Soil gas data are collected manually by the Volcano Monitoring Group (VMG) at Earth Sciences New Zealand (ESNZ) to monitor gas discharge rate through the ground in volcanic and geothermal areas.
They are measured with a soil gas flux meter, a bucket-shaped metal accumulation chamber placed on the ground with the gases pumped through a back-pack analyser to derive a flux (emission rate). We can measure carbon dioxide (CO2), hydrogen sulphide (H2S), and methane (CH4) gases in this way.
Soil gas flux measurements were made regularly for monitoring changes at Whakaari White Island until the 2019 eruption. It that case, pegs were used to mark measurement points, so measurements could be made at exactly the same positions each time. Those data constitute a time-series, and are therefore available through Tilde.
Soil gas flux measurements have also been made at Raoul Island, Ngauruhoe, Tongariro, Moutohorā Whale Island, and several other volcanoes, and geothermal areas. In these cases, pegs were not used to mark measurement points, so measurements could not be made at exactly the same positions each time. Instead, measurements are made in broadly the same areas, but subject to constraints such as access and time availability, which will vary from survey to survey. For this reason, making the data available through Tilde is not an option. Those data are available through this repository.
The location of each gas flux measurement is measured by a phone with a built-in GPS and recorded alongside the flux measured. The ground temperature at a depth of 10 cm is commonly measured immediately after the soil gas measurement by inserting a thermocouple in the ground at the middle where the accumulation chamber was located.
Measurement locations are provided in the New Zealand Transverse Mercator 2000 (NZTM2000) grid, rather than latitude and longitude in the World Geodetic System 1984 (WGS84) coordinate system that is commonly used for GeoNet spatial data.
The original data are stored as Excel spreadsheets by the VMG at ESNZ. The spreadsheets contain original observations, calculations, and flux values plus associated ground temperatures. Because of the age of some of the observations, the original measurement locations were recorded in various coordinate systems. These have been converted to New Zealand Transverse Mercator 2000 (NZTM2000) grid using an online coordinate converter provided by Toitū Te Whenua Land Information New Zealand. The content has been simplified to contain just the locations, flux values and temperatures. For original data files and further information on how fluxes were calculated, contact the VMG at info@geonet.org.nz.
The number of digits shown to the right of the decimal point in original Excel spreadsheet flux files was not consistent. Fluxes in CSV files have the same number of digits to the right of the decimal point as in the corresponding spreadsheet, but ground temperatures are typically shown with one digit to the right of the decimal point.
In a limited number of cases, CO2 measurements were made with the accumulation chamber floating on the surface of a lake. Lake and ground observations can be combined to map gas emission rates without any further modifications. In the case of data from Taupo-Horomatangi, absorption of CO2 by the lake water resulted in the concentration of CO2 in lake water being lower than in the air, which in turn, resulted in some negative fluxes (Lohila et al. 2015 and Mazot et al. 2014).
Each file in this repository contains the data collected from one survey of one volcanic area. Files are in CSV (comma-separated values) format.
A filename consists of three parts:
- The location, e.g "MoutohoraWhaleIsland", "Taupo-Horomatangi", "Okataina-Tarawera". The first part of the location is the name of the volcano or volcanic area where data were collected. If both Te Reo and English names are commonly used for the volcano, the Te Reo name is followed by the English name. There are no spaces in the volcano name, and no macrons are used for Te Reo names. The second part of the location is optional, and is provided if measurements have been made at distinct areas at a single volcano or volcanic area, and clarity is improved by naming that area. For example, "Tongariro-CentralCrater", "Tongariro-Oturere", "Tongariro-RedCrater", and "Tongariro-TeMaari". The two parts of the location are separated by a hyphen "-".
