Ruapehu 1995-96


The 1945 eruption of Ruapehu volcano produced deposits of several milimeters thick throughout the North Island of New Zealand, which caused problems for the water supply in the town of Taumarunui (Johnston, 1997). Ash suspended in the Wanganui River, from which the town draws its supply, blocked filters at the supply's intake structure. Pumping was reduced from 90,000 litres/hour to 31,500 litres/hour (Wanganui Herald 26/11/45). Turbidity problems were also experienced in the Whakapapa Village stream-fed water supply, located at the base of the mountain, forcing the Chateau, which was a hospital at the time, to close. Further problems were reported 10 years later when ash that was deposited in 1945 on Mt Ruapehu's snow fields was washed into streams that fed the Whakapapa Village water supply (Houghton and others, 1987).

The 1969 Ruapehu eruption deposited 6-7 milimeters of ash over an areas that contaminated the water supply of Iwikau Village (located at the Whakapapa Skifield) (Collins, 1978). Water is drawn from the roofs of most of the buildings in the village. The drain pipes were cut after the eruption began, but a number of storage tanks were found to be contaminated. Acidity of the tank water ranged from pH 6 to 4.4, and excessive fluoride concentrations (6.0 ppm) were measured in one tank. Also, Whakapapa Village received 1-6 milimeters of ash causing the pH of the stream fed water supply to drop to 5.3 and the turbidity to increase markedly. The Taumarunui Borough found for a short period after this eruption that the pH of their water supply dropped to 5.6 pH and turbidity was high.

During the 1995-96-eruption sequence of Ruapehu, volcanic ash was dispersed over a wide area of the North Island. Contamination of water supplies was a common concern, and the public was advised to disconnect roof-fed water tanks as a precaution (Johnston et al., 2000). In some cases this proved to be very difficult to accomplish, especially newer enclosed systems. The Department of Conservation disconnected roof-fed water supplies at many of the huts in the Tongariro National Park. Many communities initiated special or enhanced monitoring of their water supplies due to the potential for ash contamination. In some cases, extra supplies were stored.

For example, at the Waiouru Military Base water was stockpiled in jerry cans, rubber bladders and fire engine tanks and the stream supply was monitored regularly (New Zealand Herald, 27 October 1995). In October 1995 the Rotorua District Council constructed enclosures (costing $120,000 NZD) over the Rotorua city and Reporoa spring supplies to mitigate the potential of ash contamination (Johnston, 1997). This was to prove valuable in protecting the supply during the 17 June 1996 ashfall. However, Rotorua almost ran out of water after the ashfall when a resident washed ash into a power transformer. The transformer subsequently exploded, cutting electricity to the town's water pumps. Furthermore, the cleanup efforts of the city's residents almost drained the water supply; the district council imposed a hosing ban until the power supply was restored to the water supply headworks (Daily Post, 19 June 1996). On 17 June 1996, the water supply from the Raymond Dam in the Western Bay of Plenty was disconnected for four hours after the ashfall, while water analysis was carried out. The supply feeds Pukehina, Maketu, Pongakawa and Paengaroa and Te Puke. Some areas were without water for several hours (Bay of Plenty Times, 18 June 1996) but supplies were fully restored by the following day.


Air travel was the most widely impacted form of transportation (Johnston, 1997). Airspace was restricted due to ash clouds and sulfur dioxide hazes, resulting in re-routing and cancellation of many flights. Due to constantly changing ash clouds, regular pilot briefings on the stateof the eruption created an additional workload for all parties involved. Airlines suffered a lot of additional costs due to increased fuel usage and flight times. At any one time, during the eruption sequence, up to 13 airports were impacted, either closed or disrupted.

During and following periods of intense ashfall, visibility was reduced on the roads. Desert Road, adjacent to the volcano, was closed 3 times during the 1995-96-eruption sequence. Each of these were followed by rainfall creating a ash-sludge on the road that required clean up and diversions. It is worth noting that the number of disruptions was only minor compared to the annual disruptions from snow and ice. Rail was not disrupted during the eruption sequence (Johnston, 1997).


There were only a few claims for building damage (~25) with most of these for non-structural elements such as guttering and water pump damage. There were a few reports of structural damage; the majority of these came from buildings on the flanks of the volcano. Many building operators and owners enforced mitigation measures such as shutting off air conditioning units. Ski operators ensured ski lifts were turned of and motors covered. Even with this measure in place, there were documented cases of malfunctions due to corrosion and structural elements of the ski lift showing rust, requiring re-galvanizing (Johnston, 1997).

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