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Geothermal systems occur in many parts of New
Zealand. High temperature geothermal fields are
principally located in the Taupo Volcanic Zone,
with another high temperature field at Ngawha
in Northland. Moderate to low and very low temperature
systems are more widely scattered. Some are associated
with areas of young volcanism: in Northland, Hauraki
Plains, and the coastal Bay of Plenty. Many hot
springs, particularly in the South Island, are
associated with faults and tectonic features.
 By
the 1980s it was believed that all of New Zealand's
high temperature geothermal resources had been
identified, a situation that few other countries
can claim even today. Of New Zealand's 129 identified
geothermal areas, fourteen are in the 70-140ºC
range, seven in the 140-220ºC range and fifteen
in the >220ºC range.
The Taupo Volcanic Zone extends from White Island
in the Bay of Plenty southwest to Mt Ruapehu.
Geothermal fields are associated with young and
active rhyolitic volcanism. Magma intruded into
the stretched and fractured crust of the zone
has resulted in temperatures of at least 350ºC
at depths of less than 5 km. This has provided
a huge heat source from which geothermal systems
have developed and been sustained for periods
of up to hundreds of thousands of years. A total
of 29 geothermal areas have been identified, although
only about half of these have potential for resource
utilisation. Individual fields are typically about
12 sq km in area and spaced 15 km apart, and include
all those in New Zealand that discharge boiling
water.
An independent company has recently undertaken
a comprehensive review of geoscientifc data from
the Hauraki region and Taupo Volcanic Zone and
is conducting supplementary surveys. This review
may have identified new potential geothermal resources
that have no surface expression.
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Links
http://www.eeca.govt.nz/renewable-energy/maps-geo.html
http://www.ew.govt.nz/enviroinfo/geothermal/fieldsmap/index.htm
http://www.envbop.govt.nz/water/geothermal/geothermal-resource.asp
Ngawha
The Ngawha geothermal field is located 6 km east
of Kaikohe in Northland and is the only high temperature
geothermal field outside the Taupo Volcanic Zone.
The surface expression of the underground system
at Ngawha is small and includes a number of small
fossil sinter deposits, two large areas of hydrothermal
clay deposits and about 20 hot springs near Ngawha
village. Natural geothermal activity is characterised
by the large volume of gas (mainly CO2)
given off over the field. Mercury vapour is also
given off, and mercury deposits exist within and
adjacent to the field.
Geothermal investigations at Ngawha began in
the 1960s, including the first well. Sixteen other
wells were drilled between 1977 and 1983 to depths
ranging from 600 to 2300 m. The investigations
identified a large but relatively low enthalpy
resource with the wells producing fluid at 225-230°C
with high levels of dissolved minerals including
boron and mercury. Thirteen of the wells were
tested, of which six were good producers with
a mean fluid enthalpy of about 975 kJ/kg. Gas
ratios suggest that a deeper reservoir at 300-320°C
is contributing to the system and one well proved
these temperatures exist.
The current development at Ngawha is a joint
venture between local Maori interests and Top
Energy which commissioned two 4.5 MW binary units
in 1998. Resource consents were granted for only
a 12 year period on the condition that development
should not cause any detectable changes to the
surface features because of their high cultural
value. Further expansion of the Ngawha project
is just underway with Top Energy bringing the
project up to a total of 25 MW. The expansion
will include additional Ormat binary cycle units.
Ngawha is a large energy resource with significant
investment in unused production wells. The relatively
low heat content, the high levels of dissolved
material in the fluids and high gas content produced
from the wells (more than would be produced from
a gas-fired power station for the same output)
are drawbacks for electricity generation. Of greater
concern is the need to protect the surface features.
The potential for industrial process heat and
tourism has been investigated by a number of groups.
The field is regulated by Northland Regional Council.
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Wairakei-Tauhara
The Wairakei-Tauhara geothermal system includes
the Wairakei geothermal field located 8 km north
of Taupo and the Tauhara field to the southeast,
with the boundary between the interconnected fields
placed at the Waikato River. The Wairakei field
is exploited by the Wairakei,Poihipi Road, and
Wairakei Binary power stations.
