The Hurunui River in North Canterbury, catchment area 1,020 sq. miles, rises on the main divide of the Southern Alps and flows eastward to the Pacific Ocean. At its head is the Harper Pass (Hurunui Saddle), which leads to the valley of the Taramakau River and was the main route to the West Coast from Canterbury, both for Maori and for European, before the construction of the road over Arthur's Pass. In the headwaters of the river, which were strongly glaciated during the Pleistocene, are several lakes dammed by glacial moraines, of which the largest is Lake Sumner. A formerly glaciated tributary, the South Branch, joins the main river 8 miles below the lake. The other main tributaries are the Seaward, Mandamus, Waitohi, and Pahau Rivers. In the middle part of its course the river crosses the Culverden Plains, which were formed in part by gravel deposited by the Hurunui. Upstream from these plains the river has cut gorges through the hard greywacke of the Southern Alps and foothills; down stream it flows through two more greywacke gorges and across softer Tertiary siltstone and sandstone.
The meaning of the Maori name is obscure.
by Donald Rowe Gregg, M.SC., New Zealand Geological Survey, Christchurch.