The Tongariro geothermal system contains the Ketetahi Geothermal Field which is privately owned and considered sacred by Tangata Whenua. The public are requested to respect this by not visiting the site. Tongariro system also includes the Tongariro summit craters and the nearby Te Maari craters. In August 2012 a hydrothermal eruption occurred near the Te Maari craters. This was believed to be the first eruption since the period from 1869 to 1900 during which there were at least four occasions when eruptions occurred. There was no definite eruption in the 1900s although a questionable event was reported in the 1920s.
The Tongariro geothermal system has:
- three to five acid geysers
- hot springs and pools, steam and gas vents, fumeroles, mud pools, sulphur deposits and a hot stream
- New Zealand's only high altitude geothermal system
- unique high altitude geothermal vegetation and a unique insect species (midge).
Tongariro is classified as protected by Waikato Regional Council.
Tangata Whenua have retained ownership of the land directly around Ketetahi. Outside of the privately owned area, Tangata Whenua have gifted the land to the people of New Zealand (Tongariro National Park) and it is legally protected.
The Ketetahi geothermal area is considered sacred by Tangata Whenua, and the public are requested to respect this by not visiting the site.