Volcanoes are classified according to their periodicity of eruptions and the state of activity such as 
(i) Active volcano
(ii) Dormant volcano
(iii) Extinct volcano

A volcano is a vent or an opening in the earth's crust through which hot magma erupts from deep below the surface. The opening is usually circular in form

The earthquake waves are recorded by an instrument known as Seismograph

A sudden movement of a portion of the earth's crust which produces a shaking or trembling is known as an earthquake.

The innermost layer of the earth is called the core. It is also known as barysphere. It is separated from the mantle by a boundary called Weichart-Gutenberg discontinuity. The core is also divided into two parts.
(i) The outer core, which is rich in iron, is in liquid state.
(ii) The inner core, composed of Nickel and Ferrous (Nife), is solid in state.

The layer of the earth beneath the crust is called the mantle. It is separated from the crust by a boundary called Mohorovicic discontinuity.

(i) The chief cause of earthquake is the sudden slipping of the-portion of the earth's crust along fractures or faults.
(ii) Another cause of earthquake is volcanic activity.

On the basis of shape, there are three types of volcanoes. They are:
(i) Shield volcano
(ii) Cinder-cone volcano
(iii) Composite volcano