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Volcanoes

A cross-section through a volcano. In an explosive volcanic eruption, magma is blasted out of the crater. The erupted magma,...Read More >>A cross-section through a volcano. In an explosive volcanic eruption, magma is blasted out of the crater. The erupted magma, called lava, is shattered into pumice and ash, which form a huge cloud billowing into the sky. At the same time, thick lava flows slowly down the volcano’s slopes, cooling and hardening close to the crater. As the volcano erupts time after time, the lava layers build up to form a cone-shaped mountain. A volcano—often, but not always, a cone-shaped mountain—is an opening in the Earth’s crust through which molten rock, called magma erupts. When a volcano erupts and hurls out its red-hot rock, this is one of the most awesome events of nature. It happens at a hole, crack or weak point in the solid rocks of the Earth’s crust. Melted rock called magma from deep below forces its way up under incredible temperature and pressure. As it emerges it is called lava. When it cools and hardens, it forms a type of rock known as igneous rock.



Anak Krakatau erupting in a violent explosion

Explosive eruptions

In a volcanic eruption, magma is blasted out of the volcano’s crater. If the magma is thick and pasty, the gas trapped inside it cannot escape, so it builds up and up until it explodes. The eruption will be a very violent one. The erupted magma, called lava, is shattered into pumice, fragments of rock once full of gas bubbles, and ash, lava blown to powder by the force of the explosion. The pumice and ash form a huge cloud. In explosive eruptions, the thick lava moves slowly and hardens close to the volcano’s vent or crater. As this type of volcano erupts time after time, the lava builds up in layers to form a cone-shaped, steep-sided mountain known as a stratovolcano.

Methods to predict an eruption include studying the behaviour of local animals. For some reason, some may become agitated before an eruption happens.

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