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

Type of Volcvolcanooanoes and Volcanoes Eruption

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