The mantle of the Earth contains molten rock known as magma. Since the pressure inside the Earth is very high, the molten magma and gases are sometimes forced to escape through cracks or openings on the Earth’s crust. Such cracks or openings form volcanoes.
Volcanoes are usually in the form of conical mountains. The molten magma and gases escape through a vertical tunnel called a vent. Once the magma reaches the Earth’s surface, it is called lava. The bursting of the magma from the vent is called an eruption. As the lava flows, it cools down and hardens to form solid rock. When it hardens around a vent in the shape of a hollow bowl, it forms crater.
Depending on the nature of their eruption, volcanoes can be either extinct, dormant or active.