Cause and Effect of Volcanoes
Any natural opening in the Earth's crust, called a fissure, where melted rock, ash, gases, and steam come out is called a volcano. Volcanoes look like mountains, but they are really flat land that is pushed upward because of the pressure below the earth. The pressure comes from hot magma and gases that build up below the earth's surface and that work up to the surface through cracks in the earth's plates. As it is forced up to the surface, the gases and magma push the earth up with it forming the mountain shape. When the magma gets near the surface of the earth it sometimes erupts violently, but can also erupt without violence.
A volcano is actually an opening or a fissure, in the Earth's crust, through which lava or molten rocks, ash and toxic gases present below the surface of Earth are discharged by a sudden, violent eruption. Sometimes, it can be a mountain-like structure with a bowl-shaped depression at the top, through which these substances are expelled. The term 'volcano' is derived from the name of the Roman God of fire, Vulcan.
Volcanic structures are usually formed at places where the tectonic plates are either converging or diverging. A stretching or thinning of the Earth's crust, can also lead to the formation of volcanoes. They are often classified into three types, on the basis of their frequency of eruptions, i.e. active, dormant and extinct. The active volcanoes are characterized by regular eruptions, while the dormant volcanoes are those that erupted in the past, but are silent now. On the other hand, an extinct volcano is the one that erupted in the remote past and is unlikely to erupt again.
Volcanoes are not always erupting. Sometimes they lie quietly for thousands of years in between eruptions. Some volcanoes have areas around them that experience earthquakes and release gases, but do not erupt with magma.
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