A volcano is a fissure or crack in a planet’s surface through which molten lava, gases and ash erupt from below the planet’s surface. The word volcano comes from the name of the roman god of fire Vulcan. The cone that surrounds the fissure in the planet’s surface is built up of lava. A volcano is considered active if it vents lava, gas, or generates seismic activity (earth tremors). Dormant volcanoes are ones which have not erupted for many years but still have the potential to do so. Extinct volcanoes are those which have lay dormant for 100,000 years or more. There are at least 3 different types of volcano these are; the shield volcano, the Strato volcano and the Caldrea volcano.
How do Volcanoes Erupt?
While the shape and size or a volcano may vary the way that it erupts does not. Every volcano has what is known as a magma chamber. This is where hot, molten rock from the earth’s mantle collects. The process of a volcano erupting begins when the pressure in a magma chamber begins to build. This may be caused by the movement of the tectonic plates forcing the magma into smaller areas or the buildup of gases as more magma fills the chamber as plates move apart. The building pressure causes the magma to rise up a series of conduits inside the volcano. When it reaches the fissure or crack at the top of the volcano it erupts. The size of the eruptions depends on a number of factors such as:
- How much magma is in the chamber prior to eruption
- How much gas is present in the chamber and the magma itself
- How much silica is in the magma
- If there was any water present
If there is only a small amount of silica and water a volcanic eruption will be slow and the lava will flow gradually from the opening. The small amounts of silica cause the lava to be runny and less sticky. Small amounts of water cause only small reactions with the hot magma making to explosive nature less spectacular. In the same way large amounts of silica will make the magma sticky and thick and would create a lave dome on top of the volcano. If high levels of both water and silica are present the eruption would be highly explosive. The water would create steam and lead to fountains of lava.
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