Volcanoes erupt when molten rock, known as magma, is forced to the Earth’s surface by the movement of the Earth’s tectonic plates. Sometimes a volcano explodes, sending thick clouds of ash high into the atmosphere. Other volcanic eruptions produce rivers of red-hot lava that flow over the landscape covering everything in their path. Whichever way a volcano erupts, it is one of the natural world’s most powerful and destructive forces.
Many of us only notice volcanoes when they are about to explode or disrupt our travel plans, but these spectacular forces of nature can have a significant impact on people living in the local area. While volcanoes can be destructive, they are also responsible for creating rich agricultural soil, minerals like gold and silver, diamonds, hot springs and geothermal energy.
A volcano is like a chimney that allows hot liquid rock, called magma, to flow from a layer within the Earth and erupt onto the surface. The magma can come from as far down as 200 kilometres in the mantle and once it erupts — at a piping hot 700 to 1,200 degrees Celsius — it is called lava.
As magma rises through many kilometres to the Earth’s surface, dissolved gases contained within it form expanding bubbles. These bubbles increase the pressure of the magma and, if this pressure is great enough, the volcano will erupt. The amount, temperature and composition of magma, including the amount of trapped gas contained in it, determines the type of volcano formed. The three most common large types of volcanoes are strato, shield and caldera.
Strato volcanoes are cone-shaped mountains that have been built up from layers of ash and lava. They are generally the tallest type of volcano and are known for their violent explosions. Bubbles of gas build up in the magma — which has a high silica content — and explode creating volcanic ash, consisting of tiny gritty sharp fragments of glassy snap-frozen magma and rock from the sides of the volcano vent.
Examples of strato volcanoes include Agung in Bali, Yasur in Vanuatu, Etna in Italy and Fuji in Japan.
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