Geothermal surface features in New Zealand are hydrothermal in nature (water or steam dominated) with most groupings having gradational boundaries. The surface features range from those that are in high energy states (fluid or steam), through to over-flowing and non-over-flowing pools (lower energy).
The Bay of Plenty Regional Policy Statement defines four feature categories.
Primary Fluid type, alkaline chloride pools
A geothermal spring which maintains a continuous (or regular intermittent) overflow of chloride-enriched primary geothermal water, or, a depression, that naturally receives primary geothermal waters from depth. These are very likely to be sinter-lined and deposit sinter in the overflow channel. The waters in the pools will be clear and hot. The geysers of Rotorua are primary fluid features.
Mixed fluid type, mixed chemical pools
A geothermal spring which has an overflow of mixed geothermal fluid (chloride-enriched water and ground water) or a depression that naturally contains mixed geothermal water. The waters will be coloured and maybe milky.
Steam heated type
Steam rising from depth mixes with ground water to make acid water. This results in the grey pools and when soils and clay are included the mud pools form.
Heated Ground (steam fed)
A ground area that radiates heat from underground geothermal sources, discharging steam, diffusively through surface soils. If the steam flow is strong enough a fumarole may form.
There are also three habitats associated with surface geothermal features, the aquatic one (springs and steams); the terrestrial one (warm and heated ground) and the micro-climate atmosphere. The classification table below describes the physical and associated habitats of these features.
Geothermally influenced landscapes are dynamic ecosystems that provide unique habitats for threatened species and represent areas of high biodiversity value.
The heat and soil chemistry of geothermally-active soils influence vegetation composition and structure. Geothermal surface features provide microclimates as they make the immediately surrounding area different than the wider environment. This allows plants and animals to develop and interact in unique ways.
There are many unique plants and organisms which have adapted to living in and around geothermal surface features Certain plants such as prostrate kanuka can only be found in geothermal areas and many are listed as threatened or at risk. Some geothermal areas have plant associations that are found nowhere else in the world.
Geothermal habitats are rare ecosystems in New Zealand. Stream sides, heated ground and hydrothermally altered ground are classified as ‘Critically Endangered’ ecosystem types. In our region, we have a quarter of New Zealand’s geothermal vegetation.
Diverse life forms and their genetic material provides many unique opportunities for the future. An example of this is the use of bacteria that thrive at extreme temperatures being used in industrial processes.
For more information, visit the one thousand springs website which is a catalogue of the microbial biodiversity and geochemical information for geothermal features across the Bay of Plenty and the central North Island. This research is being jointly undertaken by GNS Science and the University of Waikato, with funding support from Central Government.