Volcanoes are one of Earth’s great natural phenomena. Find our more about them on this expedition.

This story was created for the Google Expeditions project by Vida Systems, now available on Google Arts & Culture.

Tolbachik Volcano by ePP

In this expedition, we explore the inner and outer workings of a volcano and take a look at what makes volcanoes such a powerful force.

What is a Volcano?

A volcano is formed by a crack in the crust of the Earth from which hot magma and gases from deep within the Earth erupt.

Magma Chamber

Magma is melted rock deep inside the Earth.


Lava is what we call magma, once it flows out of a volcano.


Lava cools slowly because it is a poor conductor of heat. Lava flows slowly and hardens as it cools.

Earth’s Crust

The Earth’s crust is the outermost layer of the Earth. It is very thin - only about 3-5 miles thick under the oceans (oceanic crust) and about 25 miles thick under the continents.


The word "volcano" comes from the Roman name “Vulcan” - the Roman god of crafting and fire.

What Causes Volcanoes?

Volcanoes occur when material that is much hotter than its surroundings escapes from the interior of a planet or moon, causing an eruption.

The material that comes out from the Earth can be liquid rock ("lava" when it's on the surface, "magma" when it's underground), ash, cinders, and/or gas. 

The eruption can be explosive, firing lava and ash in the sky, or it can be just a liquid mixture, flowing down the sides of a mountain.

Rising magma

Magma rises to the surface when the pressure builds deep inside the earth, or when the earth cracks due to tectonic activities.

Earth Crust

The earth's crust isolates us from the hot magma, usually.

Volcanoes from Melted Crust

As the crust is pushed deep into the earth in a process called subduction, the intense heat and pressure melts the rock into magma.

Underwater volcanoes

Underwater volcanoes are volcanoes that erupt underwater. The lava that forms underwater is often round due to the way it is cooled down. These rock formations are called pillow lava.

Hot Spot Volcanoes

Hotspots are regions where the mantle is unusually hot compared to the surrounding mantle.

Different Stages of Volcanoes

Scientists have classified volcanoes into 3 main categories: active, inactive (or dormant), and extinct.

Extinct Volcano

An extinct volcano is one that has erupted before, but it is unlikely to do so again because there is no more magma left to erupt.

Active Volcano

Volcanoes have a long lifespan. Those that are currently erupting and showing signs of eruptions along with those that have erupted in the last 10,000 years are considered active.

Dormant Volcano

A dormant volcano is one that has not had any eruptions for a period of time. However, the possibility exists that the volcano will erupt again sometime in the future.

Volcanic Eruption

Volcanic eruptions are so powerful that they can entirely change the landscape of a certain area. Volcanic eruptions have been known to flatten forests and destroy entire cities.

Volcanic Islands

Though volcanoes destroy, they also create mountains, islands, as well as fertile land. 

The sudden release of ash, gases, and pyroclastic flow can even have fallout hundreds of miles away. Others can release massive amounts of invisible gases like carbon monoxide.

Effusive Volcanoes

Some volcanoes like Mauna Loa in Hawaii are effusive. Instead of violent explosions, the lava just pours or flows out of them. While not so destructive or fatal because people can usually outrun the lava, some released gases can be dangerous.


Volcanic eruptions can also send lava flowing in all directions. The flowing lava can cause plenty of damage by burning, melting, and destroying everything it touches, including farms, houses, and roads.

Different Types of Volcanoes

You might typically picture a volcano as a large, slope-sided mountain, but volcanoes can actually be a variety of shapes. Other possible shapes for volcanoes include shield (flat), composite (tall and thin), cinder cones (circular or oval), and lava domes.

Shield Volcanoes

Shield volcanoes are made up mostly of basalt lava that pours out quietly from long fissures. The lava flows then build a broad, domical shape and form broad plateaus that look like a shield. 


Some of the Earth's biggest mountains are composite volcanoes, also called stratovolcanoes. These are formed layer by layer from different eruptions.

Composite Volcanoes

The powerful explosive eruptions of composite volcanoes are one of the most dangerous to human life. They are the most likely to produce toxic ash clouds and destroy nearby buildings.


Caldera is a volcanic depression. The word is Spanish, meaning “cooking pot,” because after an eruption, a large depression or crater is left behind that resembles a pot.

Pyroclastic Flow. Lahar. Pumice.

Not only is molten lava erupted from a volcano, but also non-molten solid objects and hot gases can be ejected. The multitude of materials released from a volcanic eruption can cause disaster, but also create unique materials as the mineral and gaseous elements cool.

Pyroclastic Flow

A pyroclastic flow is a mixture consisting of solid to semi-solid fragments along with hot, expanding gases. This combination flows down the sides of a volcano very much like an avalanche.


A lahar is a type of mudflow composed of pyroclastic material, rocky debris, and water. The material flows down from a volcano like heavy cement, destroying everything in its path.


Pumice is a unique volcanic rock formed by all types of magma. It consists of gas bubbles frozen in fragile volcanic material making it so light and porous that it can float in water. It is popularly used as an abrasive.

The Ring of Fire

The Pacific Ring of Fire is a volcanic chain encircling the basin of the Pacific Ocean with more than half of the world’s active volcanoes. It is also the zone where 90% of the world's earthquakes - and 81% of the largest ones, happen.

It is the place where the Pacific oceanic plate is surrounded by other continental plates that move and push against each other leading to earthquakes and the formation of volcanoes.


Japan sits right on top of the Pacific Ring of Fire. Japan’s most famous mountain - Mount Fuji - is an active volcano.


The islands of Hawaii were formed by volcanic activities. In fact, volcanic activities are still happening on the youngest island - Hawai’i, more commonly known as ‘The Big Island’.


Popocatépetl is considered one of the most dangerous volcanoes in the Ring of Fire. The mountain is also one of Mexico’s most active volcanoes, with 15 recorded eruptions since 1519.

Volcanos and the Solar System

Volcanoes are not only found on Earth. Scientists have observed volcanoes on different planets in the solar system. The biggest one discovered so far, Olympus Mons, is on Mars and it’s more than twice the height of Mount Everest.

Io, one of Jupiter’s moons, has the most volcanic activity in our solar system with more than 400 active volcanoes.

Olympus Mons

The main difference between the volcanoes on Mars and Earth is their size. Volcanoes in the Tharsis region of Mars are 10 to 100 times larger than those anywhere on Earth.

Jupiter’s Moon

Io is about the same size as the Earth's moon. The gravitational influence of Jupiter and several neighboring moons create tidal heating within Io’s interior causing its impressive and unusual volcanic activity.


Jupiter is the fifth planet from the Sun and the largest planet in the solar system.


The sun is the center of the solar system and the most important source of energy for life on Earth.

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
Explore more
Google apps