The Earth consists of three layers. The outer layer of Earth where we live, which is about 18 miles thick, is called the “crust.” Below the crust lies a layer called the “mantle,” which is 1,800 miles thick.

A combination of molten rock and gases called “magma” lies between the Earth’s crust and the mantle. The innermost layer is called the “core.”

A volcano is a mountain that extends down to a pool of magma between the crust and mantle. It’s basically a hole in the Earth from which magma can erupt. The name “volcano” comes from the name of Vulcan, a god of fire in Roman mythology.

Volcanoes are like huge safety valves that release the pressure that builds up inside the Earth. When pressure builds up, eruptions occur. Magma shoots up through the volcano and flows down its sides.

Magma that flows out of a volcano is called “lava.” Fresh lava can be as hot as 2,200° F, glowing red or white as it flows.

Eruptions can cause mudslides, avalanches and floods. Volcano eruptions have knocked down entire forests, and they’ve triggered tsunamis and earthquakes.

As they erupt, volcanoes spew huge clouds of volcanic ash into the atmosphere. The ash consists of tiny bits of rock and glass.

Ash clouds can cover hundreds of miles, creating problems for airplanes and changing weather patterns. Volcanic ash can also damage the lungs and cause other respiratory problems for those who breathe it.

The United States contains several active volcanoes, mainly in Hawaii, Alaska, California, Oregon and Washington. Hawaii and Alaska have the greatest chance of experiencing eruptions near areas where many people live.

Want to keep a closer eye on volcanoes? Visit Volcano Live to access links to live volcano webcams across the world. If you want to see some great video clips of volcanic activity on Hawaii, head on over to the video gallery to see what’s happened at the Kilauea volcano!

More burning facts about volcanoes:

• Historical records exist for almost 600 volcanoes around the world, while some scientists believe there are more than 1,500 active volcanoes! No one really knows for sure how many volcanoes exist under the oceans.
• Over half of the world’s volcanoes arise in a belt around the Pacific Ocean called the “Ring of Fire.”
• On any particular day, approximately 20 volcanoes are in the process of erupting.
• The “danger zone” of a volcano extends for up to 20 miles in all directions.
• On May 18, 1980, Mount St. Helens erupted in Washington, killing 58 people and causing more than $1 billion in property damage.