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Volcanoes

A volcano is best described as an opening in the Earth's crust through which

  • molten lava,
  • vapours and gases (also called 'volatiles'),
  • shattered lava and crustal rock (also called 'pyroclastics')
are erupted.

Some volcanoes build up into the symmetrical, conical shape which we think of as the typical volcanic shape. Other volcanoes are flat. Some are steep sided, others have gentle slopes.
Volcanoes come in many shapes and sizes!

The shape of a volcano depends on a number of factors:

  • the type of lava;
  • the temperature of the lava;
  • the amount of shattered (pyroclastic) material erupted;
  • the nature of the vent(s).
 Mauna Kea

Here, the shadow of the Mauna Kea volcano cast by the setting sun shows its gentle slopes.
(The hill in the sunlight is one of the small peaks which make up the summit, 4206m above sea level)

The type of lava depends on the composition of the molten rock (magma) which rises within the crust to erupt through the volcano.

This in turn controls

  • how easily the lava flows;
  • how far the lava flows;
  • how violent the eruptions are.
 Etna

The structure of volcanoes shows a number of variations:

  • volcanoes built up only of lava flows;
  • volcanoes built up only of pyroclastics;
  • volcanoes built up of alternating layers of lava, volcanic ash and other shattered materials;
  • the nature of the summit - a crater or a caldera.
 Cone

In some cases, a layer of lava will cool down to form the characteristic pillar-like structure called columnar jointing. This photograph shows a section of the longest outcrop of columnar jointing in Iceland.

Raudamelsfjoli

Modern volcanoes are found in certain zones of volcanoes around the world. This suggests that these belts are particularly active; they provide much of the evidence on which the theory of Plate Tectonics is based.

The Study Topics
  • Shape of Volcanoes
  • Types of Lava
  • Structure of Volcanoes
  • Columnar Jointing
  • Volcanoes around the World
are included in the Geopix "Volcanoes" Study Guide. The Guide also contains a selection of 40 multiple choice questions (with answers!) which help to test understanding of Volcanoes.

To order the "Volcanoes" Study Guide please visit the Geopix Online Store

TENERIFE
Some individual areas show a wide range of volcanic features and a visit - either in real life or on a virtual tour - can be used to discuss the origins and shapes of volcanoes in general. Tenerife is one such area. Developed at a hot spot, the island is made of three basalt shield volcanoes surmounted by a large strato-volcano whose top has collapsed to form a caldera. Within the caldera, the modern volcano of El Teide now sits, waiting to erupt again.

Teide