ERUPTIONS

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ERUPTIONS
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EXTRUSIVE VULCANICITY
Types of Volcanoes

• Click on the following for further information of
  earth structure.
• Flood basalts
• Hawaiian eruptions
• Icelandic eruptions
• Pelean eruptions and
  nuees ardentes
• Phreatic and phreatomagmatic
  eruptions

• Plinian eruptions
• Strombolian eruptions
• Subglacial eruptions
• Submarine eruptions
• Surtseyan eruptions
• Vulcanian eruptions

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ERUPTIONS
Flood basalts

• They are volcanic outpourings characterized by
  extremely fluid basaltic lavas.
• In most cases the lava erupts from fissures.
• The molten material is so fluid that it does not
  pile up into singular, discrete landforms, but
  spreads out into horizontal lava flows which
  cover an area like the flood of a river.
• Eruptions are quiet, and virtually no volcanic
  ash is ejected.
• In times past, flood basalts covered portions of
  Washington and Oregon with flows nearly two miles
  thick.
• They are also associated with rift features and
  basaltic outpourings form the ocean floor. 

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ERUPTIONS
Hawaiian eruptions

• These eruptions consist of basaltic, highly fluid
  lavas of low gas content, that produce effusive
  lava flows and some pyroclastic debris.
• The eruptions are steady and quiet.
• The lava from these eruptions are either Pahoehoe
  or Aa.
• Thin, fluid lava flows can gradually build up
  large broad shield volcanoes.
• The lava fountains can reach up to 2000 feet in
  height .
• Pyroclastic material occurs as bombs.

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ERUPTIONS
Hawaiian eruptions

• Most of these eruptions start from fissures,
  commonly beginning as a line of lava fountains
  that eventually concentrate at one or more
  central vents.
• Most of the vesiculating lava falls back in a
  still molten condition, coalesces and moves away
  as lava flows. If fountains are weak, most lava
  will quietly well out of the ground and move away
  from a vent as a lava flow.
• Much lava in shield volcanoes is transmitted
  through tubes enclosed within lava flows. Small
  spatter cones and basaltic pumice cones may form
  around vents.

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ERUPTIONS
Icelandic eruptions

• Also called Fissure Eruptions.
• Icelandic eruptions flood the surface of the
  Earth with massive amounts of very hot, very
  thin, runny lava.
• It occurs when basaltic magma flows up through
  long cracks (fissures) in the ground and leaks
  out onto the surface.
• These often occur where plate movement has caused
  large fractures in the earth's crust, and may
  also spring up around the base of a volcano with
  a central vent.
• The eruptions are quiet.
• Plateaus can be built.

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ERUPTIONS
Pelean eruptions

• Pelean eruptions are the most dangerous and
  explosive of the eruption types.
• Pelean eruptions are named after the eruption of
  Mt. Pelee on May 8, 1902 that destroyed the town
  of St. Pierre.
• Pelean eruptions occur when a deep plug of cooled
  magma is violently forced out of the volcanic
  vent.
• Large amounts of nuee ardente, ash and pumice are
  also rapidly ejected during the eruption.
• This eruptive style builds a large stratovolcano.

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ERUPTIONS
Nuee ardente

• Nuee ardente is a french term means glowing cloud
  and was named for the pyroclastic flows seen at
  Mount Pelee.
• These flows were often accompanied by a cloud of
  ash elutriated from the flow.
• When the incadescent ash particles are observed
  at night, the flow looks like a glowing cloud
  moving away from the volcano.
• Nuees ardentes have been known to extend 50
  kilometers from their source.
• It is a mixture of hot gases and fine ash.
• It can travel up to 100 km/hour with an internal
  temperature of 1300 F.

