Recent evolution of the Mangawhai Spit dunefield

Abstract

Abstract Development of the Mangawhai Spit dunefield since about 800 years B.P. is reconstructed on the basis of palaeo-environmental evidence. A buried soil with abundant charcoal beneath the present high dune suggests the former existence of forest on a low hill. Radiocarbon ages of charcoal samples are consistent with destruction of this coastal vegetation around 800 years B.P. Sites containing Kaharoa ash, assumed age c. 650–670 years B.P., usually overlie undifferentiated dune sands, indicating that dunefield development had already begun at that time. A number of middens (shell refuse heaps) dated to c. 400 years B.P. are now found on isolated sandy pedestals near the coast. At the time of their origin it is assumed that there must have been a foredune closer to the sea than the nearest one now is. Net east to west movement of sands has resulted in a large deflation surface near the coast, and the development of a 50 m high dune burying the former low coastal hill and associated soil.