Hold on tight while we explore the chamber deep inside a volcano and come up through the vent. First you will read the introduction paragraph to find this answer. A volcano is an opening in the Earth's crust. A volcano is formed when magma gushes up from the mantle and breaks through a crack or weak spot in the crust. The magma lies in a chamber deep inside a volcano.
Pressure builds up, forcing the magma to escape through a passageway called a vent.
Once the magma reaches the surface it is called lava. The shape of the three main types of volcanoes depends on the type of eruption. The way a volcano erupts depends on the type of magma, the length of the vent, and the amount of pressure present in the vent. Volcanoes that erupt regularly are called active . Volcanoes that no longer erupt are extinct , or dead.