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Volcanoes

Volcanoes are mountains that contain molten rock, called magma, below the surface. They are natural, caused by the pressure and temperature inside the Earth. An eruption can cause rocks to shoot out through the opening and fill the air with gases. Magma is lava when it is above the surface of the Earth.

An image of a volcano erupting.

A volcanic eruption.

How are volcanoes formed? 

Volcanoes form as magma from the Earth’s mantle rises towards the surface. We call this rising magma a mantle plume. Once at the surface, the magma can erupt from the vent, known as an orifice. Remember, we call magma on Earth’s surface ‘lava.’ As the vent continues to erupt, the lava forms new igneous rock. This causes the mountain to grow bigger.

An illustration showing how volcanoes grow.

This diagram shows how a volcano is built over time.

Volcanoes form at the divergence or convergence of tectonic plates. Most divergent plates are at the bottom of the ocean. For example, there is the Ring of Fire which includes over 1,000 oceanic volcanoes in the Pacific Ocean.

An illustration showing different types of tectonic plate boundaries.

The top right picture features divergent tectonic plates. The picture on the bottom right contains convergent tectonic plates. Volcanoes can form on either of these fault lines.

What are some well-known volcanoes?

One of the most famous volcanoes is Mount Vesuvius, which is in Italy. It infamously erupted to completely cover the city of Pompeii in A.D. 79. The city was not rediscovered until the 18th century!
 

Information on current volcanic activity around the world available here.

An image of Pompeii in front of Mount Vesuvius.

Pictured in the back is the volcano Mount Vesuvius, mentioned above. In the front are the ruins of Pompeii preserved centuries after the eruption.

What are the different types of volcanoes? 

There are three main types of volcanoes composite, shield and cinder cone.

Composite

These are also known as stratovolcanoes. They have steep sides formed from layers of ash and lava. When they erupt- they are explosive. This is not the case for all volcanoes.

Shield

These volcanoes have gently sloping sides formed from layers of lava. When they erupt, they project fast flowing lava that can travel for miles. Eruptions tend to be more frequent with this type.

Cinder cone

These have steep sides coming off a circular vent. This forms what looks like a cone. Cinder cones form around very hot vents where magma tends to erupt violently. After the explosion, hardened pieces of rock fall back down onto the volcano in a cone-shape.
 An illustration showing parts of a volcano.
Pictured are the parts of volcanoes.

Other Great Resources:

USGS On Volcano Types: https://pubs.usgs.gov/gip/volc/types.html

Shorter Overview of Types with Diagrams: https://www.zmescience.com/other/science-abc/types-of-volcano/

Bill Nye on Volcanoes: https://www.youtube.com/watch?v=4F9ovQf9-dg

Volcano Facts Video: https://www.youtube.com/watch?v=x-6bGUffwtA

Written by: Cristina Kinslow