A volcano is an opening in the Earth’s surface in the shape of a mountain or hill that allows for magma, ash, rocks, hot vapor and gas to escape from the Earth’s center. As the tectonic plates move and hit each other, one of the plates becomes so hot that the ground turns to liquid. The liquid is called molten lava and it stays inside of the volcano until the gas build-up is so high that the volcano has to explode to get rid of the gas. There is not just one type of volcano, however. They differ based on how they erupt and how their shapes are built.  Volcanoes can be separated into three main categories: Composite, shield, and cinder cone.

Composite

Most of the Earth’s greatest mountains (such as Mt. St. Helen) are composite volcanoes, also known as stratovolcanoes. This type of volcano is very steep and comprised of mountainous layer-building of lava flows, volcanic ash, cinders, blocks and bombs. These volcanoes have a crater in the center which acts as a vent that lava flows through. When the lava hardens, it builds the core of the volcano. As this process repeats itself, it creates the shape of the volcano.

Shield

The shape of this volcano is a flat dome with a large slope, which is due to the fact that it is comprised of liquid lava flows. As the lava flows, it keeps the shape of the volcano. These are some of the largest volcanoes, and are relatively safe when they erupt because they don’t expel pyroclastic materials. Pyroclastic materials include hot lava and ash flowing through the air.

Cinder Cone

Cinder cone volcanoes are built by hot lava shooting through the air and landing around the vent of the crater. This lava hardens over time and creates the cone shape. In addition to the cone shape, it also has very steep sides and a bowl shaped mouth at the top of the mountain. These are the simplest volcanoes that are found in the most volcanic regions of the world.