Kinds of volcanic materials

There are three basic kinds of materials from the volcano. They are lava, rock fragments and gas. The material that erupts is dependent on the stickiness and how fluid a volcano's magma is.

Lava is the name of magma which has reached the earth's surface. Lava is extremely hot when it is at the surface, and can reach a temperature of 1100oC. Fluid lava flows down fast, while stickly lva flows slowly. As lava cools, it hardens into different kinds of solid. Smooth folded sheets of rock is called pahoehoe. Stickier lava cools into rough, jagged edges of rock called aa.

Rock Fragments are generally called tephra, which are formed from sticky magma. Such magma is so sticky that it cannot easily escape when magma nears the surface. Finally, the trapped gas is under so much pressure that it blasts the magma into fragments. Tephra include volcanic dust, volcanic ash and volcanic bombs.

• Volcanic dust consists of small particles less than 0.25 mm in diameter, and are generally not dangerous. However, they may affect the climate by reducing the amount of sunlight that reaches earth.

• Volcanic ash is made up of small pieces less than 0.5cm in diameter. These, when combined with water, may form a boiling mudflow which can travel at a speed of 100 km/h and is very destructive.

• Volcanic bombs are large, mostly ranging from the size of a rugby ball to that of a basketball. The largest bombs may measure more than 1m across. Small volcanic bombs are called cinders.

Gas pours out of the volcano in large amounts during eruption. It is mainly made up of steam. However, it consists of carbon dioxide, nitrogen, sulphur dioxide and other gases. Volcanic gas brings along with it large amounts of volcanic dust. This makes the combination look like black smoke.