Volcanoes Made Easy!
A volcano is a vent or weak spot in the Earth’s crust through which magma (hot, melted rock) escapes as lava. In some places, lava oozes slowly out of the ground. In others there is a violent eruption.
A volcano erupts when magma wells up deep inside the earth. In violent eruptions, the magma fills a hollow chamber below a vent blocked by cooled and hardened rock. Gas and water mingle with the magma, forming an explosive mixture.The pressure builds up in the chamber until the magma, gas and steam are forced upwards and blast through the vent.
Are all Volanoes dangerous?
There are around 25 major volcanic eruptions on land every year and thousands of minor ones, many of which take place under the sea. Active volcanoes are those that may erupt at any time Dormant (sleeping) volcanoes have not erupted for centuries but may still do so. Extinct volcanoes are no longer likely to erupt.
Lava is the name given to magma once it has reached the earth’s surface. Lava may be thick and sticky or thin and runny, depending on the minerals the lava contains and the temperature and pressure when it was formed.
Different volcano shapes.
|The fissure volcano:||Is a long crack in the earth’s surface through which magma erupts. These cracks may form as two tectonic plates pull apart.
You’ll find them mainly near mid-ocean ridges.
|The shield volcano:||This is a broad, shallow volcanic cone, which arises because the running lava, which is fluid and hot, cools slowly.|
|The dome volcano:||This one has a steep, convex slope from thick, fast-cooling lava|
|The ash-cinder volcano:||Throws out – besides lava – much ash into the air. Through this the volcanic cone is built up from alternate layers of ash and cinder.|
|The composite volcano:||These are also built up from alternate layers of lava and ash but, besides its main crater, it has many little craters on its slope.|
|The caldera volcano:||An older volcano with a large crater which can be 62 miles(100km) wide. In this crater many little new craters are formed.|