The island is considered to be the largest sand island in the world at 1840 km². The island has rainforests, eucalyptus woodland, mangrove forests, wallum and peat swamps, sand dunes and coastal heaths. It is made up of sand that has been accumulating for approximately 750,000 years on volcanic bedrock that provides a natural catchment for the sediment which is carried on a strong offshore current northwards along the coast.