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 Indonesia shot dust 17 miles into the air. The dust was
carried around the Earth several times and produced brilliant red sunsets in
many parts of the world. Some scientists assume large quantities of volcanic
dust can affect the climate by reducing the amount of sunlight that reaches the
Earth.

Volcanic ash is made up of fragments less than one fifth inch in
diameter. Nearly all volcanic ash falls to the surface and becomes welded
together as rock called volcanic tuff. Sometimes, volcanic ash combines with
water in a stream and forms a boiling mudflow. Mudflows may speeds up to 60
miles per hour and can be remarkably shattering.

Volcanic bombs are large fragments. Most of them range from the size of
a baseball to the size of a basketball. The largest bombs can measure up to more
than four feet across and weigh up to 100 short tons. Small volcanic bombs are
generally called cinders.

Gas

Gas pours out of volcanoes in ...