Volcanoes

Volcanoes

Intrusive vs Extrusive Volcanism

  • Intrusive Volcanism:
    • Occurs when magma intrudes into the Earth's crust and cools below the surface.
  • Extrusive Volcanism:
    • Occurs when lava erupts onto the Earth's surface.

Types of Volcanoes Based on Activity

  • Active Volcanoes:
    • Erupt fairly regularly along active plate boundaries.
  • Dormant Volcanoes:
    • "Sleeping" volcanoes that have not erupted for many years, but scientists are uncertain if they are extinct.
  • Extinct Volcanoes:
    • "Dead" volcanoes that are not expected to erupt again.

Types of Volcanoes Based on Structure

  • Cinder Cone Volcano:

    • A steep-sided volcano made of cinders (hardened lava fragments) and ash.
    • Typically associated with violent eruptions.

  • Shield Volcano:

    • A gently-sloping volcano made up of very fluid lava.
    • The lava, when hot, becomes very runny and can spread over thousands of kilometers.

  • Lava Dome:

    • A small mass of thick, viscous lava that solidifies close to the vent, forming a dome shape.

  • Composite Volcano:

    • Composed of alternating layers of ash, cinders, and lava.
    • Structure includes:
    • Crater
    • Main vent
    • Lava
    • Magma
    • Ash, steam, and gas
    • Volcanic bombs
    • Magma chamber
    • Secondary cones
    • Secondary vent

Structure of a Composite Volcano

  • Components:

    • Crater
    • Pipe
    • Ash
    • Lava
    • Vent
    • Magma chamber

  • Cross-section Features:

    • Conelet
    • Magma chamber
    • Earth's crust
    • Mantle
    • Crater
    • Vent
    • Lava layer
    • Ash layer
    • Pipe
    • Figure 3.64 illustrates a cross-section through a composite volcano showing how magma forces its way through a fissure.

  • Definitions for Figure 3.64:

    1. A saucer-shaped area at the summit of a volcano from which materials are ejected.
    2. The central stem up which magma travels.
    3. The hole in the ground out of which magma erupts.
    4. A small volcanic hill on the side of the main volcano.
    5. Molten rock within Earth's crust.
    6. Molten rock that has come out of a volcano.

Negative Impacts of Volcanoes

  • Lava can:
    • Burn plants and buildings.
    • Bury entire areas under molten rock.
  • Volcanic ash can:
    • Cover buildings and plants.
    • Cause respiratory issues in people when inhaled.
  • Physical hazards:
    • Lava bombs can cause injury or death.
    • Secondary hazards such as mass movements (e.g., rock falls, mudslides) can be triggered.

Positive Impacts of Volcanoes

  • Soil Fertility:
    • Ash from eruptions can fertilize the soil.
    • Basalt (from lava) weathers into fertile soil.
  • Tourism:
    • Hot springs and geysers attract tourists.
  • Geothermal Electricity:
    • Heat from underground is used to generate electricity through steam turbines.

Geothermal Energy Process Overview

  • Geothermal fluid is pumped to the surface through production wells.
  • The fluid is recycled to the reservoir through injection wells to complete the geothermal energy cycle.

Activities and Case Studies

Activity 26 - Investigate Volcanoes and Their Effects
  1. Identify Iceland on an atlas map and explain its position on a volcanic 'hot spot'.
  2. From descriptions, identify the type of volcano that erupted in Iceland in 2010.
  3. Discuss the danger of widespread flooding caused by volcanic activity.
  4. Compare the number of deaths from the 2002 Goma eruption and the 2010 Iceland eruption.
    • 4.1 Discuss how the death toll differed.
    • 4.2 Provide evidence accounting for the differences.
  5. Explain why the ash cloud posed a threat to aircraft.
  6. Identify three other businesses affected by flight disruptions beyond fresh vegetable exports from Kenya.
  7. Discuss why Iceland has bubbling hot waters, spas, and heated pools.
Activity 24 - Positive and Negative Effects of Volcanoes
  1. Discuss reasons for dense populations and farming on islands like Java and the Philippines with active volcanoes.
    • 1.1 Explain the occurrence of active volcanoes in these regions.
    • 1.2 Explain the soil fertility on these islands.
    • 1.3 List three advantages of living near active volcanoes.
  2. Investigate volcanic activity in the Rift Valley region.
    • 2.1 Explain why there is volcanism.
    • 2.2 Describe benefits to East African populations from living in an unstable crust.
    • 2.3 Discuss the hazards of residing in such an area.