Volcanoes

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Volcanoes!
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What is a volcano anyway?

• Vents in the earths surface from which molten
  rock, debris and steam issue
• Volcanoes can provide valuable mineral deposits
  and fertile soils
• They also build new land -- Hawaii

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Structure of a Volcano
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How do Volcanoes Erupt?

• Begins when magma rises to the surface
• Explosiveness versus Viscosity
• Dissolved gases in the magma determine if the
  eruption will be explosive or non-explosive

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• Characteristics of a more non-violent eruption
• Low amounts of dissolved gases
• Lover viscosity
• Dissolved gases are able to escape and the
  eruption lava is more fluid and runny
• Pahoehoe or aa lavas

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• Characteristics of a VIOLENT eruption
• Higher amounts of dissolved gases
• High Viscosity magma traps dissolved gases
• Pressure builds, until gases violently erupt
• Pyroclastic materials

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How do Volcanoes Form?

• Island Arcs and Subduction Zones
• Hot Spots
• Spreading Centres

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• Island Arcs
• Two oceanic plates meeting
• A chain of island formed
• Subduction Zones
• Heat from deep in the earth melts the descending
  plate
• Melts into magma
• Magma moves up to surface

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• Hot Spots
• 5 of all known volcanoes
• Intraplate Volcanoes
• Magma erupts through cracks on the suface,
  forming volcanoes
• Spreading Centres

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Types of Volcanoes (6)

• Fissure Volcano
• Long crack in earths surface
• Most likely formed by plates pulling apart
• Gentle slope of cooled lava created from eruptions

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• Shield Volcano
• Composed mostly of lava
• Some minor escapes of gases and steam
• Accumulation of flow on top develops a gentle
  slope on cone

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Types of Volcanoes

• Dome Volcano
• Steep slope
• Thick, fast cooling lava has developed these
  steep slopes

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Types of Volcanoes

• Ash-Cinder Volcanoes
• Relatively small
• Steep, cone-shaped hills
• Made up of mostly ash and cinder
• Tend to be explosive
• Produce mostly pyroclastics

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Types of Volcanoes

• Composite Volcanoes
• Also known as Stratovolcanoes
• Most well known
• Consists of a mix of lava flow and pyroclastic
  materials

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Types of Volcanoes

• Caldera Volcano
• Older volcanoes
• Large craters
• Volcanic feature formed by the collapse of land
  following a volcanic eruption

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Case Study Kilaua, Hawaii

• Shield Volcano
• Formed from Hot Spot
• Mostly Lava flows
• Infrequent powerful eruptions
• For the most part, this volcano drools lava

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