Rangitoto was formed during a single phase of eruptions that may have lasted only 5-10 years, about 600 years ago. Previous inferences that it was formed by a series of eruptions commencing at least 6000 years ago have been disproved by the most recent research. The first part of the eruption was wet and produced surges of volcanic ash that mantles neighbouring Motutapu Island. The later part of the eruption was dry and built most of Rangitoto, erupting all the lava flows and scoria cones at the apex. The of material that erupted from the volcano was about equal to the combined mass produced by all the previous eruptions in the Auckland volcanic field, which were spread over more than 200,000 years.