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Types of 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 eplosive, wherefragmented lava eplodes out of a vent. !n eplosive eruptions, the fragmented rock

may be accompanied by ash and gases" in effusive eruptions, degassing is common

but ash is usually not.

#olcanologists classify eruptions into several different types. $ome 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. %ere

are some of the most common types of eruptions&

Strombolian eruption:

$trombolian eruptions are distinct bursts of fluid lava (usually basalt or basaltic

andesite) from the mouth of a magmafilled summit conduit. The eplosions usually

occur every few minutes at regular or irregular intervals. The eplosions 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 magmafilled conduit until they reach the

open air.

This 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 sie" ash" and small lava flows

(which form when hot spatter melts together and flows downslope). roducts of an

eplosive eruption are often collectively called tephra.

$trombolian 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 eplosive

eruptions, although they can still be very dangerous if bombs or lava flows reach

inhabited areas. $trombolian eruptions are named for the volcano that makes up the

!talian island of $tromboli, which has several erupting summit vents. These

eruptions are particularly spectacular at night, when the lava glows brightly.

Vulcanian eruption:

* #ulcanian eruption is a short, violent, relatively small eplosion of viscous magma

(usually andesite, dacite, or rhyolite). This type of eruption results from the

fragmentation and eplosion 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). #ulcanian eruptions

create powerful eplosions in which material can travel faster than +- meters per

second (-- 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).

#ulcanian eruptions may be repetitive and go on for days, months, or years, or they

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may precede even larger eplosive eruptions. They are named for the !talian island

of #ulcano, where a small volcano that eperienced this type of eplosive eruption

was thought to be the vent above the forge of the /oman smith god #ulcan.

Vesuvian eruption:

%ere, ashladen gas gushes out violently, forming thick cauliflower shapes of ash

clouds. !t was observed in the eruption of 0ount #esuvius in !taly, in the year 12 *.3

Peléan / Nuée Ardente eruption:

%ere, incandescent lava, together with ash and gas are blown out from the crater,

vertically upwards and falling in again. The spilling of glowing avalanches along the

slopes can be very deadly and destructive. This type of eruption occurred on the

0ayon #olcano in the hilippines in 425

Hawaiian eruption:

!n a %awaiian eruption, fluid basaltic lava is thrown into the air in 6ets from a vent or

line of vents (a fissure) at the summit or on the flank of a volcano. The 6ets 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. 7ava flows may also come from vents at the

same time as fountaining occurs, or during periods where fountaining has paused.

8ecause these flows are very fluid, they can travel miles from their source before

they cool and harden.

%awaiian eruptions get their names from the 9ilauea volcano on the 8ig !sland of

%awaii, which is famous for producing spectacular fire fountains. Two ecellenteamples of these are the 4252421: 0auna ;lu eruption on the volcano's flank,

and the 422 eruption of the 9ilauea !ki <rater at the summit of 9ilauea. !n both of

these eruptions, lava fountains reached heights of well over a thousand feet.

Phreatic say free!a!tic" eruption:

This type does not involve the outpour of lava, but usually set off when cold ground

or water comes into contact with hot molten matter. The resulting steam that is

forced upwards usually contains d=bris of surface rocks. >o new magma is erupted.

Plinian eruption:

The largest and most violent of all the types of volcanic eruptions are linian

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

- km (+ miles) high at speeds of hundreds of meters per second. *sh 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 eplosion) or an !talian pine tree" liny the ?ounger, a /oman historian,

made the comparison while viewing the 12 *3 eruption of 0ount #esuvius, and

linian eruptions are named for him.

linian eruptions are etremely destructive, and can even obliterate the entire top of 

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a mountain, as occurred at 0ount $t. %elens in 42-. They can produce falls of ash,

scoria and lava bombs miles from the volcano, and pyroclastic density currents that

rae 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 linian eruption may subsequently enter a period of inactivity.

Volcanic eruptions in the sea

Though ocean floors are thousands of miles below the water surface, they alsoeperience many volcanic activities.

!n shallow waters, eruptions tend to involve cold water coming into contact withetremely hot lava from beneath that ocean floor. The steam escapes high above thewater surface. !f the eruptions occur deeper in the ocean, the weight and pressureof the water above it suppresses its epulsion and keeps it mild. This means theocean floor is not necessarily affected in any way.

$ometimes, lava which erupts into shallow water cools of very quickly and breaksdown into d=bris or sand. !t is believed that %awaii@s black sands beaches are aresult of lava interacting with sea water.

$ometimes, lava settles on the water in the form of d=bris, which is carried farther

away by ocean currents.