Volcanoes

A volcano is a place on the Earth's surface (or any other planet's or moon's surface) where molten rock, gases and pyroclastic debris erupt through the earth's crust. Volcanoes vary quite a bit in their structure - some are cracks in the earth's crust where lava erupts, and some are domes, shields, or mountain-like structures with a crater at the summit.Magma is molten rock within the Earth's crust. When magma erupts through the earth's surface it is called lava. Lava can be thick and slow-moving or thin and fast-moving. Rock also comes from volcanoes in other forms, including ash (finely powdered rock that looks like dark smoke coming from the volcano), cinders (bits of fragmented lava), and pumice (light-weight rock that is full of air bubbles and is formed in explosive volcanic eruptions - this type of rock can float on water).
Volcanic eruptions can cause great damage and the loss of life and property.
The Word Volcano:
The word volcano comes from the Roman god of fire, Vulcan. Vulcan was said to have had a forge (a place to melt and shape iron) on Vulcano, an active volcano on the Lipari Islands in Italy. 

Extreme Volcanoes:
The largest volcano on Earth is Hawaii's Mauna Loa. Mauna Loa is about 6 miles (10 km) tall from the sea floor to its summit (it rises about 4 km above sea level). It also has the greatest volume of any volcano, 10,200 cubic miles (42,500 cubic kilometers). The most active volcano in the continental USA is Mt. St. Helens (located in western Washington state).
The largest volcano in our Solar System is perhaps Olympus Mons on the planet Mars. This enormous volcano is 17 miles (27 km) tall and over 320 miles (520 km) across.

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'

What are lahars and pyroclastic flows?

The most destructive aspect of volcanoes are lahars and pyroclasic flows. Lahars are volcanic mudflows created when water (from rain or meltwater from glaciers) and ash mix. This deadly combination can have devestating 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.

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.

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.

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.

The formation of volcanoes explained in geological terms: an animation depicts Iceland on the mid-Atlantic ridge, a great fault lying between the Americas and Africa; the Earth's surface is divided into plates; the plates move across the Earths surface causing continental drift; an animation shows a cross-section of the Earth, each layer is described and named, the theory of plate tectonics is introduced; an animation demonstrates the constructive and destructive elements of plate tectonics and how volcanoes are formed along plate boundaries; an animation of 'hot spot' volcanoes forming on the Pacific plate, Mount Kilauea, Hawaii being a good example.