Abstract

Abstract Studies in the pumice country of the central North Island, at Reporoa and Whakamaru, show that erosion is practically confined to the Taupo Pumice deposits of ash erupted about a.d. 131. Gullying by headward erosion has occurred in valleys which are normally dry but have carried flood waters at times of heavy rainfall. Scouring ceased at the level of the underlying older and more compact ash deposits, or alternatively ignimbrite. Numerous dry valleys in the region were presumably formed the same way, many probably by heavy precipitation immediately after the last eruptions. Recent erosion is primarily due to higher than average rainfall, though this has been accentuated by land development with sowing of pastures and clearing gullies of vegetation. The presence in the gully bottoms of several layers of alluvial sand carrying buried soils indicates that similar minor fluctuations in rainfall have occurred in the past. Detailed geological studies of physiography and Recent deposits provide the best...

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