Between 18,000 and 32,000 years ago, a large glacier would have dominated the scene in front of you, filling the valley. This glacier eroded the landscape creating the classic U-shaped valley (now occupied in part by Lake Ōhau). Gravels from this erosion melted out of the glacier as it retreated. These gravels form the glacial moraine that you are currently standing on. The horizontal benches visible on the far valley side are similar moraine deposits. These moraines represent the former ice surface. They show the former glacier was once several hundred metres thick.
Insights into past climatic conditions
Lake Ōhau was created as the former glacier retreated and the basin filled with meltwater. Since then, sediment eroded from the mountains and carried along the Dobson and Hopkins Rivers has been accumulating on the lakebed as annual layers. These sediment layers contain pollen washed or blown into the lake. The sediment also holds microscopic plankton remains (microfossils). In 2016 geologists drilled into these sediments. They recovered an 80-metre sediment core from the southeast arm of the lake. The microfossil content and changes in the sediment layers in this core oer detailed insights to past climatic and environmental change in this region.
The Tasman Glacier and lake near Aoraki / Mt Cook is an analogue for how the scene in front of you might have looked like between 18,000 and 32,000 years ago. © Dr Shaun Eaves, Victoria University of Wellington
Trapping mature tuna for transfer below the hydro dams to allow them to migrate to Te Moananui-a-Kiwa/Pacific Ocean for breeding.
An x-ray image of the sediment core recovered from Lake Ōhau. Can you see the different thin layers of pollen and microfossils?
© Dr Shaun Eaves, Victoria University of Wellington
An ancient food and resource gathering place
Together with nearby lakes Pūkaki and Takapō, Ōhou (Lake Ōhau) was an important part of the traditional Kāi Tahu mahika kai (seasonal food and resource gathering). It was renowned for tuna (eels) and weka that were gathered and preserved for the upcoming winter months. The lake and its surrounds continue to be a significant mahika kai and is respected for the quality of food that grows in these pristine waters. Kāi Tahu whānui is actively working to restore the habitat and stocks of mahika kai through native forest restoration and trap and transfer work to assist the natural migration patterns of species to return here.
The last glacial period peaked around 18,000 years ago.
During glacial periods sea levels are lower due to more water being frozen in growing glaciers.
This was one of the lakes dug by the ancient famous Waitaha explorer Rākaihautū with his kō (digging tool) named Tūwhakaroria.
To learn more you can listen to the Sasha Say’s podcasts on Ohau Moraines here.
Please be aware the following hazards following: water, cycling traffic, and uneven surface. Tsunami risk - If an earthquake is strong or long, get gone.
Scenic views & Photo opportunities
The Ohau Moraines are located inland of Omarama. Take SH8 between Twizel and Omarama. Turn onto Lake Ohau Rd 16km north of Omarama. As you are approaching Lake Ohau, you will drive through a hummocky landscapes - the Ohau Moraines.
Protection and guardianship are at the heart of the Geopark philosophy. We ask you to treat this site with respect, do not remove anything from this site and preserve it for our future generations.