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Volcanoes

Volcanoes are some of the most devastating natural hazards and when they erupt they can evoke awe and wonder in us all.  Volcanoes are basically mountains that can explode with violent consequences.  Volcanoes are a geological landform created by the intrusion of magma into the earth's crust and by the eruption of that magma onto the Earth's surface through a vent.  There are many different types of volcano, and they are classified in different ways according to their type of eruption, the material ejected and their activity.  You can see the BBC's animated guide to volcanoes here.

Volcanic activity

According to the activity of volcanoes, there are extinct, active, and dormant categories. Easily recognized volcanoes are active volcanoes, but dormant and extinct volcanoes are difficult and dangerous sometimes.  The people living near known extinct and dormant volcanoes must always be on the lookout.  Volcanoes can erupt at any time without warnings.

The constantly erupting volcanoes are active.  The eruption is usually quiet but can sometimes be violent.  Stromboli, which lies on an island near Italy, is a famous active volcano. 

Intermittent volcanoes erupt at fairly regular time periods.  Mount Asama, Mount Etna, and Hualalai are some intermittent volcanoes.

Inactive volcanoes that have not erupted for an amount of time but can’t be called extinct are dormant volcanoes. They can be called “sleeping” volcanoes. (see Thinkquest for more)  

Inactive volcanoes which have not erupted since the beginning of recorded history are extinct volcanoes.  They will never erupt again unless they are still dormant and have been mistaken for extinct volcanoes. 

Types of volcano

Think about it

Take National Geographic's red hot volcano quiz

Play the BBC's Super volcano game

Play Discovery Kids Volcano game - build your own volcano!

Volcano World on Mount St Helens

Mount St Helens Links page

Try a quiz on Volcano structure

Shield volcanoes
Hawaii is an example of a place where volcanoes extrude huge quantities of basaltic lava that gradually build a wide mountain with a shield-like profile. Their lava flows are generally very hot and very fluid, contributing to long flows. The largest lava shield on Earth, Mauna Loa, rises over 9,000 m from the ocean floor, is 120 km in diameter and forms part of the largest Island of Hawaii.

Stratovolcanoes
These are tall cone shaped (conical) mountains composed of lava flows and other ejecta in alternate layers, the strata that give rise to the name. Stratovolcanoes are also known as
composite volcanoes. Classic examples include Mt. Fuji in Japan, Mount Mayon in the Philippines, and Mount Vesuvius and Stromboli in Italy.

Volcano structure

Volcanoes are often made up of several layers of dust, ash, pyroclastic (blast) material and lava.  The amount of each material depends upon the eruption history of the volcano.  You can see a cross section of a volcano above, as you can see there is also a complex system of vents and faults along which volcanic material can travel. Watch an animation of volcano formation here.

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Some of the World's Volcanoes An explosive volcanic eruption Kilauea Volcano Erupts