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ERUPTIONS
Phreatic and Phreatomagmatic Eruptions
Phreatic Eruptions

• A phreatic eruption is a steam eruption without
  lava ejection.
• Phreatic eruptions are steam-driven explosions
  that occur when water beneath the ground or on
  the surface is heated by magma, lava, tephra or
  pyroclastic-flow deposits.
• The intense heat of such material causes water to
  flash to steam, thereby generating an explosive
  eruption.
• These eruptions form diatremes below ground and
  explosion craters, or maars on the surface,
  surrounded by a rim of shattered fragments
  consisting of varying proportions of new magma
  and country rocks

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Eruptions
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ERUPTIONS
Phreatic and Phreatomagmatic Eruptions
Phreatomagmatic Eruptions

• A phreatomagmatic eruption is an explosive
  water-magma interaction.
• . Phreatomagmatic eruptions occur when hot magma
  comes into contact with water, either as
  groundwater, lakes or oceans.
• The result on land are usually big holes in the
  ground.
• This type of eruption produces fine grained
  tephra.
• Large amounts of steam and magmatic gases are
  emitted.
• The Hatepe ash and Rotongalo ash are two
  classical widespread phreatomagmatic fall
  deposits.

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ERUPTIONS
Plinian eruptions

• Plinian eruptions are named after Pliny the
  Younger, who observed the disastrous eruption of
  Vesuvius in 79 A.D.
• Such eruptions are large explosive events that
  form enormous dark columns of tephra and gas high
  into the stratosphere.
• Plinian eruptions send a large column of ash and
  rocks into the sky at the speed of sound. The ash
  will reach the atmosphere, and begin to
  circulate.
• In this eruption, few lava flows are erupted, and
  ash is scattered about everywhere, after a long
  period of quiet.
• Such explosions are the second most violent
  eruptions known to man, and are quite common at
  composite volcanoes.

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ERUPTIONS
Strombolian Eruptions

• Strombolian eruptions are named after the island
  Stamboli located off the coast of Italy.
• These eruptions are quite violent and noisy.
• It involves a cinder cone and consists of
  explosive bursts of red hot pyroclastic fragments
  that reach up to 100 metres above the crater. 
• Masses of lava and ash are periodically thrown
  into the air.
• Each eruption will last for only an one hour.
• The land forms produced by this type of eruption
  are steep-angle slopes composed of alternating
  layers of lava and ash.

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ERUPTIONS
Subglacial Eruptions

• Subglacial Eruptions are eruptions beneath a
  glacier or beneath the surface of a lake within a
  glacier.
• Subglacial eruptions occur in volcanic regions at
  high latitudes and at some large strato-volcanoes
  in other areas.
• Subglacial eruptions may build up hyaloclastite
  mountains and if the eruption lasts long enough
  for the volcanic crater to emerge from the icy
  cover or glacial water, lava begins to flow and
  covers the earlier fall-out from the eruption.
  Some mountains formed in this way.
• Subglacial eruptions can create large lakes that
  may escape through floodchannels causing glacier
  bursts or jokuhlaups.

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ERUPTIONS
Submarine Eruptions

• Submarine eruptions occur under the sea chiefly
  emerging from vents aligned along fissures of
  mid-ocean ridges.
• Explosive submarine eruptions produced volcanic
  breccia which was subsequently lifted above sea
  level and covered by subaerial lava flows.
• Submarine eruptions of basalt may form submarine
  shield volcanoes.
• Pillow lava forms during submarine eruptions.
• Violent submarine eruptions can cause tsunamis to
  sweep over nearby areas.

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ERUPTIONS
Surtseyan Eruptions

• Surtseyan eruptions are caused by explosive
  water-magma interactions.
• Surtseyan eruptions take place mainly in shallow
  seas and lakes. 
• Surtseyan eruptions are considered to be the
  "wet" equivalents of Strombolian-type eruptions,
  although they are much more explosive.
• Surtseyan eruptions produce characteristic
  "rooster tail" ejections of ash and clasts. The
  tephra is fine grained and deposited as base
  surge or air fall deposits.
• Magma is erupted into water.

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ERUPTIONS
Vulcanian Eruptions

• Vulcanian eruptions are caused by discrete,
  powerful eruptions of ash, bombs, lava and gas
  from a vent.
• Vulcanian eruptions are named after the island of
  Vulcano off the coast of Italy.
• This type of eruption very explosive and
  dangerous due to violent nature of eruptions and
  the unpredictable nature of ejected ballistics.
• Vulcanian eruptions contain high dark clouds of
  steam, ash, and gas. The ash plume builds a
  cauliflower shaped head and a thinner more
  treetrunk-like base.
• Vulcanian eruptions usually build a steep sided
  strovolcano cone.

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