Paleo‐equilibrium line altitude estimates from late Quaternary glacial features in the Inland Kaikoura Range, South Island, New Zealand

Abstract

A reconnaissance investigation of glacial features in the Inland Kaikoura Range (IKR), South Island, New Zealand, confirms that over 30 km of the length of the range, with a maximum elevation of 2885 m, has been extensively glaciated in the past, in contrast to previous reports. Identified glacial features include cirques, lateral moraines, moraine fragments and associated features, and rock glaciers. Up to five glacial advances have been identified in any one catchment in the range, with the most complete sequence found in Branch Stream, which drains the steep southeastern flank of the highest portion of the range. The lateral moraines of Branch Stream are impressive; they range in elevation from c. 1700 to 1200 m, and, because of their large size and relatively good state of preservation, they are interpreted to be of late Otiran age. Glacial features that are less well preserved and more fragmentary are found at lower elevations in other catchments (e.g., Dart, Muzzle, and Bluff Streams), and are here inferred to be of early‐mid Otiran age. The lack of preservation of older glacial landforms is attributed to the steep, unstable terrain of the IKR generated by the relatively high uplift rate (c. 5 mm/ yr), and consequent high erosion rate in the range, which is located in the hanging wall of the active Clarence Fault. A sequence of paleo‐equilibrium line altitudes (paleo‐ELAs) for the past glaciers in the IKR have been derived using cirque floor elevations, accumulation‐area ratios (AARs) and interpolated estimates, and give snowline depressions below the present (2530 m) of 830 m for the early‐mid Otiran, 740 m for late Otiran, 575 m for final Otiran, 450 m for Late Glacial, 270 m for Neoglacial, and 150 m for the Little Ice Age. Because glacial features in the IKR have yet to be directly dated, these age estimates should be regarded as interpretive in nature and are based solely on relative size, elevation, sequence position, and degree of preservation. The paleo‐ELAs have been normalised to a southerly aspect using a correction established in the northern Southern Alps that has yet to be tested in the IKR. Correcting for accrued uplift over the past c. 18 000 yr conceivably provides an additional c. 90 m of depression, suggesting a total ELA depression of as much as c. 830 m during the late Otiran compared to modern climate. The paleo‐ELA depression estimates for the IKR appear to be similar to estimates calculated in other areas in the South and North Islands. Evidence of glacial features in the IKR, and the apparent similarity of ELA depressions in the range with that elsewhere in New Zealand, suggests that past climate fluctuations in the IKR have been, to at least some degree, “in harmony” with those throughout the remainder of the country.