- The date the data were collected, e.g. "2025-01-29". This uses local time (NZST or NZDT). The date is separated from the volcano name by an underscore “_”. If the data are sampled over multiple days, the convention
start-date_end-dateis used instead ofsample-date. - A “csv” suffix. This indicates a CSV file format. The suffix is separated from the date by a dot “.”.
| Field | Description |
|---|---|
| MeasurementNumber | A number, or letters and numbers, assigned to a measurement location. Measurement numbers from one survey (data file) have no relation to measurement numbers from another survey (data file). Measurement numbers are the same as used in the original spreadsheets to preserve the link with those files. |
| NZTM-mE | New Zealand Transverse Mercator 2000 projection East coordinate, in units of metres. |
| NZTM-mN | New Zealand Transverse Mercator 2000 projection North coordinate, in units of metres. |
| CO2 | Carbon dioxide (CO2) flux, in units of g/m2/day (grams per square metre per day). |
| CH4 | Methane (CH4) flux, in units of g/m2/day (grams per square metre per day). Not present if methane data were not collected. |
| H2S | Hydrogen sulphide (H2S) flux, in units of g/m2/day (grams per square metre per day). Not present if hydrogen sulphide data were not collected. |
| GroundTemperature | Temperature of the ground at a depth of approximately 10 cm, in units of oC (degrees Celsius). Not present if ground temperature data were not collected. |
CO2 is always measured, but depending in the date of the observations and the equipment used, H2S, CH4 and ground tempertuare may not have been measured. If no measurement was made, the corresponding field is empty. A zero flux indicates a measurement was made, but no gas was observed.
To improve understanding of the area covered by CSV files, they are each accompanied by a map file showing the distribution of observation points. Maps use an OpenStreetMap basemap, show observation points as red-coloured circles, and a map scale, in units of metres (m) or kilometres (km), in the top right. All maps are PNG format files. Maps show the locations using the NZTM-mE and NZTM-mN fields. This normally implies CO2 flux data at these points. To understand if CH4, H2S, or ground temperature data are present, refer to the corresponding CSV file.
This dataset is part of GeoNet's manually collected volcano dataset, please use the DOI and cite accordingly.
DOI: https://doi.org/10.21420/PSP7-KW60?x=y
Cite as: GNS Science. (1954). GeoNet Aotearoa New Zealand manually collected volcano data [Data set]. GNS Science. doi:10.21420/PSP7-KW60?x=y
The following references provide some background information on soil gas measurements and how the data are commonly used:
- Cardellini, C., G. Chiodini, and F. Frondini, 2003. Application of stochastic simulation to CO2 flux from soil: Mapping and quantification of gas release, J. Geophys. Res., 108(B9), 2425, doi:10.1029/2002JB002165.
- Lohila, Annalea & Tuovinen, Juha-Pekka & Hatakka, Juha & Aurela, Mika & Vuorenmaa, Jussi & Haakana, Markus & Laurila, Tuomas, 2015. Carbon dioxide and energy fluxes over a northern boreal lake. Boreal Environment Research. 20. 474-488.
- Mazot, A., F. M. Schwandner, B. Christenson, C. E. J. de Ronde, S. Inguaggiato, B. Scott, D. Graham, K. Britten, J. Keeman, and K. Tan (2014), CO2 discharge from the bottom of volcanic Lake Rotomahana, New Zealand, Geochem. Geophys. Geosyst., 15, 577–588, doi:10.1002/2013GC004945.
- Werner, C. and Cardellini, C., 2006. Comparison of carbon dioxide emissions with fluid upflow, chemistry, and geologic structures at the Rotorua geothermal system, New Zealand. Geothermics, 35, doi.org/10.1016/j.geothermics.2006.02.006.
- Yang, T.H.J., Chambefort, I., Rowe, M., Mazot, A., Seward, A., Werner, C., Fischer, T., Seastres, J., Siega, F., Macdonald, N. and Brakenrig, T., 2024. Variability in surface CO2 flux: Implication for monitoring surface emission from geothermal fields. Geothermics, 120, doi.org/10.1016/j.geothermics.2024.102981.