volcanoes

• Three types of families of volcanoes:

  • Dome volcano: formed from viscous (acidic) lava, with a steep-sided cone
  • Ash and cinder volcano: formed from acidic lava, with violent eruptions and a volcanic cone mainly made out of ash and cinder
  • Composite volcano (Strato-Volcano): has alternating layers/bands of ash and cooled lava, with violent eruptions
• Volcanoes can be categorized as:

  • Active: where eruptions occur frequently
  • Extinct: where the volcano has not had an eruption in at least 10,000 years and will never erupt again
  • Dormant: where eruptions are infrequent and have not occurred for some time
• Intrusive volcanic features:

  • Batholith: forms when a giant underground reservoir of magma cools and hardens
  • Laccolith: the result of a relatively large amount of magma moving between bedding planes, causing the overlying layers of rock to arch upwards
  • Sill: formed when magma moves horizontally and lies along bedding planes when it cools and solidifies
  • Dyke/Dike: formed when magma moving diagonally up towards the surface cools and solidifies within the crust
• Key volcanic terms:

  • Hot spots
  • Pyroclastic flows
  • Lava flows
  • Volcanic gases
  • Tephra
  • Lahar
  • Plug
  • Caldera
• Two main types of lava:

  • Acidic lava: rich in silica, very thick and sticky, produces explosive, violent eruptions, and steep-sided volcanic cones
  • Basic lava: low in silica, non-viscous, flows more easily, produces less violent eruptions, and lower, less steep-side cones with a gentle gradient
• Extrusive volcanic features:

  • Dome volcano: formed from viscous (acidic) lava, with a steep-sided cone
  • Ash and cinder volcano: formed from acidic lava, with violent eruptions and a volcanic cone mainly made out of ash and cinder
  • Composite volcano (Strato-Volcano): has alternating layers/bands of ash and cooled lava, with violent eruptions
  • Shield volcano: gentle slope, formed from basic, less viscous lava