A volcano is a landform (mountain) where magma erupts through the surface of the Earth’s crust. When most people think of a volcano, they usually think of images from films and books: a huge, alarming mountain that explodes and spews out masses of lava which falls on everything and will kill everyone!!
While those types do indeed exist, destroying everything in their reach within minutes, other volcanoes release lava so slowly that you can safely walk all around them, there are different types of volcanoes but we’ll get to them later...
The Earth's surface is broken into a dozen or so large solid slabs (tectonic plates.) The greater part of the world's active volcanoes, above and below the sea, are found along or near the boundaries between these shifting plates.
Molten rock that has not erupted is called magma. Magma is made when rock deep underground melts due to the high temperatures and pressures inside the earth. Because magma is lighter than the nearby rock, it tends to rise.
Molten rock that has erupted is called lava. When lava comes to the surface, it is red-hot, reaching temperatures as high as 1200° C. ~ Now that’s hot!
There are more than 1500 active volcanoes on the Earth. At least 80 are known to be under the oceans. Sometimes when they erupt their cones burst above the sea to create islands.
Icelandic warriors named these volcanic mountains shield volcanoes many centuries ago because they thought the shape of a local volcano looked like the round fighting shields that they carried into battle.
A live volcano is one that may erupt in the future. A dead volcano is one which erupted in the past but will not again.
Volcanoes have a wide range of effects (both tricky and useful for humans) Many people rely on volcanoes for their everyday survival. Energy can be harnessed by using the steam from underground which has been heated by the Earth's magma. This steam is used in power stations to produce electricity. Countries such as Iceland and New Zealand use this method of generating electricity.
Shield volcanoes are common in Hawaii and Iceland, they are formed when lava is very hot and very runny. A shield volcano is a roundish, mound like volcanic mountain with very gentle slopes. They consist of many thin layers of rock.
Composite volcanoes are constructed from multiple eruptions, they are steep sided volcanoes. They consist of layers of ash and lava. Composite volcanoes are very explosive because the lava is very thick.
Cinder cones are simple volcanoes which have a cone shape and are not very big. It is made up of a pile of loose fragments that have built up around a vent they form during eruptions that are not super explosive. Lava rarely issues from the top (except as a fountain) because the loose fragments are too weak to support the pressure exerted by molten rock as it rises toward the surface.
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