Volcano is an opening on the surface of Earthâs crust. There are three types of volcanoes: (i) Active volcanoes are those which are currently erupting or have erupted in the last 10,000 years. (ii) The dormant volcanoes are in a state of sleep. This means that they had erupted in the past but can erupt again, however, at the moment they are asleep. (iii) Extinct volcanoes are those that have been inactive for thousands of years and are not expected to erupt again. The liquid that comes out of a volcano is called lava. Richter scale measures magnitude of earthquakes and was developed by Charles Richter in 1935.