Geysers and sinter springs

Why we monitor geysers and sinter springs •
Results - data and trends •
Methods - how we monitor geysers and sinter springs •
More information

Why we monitor geysers and sinter springs

Geysers and sinter springs are important indicators of the state of our geothermal systems. This is because activities near one geothermal feature or field (such as water extraction) can affect features in another field if they are part of the same geothermal system.

Waikato Regional Council monitors the number, chemistry and location of geysers and sinter depositing springs in the main geothermal systems in the region to help us detect changes that may be occurring within these systems.

Results - data and trends

Our monitoring has shown that the number of sinter depositing springs and active geysers in the Waikato region has been relatively stable since 1961. The Resource Management Act 1991 empowered us to protect vulnerable and rare surface features through our Regional Policy Statement, Waikato Regional Plan and resource consent conditions.

Unfortunately, past human activities have destroyed large numbers of springs and geysers. Threats to our geothermal features include:

geothermal power development
land drainage
road works
tourism
vegetation clearance
rubbish dumping
use of geothermal water for bathing and space heating.

Many of our remaining springs and geysers have been significantly modified by human activity. As a result, natural features such as sinter terraces are becoming increasingly rare in many geothermal fields.

The technical report below explains sinter-forming springs and geysers in the Waikato region.

Technical report - Sinter-forming springs and geysers of the Waikato region
2.6 MB

These graphs show change in the number of sinter depositing springs and active geysers in the past 50 years.

Over half of the region’s geysers and sinter depositing springs have ceased activity or have been destroyed. Most of these features were lost after the Wairakei power station was commissioned in 1958 and Lake Ohakuri was created in 1961 as part of the Waikato River Hydro Scheme.

Number of active geysers in Waikato geothermal fields

Graph showing number of active geysers in Waikato over time

Number of active sinter springs in Waikato geothermal fields

Graph showing number of sinter springs over time

The Excel spreadsheet below contains the source data to this indicator's graphs and any additional data. Current data are based on monitoring records since 1995. Historical data are based on records collected from about 1900 to 1995.

Download the data file
12 KB

Methods - how we monitor geysers and sinter springs

Where and how we collect the data

Waikato Regional Council has a routine monitoring program for geothermal areas. This tells us the activity status of geysers and sinter depositing springs at selected geothermal fields.

Monitoring sites

Geothermal field
Atiamuri
Horohoro
Mokai
Ngatamariki
Ohaaki
Orakei Korako
Reporoa
Tauhara
Wairakei
Te Aroha
Te Kopia
Tokaanu
Whangairorohea
Waikite Valley
Waiotapu
Wairakei

View our monitoring sites map for more information on these sites, including photographs,

Monitoring frequency and history

We monitor annually at the selected geothermal fields. We monitor quarterly at Ngatamariki, Orakei Korako, Tauhara, Te Kopia, Tokaanu, Waikite Valley and Waiotapu, as these fields are considered especially vulnerable to change or damage.

Historical data are taken from records collated from about 1930 to 1995.
Current data are taken from Waikato Regional Council’s monitoring programme since 1995.

Waikato Regional Council commissioned research to collate all known records of geothermal activity in the region prior to 1995. Earliest records date from the 1930s.

Measurement techniques

Most monitoring is carried out by visual inspection and then comparison is made to photographic records of previous years. The status of a spring or geyser is based on the expert judgement of the monitoring officer. Sometimes this is based on anecdotal evidence, particularly for geysers that erupt infrequently (eruptions may not be witnessed by the monitoring officer).

Water temperature, colour, flow, pH and several other parametres are measure in the field. Water samples are collected every few years from geothermal springs and bores, then analysed for the concentration levels of a range of indicator chemicals. Read more about this in in our technical report REGEMP II Regional geothermal geochemistry monitoring interpretation 2022.

Waikato Regional Council uses the following assessment of geothermal features in this indicator:

Sinter depositing springs generally produce neutral to alkaline fluids of deep geothermal origin at or near boiling temperature. The water contains a high concentration of silica or calcium carbonate, which precipitates to form sinter. The springs are chemically distinct from shallow hot springs, which produce water with few geothermal contaminants that has been heated either by steam or by contact with hot tectonic rocks. Acidic springs can also dissolve and deposit sinter, but usually to a far lesser degree than alkaline springs.

Many sinter springs have been significantly modified by human activities, for example channelling of outlets, and as a result natural sinter deposition (in terraces) is no longer occurring in many springs. However, where sinter is being deposited in the drainage channel, the spring is classed as depositing sinter for this indicator, reflecting the chemistry of the spring, not the physical drainage characteristics of the surrounding geology.

Geysers are defined as hot springs which boil and throw out blobs of water entrained in steam with a repetitive cycle of alternating calm and eruption. The intervals between eruptions can vary over minutes to hours or days, as can the length of the eruptions. However, there is usually some regularity or predictability involved in their behaviour. Geyser eruptions can range in height from a few centimetres to several metres.

From time to time, data loggers with temperature sensors are placed on selected geysers to record the frequency of the eruption. This provides a wider picture of how the geyser is changing over time and if so, we can try to find the cause.

Geysers listed as active are those which have been active in the past 20 years. Others have very extended periods of inactivity lasting many years and have been excluded from this list. Inactivity of geysers may be due to natural variations in the supply of fluid or the geyser's upflow channels.

Alternatively, their inactivity may be due to human interference with the parent geothermal systems by reducing feed pressure and water levels until geysers can no longer function. Wairakei, Tauhara, Ohaaki and Ōrākei Kōrako have all lost geysers due to humans making physical changes to those systems.

This indicator is compiled from the results of our routine monitoring program for geothermal areas. Data are presented as the total number of springs actively depositing sinter, or the total number of active geysers.

Historical (about 1930 to 1961) data, including two major events which resulted in the loss of large numbers of springs and geysers in the region (Wairakei, 1958 and Ohakuri, 1961, power station developments), is compared with current status (activity since then). Although this represents a disproportionate time period for comparison, the historical data are intended to present a baseline to compare with future indicator updates.

Trends in geyser and sinter spring activity are calculated as a percentage of new or lost sinter depositing springs or geysers.

Quality control procedures

For this indicator, monitoring of the activity of each geothermal system is carried out by visual inspection and comparison with photographic records of each spring and geyser.

To ensure accuracy, photographs are taken at each feature from the same location (determined by GPS) every time. Inspections are carried out at the same time of year to avoid any seasonal influences on activity.

Monitoring includes observation of external influences (such as drilling, drainage and forestry) on the activity of any system or feature.

Limitations

This indicator is based on periodic visual inspection of sites and anecdotal evidence. It is a ‘snap shot’ of activity and may not detect geyser activity occurring at other times.

There are a number of geothermal features that are inaccessible, or have yet to be monitored. Therefore, this indicator does not represent the complete suite of geysers and sinter depositing springs in the Waikato region. There are no plans to undertake more detailed surveys in order to locate and describe features not captured in the scope of this indicator.

More information

When this indicator is updated

This indicator is only updated if significant changes are detected, as lasting changes in geysers and sinter springs are unlikely under the current policy regime that protects significant geothermal features.