Volcanoes and Eruptions

A volcano is an opening in the Earth's surface through which molten rock, gases and fragments from deep inside the planet reach the surface. Beneath the crust the rock is extremely hot, and in certain places it melts to form magma. Because magma is less dense than the surrounding solid rock, it tends to rise; when it reaches the surface and erupts, the molten rock is called lava. Over many eruptions, the erupted material can build up into the familiar mountain shape of a volcano.

Most volcanoes occur along the boundaries between the great plates that make up the Earth's outer shell, where plates pull apart or collide. A notable concentration rings the Pacific Ocean, an active zone often called the Ring of Fire. Eruptions vary widely in character. Some, as in Hawaii, produce runny lava that flows out relatively gently and travels far. Others involve thick, sticky magma that traps gas and can erupt explosively, hurling out ash, rock and clouds of volcanic gas.

The products of an eruption include flowing lava, showers of ash and cinders, and gases such as water vapour and sulphur compounds. Volcanic activity can be highly destructive, burying land and threatening nearby communities, yet it also creates new land and fertile soils and is part of the natural processes that have shaped the planet's surface over geological time. The scientific study of volcanoes is called volcanology, and those who carry it out are volcanologists.

Frequently asked questions

What is the difference between magma and lava?

Magma is molten rock while it is still beneath the surface; once it erupts and reaches the surface, the same molten rock is called lava.

Why are some eruptions explosive and others gentle?

It depends on the magma. Runny magma lets gas escape and flows out quietly, while thick, sticky magma traps gas, which can build pressure and erupt violently.

Where do most volcanoes occur?

Mainly along the boundaries of the Earth's tectonic plates. A large number ring the Pacific Ocean in a zone known as the Ring of Fire.