The Wairakei station was first commissioned in
1958 and is now owned by Contact Energy. The field
has been a consistent and reliable producer, with
annual generation averaging 1250 GWh equivalent
to a load factor of 93%. Present output is 140
MWe. At least 150 wells have been drilled in the
field. The maximum temperature measured at Wairakei
is 271 °C, but wells generally produce fluid
at temperatures between 209 and 261°C. About
5300 tonnes of fluid per hour is currently taken
from the reservoir for this station. Of this fluid,
about 1500 tonnes per hour is steam and 3800 tonnes
per hour is water at a temperature of about 130°C
after separation in surface equipment. Some of
the steam is taken directly from shallow dry steam
production wells (up to 500 m depth) and piped
to the turbines. Separated water from the Wairakei
field is used to provide fluids for the Netcor
tourist facility, and a heat source for a prawn
farm adjacent to the Wairakei power station. About
half of the separated water is now reinjected
and half is discharged to the Waikato River. All
steam condensate is discharged to the river.
The Poihipi Road station was commissioned in
1996 and is sited on the edge of the Wairakei
field. The generator consists of a single condensing
steam turbine fed by four dry steam wells. It
was developed by a Taupo entrepreneur and is now
owned by Contact Energy and operated as an integral
part of the Wairakei facility. Although the plant
has a capacity of 55 MWe, resource consent restrictions
on steam draw down limit production to an average
of about 24 MWe. In practice it is operated as
a two shift station with an output of about 29 MWe
during the day when electricity prices are higher,
and at about 19 MWe at night. The station
currently generates around 200 GWh per year. About
half of the steam condensate is reinjected while
the remainder is discharged to air through the
cooling towers.
The Wairakei Binary Cycle power station was commissioned
in 2005 and generates an additional 14.4 MWe
from the separated water before reinjection or
use by the prawn farm.
Liquid drawdown from the Wairakei reservoir has
caused a loss of pressure in the Tauhara field
and the formation of steam zones over a large
portion of the field, especially in the Karapiti
area in which the 'Craters of the Moon' thermal
area is situated. Other surface effects of this
drawdown have been a decline in the flow of chloride
springs, an increase in the extent and temperature
of the shallow aquifers and hot ground in Tauhara,
and the occurrence of a number of shallow hydrothermal
eruptions to the northeast of Taupo township.
Subsidence has also occurred in an area between
the borefield and the Wairakei station, and some
local subsidence north of Taupo may be geothermally
related.
Steam production from the older parts of the
Wairakei field has declined. Periodic drilling
of make-up wells allows steam production to be
maintained. Since 1985, the steam zone which formed
in the western part of the field as the result
of drawdown has been exploited with shallow wells.
At Tauhara, the shallow steam-heated aquifer
that underlies part of Taupo township and land
further to the east and north has been extensively
exploited, with over 400 shallow wells extracting
heat or steam or water for domestic, commercial
and other uses. Contact Energy commissioned a
new 20 MWth process heat supply to Tenon for kiln
drying in 2006. Four deep wells drilled at Tauhara
have found higher temperatures than Wairakei,
adding to the evidence for multiple upflows. The
maximum temperature recorded is 279°C. Production
temperature is 265 °C.
Contact Energy is now considering new arrangements
for the Wairakei-Tauhara resource including possible
replacement of the existing Wairakei station and
development of a new 200 MW station at Tauhara.
Development will have to take into account potential
adverse environmental effects on the surrounding
Taupo urban area.
Field use is regulated by Environment Waikato.
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Ohaaki-Broadlands
The Ohaaki-Broadlands geothermal field is located
20 km northeast of Taupo immediately south of
State Highway 5. The Ohaaki power station, with
its conspicuous 105 m high cooling tower, was
commissioned in 1989 and is owned by Contact Energy.
The station had a capacity of 114 MWe (although
the station has had a series of deratings including
decommissioning of high pressure turbines) produced
from twenty-five wells extracting around 1500
t/hr of fluid from the Ohaaki area of the field.
Steam production has continued to decline due
to cool water from the field margins encroaching
on production wells, and output has declined to
about 40 MWe. Several new wells have been drilled
to restore and maintain production at the 50MWe
level.
There have been significant environmental effects
at Ohaaki, including subsidence leading to flooding.
The water rights granted for the station specified
waste water re-injection at depth to avoid contaminating
the Waikato River or adjacent groundwater.
Wood drying kilns use waste geothermal energy
directly as a heat source for the drying process.
