Rotorua's geothermal treasures
Introduction
Rotorua's geothermal field is a visually spectacular expression of the power of creation. It contains 1200 geothermal features which include geysers, hot springs, mud pools and fumaroles, as well as silica terraces and flats.
Natural forces at work: A geothermal field is created in the presence of water, heat and rapid access to the earth's surface for geothermal water. Cold rainwater passes through cracks in rocks towards a geothermal heat source, heating as it descends. It then rises quickly to the surface to discharge as geysers, fumaroles and hot springs.
Orakei Korako geothermal area
Rotorua's geothermal wonders have been internationally famous for over a century. The city's steaming footpaths, mud pools, bathing hot pools and geothermal backdrop form a unique environment which continues to attract visitors from around the globe. Rotorua's fascinating geothermal features are outstanding in the world, yet few residents and visitors appreciate their significance. According to the Inventory of NZ Geothermal Fields and Features, Houghton, Lloyd, Keam and Johnston 1998, the Rotorua geothermal field is ranked as being internationally important and recommended for complete protection.
The Rotorua geothermal field and its associated surface features are national and international taonga (treasures). One example is Whakarewarewa's geyser flat, which ranks alongside the geysers of Yellowstone National Park as one of very few geyser fields left.
Since its earliest habitation people have taken Rotorua's waters in one way or another. For Maori, geothermal areas have traditional cultural significance and uses. In early colonial days an enthusiastic 19th century tourist trade soon developed around the various geothermal marvels. As the 19th century spa era faded, however, Rotorua's wonders continued to attract attention from a variety of users who saw a new kind of potential in them.
Learn about the impact of those uses, why protection and rehabilitation are vital to preserve what is left of this amazing heritage and what you can do to help.
Types of geothermal features
The Rotorua geothermal field contains over 1200 geothermal features including Whakarewarewa's 120 alkaline chloride springs, hot springs, mud pools, silica terraces and flats, fumaroles and steaming ground. Other features are the hot lakes at Kuirau Park and Ngapuna spring - and the Rachel Spring, the only remaining alkaline spring in the Government Gardens.
These sites: Whakarewarewa, Kuirau Park, Ohinemutu, Sulphur Bay and the remnant Rachel Spring - are all part of the Rotorua geothermal field.
Boiling and/or flowing alkaline springs (including geysers) are deep geothermal waters reaching the ground surface. They are clear and deposit dissolved silica as they cool (called sinter). This hard white-grey material may in some places be comprised of calcium carbonate.
Muddy hot pools are local groundwater heated by steam and gases from buried geothermal waters. Oxidation in the air allows sulphide to form sulphuric acid, which breaks down surrounding ground. Fine silica particles are held in suspension, although there may be some grey or black colouring due to iron sulphide or black sulphur. These acidic pools do not form sinter deposits.
Occasionally pools are found with massive sinter deposits around the walls and rims and are also muddy and acidic. This indicates the pool was once a flowing alkaline spring which lost its supply of geothermal water and is now heated by gases and steam.
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