seawater could no longer reach the vent,
and the eruption transitioned to Hawaiian and Strombolian styles. More recently, in
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March 2009, several vents of the volcanic island of Hunga Ha'apai near Tonga began
to erupt. The onshore and offshore explosions created plumes of ash and steam that
rose to more than 8 km (5 miles) altitude, and threw plumes of tephra