What are the different types of volcanoes?

What is a volcano?

A volcano is an opening in the Earth’s crust where magma, molten rock deep below ground, comes to the surface as lava. Volcanoes come in many shapes and sizes. A typical volcano formed from layers of lava and ash built up from previous eruptions. It is known as a composite volcano.

Volcanoes can be described in one of three ways:

• Active volcanoes erupt regularly. Mount Etna, on the Italian island of Sicily, is the most active volcano in Europe, erupting every few years.

• Dormant volcanoes have been inactive, or asleep, for a long time. These volcanoes are less predictable and, therefore, more dangerous. Anak Krakatoa erupted in 2018 with the loss of 437 lives.

• Extinct volcanoes have stopped erupting altogether. The city of Edinburgh, in Scotland, is built on an extinct volcano.

Volcanoes erupt when pressure builds up inside the Earth. Deep below the ground surface is a magma chamber. 

Magma is forced to rise through cracks and weaknesses in the Earth’s crust (a pipe called a vent) and, when the pressure is too great, explodes at the surface. Lava flows from the crater and cools to form a layer of solid rock. 

Composite Volcanoes

Examples of composite volcanoes are Soufrière Hills, Montserrat and Mount Etna.

• These occur in areas of destructive plate boundaries.

• The eruptions are violent, ejecting thick and sticky lava.

• Ash and lava are ejected into the air and descend as slow-flowing, thick lava. The process is then repeated, building up layers of ash and lava.

• Pyroclastic flows (hot gas and ash) travelling more than 160 km per hour can flatten and burn everything in their path.

• Lahars (melted ice or rain mixed with ash) can occur.

• Thick layers of ash leave areas uninhabitable.