The MacKenzie Basin in South Canterbury is an oasis of flat land surrounded on all sides by several mountain ranges, and contains some of the most extensive tussock country in New Zealand. The blocking effect of the surrounding mountains creates an almost continental-style climate here: in summer the basin is frequently parched by 30 degree-plus temperatures and buffeting winds with very low humidity, whereas winters are bitterly cold and the ground may be snow-covered for days, or even weeks, at a time.
The MacKenzie Basin owes its physical character to the shaping forces of water and ice. During the peaks of numerous past ice ages, large areas of the basin were buried under enormous ice sheets which carried millions of tonnes of debris down from the Southern Alps. Most of the basin is now underlain by these old glacial moraines, or riverbed deposits made up from eroded moraines, laid down over the course of repeated ice ages during the last several million years. The landscape between Lakes Tekapo and Pukaki is especially notable for its distinctive low hummocky character and numerous parallel ridges, typical of relatively recent glacial moraines.
The large boulder in this photograph lies atop one of these low ridges and is most likely to have been left behind by a melting glacier during the dying stages of the most recent ice age, which ended about 10,000 years ago.