Field use is regulated by Environment Waikato.
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Rotokawa
The Rotokawa geothermal field is located about
14 km northeast of Taupo and 9 km east of Wairakei.
The associated thermal area has extensive surface
features including fumaroles, eruption craters
and collapse pits. Lake Rotokawa fills one crater,
and there are large deposits of sulphur surrounding
and beneath the lake.
The energy potential of Rotokawa was recognised
in the early 1950s. Drilling has identified a
large high-temperature resource of about 18 sq
km with an energy potential estimated at least
250 MWe. Production is from around 2000 - 2500
m with temperatures up to 320°C.
The 29 MWe Rotokawa power station (an Ormat
geothermal combined cycle station) was commissioned
in 1997 (and subsequently expanded to 35 MWe
in 2003). The Rotokawa project is divided into
two companies; Rotokawa Joint Venture (a 50:50
joint venture between Tauhara North No.2 Trust
and Mighty River Power) which owns the steamfield,
and Rotokawa Generation (100% Mighty River Power)
which owns the generation plant. Mighty River
Power operates both the station and the steamfield.
Annual generation is about 250 GWh.
There are no readily identifiable environmental
constraints to development. Hydrothermal eruptions
have occurred in the past at Rotokawa, and drawdown
due to a large development may increase the probability
of further eruptions. Shallow acidic fluids have
posed problems for well casing. The field is classified
as open to development by Environment Waikato
subject to the resource consent process.
Rotokawa is well located, with Taupo, Ohaaki
and existing transmission lines close by. The
field is close enough to Wairakei, Tauhara or
Taupo township to make piping steam to those sites
a possibility.
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Mokai
The Mokai geothermal field is located 20 km north
of Taupo, remote from geothermal tourist attractions.
The field lacks the spectacular thermal activity
present at many other fields, consisting only
of small areas of steam-heated activity.
 Geoscience
and drilling in the 1980s indicated the potential
of the Mokai field. The field has some of the
hottest geothermal wells in New Zealand with downhole
temperatures of up to 326°C recorded. One
well was capable of generating 25 MWe. The high
reservoir temperatures mean that wells tend to
produce high steam content fluids with high chloride
and silica content. Energy potential is estimated
at greater than 100 MWe.
The Mokai power station was commissioned in 2000.
It is the first in New Zealand to be fully owned
by a Maori trust (the Tuaropaki Trust which subsequently
placed assets in the Tuaropaki Power Company),
with Mighty River Power contracted to operate
and maintain the Ormat geothermal combined cycle
station which has installed capacity of 55 MWe.
Mighty River Power has recently bought a 25% share
in Tuaropaki Power Company. All condensate and
cooled brine is reinjected. A 39 MWe expansion
of similar design was commissioned in 2005, and
a large geothermally heated greenhouse complex
has been developed nearby. A further binary unit
has just been installed at the station to take
account of the changing steam/water ratios due
to the effects of exploitation.
The field is classified as open to development
by Environment Waikato subject to the resource
consent process.
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Kawerau
The Kawerau geothermal field is located immediately
east of Kawerau township. Most of the surface
thermal features are believed to have been in
a natural state of decline prior to development,
which arose from the energy requirements of the
large Tasman pulp and paper processing plant built
in the 1950s.
Seventeen wells (including redrills) had been
completed by the end of 1957 when Kawerau became
the first production field in New Zealand. In
the late 1950s four of the wells were deepened
following a decline in field production and further
drilling commenced in 1966 after continued field
decline. The Crown had an active drilling program
from the mid-1970s through to mid-1980s, aimed
both at maintaining steam supply to the mill and
investigating a major expansion for power generation
or other process steam supplies. Wells have required
frequent cleanouts of calcite scale. New wells
have occasionally been drilled to maintain supplies.
Until the commissioning of the Ohaaki power station
at Broadlands-Ohaaki, Kawerau was the second largest
producing field in New Zealand and its steam supply
for industrial use equates to half of the worlds
total steam supply for industrial applications.
Downhole temperatures recorded in the field range
from 250 to 310°C. A total available resource
greater than 350 MWe has been estimated. Around
270 tonnes per hour of steam is provided to the
Norske Skog Tasman mill where it is used for process
heat, electricity generation and timber drying.
