Auckland's volcanoes are fuelled entirely by basaltic magma, unlike the explosive subduction-driven volcanism in the central North Island, such as at Mount Ruapehu and Lake Taupo which are of tectonic origin. The most recent and by far the largest volcano, Rangitoto Island, was formed within the last 1000 years, and its eruptions destroyed the Māori settlements on neighbouring Motutapu Island some 700 years ago. Rangitoto's size, its symmetry, its position guarding the entrance to Waitematā Harbour and its visibility from many parts of the Auckland region make it Auckland's most iconic natural feature. Because of its rich acidic soil and the type of flora growing out of the rocky soil, only a few birds and insects inhabit the island.