The Clarence River (; officially Waiau Toa / Clarence River) is a major river which flows through the Kaikōura Ranges in the northeast of New Zealand's South Island. At roughly long, it is the longest river in Canterbury and the eighth longest in New Zealand. For its first , the river runs in a generally southeastern direction. It then turns northeast, running down a long straight valley between the Inland and Seaward Kaikōura Ranges. At the end of the Seaward Kaikōuras, the river meanders through undulating hill country before draining into the Pacific Ocean near the town of Clarence. A large part of the river is within the boundaries of Molesworth Station. The river and its tributaries cut through rock formed on the seafloor of the Pacific during the late Cretaceous through to the middle Eocene, during which period the majority of New Zealand was at points almost entirely submerged. This provides a useful record of this time period, and has contributed to our understanding of several events which took place during that era. The area also provides valuable insight into more recent geological events, having been heavily affected by the 2016 Kaikōura earthquake. History and name The area around Waiau Toa has a long history of pre-European habitation and was once one of the most populated areas of the island, with multiple iwi having ties to the region. While archaeological evidence on the northern side of the river, such as a series of middens, suggests early habitation in the area by the Waitaha iwi, the earliest concrete evidence of permanent Māori habitation relates to a Kāti Māmoe pā at Waipapa on the southern side of the river mouth. A raid on the settlement at Waipapa by Rangitāne proved instrumental in expanding Māori settlement of the region, as a subsequent attack on Rangitāne by Ngāti Kurī led to the latter returning captives and marrying into the area. Following a breakdown of the relationship between Ngāti Mamoe and Ngāti Kurī, Waipapa was occupied by Ngāti Kurī, driving Ngāti Mamoe from the area and giving Ngāti Kurī mana whenua over the region to this day. Further settlements were then established in the area, including at the mouth of the Waiau Toa near a waka landing site. The frequency with which the iwi local to Waiau Toa changed is partially related to its importance as a (food gathering place). The area traditionally provided