In addition, Bay of Plenty Electricity operate
two binary plants rated at a total of 6 MWe which
use some of the separated geothermal water as
a heat source. These are linked to separator plants
physically either side of the Tarawera River.
In 2004, Norske Skog Tasman replaced their existing
geothermal turbo-alternator with a refurbished
ex-US Navy 8 MWe turbo-alternator.
Wells at Kawerau tend to suffer rapid run-down
due to mineral deposition and cold water inflow.
Various measures are used to maintain output.
Production from the field has adversely affected
the already declining natural features. Most waste
water from the field is discharged into the Tarawera
River after passing through a cooling channel,
and current resource consents require ongoing
efforts to reduce brine discharge. Re-injection
of a limited quantity of fluid is undertaken.
Future development options at Kawerau are constrained
by the need to maintain steam supply to the Tasman
processing plant. From 2004, Mighty River Power
began an exploration programme in a new area of
the Kawerau field. In 2005, a consent application
was lodged by Mighty River Power for the development
of a 70-80MW power station (See external
site). Consents have been granted and Mighty
River Power is now installing the largest single
condensing geothermal turbine in New Zealand’s
history.
In July 2005 after careful negotiation, the Crown
transferred wells, steamfield equipment and contracts
to Mighty River Power, who had a back-to-back
transfer arrangement with Ngati Tuwharetoa Geothermal
Assets. The negotiations involved a balancing
of government commitments, Treaty obligations
and commercial interests. The transfer marks a
change from what has been a caretaking role to
a development focus.
The resource is regulated by Environment Bay
of Plenty.
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Rotorua
The Rotorua geothermal field underlies much of
Rotorua City and the southern margin of Lake Rotorua.
The natural features associated with the field,
particularly the geysers and hot springs of Whakarewarewa,
are one of New Zealand's foremost tourist attractions.
Whakarewarewa has the largest remaining concentration
of geysers in New Zealand. There are also thermal
features at Kuirau Park, Government Gardens, Ohinemutu,
and Sulphur Point. A hot spring on Mokoia Island,
and several warm springs at Lake Rotokawa are
probably also associated with the field.
More than 900 shallow wells have been drilled
at Rotorua to provide hot water for private homes,
hospitals, schools, motels, hotels, and other
commercial and industrial uses. At peak use, around
430 wells were operating. Currently less than
300 are operating. About 90 of the wells are less
than 200 m deep and typically recover geothermal
fluid at temperatures of 120 to 200°C. The
development of the field has been carried out
in an unplanned way and although the domestic,
commercial and industrial heating systems that
were developed were generally cost-effective,
they were also inefficient and were characterised
by their wastage of geothermal heat.
In the late 1970s there were significant changes
to the surface features at Whakarewarewa and there
were concerns that this was related to a decline
in the geothermal aquifer pressure resulting from
the level of draw-off from the Rotorua wells.
In 1982 the Government set up a programme to monitor
the geothermal reservoir. Initial work under the
monitoring programme established that the output
from the production wells represented a net withdrawal
from the aquifer equivalent to a total mass flow
rate of between 30,000 and 35,000 tonnes per day
of geothermal fluid. This compared with a natural
discharge of around 8000 tonnes per day from Whakarewarewa.
In 1985 the then Ministry of Energy published
a comprehensive report concluding that there had
been a dramatic decrease in natural activity at
Whakarewarewa, including a 30% drop in natural
heat flow between 1967 and 1985. The Government
responded by embarking on a programme of compulsory
well closure within 1.5 km of Pohutu Geyser. A
field management regime was also put in place.
By 1990, less than 150 wells were still operating
at Rotorua. Since the completion of the programme,
the water level in the main production aquifer
has largely recovered and natural features are
recovering.
Ultimately it may be possible for some alternative
use of geothermal energy at Rotorua such as the
use of downhole heat exchangers and district heating
schemes. The potentially large resource is unlikely
to be used for electricity generation because
of the effect this would have on the Whakarewarewa
geyser field. The resource is regulated by Environment
Bay of Plenty.
