History of the Waikato River

The Formation of Waikato Wetlands

The landscape observed today in the Waikato and Hauraki Plains has been carved, scoured and sculptured over time by the movemen

ts of the Waikato River over many thousands of years.

Observing the relative serenity of the Waikato River today, it is hard to imagine the forces involved in shaping the landscape. The course a river takes over time is not static and this can be dramatically illustrated by looking at past movement of the Waikato River.

Prior to about 20,000 years before present (B.P.), the Waikato River flowed out into the Firth of Thames, forming the Hauraki Plains. About this time large amounts of volcanic ash and pumice billowed from volcanic activity in the ‘Taupo Volcanic Zone’. This volcanic material got washed down into the river, increasing its ability to build up the flood plain, and resulting in increased meandering of the river.

Around 20,000 B.P. the Waikato River dramatically changed course (probably due to valleys being blocked by volcanic material), and cut into the Karapiro Valley. Here it flowed through a narrow gorge (near the present location of Cambridge), and emerged to deposit vast ‘fans’ of ash, pumice and other sediment across the lower Waikato Plains. While the river carved its way through these plai

ns it created a series of channels and depressions, many of which later formed lakes and swamps. The high sediment load of the Waikato River meant that many smaller rivers and streams became cut off and dammed, forming lakes such as Lake Maratoto.

Approximately 12,000 B.P. the amount of volcanic activity in the ‘Taupo Volcanic Zone’ dropped off dramatically, reducing the amount of sediment being carried in the Waikato River. The river became more stable and cut the channel it presently flows through today.

Volcanic activity had not completely ceased and around 2000 B.P. there was another massive eruption in Taupo. The outflow from Lake Taupo became blocked by massive amounts of pumice and ash, which also blocked and dammed sections of the Waikato River. As these ‘dams’ gave way massive volumes of pumice and ash were swept down river, blocking valleys further down. Many of the larger lakes present today near Huntly, such as Lake Whangape and Lake Waahi, were formed in this way.