New research published by Henrik Rother from the Institue for Geography and Geology at the University of Greifswald in Germany indicates that twenty four and a half thousand years ago the Castle Hill basin was full of ice with a glacier tongue reaching down through the Waimakariri Gorge. While the evidence for the “Waimakariri Glacier” reaching beyond the gorge has long been known, the previous estimate of when the ice was below the gorge was 300 thousand years ago, so this new twenty four and a half thousand years ago estimate is a considerable revision of the timing. The paper reference is available here