Hot plates and melting pots: Why do Volcanoes erupt?

512px-Hawaii_Volcanoes_NP_MagmaThe Earth’s crust is made up of huge slabs called plates. These massive plates fit together rather like a jigsaw puzzle. Sometimes these plates move, and the friction that action causes, can lead to both earthquakes and volcanic eruptions.

A volcanic eruption occurs when the pressure and high temperatures beneath the plates cause rocks to melt. This melted rock turns into a liquid known as magma (or molten rock), which seeps through the Earth’s crust, before gradually making its way up to the top of the volcanic mountain, and eventually form into rivers of magma that brim beneath a volcano’s surface.

The pressure in this magma chamber fills and builds, like water and steam in a boiling kettle. It is when this pressure reaches breaking point that the eruption occurs. Gases and rock shoot up through the opening in the top of the mountain, spilling over its edge. The moment magma reaches the top of the volcano it becomes lava, which flows down the sides of the volcano.

The lava flows are only part of the devastating effects of a magma explosion. As the air around the volcano blast fills with lava fragments, hot ash adds to the lava flow, as well as sparking mudslides, avalanches, falling ash and floods.

The most powerful volcanoes release a pyroclastic flow. This is a fluid mixture of solid to semi-solid boiling hot fragments that include expanding gases, which cascades down the sides of a volcano. Volcano eruptions can also trigger tsunamis, flash floods, earthquakes, and rock falls.

There are three recognised stages of volcanic action. They are either 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 has not erupted in a long time, but there is a possibility it might erupt in the future. An extinct volcano is one which has erupted thousands of years ago and will never erupt again.

There are more than 1500 active volcanoes on the Earth. Another 80 have been discovered under the ocean, and there are believed to many more hidden beneath its waves. The world’s largest, active volcano is Mauna Loa in Hawaii. It is 13,677 feet above sea level, and from its base below sea level to its summit, Mauna Loa is taller than Mount Everest.

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Dr Kathryn Bates is a graduate of archaeology and history. She has excavated across the world as an archaeologist, and tutored medieval history at Leicester University. She joined the administrative team at Oxford Open Learning twelve years ago. Alongside her distance learning work, Dr Bates is a bestselling novelist, and an itinerant creative writing tutor for primary school children.

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