Late quaternary snowlines and cirque moraines within the Waimakariri watershed

A study of the glacial geology and present and past snowlines of tributaries to the Waimakariri River, South Island, New Zealand, has yielded a glacial chronology from late Pleistocene times up to the present day. Three advances of the ultimate (Otiran) Pleistocene glaciation were recognized and named the Kowai, Porter and Tims stream advances. Ice limits were established for an early Holocene (McGrath) advance and for three following Neoglacial ice resurgences, named Arthur's Pass, O'Malley and Barker advances. Moraine-headwall and area-altitude methods were used to compute past snowline evaluations from which snowline surfaces have been constructed. Compared with the present snowline, depressions of up to 970m for the Pleistocene, 480m for the McGrath advance and 400m, 300m and 200m for the Neoglacial events are indicated. Isopleth maps of the snowline surfaces show a steep upward gradient towards the east, with strong topographically-induced irregularities superimposed upon this pattern. Weathering rind studies on surface boulders of the Holocene deposits showed a systematic increase in thickness with increase in age. Radiocarbon dates with rind thicknesses from landslide deposits provided the basis for a rind thickness growth curve. This curve was used to age and correlate the glacial events. Parallelism of the different snowline surfaces suggests that climatic patterns remained similar throughout the Holocene. Early Holocene deposits suggest a cool wet period between the Tims Stream and McGrath events, while a number of rock glacier deposits indicate a cool drier climate for the beginning of the Neoglacial advances