540 volcanoes on land are known June 10, 2014 in Earth Facts / World Facts, Nature Facts About 540 volcanoes on land are known. No one knows how many undersea volcanoes have erupted through history. About 540 volcanoes on land are known. No one knows how many undersea volcanoes have erupted through history. Review OverviewUser Rating: Be the first one ! 0 facts 2014-06-10 Admin Share ! tweet