Norfolk Island rose out of volcanic activity at the base of Mt Pitt and Mt Bates. Basaltic rock formed through this volcanic activity underlies most of the park and is the source of the krasnozem (red soils) and skeletal (thin) soils which are found throughout the Mt Pitt section of the park. Skeletal soils are found along the summit ridge from Mt Pitt to Mt Bates, and from there to the northern coastline. The northern coastline consists of a series of cliffs with little soil formation or retention. Krasnozem clays of various classes are found on the eastern and western slopes of this section of the park.
Norfolk Island soils, being basaltic in origin, are nutrient rich and well structured, but they are also friable and porous. They are prone to mass movement such as soil creep, slumps and landslips if vegetation cover has been degraded or lost, or after a period of particularly heavy rain.
Fossiliferous limestone inclusions in tuffs on the Island have confirmed its existence in the Miocene epoch (approximately 20 million years ago). Volcanic activity took place between 2.3 and 3.2 million years ago. The total exposure afforded by the cliffs and bare, gullied slopes shows that Phillip Island consists equally of basalt lava and tuff.
The terrain varies from deeply dissected bare earth in the interior, to wave-washed rock platforms and boulder strewn coastal margins. Wind-sculpted monoliths and exposed dyke ridges prevail in the upper regions.