The hill's scoria cones were erupted from three craters - one is intact and two have been breached by lava flows that rafted away part of the side of the scoria cone. Lava flows went in all directions, many towards Onehunga, covering an area of , making it the second largest (in area covered) of the Auckland volcanic field, behind Rangitoto Island. The volcano erupted approximately 60,000 years ago.