Shield and composite volcanoes

Volcanoes can be described in terms of activity and can be:

  • still active and erupt frequently
  • dormant (temporarily inactive but not fully extinct)
  • extinct (never likely to erupt again)

Volcanoes can also be described by their shape or type - shield or composite.

Shield volcanoes

Diagram showing composition of a shield volcano
  • Shield volcanoes are usually found at constructive or tensional boundaries.
  • They are low, with gently sloping sides.
  • They are formed by eruptions of thin, runny lava.
  • Eruptions tend to be frequent but relatively gentle.

Composite volcanoes

Diagram showing composition of a composite volcano
  • Composite volcanoes are made up of alternating layers of lava and ash (other volcanoes just consist of lava).
  • They are usually found at destructive or compressional boundaries.
  • The eruptions from these volcanoes may be a pyroclastic flow rather than a lava flow. A pyroclastic flow is a mixture of hot steam, ash, rock and dust.
  • A pyroclastic flow can roll down the sides of a volcano at very high speeds and with temperatures of over 400°C.