This paper introduces audiences to the Horizons Regional Council (HRC) lahar monitoring system on Mount Ruapehu and the Whangaehu River in the Central Plateau of New Zealand’s North Island. The causes and effects of this destructive natural hazard are explained as are the impacts these can and have had on the local area including the risks to public safety, river health, and infrastructure. The history of lahar monitoring in the region is outlined before focus is turned to the implementation of the current monitoring network which has been upgraded by Horizons and Massey University over the past eight years, with permission and assistance from local Iwi Ngati Rangi.
This network overview focusses on the technical application and installation of monitoring equipment, especially the installation of a web camera and radar at the Tukino ski-field on Mt Ruapehu, the installation of a web camera, radar, and water quality sensors at the Tangiwai memorial, and the installation of a web camera monitoring Crater Lake on Mt Ruapehu. The issues associated with the installation and maintenance of these sensors in one of the harshest environments in the country is also detailed. The low pH of the Whangaehu River proved an issue for in-situ sensors as did the high risk of damage from lahars. On the mountain itself the extreme low temperatures proved an issue for electronic equipment, and extreme winds and harsh scoria also combined to damage the web camera lens and lead to innovations in the deployment of these instruments in harsh environments. The monitoring and sampling procedures during events are explained and the monitoring of the last lahar event in 2007 with recorded stage heights, photos, and videos capturing the event, is outlined.