Volcano is a vent or opening in the earth's crust through which molten material Ash, stream and other hot gases are emitted slowly or forcefully in the course of an eruption. These materials are thrown out from the hot interior of the earth to it's surface.

The hot material beneath the earth's surface is known as magma. When this magma comes out it is called lava.

Types of volcanoes: Volcanoes are mainly three types:

1. Active Volcanoes: Volcanoes which erupt frequently or have erupted recently are called active volcanoes.

Example: Barren island volcano in India.

2. Dormant Volcanoes: Volcanoes which have not erupted in recent times are known as dormant volcanoes.

Example: Kilimanjaro in Tanzania.

On the basis of mode of eruption these are divided into two types:

1. Central types of Volcanoes: When the eruption in a volcano takes place from a vector or hole, it is called the Central type of volcano. Conical hills and domes are formed by this type of volcano.

2. Fissure type of Volcanoes: Some time deep elongated cracks develop due to earthquakes or faulting. The magma starts flowing through the fissure. This mode of eruption is called fissure type of eruption.

On the basis of fluidity of lava:

1. Volcano of basic lava: It has great fluidity. It flows far and wide quietly with greater speed. It forms a shield.

2. Volcanoes of acid lava: It is highly viscous. The acid lava volcanoes cause the formation of usually higher land features with steeper slopes.