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Tikitere
The Tikitere geothermal field is located about
18 km northeast of Rotorua City on the southeast
shore of Lake Rotoiti and comprises the Tikitere
geothermal area and the Ruahine Springs several
kilometres to the northeast. Thermal features
included steaming ground, boiling springs and
vigorous steam and gas discharges. The Hell's
Gate thermal area is a popular tourist attraction
Several shallow wells that discharged steam and
hot chloride water have been drilled close to
Hell's Gate and have temperatures estimated at
140 to 190°C. Energy potential of the field
has been estimated at greater than 160 MWe, but
significant production could affect the natural
features of the field. The Tikitere Trust which
operates the Hell's Gate facility is investigating
a limited development for electricity generation.
The field is regulated by Environment Bay of Plenty.
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Ngatamariki
The Ngatamariki geothermal field is located 5
km south of Orakeikorako and 20 km north-northeast
of Taupo. This undeveloped field has been explored
by wells drilled in the 1980s which identified
a substantial geothermal resource with downhole
temperatures of 270-280°C being recorded.
Further work is required to fully define the size
of the resource. Energy potential is estimated
at greater than 140 MWe.
Most of the geothermal field is planted in exotic
pine forests. The natural surface geothermal features
are located at the Ngatamariki hot springs where
sinter, pools and hot springs are part of a reserve
administered by the Department of Conservation.
A hydrothermal eruption was reported in 2005.
The field is classified as open to development
by Environment Waikato subject to the resource
consent process.
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Mangakino
The Mangakino geothermal field is located east
of Mangakino township. At least one boiling spring
was known at Mangakino but is now submerged by
Lake Maraetai. Resistivity surveys have identified
a low resistivity anomaly. Other investigations
have also been carried out, and one well was drilled
by the Crown to about 600 m which produced a highly
gaseous discharge. The area has been recently
investigated by Mighty River Power. While details
are confidential, it is known that very high temperatures
were encountered but formations were relatively
impermeable. A fresh assessment of potential is
needed. The field is classified for development
by Environment Waikato.
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Horohoro
The Horohoro geothermal field is located about
15 km southwest of Rotorua City. The thermal waters
of the surface features are very dilute, and geothermometry
suggests temperatures of 150 to 160°C in the
aquifer. A very large low resistivity anomaly
identified to the west of the Horohoro rhyolite
dome and extending beneath the Mamaku Plateau
is believed to be the result of hydrothermal alteration
or to be a conductive ignimbrite. Several shallow
wells drilled just south of the Horohoro dome
recorded a temperature gradient much lower than
that measured in the 600 m deep well in the Matahana
Basin. The field is classified as open to development
by Environment Waikato subject to the resource
consent process.
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Atiamuri
The Atiamuri geothermal field is located north
of the Waikato River between Atiamuri and Ohakuri
and about 40 km north of Taupo. Several hot springs
and pools with temperatures up to 73°C are
found in this area and two other pools have been
submerged by Lake Atiamuri. The two main pools
produce dilute chloride water which is used to
supply thermal baths. Geothermometer temperatures
indicate deep source temperatures of 180 to 200°C.
One well has been drilled at Atiamuri, about
1 km southwest of the main pools. The well encountered
a maximum temperature of 165°C between 350
m and 600 m depth. There is no known evidence
for a high-temperature resource at Atiamuri. The
resource may be useful for small-scale direct
heat processing of local agricultural or forest
products. The field is classified as open to limited
development by Environment Waikato subject to
the resource consent process.
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Tokaanu-Waihi
The Tokaanu-Waihi geothermal field is located
at the southern end of Lake Taupo about 10 km
northwest of Turangi. There are two main areas
of thermal activity. At Tokaanu the thermal activity
is characterised by chloride hot springs, pools
and a geyser. Further west at Hipaua, fumaroles
are present on the cliffs above Tokaanu while
at Waihi there is an area of steaming ground and
acidic springs. Springs occur on the shore of
Lake Taupo.
Hot chloride springs at Tokaanu and Waihi have
long been used for domestic purposes and recreational
bathing, but otherwise the field is essentially
undeveloped and the subsurface structure and extent
of the field is poorly known.
High-temperature fluids are believed to exist
at depth. A number of shallow holes have been
drilled to obtain hot mineral water for the thermal
baths and for commercial and domestic heating,
and several holes were drilled for site investigations
for the Tokaanu Powerhouse and tailrace. At Tokaanu
two shallow wells have temperatures of 154°C
at 76 m and 169°C at 107 m, and geothermometer
temperatures indicate a deep hot fluid of at least
250°C.
