<human>: How is a volcano formed?
<bot>: A volcano is formed when magma, or molten rock, rises from the Earth's mantle and erupts through the crust. This causes the land to rise up and form a cone-shaped structure called a volcano. The magma is usually composed of a mixture of different minerals such as silica and sulfur. As the magma cools and solidifies, it forms layers that can be seen in the shape of the volcano.