Volcanoes
VIDEO: Top Ten Biggest Volcanic Eruptions
PDF: Volcano – what to do after a volcanic eruption
DIAGRAM: Cross Section of a Volcano
MAP: The "Ring of Fire"
WHAT IS A VOLCANO?
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A volcano is a mountain with a crater or vent which allows hot lava, rock fragments, volcanic ash and gases to erupt from the earth’s crust. Volcanoes are like giant safety valves that release the pressure that builds up inside the Earth because of this hot lava and gas.
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Volcanoes are usually located along fault lines where tectonic plates meet. When these plates move, the friction can cause earthquakes and volcanic eruptions near the edges of the plates.
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Scientists have categorized volcanoes into three main categories: active, dormant, and extinct. An active volcano is one which has recently erupted and there is a possibility that it may erupt soon. A dormant volcano is one which has not erupted in a long time but there is a possibility it can erupt in the future. An extinct volcano is one which has erupted thousands of years ago and there’s no possibility of eruption.
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There are more than 1500 active volcanoes on the Earth. We currently know of 80 or more which are under the oceans. The Pacific Ring of Fire is an area of frequent earthquakes and volcanic eruptions encircling the basin of the Pacific Ocean. The Ring of Fire has 452 volcanoes and is home to over 50% of the world’s active and dormant volcanoes. Ninety percent of the world’s earthquakes and 81% of the world’s largest earthquakes occur along the Ring of Fire.
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Lava is semi-fluid rock which has been heated under the surface of the earth. Initial flows of lava can move at up to 10 km/h. Once a lava flow becomes established, it can move as fast as 60 km/h.
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Along with lava and ash, volcanoes release gases. Common volcanic gases include water vapour, carbon dioxide, sulphur dioxide, hydrogen chloride and hydrogen sulphide.
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Volcanic eruptions can vary in their size and level of explosiveness. Scientists use the Volcanic Explosivity Index (VEI), based on a range of characteristics, to measure the size of a volcanic eruption.
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The word "volcano" comes from the little island of Vulcano in the Mediterranean Sea off Sicily. Centuries ago, the people living in this area believed that Vulcano was the chimney of the forge of Vulcan -- the blacksmith of the Roman gods. They thought that the hot lava fragments and clouds of dust erupting from Vulcano came from Vulcan's forge as he beat out thunderbolts for Jupiter, king of the gods, and weapons for Mars, the god of war.
WHAT ARE PLATE TECTONICS?
The theory, or idea, of plate tectonics says that Earth’s outer layer is made up of large, moving pieces called plates. All of Earth’s land and water sit on these plates. The plates are made of solid rock. Under the plates is a weaker layer of partially melted, molten rock. The plates are constantly moving over this weaker layer.
As the plates move, they interact at their boundaries in different ways. At one type of boundary the plates slide alongside each other. At another type, the plates crash into each other. In this case the edge of one plate may slide under another plate and be destroyed. Or the two edges of the plates may rise up and form mountains. At the third type of boundary the plates move apart from each other. When they do, the melted rock beneath the plates rises up. This melted rock, or magma, cools as it rises and forms new crust.
Earthquakes and volcanoes often happen along plate boundaries. There are so many earthquakes and volcanoes at the edges of the Pacific Plate that this region is called the Ring of Fire.
VIDEO: How do Volcanoes form?
