Craters of the Moon Thermal Area (or Karapiti in Māori language) is a region with geothermal activity north of Taupo, New Zealand. It is a part of Wairakei, the largest geothermal field in New Zealand, with a surface area of about 25 km2, which lies in the Taupo Volcanic Zone.
Craters of the Moon
The name springs from the many hydrothermal eruption craters, which are in part barren and which have bright colours. Combined with the numerous steam vents, constantly shifting, collapsing and reforming giving the whole area desolate appearance, and the sulphur smell, the whole area has an “unearthly” atmosphere. The craters are a relatively recent feature of the area and appeared as a result of human activity in the region.
The site is Crown Land, administered by the Department of Conservation, with help from the Craters of the Moon Trust, a volunteer organisation that provides information for visitors and passive vehicle security.
Features of Craters of the Moon
Craters of the Moon is a steamfield with a total of about 36 hectares (0.36 km2) of heated ground. It has an average altitude of 435 m. It has – of course – craters, but it also has fumaroles (“blowholes”) and a mudpool. Vegetation around the area of the Craters of the Moon is quite uncommon.
All the craters at The Craters of the Moon are the result of hydrothermal eruptions. The pressure of the steam beneath the surface exceeds the pressure exerted by the weight of the overlying ground. This results in an explosion. A mixture of hot water, steam, hot mud and pumice is ejected into the air. Material may be blown up to 100 m, leaving behind holes or craters as deep as 20 m. Hydrothermal eruptions occur about once a year.
The openings in the earth surface, where geothermal steam and gases are emitted, are called fumaroles. These vary in size from one centimetre to half a meter in diameter.
The most powerful fumarole observed at Craters of the Moon occurred December 1967. It had a heat output of 116 MW.
Currently, only one of the craters has a mudpool. Here the gases (mainly H2S) react with water to form sulphuric acid. This reacts with the rocks, turning it to clay. When there is water present, this forms the grey coloured mudpools “that bubble and burp as steam and gas escape through them”.
Much of the ground at Craters of the Moon is warm or hot. This of course affects the vegetation. Only few species can survive. One is the Prostrate Kānuka, a variety of Kānuka (Kunzea ericoides var. microflora). Other species include ferns and mosses that usually grow only in the tropics or warmer frost-free climates.