some volcanoes are more active than others because some volcanoes lie on plate boundaries that move frequently which adds more pressure to the magma chamber where all of the lava is stored. Other volcanoes are formed but do not gain much pressure because they have been formed slowly or have errupted many times before and do not gain any more pressure. Some volcanoes are temperarily dormant which means they are not active. Some volcanoes have been dormant for hundreds of years because there is not enough pressure for the volcano to errupt. Hot countries may have an affect or volcanoes that started off very close to the epi-center of the earth, that has lava flowing up to the volcanoes frequently from there, which may set them off more. I hope this has answered your question.