table 1. Range of geyser counts and summary of human impacts to geysers.
aged some features, although these infrastructure impacts are poorly documented. While these impacts do not often alter entire geyser basins, they are responsible for impacting indi- vidual features.
Global Summary of Impacts
Half of the major areas containing geysers have been hydrologically altered by geothermal energy development, and individual springs and geysers at four or more locations have been altered as a result of tourism (Table 1). The Valley of the Geysers on the Kamchatkan peninsula and the geysers on Umnak Island in Alaska have sustained few, if any, impacts
due to their relatively remote locations, while the geyser basins of New Zealand and Iceland were severely altered due to their location in areas where substantial populations needed energy resources. New Zealand, in particular, has suffered the loss of more geysers than anywhere else in the world. The exact num- ber of features altered at most locations is uncertain, owing to the dynamic nature of geysers and lack of long-term docu- mentation.
New Zealand. The geyser basins of New Zealand once contained the second largest concentration of geysers in the world outside of Yellowstone. More than 20 geothermal areas are located in the Taupo Volcanic Zone on the North Island, five of which (Wairakei, Orakeikorako, Rotorua, Waimangu, and Waiotapu) have contained geyser activity. It is estimated that more than 220 geysers existed in these basins as recently as the 1950s. By the 1990s only 55 geysers remained, with many losses due to geothermal resource development (Scott and Cody 2000).
The withdrawal of geothermal fluids for electricity pro- duction in the Wairakei basin resulted in the extinction of all geysers (about 70), loss of approximately 240 hot springs (Scott and Cody 2000), and ground subsidence of 14 meters, the largest ever recorded for any type of fluid withdrawal including gas and oil (Allis 2000). At Orakeikorako, nearly 70 geysers and 200 hot springs were flooded by the creation of Lake Ohakuri in 1961 when the Waikato River was dammed for hydroelectric power production (Environment Waikato Regional Council 2006).
Waimangu Geyser, the largest geyser ever documented in terms of height and volume, formed in 1900 near Mt. tara- wera in New Zealand, and became extinct in 1904 as a result of landslide materials blocking its vent. (A. Shepherd, 1903. Printed with permission of the Museum of New Zealand te Papa tongarewa, #C.016361).
The exploitation of geothermal resources at Roto- rua began in the 1920s, primarily to pipe geothermal water through homes and businesses for heating. By 1980 more than 500 geothermal wells were producing electricity. The increased fluid withdrawals, combined with a long-term decrease in pre- cipitation, caused many geysers to stop erupting, while oth- ers showed the largest decreases in activity seen in 140 years. Government regulations later forced the closure of many wells to protect the remaining geysers. Some geysers have reverted back to their former state while others show sporadic recovery and many remain dormant (Allis and Lumb 1992, Scott and Cody 2000). Several geysers in Rotorua were soaped to induce
17(1) • 2009