Volcanoes

• What is a volcano?

  An extrusive feature through which gas, lava, and ash erupt from.
• How are volcanoes related to plate tectonics?

  They are closely related to plate tectonic movement causing pressure and magma to rise to the surface.
• What does the Volcanic Explosivity Index measure?

  It measures the size and force of volcanic eruptions using several factors.
• What is the range of the Volcanic Explosivity Index?

  The range is from 0 to 8.
• What factors are considered in the Volcanic Explosivity Index?

  Height of ejected material, duration, and qualitative descriptive terms.
• What is a harmonic tremor?

  A harmonic tremor is a sustained release of seismic and infrasonic energy associated with the underground movement of magma.
• Why does the amount of death and destruction vary between volcanic eruptions?

  It varies due to factors such as location, population density, and the type of eruption.
• What are primary impacts of volcanic eruptions?

  Primary impacts include lava flow, pyroclastic flow, tephra and ash fall, and gas eruptions.
• What are the primary impacts of explosive volcanic eruptions?


  • Lava Flow: Very hot (>1,170°C), destroys everything in its path.
  • Pyroclastic Flow: Very hot (>700°C), travels fast, destroys everything.
  • Tephra and Ash Fall: Volcanic material blasted into the air, varying sizes.
  • Gas Eruptions: Gases released can travel thousands of kilometers.
• What are secondary impacts of volcanic eruptions?

  Secondary impacts include lahars and jökulhaups.
• What are the secondary impacts of explosive volcanic eruptions?


  • Lahars: Rock, mud, and water traveling quickly down volcano flanks.
  • Jökulhaup: Sudden flooding from melting ice and snow due to volcanic heat.
• What is a pyroclastic flow?

  A pyroclastic flow is a gravity-driven, rapidly moving mixture of rock fragments and hot gases.
• What temperatures can pyroclastic flows reach?

  Temperatures may be as hot as 900°C.
• What is the only effective method of risk mitigation for pyroclastic flows?

  Evacuation prior to eruptions from affected areas.
• What are lahars?

  Lahars are debris flows that are mixtures of water and volcanic particles.
• How fast can lahars move?


  Lahars can move with velocities up to 40 m/s.
• What are the major hazards of lava flows?

  Major hazards include burying, crushing, covering, and burning everything in their path.
• What is tephra?


  Tephra consists of pyroclastic fragments of any size and origin.
• What are the sizes of tephra?

  Tephra ranges from ash (<2 mm) to lapilli (2-64 mm) to blocks and bombs (>64 mm).
• What are the effects of tephra fall and ballistic projectiles?

  They endanger life and property through impact, loss of agricultural land, and clogging of filters and vents.
• What can happen when tephra is dispersed widely over a drainage basin?

  It can change rainfall/runoff relationships and lead to hazardous floods.
• What are the three classifications of volcanoes?

  Active, dormant, and extinct.
• What determines the shape of a volcano?

  The shape is often based on the type of lava that is erupted.
• How can volcanoes be classified based on lava type?


  • Basaltic: Low silica (45%), flows quickly.
  • Andesitic: Intermediate silica (60%), moderate flow.
  • Rhyolitic: High silica (75%), slow flowing.
• Where do fissure volcanoes occur?


  Fissure volcanoes occur at constructive plate boundaries.
• What is the characteristic of acid or dome volcanoes?

  They produce a steep-sided, convex cone from acid lava solidifying on exposure to air.
• What is an example of an acid or dome volcano?

  Mt. Pelee in Martinique.
• What characterizes basic or shield volcanoes?

  They have long, gentle sides made up of many layers of lava.
• What is an example of a basic or shield volcano?

  Mauna Loa.
• What defines composite volcanoes?


  They result from alternating types of eruptions, forming layers of ash and lava.
• What is an example of a composite volcano?


  Mt. Etna.
• What is a caldera?


  A caldera is formed when the magma chamber empties and the summit collapses inward.
• What is an example of a caldera?


  Krakatoa.
• What gases are most abundant in magma?

  Water vapor, carbon dioxide, and sulfur dioxide.
• How does the viscosity of magma affect gas release?


  Less viscous magma allows gas to escape easily, while high viscosity traps gases.
• What is the temperature range for andesite lava?

  650 to 800°C.
• What is the characteristic of basaltic lava?


  Basaltic lava is the hottest, ranging from 1,000 to 1,200°C, with low gas content.
• How are supervolcanoes formed?

  Supervolcanoes are formed by melting of lithospheric mantle and slabs of previously subducted plate.
• What are the key differences between basalt and andesite lava?

  • Basalt:
  • Temperature: 1,000 to 1,200°C
  • Gas content: Low (0.5 to 2%)
  • Flow characteristics: Thin and runny (low viscosity)
  • Andesite:
  • Temperature: 650 to 800°C
  • Gas content: High (4 to 6%)
  • Flow characteristics: Thick and stiff (high viscosity)
• What is the process of assessing volcanic hazards?

  It involves identifying the hazard as primary or secondary, describing it, and giving an example of a volcanic eruption that caused it.