Volcanoes Notes

Volcanism

  • Volcanism is the process where molten magma from the mantle moves to the Earth's crust.

Volcano Anatomy

  • Eruption cloud
  • Ash (tephra) fall
  • Eruption
  • Prevailing wind
  • Bombs
  • Pyroclastic debris
  • Landslide
  • Magma
  • Pyroclastic flow
  • Fumaroles and hot springs
  • Ground

Plate Convergence and Volcanism

  • Ocean-Ocean Convergence
    • Mid-ocean ridge
    • Ocean plate
    • Asthenosphere
    • Hot spot volcanism
    • Active volcano over hot spot
    • Extinct volcano
    • Mantle plume
  • Ocean-Continent Convergence

Guyot Formation

  • Progressively older
  • Wave erosion
  • Mantle plume
  • Subsiding seafloor

Types of Volcanism

  • Intrusive
  • Extrusive

Intrusive Volcanism

  • Occurs when magma forms igneous intrusions into the rocks of the Earth's crust.
  • Ancient Volcanic Features:
    • Ash plume
    • Cinder cone
    • Recent lava flows
    • Stock with radiating dikes
    • Palisade
    • Stock
    • Volcano conduit
    • Laccolith
    • Sill
    • Dike
    • Magma chamber
    • Pluton
    • Batholith

Intrusive Landforms

  • Batholith:
    • The largest type of igneous intrusion.
    • Forms deep in the crust.
    • Large round shape.

Granite Dome

  • A batholith exposed on the surface.

Laccolith

  • Mushroom-shaped structure where magma forces the overlying strata upwards.
  • Size: 100s of meters.

Lopolith

  • Similar to a laccolith.
  • The weight of the overlying strata causes the lopolith to sink into a saucer-shaped structure.

Sill

  • Forms where magma intrudes horizontally between layers of rock.

Dyke

  • Forms when magma intrudes vertically between layers of rock.

Extrusive Volcanism

  • When magma reaches the surface it is called lava.
  • The volcano also ejects rocks, ash, and steam.
  • Gases emitted include sulfur dioxide, carbon dioxide, and nitrogen.

Volcanic Eruptions

  • Steam raises the humidity of the air, causing heavy rain.
  • Rain combines with ash and dust to form mud.
  • The central pipe is widened, and a crater is formed.

Composite Volcano

  • Consists of alternating layers of ash and cinders and lava.
  • Cone-shaped.
  • Side vents or fissures allow trapped magma to reach the surface.
  • Conelets are built up on the sides of the volcano.
  • Other types: shield cone, cinder cone.

Volcano Diagram

  • Lava
  • Older Layers
  • Gases, Ashes, & Cinders
  • Crater
  • Dike
  • Sill
  • Magma Under Pressure

Types of Volcano

  • Fissure volcano:
    • Gentle basaltic slope of lava
  • Shield volcano:
    • Gentle slope of basaltic lava
  • Dome volcano:
    • Steep convex slope from thick, fast-cooling lava
  • Ash-cinder volcano
  • Composite volcano
  • Caldera volcano:
    • New cone
    • Branch pipe
    • Old cone

Calderas

  • Form when a volcano has not erupted for a long period of time.
  • Lava builds up and solidifies in the crater.
  • A huge explosion blows off the top of the mountain.

Lake in a Caldera

  • Sometimes the caldera will fill with water to form a lake.

Lava Plateaus

  • Fissure eruptions occur when lava flows from a number of cracks.
  • The lava is very fluid and flows for thousands of kilometers.
  • The lava cools and solidifies into volcanic rock (basalt).
  • Example: The highest parts of the Drakensburg (1300 m thick).

Active and Dormant Volcanoes

  • Active: volcanoes which still erupt.
  • Dormant: volcanoes which are resting (recorded activity in the past).
  • Extinct: volcanoes that have not erupted in recorded history.

Active Volcanoes, Plate Tectonics, and the "Ring of Fire"

  • Eurasian Plate
  • North American Plate
  • Pacific Plate
  • Antarctic Plate

Examples of Volcanoes

  • Vesuvius
  • Vulcano
  • Stromboli
  • Mt. Etna

Effect of Volcanoes on People

  • Lava flows burn and bury vegetation and buildings.
  • Ash can cover buildings and smother vegetation.
  • Respiratory problems due to breathing in ash and poisonous gases.
  • People can be killed by lava bombs.
  • Volcanoes set off mud slides.

Positive Effects of Volcanic Activity

  • Volcanic ash can act as a fertilizer for soil.
  • Lava weathers into fertile soil.
  • Hot springs and geysers are associated with volcanoes and they become tourist attractions.
  • Underground heated water and steam is used for electricity and heating systems.

Geothermal Power

  • Production Well
  • Injection Well