Below are revision notes for volcanoes. If you require more detailed information take a look at the volcanoes geotopic.
A volcano is a vent or fissure in the earth's crust through
which molten lava and gases erupt. They occur where there is a weakness in the earth's crust. Magma can then rise to the surface where it forms lava.
Volcanoes can be in three states active, dormant and extinct. An active volcano is one that has erupted recently or is likely to erupt in the near future. A dormant volcano is one that last erupted in historical times. An extinct volcano is one that will never erupt again.
Eruptions create a volcanic cone. The shape of a volcanic cone depends on the type of material and the composition of the lava. Composite volcanoes have a steep sided cone. This is because the lava is viscous (thick and sticky like treacle!) and does not travel far before it cools. These types of volcanoes tend to be explosive and are know as composite volcanoes because they are made up of alternate layers of lava and ash. Mount Pinatubo is an example of a composite volcano. When lava is thin and non-viscous shield volcanoes are formed. These have gently sloping flanks as lava tends to travel a long distance. Mount Kilauea on Hawaii is an example of a shield volcano.
When volcanoes erupt a range of products can be released such as pyroclastic flows (super heated clouds of ash, dust and gas - these are also known as nuees ardents), lahars (volcanic mudflows), ash, pumice, volcanic bombs and poisonous gas.
Case study examples of volcanic eruptions include Mount Pinatubo, Mount St Helens, Mount Etna and Mount Kilauea.
Despite their danger many people choose to live close to volcanoes. This is because soils are very fertile. The tourist industry thrives in volcanic regions as people like to see volcanic springs, geysers and boiling mud. Geothermal energy provides electricity.
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