Introducing volcanoes
An erupting
volcano is one of the most spectacular sights in the world. It is also extremely
dangerous. In just a few minutes the huge explosive power of a volcano can eject
poisonous gases and millions of tones of dust into the earth’s atmosphere. It
can cover an entire landscape in red-hot lava or ash, killing vegetation and
wildlife, destroying settlements and disrupting communications. Some eruptions
can also lead to huge loss of life.
What is a volcano?
A volcano is
really just an opening in the earth’s surface through which molten rock called
magma can escape, often with gas and dust. Usually we only hear about the very
powerful eruptions which affect large numbers of people. But at any one time, up
to twenty volcanoes may be erupting somewhere in the world. Volcanoes come in
different shapes and sizes, and there are several types of eruption. An eruption
can be very destructive, killing thousands of people and destroying farmland and
settlements. It changes the landscape completely. But an eruption can create new
land as well as destroying it.
How many volcanoes are there?
There are about 550 active volcanoes on land. Each year around 50 of these erupt, though only a few eruptions are serious enough to affect peopl4e or cause great damage. Not all volcanoes are still active. Some, like Mount Kilimanjaro in Kenya, have not erupted for many thousands of years. These are called extinct volcanoes. Others have remained quiet for a long time. Known as sleeping or dormant volcanoes, they can suddenly come to life and erupt again. One example is Mount Fuji in Japan, which last erupted in 1707.
Apart from the 550 or so active volcanoes on land, there are many more on the floors of our seas and oceans. These bubble away mostly unseen. In fact, over 80 per cent of the earth’s surface (above and below sea-level) is actually volcanic in origin. Volcanoes have played a key role in the development of the earth. Not only do they help to create new rock, but gas emissions from the early volcanoes, hundreds of millions of years ago, formed the earth’s atmosphere, which in turn provided the conditions which helped life to develop.
Where are volcanoes found?
Although there are several hundred active volcanoes, they are not distributed evenly around the world. There is a pattern to their location. Most are concentrated around the edges of the continents, as the map above shows. Others form chains of islands, or long, underwater mountain ranges in the oceans. More than half the world’s active volcanoes above sea-level circle the Pacific Ocean, and are known as the ‘Ring of Fire’.
