Major periods of erosion and alluvial sedimentation in new zealand during the late holocene

Abstract

During the last 1,800 years there have been eight major periods of erosion and alluvial sedimentation in New Zealand. These and their probable times of occurrence are: Taupo (1,764 years BP), Post-Taupo (1,600–1,500 years BP), Pre-Kaharoa (1,300–900 years BP), Waihirere (680–600 years BP), Matawhero (450–330 years BP), Wakarara (180–150 years BP), Tamaki (1870–1900 AD) and Waipawa (1950 to present). The Taupo period, which is identified only in North Island, possibly resulted from heavy rainfalls induced by the Taupo Pumice eruption. The other seven periods, which probably occurred universally in both main islands of New Zealand, were almost certainly caused by increased northerly airflow and atmospheric warming over New Zealand, and the associated increased magnitude of major rainstorms and floods, producing increased rates of erosion and channel sediment transport. Such changes were due primarily to a temporary strengthening of the meridional upper atmospheric circulation in the Southwest Pacific region.The total amount of sediment deposited in successive erosion periods has generally decreased, even though, since c. 1,000 years BP, human populations and their impacts on the environment have generally increased. In some other regions of the earth, periods of greater alluvial sedimentation or storminess have coincided with one or more of the last seven periods recognised in New Zealand since 1,600 years BP. Within New Zealand, periods of alluvial sedimentation have coincided closely with episodes of coastal sand deposition.If sedimentation periods are dominated by meridional atmospheric circulation, soil-forming intervals are dominated by zonal circulation (westerly) with cooler air temperatures and less storminess. Accordingly, this chronological pattern represents long-term irregular fluctuations of warm, stormy periods separated by cooler, less stormy intervals. This periodic climatic regime fluctuation may constitute a widely applicable unifying hypothesis to explain many patterns of environmental change with time which are not understood. In particular, it can illuminate important aspects of indigenous vegetation and cultural history. © 1985 Journal of the Royal Society of New Zealand.