face it cools down and sometimes the flow of magma stops in the inner part. In other places, magma unites with gas and creates chambers below the surface of the earth. When the gas pressure gets higher, magma becomes lighter and it spews out of openings, cracks or vents at the surface.
Volcanic eruptions
When a volcano erupts three types of material come to the surface: lava, small pieces of rock or ash, and gas.
Magma that spreads out of a volcano slowly is called lava. It can reach temperatures of up to 1,200 C and glows red to white when it flows. In most cases, lava mixes with steam and gas. All types of lava contain silicon and oxygen. As lava moves down a volcanos slope it cools down and becomes harder, creating very rough blocks or rock.
Small pieces of rock erupt from a volcano when magma is trapped inside and cannot get out. Gas pressure in the magma chambers gets high and suddenly material is blown out and thrown high into the sky.
Often, the pieces of rock are so tiny that they form ash or dust. Strong winds can blow volcanic dust hundreds or thousands of kilometers away from the place of eruption.
Types of volcanoes
The two most common types of volcanoes are strato volcanoes and shield volcanoes.
Strato volcanoes are formed like a cone. The base is rather flat and they become steeper towards the peak. A crater usually forms at the top of the volcano. Such volcanoes develop when lava and ash come up from the inner part of the earth and build up layers. First, lava spreads over the surface of the volcano, cools down and becomes hard. Then pressure builds up underneath the layers of lava and ash and other materials are blown out. One of the most famous strato volcanoes is Mount Fuji in Japan.
Shield volcanoes are dome
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