VOLCANO AND VOLCANISM

• roman god of fire

  vulcan
• place on earth's surface where molten rock, gases, and pyroclastic debris erupt through the earth's crust

  volcano
• can be a mountain, vent , or caldera

  volcano
• why do volcanoes erupt?

  due to decompression and magma is lighter than the solid around it (magma rises)
• progress of decompression :

  1. eruption onset
  2. pilinian phase
  3. minor ignimbrite phase
  4. caldera collapse
• slopes are gentle (2-10 degrees); shapes resembles a roman shield lying on the ground

  shield
• made up of successive lava flows

  shield
• steep slopes (30-40 degrees); made up of pyroclastic materials

  cinder cones
• layered structure of alternating tephra and lava flows

  composite / strato-volcano
• distribution of volcanoes

  • pacific ring of fire
  • hot spots
  • spreading centers
• mauna loa, hawai'i

  shield
• mauna kea, hawai'i

  cinder cones
• mayon volcano, albay

  composite
• based on number of things (plume height, volume of ejecta, etc.) that can be observed during an eruption

  volcanic explosivity index (vei)
• calmest eruption type

  hawaiian
• characterized by the effusive emission of highly fluid basalt lava flows with low gas content, steady lava fountaining and the production of thin lava

  hawaiian
• Hawaiian

  • magma : fluid
  • effusive activity : then, often extensive flow
  • ejecta : cow-dung bombs and platter, very little ash
  • structure : spatter cones and ramparts, very broad, flat lava cones
• jagged, rough blocks

  aa flows
• smooth surfaces

  pahoehoe flows
• short-lived, explosive outburst of pasty lava ejected a few tens or hundreds of meters into the air

  strombolian
• no sustained eruption column; episodic explosions with booming blast

  strombolian
• Strombolian

  • magma : moderately fluid
  • explosive activity : weak to violent ejection of pasty fluid
  • effusive activity : thicker, less extensive flows, flows may be absent
  • ejecta : spherical to fusiform bombs; cinder; small to large amount of glassy ash
  • structure : cinder cones
• occur as a series of discrete, canon-like explosions that are short-lived, lasting for only minutes to a few hours, often with high-velocity ejections of bombs and blocks

  vulcanian
• once the volcano "clears its throat", subsequent eruptions can be relatively sustained and quiet

  vulcanian
• Vulcanian

  • magma : viscous
  • explosive activity : moderate to violent ejection of solid hot fragments of new lava
  • effusive activity : flows commonly absent, thick and stubby if present
  • ejecta : essential, glassy to lithic, blocks and ash, pumice
  • structure : ash cones, block cones, block-and-ash cones
• Peleean

  • magma : viscous
  • explosive activity : like Vulcanian, commonly with glowing avalanches
  • effusive activity : domes and/or short, very thick flows, flows may be absent
  • ejecta : same as vulcanian
  • structure : ash and pumice cones, domes
• eruptive columns produce widespread dispersal of tephra which covers large areas with an even thickness of pumice and ash

  plinian
• Plinian

  • magma : viscous
  • explosive activity : ejection of large volumes of ash; caldera collapse
  • effusive activity : ash flows, small to very luminous, may be absent
  • ejecta : glassy ash and pumice
  • structure : widespread pumice lapilli and ash beds, generally no cone-building
• generated by the interaction of magma with either groundwater or surface water

  surtseyan / phreatomagmatic
• much more explosive; as the water is heated, it flashes to steam and expands explosively, thus fragmenting the magma into exceptionally fine-grained ash

  surtseyan / phreatomagmatic
• erupted with historical times (within last 600 years); accounts documented by man

  active volcanoes
• erupted within the last 10,000 years based on analyses of materials from young volcanic deposits

  active volcanoes
• morphologically young-looking but with no historical or analytical records of eruption

  potentially-active volcanoes
• no recorded eruptions; physical form has been intensively weathered and eroded, bearing deep and long gullies

  inactive volcanoes
• phivolcs

  philippine institute of volcanology and seismology
• there are 24 active volcanoes based on eruptive history according to phivolcs
• 54 known eruptions; yearly volcanic activity; 1814-most destructive (VEI: 4)

  mayon volcano (albay)
• 39 known eruptions (1911); yearly volcanic activity

  taal (batangas)
• 26 recorded eruptions; continuously monitored

  kanlaon (negros)
• 17 recorded eruptions; continuously monitored

  bulusan (sorsogon)