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ERUPTIONS

ERUPTIONS. 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

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ERUPTIONS

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  1. ERUPTIONS

  2. 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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  4. ERUPTIONS Flood basalts They are volcanic outpouringscharacterized 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.  BACK

  5. 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. Go to (2) for further information BACK

  6. 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. Go to (1) for further information BACK

  7. 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. BACK

  8. ERUPTIONS Pelean eruptions Pelean eruptions are the most dangerous and explosive of the eruption types. Peleaneruptions are named after the eruption of Mt. Pelee on May 8, 1902 thatdestroyed 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. Click to learn more about nuee ardente BACK

  9. 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. Back to Pelean Erupiton BACK

  10. 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 Click to learn more about Phreatomagmatic Eruptions BACK

  11. 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. Click to learn more about PhreaticEruptions BACK

  12. 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. BACK

  13. 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. BACK

  14. 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. BACK

  15. 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 lavaforms during submarine eruptions. Violent submarine eruptions can cause tsunamis to sweep over nearby areas. BACK

  16. ERUPTIONS SurtseyanEruptions 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-typeeruptions, 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. BACK

  17. ERUPTIONS Vulcanian Eruptions • Vulcanian eruptionsare 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. BACK

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