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By: Efraim Harari

In the innermost layers of Earth, the temperature sometimes gets so hot that it melts rocks that are deep down in the mantle and the core. This can cause extremely high pressure from inside the earth to build up, to the point where eventually it forces the melted rock up and out of the earth through vents, which are cracks or holes in Earth’s crust. This is how a volcano is created.

Oftentimes, the vent is inside of a mountain, which means that when the volcano erupts, the melted rock shoots out of the top of the mountain. Sometimes the vent is in a flat area, and after the melted rock erupts, it cools around the vent, causing mountain-like structures to form. There can even be vents in the floor of the ocean, which means that volcanoes can erupt underwater, too.

The melted rock that is pushed out of the earth is called magma. Once the magma reaches the surface of the earth and explodes out of the volcano, it is called lava. The lava flows very quickly and is very dangerous, because it is burning hot! Dangerous gases, whole rocks, and ash can also shoot out of a volcano, along with the lava.

The effects of a volcano on the land surrounding it can be very deadly. Plants and trees are often burned by the hot, flowing lava. However, the nutrients found in a volcano’s lava and ash, which spread across the land following a volcanic eruption, actually work like a fertilizer that makes the soil a perfect place for new plants to grow!

That’s a
lotta’ Lava!

About sixty volcanoes erupt every year worldwide. Flowing lava has a temperature of about 1800 degrees Fahrenheit and flows downhill at speeds of up to 60 miles per hour!

There are various types of volcanoes.
Here are a few of the most common kinds of volcanoes:

Cinder Cones.These volcanoes are a round-cone or an oval-cone shape and do not get as tall as some other kinds of volcanoes. They are formed when lava is shot up into the air from a vent in the ground and then falls back to the ground and cools off, making a little cone shape around the vent. Cinder cone volcanoes do not cause a big explosion when they erupt. These volcanoes usually have a crater at the top, which is a bowl-shaped indentation.

Composite Volcanoes.These volcanoes are also cone shaped, but they can get very tall and they have steep sides, like a mountain. Composite volcanoes are formed when thick, hot lava, together with large chunks of rock and ash, shoot up out of a vent. The lava flows downward and then cools in its place. The next time the volcano erupts, the same thing happens, and the mountain is built up even higher, with more layers of cooled lava and rock.

Most of the tall volcanoes, like Mount St. Helens and Mount Rainier in Washington and Mount Fuji in Japan, are composite volcanoes. These volcanoes usually cause a big explosion when they erupt, although between eruptions you might not even be able to tell they are volcanoes, because they are very quiet and look just like any other mountain.

Shield Volcanoes.These volcanoes are very different from the other types. They are usually very wide, because they are formed when liquid lava emerges from a vent in Earth's crust and spreads out into a flat sheet that extends a long way from the site of the vent. As the lava cools, it dips down in the center, leaving sloped sides like a shield. Some of the biggest volcanoes in the world are shield volcanoes, such as Mauna Loa on the island of Hawaii. These volcanoes do not explode the way composite volcanoes do; instead, lava just flows gently out of them.


A person who studies volcanoes is called a volcanologist. A volcanologist studies lava, as well as the water and rocks that are around the sites of volcanoes, to learn what is going on inside a volcano. The information gathered is used in tests and observations to help scientists predict when a volcano might erupt next.