Decrease in the natural thermal activity at Tokaanu
has been related to changes in water levels in
Lake Taupo, and also to the effects of shallow
wells. Any deep drilling and production could
further decrease this activity. Waihi could also
be affected. It has been suggested that the chloride
waters at Tokaanu are an outflow from the same
source as the steam-heated Ketetahi hot springs
on Mt Tongariro, and if it is established that
the fields are connected, the possible effect
of exploitation at Tokaanu-Waihi on the natural
features at Tongariro would have to be assessed.
The energy potential of the field is estimated
at greater than 150 MWe, but development potential
remains uncertain. Further development requires
the location of the deeper hot water source. The
field is classified as open to limited development
by Environment Waikato subject to the resource
consent process.
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Waiotapu
The Waiotapu geothermal field is located at the
northern end of the Reporoa Valley, 23 km south-southeast
of Rotorua City. The field has the largest area
of surface thermal activity in New Zealand with
a variety of features including geysers, large
hot pools, small lakes filling craters, extensive
sinter deposits, hot streams, mud volcanoes, and
altered and steaming ground. Waiotapu has been
a major tourist attraction for about one hundred
years.
Wells drilled in the 1950s and 1980s recorded
high temperatures up to 295°C but suffered
poor discharge and extensive calcite deposition.
Geothermal fluid was used for timber treatment
for several years until the well was forced to
close when refused a water right on the basis
that discharging the well could potentially affect
the natural features in the nearby Waimangu field.
Limited fluid is still used by Arataki Honey and
a hotel for a range of uses.
The energy potential of the field is estimated
at more than 440 MWe, but the field is classified
as protected by Environment Waikato.
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Waimangu-Rotomahana
The Waimangu-Rotomahana geothermal field is located
22 km southeast of Rotorua. Lake Rotomahana fills
the site of the largest craters formed by the
1886 eruption along the Tarawera rift. The site
had formerly been occupied by an intensively active
geothermal field which included the famous pink
and white terraces. The Waimangu field thermal
area and the activity at Lake Rotomahana formed
after the 1886 eruption. Like Waiotapu, Waimangu
has been a major tourist attraction for over one
hundred years.
Waimangu is unique in the New Zealand setting
in that surface geothermal activity began after
the 1886 eruption so began in historic times.
In the early years a large geyser used to play
but ceased many years ago.
Thermal activity includes geysers, spouters,
hot and boiling pools and streams, mud pools,
steaming ground and hydrothermal eruptions. Upwellings
of hot water occur within Lake Rotomahana. There
is strong geophysical and chemical evidence supporting
a connection between Waimangu and Waiotapu.
The energy potential of the field exceeds 180
MWe, but the field is classified as protected
by Environment Waikato.
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Orakeikorako
The Orakeikorako geothermal field is located
about 23 km north of Taupo and 37 km south-southwest
of Rotorua City. In 1961 the Waikato River was
dammed downstream of the field, creating Lake
Ohakuri which flooded most of the surface features,
including many of the geysers and sinter deposits.
Although the remaining hot springs and pools,
geysers, sinter deposits, fumaroles and steaming
ground are only part of what was once a spectacular
geyser field, the geothermal area remains a significant
tourist attraction, and the Artist's Palette-Golden
Fleece area is one of New Zealand's major geothermal
tourist attractions.
Temperatures up to 265°C were recorded in
holes drilled in the 1960s, but they were poor
producers due to low permeability. The energy
potential of the field is estimated at 125 MWe,
but the field is classified as protected by Environment
Waikato.
There is possibly a hydrological connection between
Orakeikorako and adjacent geothermal fields. Development
of these fields would need to consider possible
connections with Orakeikorako to ensure that its
natural features would not be affected.
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Tongariro
The Tongariro geothermal field is located on
Mt Tongariro and underlies the Ketetahi, Te Mari
and Red Crater thermal areas. The field is mainly
within the Tongariro National Park except for
the Ketetahi area which underlies privately owned
land. The Ketetahi hot springs are highly visible
and the field is classified as protected by Environment
Waikato.
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Map of New
Zealand Geothermal Fields
(Click to see larger map)
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Map of
Geothermal Fields in the Taupo Volcanic Zone
(Click to see larger map)
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See Other Geothermal Energy
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