Types of volcanoes

• Shield Volcanoes

  • A very wide volcano,  of 3 or 4 miles and heights of 1,500 to 2,000m

  • They are built up slowly by the accretion of thousands of flows of highly fluid basaltic (from basalt, a hard, dense dark volcanic rock) lava that spread widely over great distances, and then cool as thin, gently dipping sheets

  • Lavas also commonly erupt from vents along fractures (rift zones) that develop on the flanks of the cone.  The magma has very low gas content and is low in silica, allowing it to flow large distances

  • Non explosive

  • Shield volcanoes are usually found at constructive boundaries and sometimes at volcanic hotspots. Examples of shield volcanoes include Mount Kilauea and Maunaloa on Hawaii.

• Composite Volcanoes

  • Sometimes known as strato volcanoes.

  • Built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash

  • Unlike shield volcanoes, strato volcanoes are characterized by a steep profile and periodic, explosive eruptions. The lava that flows from strato volcanoes typically cools and hardens before spreading far due to high viscosity.

  • The eruptions from these volcanoes may be a pyroclastic flow (a superheated mixture of hot steam, ash, rock and dust) rather than a flow of lava. A pyroclastic flow can travel down the side of a volcano at very high speeds with temperatures over 400^oC.

  • Composite volcanoes are usually found at destructive plate margins. Examples of composite volcanoes include Mount Fuji (Japan), Mount St Helens (USA) and Mount Pinatubo (Philippines).

• Dome (acid cone) volcanoes

  • Acid or dome volcanoes tend to have craggy, steep-sloped sides covered with rock debris.

  • These volcanoes are typically found near large composite volcanoes. They are made of layer upon layer of lava

  • They are formed by repeated violent eruptions and slow moving lava flows, which gives the layered structure.

  • The magma is made of higher silica content which makes it viscous and high gas pressure, making the magma slow moving and explosive.

  • An example is Puy de Dome in the Auvergne region of France which last erupted over 1 million years ago.

• Cinder Cone

  • The most common type of volcano and are the symmetrical cone shaped volcanoes we typically think of.

  • They may occur as single volcanoes or as secondary volcanoes on the sides of stratovolcanoes or shield volcanoes

  • Airborne fragments of lava, called tephra, are ejected from a single vent

  • The lava cools rapidly and builds up…