Glaciation of the Tararuas - fact or fiction?

Abstract

In 1912 Adkin published a paper describing glacial landforms in the higher parts of the Tararua Range, about 70km northeast of Wellington city (Figure 1). Adkin's evidence for Pleistocene glaciation was based upon the morphology of the upper sections of five valleys, in particular the uppermost three kilometres of the Park Valley, which appeared to be U-shaped glacial troughs. He also described glacial and fluviatile hanging valleys, and cirques. Adkin's case for glaciation has been accepted uncritically by subsequent workers (Willett, 1950; Stevens, 1974a, b; Suggate, 1978) but no detailed fieldwork appears to have been carried out, possibly because of poor access to the area and unpredictable weather. This paper is based upon limited fieldwork carried out during several visits to three of the five valleys which Adkin described as glaciated, namely Park Valley, Waiohine Valley and the valley of South Mitre (Bennington) Creek. The valleys described by Adkin as glaciated have a form which is strikingly different from their deeply incised lower sections. Adkin asserted that the upper Park Valley had the form of a glacial trough but that the precipitous valley walls were subsequently buried by accumulating talus to modify the former U-shape. However, examination of sections exposed in small tributary valleys indicated that in many cases the scree merely forms a veneer over bedrock surfaces which sloped about 30°, which suggests that the valley sides may have originated as Richter denudation slopes.