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Why do volcanoes erupt?

A cross-section through an erupting volcanoA volcano is an opening in the Earth’s crust through which magma (molten rock) erupts. Some volcanoes are cone-shaped mountains with a crater at the summit. Others can be just a crack in the ground, called a fissure. A volcano may erupt lava, ash, dust, fumes, gas and lumps of rock called volcanic bombs. 


 

Explosive eruptions

The eruption of Mayon Volcano, Philippines, in September 1984. It was an explosive eruption.Some volcanoes erupt in spectacular explosions. The erupted magma, called lava, is blown to fragments (ash) and powder (dust) by the force of the explosion. The volcano shoots this ash and dust high into the air. Over time, many layers of powdered lava pile up to form a cone-shaped, steep-sided mountain. The eruptions of Vesuvius in AD 79 and Mount St Helens in 1980 are examples of explosive eruptions.
{alt}A Hawaiian volcanic eruption{more}Click to play video

Hawaiian eruptions

The word "volcano" comes from the Italian island of Vulcano. Centuries ago, people believed that it was the chimney of the forge of Vulcan, the Roman god of fire.

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