Clyde Dam Lookout

At 490 metres wide and a maximum of 100 vertical metres deep, Clyde Dam is the biggest concrete dam in New Zealand. It was constructed between 1979 and 1993, using over a million cubic metres of concrete.
The Otago Schist bedrock beneath and in the whole area surrounding the dam represents a pile of metamorphosed sediments (sandstones and siltstones) and volcanic rocks (sea floor basalts) of mainly Triassic age between 250 and 200 million years old. They accumulated along the eastern margin of Gondwana but were then subject to subduction, deep burial and hence metamorphism. The age of metamorphism (or mineral recrystallization) is Jurassic, about 170 million years ago. The original sediments (sands and silts) that make up the schist are derived from granite terrane within what is now the Queensland (Australian) sector of Gondwana.
A major geological hazard affecting the dam is the presence of faults, with the main Cairnmuir-Dunstan Fault passing about 1 km from the dam, and an offshoot called the River Channel Fault passing beneath the dam itself. Because of this, significant engineering design features have been included in the construction of the dam.
Another even greater potential hazard is the potential for large landslides falling into Lake Dunstan from the surrounding slopes. These could cause sudden huge displacements of water that might put the dam and the towns of Clyde, Alexandra and Roxburgh at risk. Assessment of the landslide hazard, and engineering efforts to reduce the risks, cost hundreds of millions of dollars and years of work. This, along with the environmental impact of the inundation of the gorge when the lake was created, made the dam very controversial. Nonetheless, over the last 25 years, the Clyde Dam and Lake Dunstan have become established Central Otago landmarks.

From the lookout, look up the lake and see if you can observe the dip of the schist bedrock on either side of the lake and work out which side of the lake is most vulnerable to landslides. Can you see evidence of past landslides and some of the work that has been done to stabilise the slopes?
Look at the information panel and find out how the dam has been designed to withstand movement caused by a rupture of the River Channel Fault that passes underneath it.