Ž . Geomorphology 38 2001 133–151 www.elsevier.nlrlocatergeomorph Dating the culmination of river aggradation at the end of the last glaciation using distal tephra compositions, eastern North Island, New Zealand Dennis N. Eden a, ) , Alan S. Palmer b , Shane J. Cronin b , Michael Marden c , Kelvin R. Berryman d a Landcare Research, PriÕate Bag 11 052, Palmerston North, New Zealand b Institute of Natural Resources, College of Sciences, Massey UniÕersity, Palmerston North, New Zealand c Landcare Research, P.O. Box 445, Gisborne, New Zealand d Institute of Geological and Nuclear Sciences, P.O. Box 30-368, Lower Hutt, New Zealand Received 22 December 1999; received in revised form 12 September 2000; accepted 4 October 2000 Abstract Ž . An extensive terrace Waipaoa-1 that can be traced for about 29 km in the Waipaoa valley, eastern North Island, New Zealand, is underlain by at least 10 m of coarse, aggradational, river gravels. Terrace cover beds contain tephras erupted from central North Island volcanoes and these provide minimum ages for the underlying gravels. Tephra or tephric layers occurring in the lower cover beds were investigated at five sites using a combination of stratigraphy, mineralogy, and the Ž . major element composition of glass shards together with discriminant function analysis DFA . The basal tephra is identified 14 Ž . as the ca. 14,700 C years old ca. 17,700 cal. years B.P. Rerewhakaaitu Tephra, erupted from Okataina Volcanic Centre. 14 Ž Using the stratigraphic relationship of Rerewhakaaitu Tephra, the end of aggradation is dated at ca. 15,000 C years ca. . 18,000 cal. years . Correlation with aggradational terraces elsewhere in North Island and northern South Island indicates that aggradation ended at the same time over a wide area and confirms a climatic origin for the terraces. Subsequent downcutting was apparently rapid because Rerewhakaaitu Tephra also occurs at the base of cover beds on a ca. 15 m lower terrace. The downcutting represents a major change in river dynamics and is most likely the response to climatic change and the resultant upper catchment landscape stability. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Tephra; River terraces; Aggradation; Last glaciation; New Zealand 1. Introduction New Zealand lies across the boundary between the Australian and Pacific crustal plates and has a ) Corresponding author. Ž . E-mail address: dne@inspire.net.nz D.N. Eden . dynamic landscape underscored by tectonic pro- cesses and sculptured by the fluctuating climates of Ž . the Quaternary Newnham et al., 1999 . In the North Island, volcanism has had a major influence on landscape development with much of the central part of the island being mantled by the products of volcanic eruptions. Tephra layers form widespread 0169-555Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-555X 00 00077-5