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Volcanoes

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Volcanoes

This paper will define and discuss the volcano to include: types of volcanoes,

formation of a volcano, and elements of a volcano; such as, lava, rock fragments, and gas.

This paper also tells a little bit about volcanic activity in different parts of the world.

What is a volcano?

A volcano is a vent in the earth from which molten rock and gas erupt. The molten

rock that erupts from the volcano forms a hill or mountain around the vent. The lava may

flow out as a viscous liquid or it may explode from the vent as solid or liquid particles.

Kinds of Volcanic Materials

Three basic materials that may erupt from a volcano are; 1. lava, 2. rock

fragments, and 3. gas.

Lava

Lava is the name for magma that has been released onto the Earth's surface. When

lava comes to the Earth's surface, it is red hot and may have temperatures of more than

2012 degrees Fahrenheit. Fluid lava flows swiftly down a volcano's slopes.

Sticky lava flows more slowly. As the lava cools, it may harden into many different

formations. Highly fluid lava hardens into smooth, folded sheets of rock called pahoehoe.

Stickier lava cools into rough, jagged sheets of rock called aa. Pahoehoe and aa cover

large areas of Hawaii, where the terms originated. The stickiest lava forms flows of

boulders and rubble called block flows. It may also form mounds of lava called domes.

Other lava formations are spatter cones and lava tubes. Spatter cones are steep hills

that can get up to 100 feet high. They build up from the spatter of geyser-like eruptions of

thick lava. Lava tubes are tunnels formed from fluid lava. As the lava flows, its exterior

covering cools and hardens. But the lava below continues to flow. After the flowing lava

drains away, it leaves a tunnel.

Rock Fragments

Rock fragment are usually called tephra and are formed from sticky magma. This

magma is so sticky that its gas can not easily escape when the magma approaches the

surface or central vent. Finally, the trapped gas builds up so much pressure that it blasts the

magma into fragments. Tephra consists of volcanic dust, volcanic ash, and volcanic bombs,

(from smallest to largest size particle).

Volcanic dust consists of particles less than one one-hundredth inch in diameter.

Volcanic dust can be carried for great distances. In 1883, the eruption of Krakatau in
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