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 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 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
Gas pours out of volcanoes in large quantities during almost all eruptions. The gas
is made up particularly of steam, but may also include carbon dioxide, nitrogen, sulfur
dioxide, and other gases. Most of the steam comes from a volcano’s magma, but some
steam may also be produced when rising magma heats water in the ground. Volcanic gas
carries a large sum of volcanic dust.
This alliance of gas and dust looks like black smoke
Types of Volcanoes
The magmas that are the most liquefied erupt quietly and flow from the vent to form
sloping shield volcanoes, a name that is conceived because they look like the shields of
ancient German warriors. The lava that flows from shield volcanoes is usually only one to
ten meters thick, but the lava may extend for great distances away from the vent. The
volcanoes of Hawaii and Iceland are typical shield volcanoes.
Magma with high gas contents .