Main Parts of a Volcano

By Eija Rissanen; Updated April 24, 2017
There are two main types of volcanoes: composite and shield.

A volcano is an opening in the Earth's surface through which magma, ash, rocks and gases eject to the Earth's surface. Besides Earth, volcanoes are also found on the other planets in the solar system, especially on rocky planets and moons. To fully understand what happens when a volcano erupts, you need to know the main parts of a volcano.

Volcanic Activity

There are about 1,900 volcanoes known to be active today and almost 90 percent of them are located in the Ring of Fire circling the edges of the Pacific Ocean and the boundaries of the plate tectonics in the area. Volcanoes and volcanic activity are found on the boundaries of plate tectonics where the plates diverge or converge underneath the Earth's surface, triggering a chain of events that can lead to a volcanic eruption and a creation of a volcano. Volcanoes are classified as active, dormant or extinct and they typically alternate between active and dormant periods. Any volcano can erupt, however, even the ones classified as extinct.

Magma Chamber

A large pool of molten rock, also called magma, sitting underneath the Earth's crust is called a magma chamber. The magma chamber can be more than three miles below the Earth's surface and the magma waits there for the pressure and gases to become too much to stay stable. The magma in the magma chamber is less tense than the mantle surrounding it, so it moves toward the surface of the Earth through cracks and flaws in the crust once a high enough pressure point is reached. Volcanic eruption is the result of magma reaching the Earth's surface.

Main Vent

The main channel through which the hot magma moves to reach the Earth's surface is called a main vent. To reach the Earth's surface, the main vent can be several miles long, having one end connected to the magma chamber and one reaching the surface. During volcanic eruption, most of the lava ejects through the main vent.

Secondary Vent and Cone

Larger volcanoes can have more than one vent for the magma to reach the Earth's surface. Secondary vents, with the main vent, are a way for the magma to move and reach the surface during volcanic eruption causing unforeseen dangerous situations when the lava flow suddenly widens or starts to flow to a different direction than previously predicted. Secondary cones form around secondary vents on large volcanoes.


Crater is the circular formation with steep sides formed around the main vent where the lava, ash and rocks reach the surface of the Earth during the volcanic eruption. Most of the time the crater is formed to the top of the volcano, where the main vent ejects to the surface but, if the volcano has secondary vents, craters can also be found on the sides of the volcano. Crater lake is often formed to the summit crater when the crater fills with water.

About the Author

Eija Rissanen is a freelance journalist living in Hawaii. She has a journalism and environmental studies degree from Hawaii Pacific University. Her articles have been published in Kalamalama, the student newspaper of Hawaii Pacific University, and some other environmental and travel publications and Web sites in Europe and the United States.