RECONSTRUCTION OF THE LOWERING OF THE POST-POULTER AGE GLACIAL LAKE SPEIGHT IN NEW ZEALAND'S SOUTHERN ALPS

A series of distinct terraces, alluvial fans, and wave-cut nicks on the Waimakariri valley walls have been interpreted by Gage (1958) as the result of intermittent lowering of the Glacial Lake Speight following a Poulter-age advance of the Waimakariri glacier in New Zealand's Southern Alps. Little formal study has been undertaken to investigate what dammed this lake and why the level lowered in intermittent periods over the course of what Gage proposed to be hundreds of years. This study is an attempt to resolve some of this uncertainty using landform analysis with aerial photographs and detailed geomorphological mapping. The distance between terraces and their heights will both be used in order to estimate the potential length of time required to form each terrace and the time required for the lake level lowering between terraces. To do so, these data will be compared to data collected at Lake Pukaki, where modern terrace formation has been observed following the damming of the lake for a hydroelectric scheme. These time estimates can be used to test Gage's hypothesis that the lake level lowering was controlled by meltout from an ice-cored moraine dam and determine if another process of formation is favored. This work can help to illuminate another piece of New Zealand's relatively poorly understood glacial history, and will investigate how modern lakes can be used to understand those of the past.