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

Shield Volcanoes

  • Shield volcanoes are usually found at constructive 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.
  • Example: Mauna Kea in Hawaii, USA or the Galapagos islands

Composite volcanoes

Composite Volcanoes

  • Composite volcanoes are made up of alternating layers of lava and ash (other volcanoes just consist of lava).
  • They are usually found at destructive 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.
  • Example: Hekla in Iceland, Mt St Helens in the USA and Mt Kilimanjaro in Tanzania.