Paterson, B.R. 1976 Volcanic contamination of the Wahianoa River, Tongariro power development. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 269 6 p.
Abstract: Since January 1976 the Wahianoa River has had a pH level considerably lower than normal. Routine two monthly sampling by MWD was increased to weekly readings after the acidity was first detected and it was generally thought that the contamination, which was attributed to a major eruption of Mt Ruapehu in April 1975, would only have a short term effect. Continuation of contamination has caused concern because diversion of the water into other catchments could have serious effects on aquatic life. Also, although the Wahianoa River has been cited as a lahar risk from future major eruptions of Mt Ruapehu (Paterson 1976), the long term effects of these eruptions were not fully realised. It is important that the situation be investigated fully in the event of design modifications being required to safeguard aquatic like in the Moawhango Reservoir and Tongariro catchment when Moawhango Diversion commences operation. In a report on the effects of the 1975 April Mt Ruapehu eruption (Paterson 1976) it was mentioned that debris was erupted onto the Wahianoa glacier some of which reached the Wahianoa River lowering the pH of the water for a period of at least several days. The Department of Internal Affairs and Ministry of Agriculture and Fisheries field party obtained a pH of 4.3 on 28 April 1975 four days after the eruption. Volcanic debris was washed into the Wahianoa headwaters during the eruption by a surge of Crater Lake water (pH 1.0 - 2.0) which washed parts of the Wahianoa glacier to clean ice (Nairn et al 1975). Presumably melted ice from the glacier and rainfall which occurred in the Wahianoa catchment shortly after the eruption (C E Page in Paterson 1976) increased runoff of contaminants. (auth)
