What is a Volcanoes? | Types, Definition, Structure, Function & Facts

What is a Volcanoes?

A volcano is a hole in the Earth’s crust where hot liquid rock from deep within the Earth, called magma, erupts to the surface.

Magma and Lava

When the rock beneath the Earth’s surface becomes very hot, it becomes liquid or molten. As long as it remains below the surface, it is called magma. Once magma erupts to the surface through a volcano, it is called lava. The hotter and finer the lava, the farther it flows. Lava can be very hot, sometimes up to 1000 degrees Celsius.

Get Free Counseling

Eventually, the lava on the surface will stop flowing and will cool and harden into rock. Rocks formed by the cooling of lava are called igneous rocks. Some examples of igneous rocks include basalt and granite.


A volcano can be active, dormant, or extinct. An active volcano is a volcano that has recently erupted or is currently erupting. An dormant volcano is a volcano that has not erupted for a long time, but has the potential to erupt again. An extinct volcano is one that scientists believe will never erupt again.

Explosive Volcanoes

Some types of volcanoes are simply lava that flows out over time. This is usually when the lava is thin. Other volcanoes have thicker lava that can clog the volcano’s vents. When this happens, pressure can build up over a long period of time. When the pressure is high enough, the volcano can erupt with a huge explosion. Large amounts of lava and ash can be ejected from the volcano.

Types of Volcanoes

We often think of volcanoes as tall, cone-shaped mountains, but there are different types of volcanoes:

Cinder cones – These are volcanoes formed from lava particles and droplets spewing from a single vent at the top. They usually do not exceed about 1,000 feet.

Composite volcanoes – These volcanoes are also conical, but formed from layers of lava over many years. They can grow into giant mountains over 8,000 feet from their base.

Shield volcanoes – They form from wide, thin layers of lava that eventually take the shape of a shield.

Lava domesĀ – These volcanoes are formed by thick lava that hardens right around the vent. They can sometimes form inside other types of volcanoes.

Interesting facts about Volcanoes

The tallest volcano we know of in the solar system is located on Mars. It’s called Olympus Mons and is 17 miles high.

A large volcanic eruption can destroy an entire forest.

The world’s largest volcano is Mauna Loa on the Big Island of Hawaii. The tallest is Mauna Kea right next door.

Ash clouds from volcanoes can be dangerous. It can harm people to breathe and make it difficult for aircraft. A large ash cloud from Eyjafjallajokull, a volcano in Iceland, closed most European airports for several days in 2010.

There are usually about 20 volcanoes erupting in the world at any given time.