What is a volcano?
A volcano is a conical hill or mountain formed by material from the mantle being forced through an opening or vent in the Earth's crust.
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What are the main features of a volcano?
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What are active, dormant and extinct volcanoes?
Volcanoes are found in three states - extinct, dormant and active. An extinct volcano will never erupt again. A dormant volcano has not erupted in 2000 years. An active volcano has erupted recently and is likely to erupt again.
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What are the different types of volcano?
There are a number of different types of volcanoes. The way they are formed depends on a number of factors e.g. the fluidity of the lava (how runny it is) and the temperature of the lava.
Shield volcanoes are common in Hawaii and Iceland. They have gentle slopes and are very wide. Shield volcanoes are formed when lava is very hot and very runny. They consist of many thin layers of rock. Composite volcanoes are steep sided volcanoes. They consist of layers of ash and lava. Composite volcanoes are very explosive because the lava is very viscous (thick). Significant pressure builds within these volcanoes and often results in spectacular eruptions. Examples of composite volcanoes include Mount Pinatubo in the Philippines and Mount Vesuvius in Italy. You can find out more about these types of volcanoes here.
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Where are volcanoes located?
Volcanoes are found along destructive (subducting) (diagram) plate boundaries, constructive (divergent) (diagram) plate boundaries and at hot spots in the earth's surface.
What is the Ring of Fire?
The 'Ring of Fire' (map) is a volcanic chain surrounding the Pacific Ocean. It is formed along a destructive (subducting) plate boundary. The BBC News Web Site contains an excellent article on the 'Ring of Fire'
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What are lahars and pyroclastic flows?
The most destructive aspect of volcanoes are lahars and pyroclastic flows. Lahars are volcanic mudflows created when water (from rain or melt water from glaciers) and ash mix. This deadly combination can have devastating results on the surrounding area. When lahars settle they can be metres thick and as hard as cement. Lahars can occur long after a volcanic eruption.
Pyroclastic flows are avalanches containing hot volcanic gases, ash and volcanic bombs. On steep volcanoes pyroclastic flows can reach speeds of over 100 miles per hour.
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Why do people live close to volcanoes?
Volcanoes have a wide range of effects on humans. These can be problematic or beneficial. It is usually the destructive nature of volcanoes which is more widely documented. However, many people rely on volcanoes for their everyday survival. Today, many millions of people live close to volcanoes for this very reason.
People live close to volcanoes because Geothermal energy can be harnessed by using the steam from underground which has been heated by the Earth's magma. This steam is used to drive turbines in geothermal power stations to produce electricity for domestic and industrial use. Countries such as Iceland and New Zealand use this method of generating electricity.
Volcanoes attract millions of visitors around the world every year. Apart from the volcano itself, hot springs and geysers can also bring in the tourists. This creates many jobs for people in the tourism industry. This includes work in hotels, restaurants and gift shops. Often locals are also employed as tour guides.
[Lava] from deep within the earth contains minerals which can be mined once the lava has cooled. These include gold, silver, diamonds, copper and zinc, depending on their mineral composition. Often, mining towns develop around volcanoes.
Volcanic areas often contain some of the most mineral rich soils in the world. This is ideal for farming. [Lava] and material from [pyroclastic flows] are weathered to form nutrient rich soil which can be cultivated to produce healthy crops and rich harvests.
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Case studies
The 1980 eruption of Mount St Helens
Mount St Helens is found in the Cascade Range, along the west coast of Washington State, USA. The volcano is 30,000 years old. This is young by geological standards. Mount St Helens erupts violently about once every 3,000 to 4,000 years. The volcano erupted most recently at 08.32 on 18th May 1980.
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The 1991 eruption of Mount Pinatubo
On 9 June 1991, Mount Pinatubo, a volcano in the Zambales Range, 80km (50 miles) north of Manila, capital of the Philippines, hit the headlines. It became one of the three largest eruptions in the world in the 20th Century. From the 9 June there were many eruptions (timeline of events). However, none matched that of 12 June. Ash turned day into night. The eruption caused the deaths of over 700 people. 200 000 buildings were destroyed. You can read a Who? What? Where? How? Why? fact file about the eruption. |
