VOLCANOES

Volcanoes are places where magma (red-hot liquid rock from the earth’s interior) emerges through the crust and onto the surface. The word ‘volcano’ comes from Vulcano Island in the Mediterranean.

There are many types of volcanoes. The most distinctive is the cone-shaped composite volcanoes, which build up from alternating layers of ash and lava in successive eruption.

From the magma chamber a narrow chimney, or vent, leads up to the surface. It passes through the cone of debris from previous eruption.

When the volcano erupts, the magma is driven up the vent by the gases within it. As the magma nears the surface, the pressure drops, allowing the gases dissolved in the magma to boil out. The expanding gases-mostly carbon dioxide and steam-push the molten rock upwards and out of the vent.

If the level of magma in the magma chamber drops, the soil of volcano’s cone may collapse into the old magma chamber. The caldera may fill with water to form a carter lake.

All the magma does not gush up the central vent. Some exist through branching side vents, often forming their own small ‘parasitic’ cones on the side of the main one.