one and burn up, or push up on each other which forms volcanoes. Websites Used: http://wiki.answers.com/Q/Why_do_volcanoes_form_at_plate_boundaries_and_hot_spots#ixzz1CjdvgNp9 http://wiki.answers.com/Q/Why_do_volcanoes_form_at_plate_boundaries 10. Why can some volcanoes form on Mars? Mars is only one half of the size of Earth and there is several volcanoes that surpass the scale of the biggest volcanoes.Both Mars and Earth