Soil CO2 emissions as a proxy for heat and mass flow assessment, Taupō Volcanic Zone, New Zealand

S. Bloomberg; Cynthia A. Werner; C.F. Rissmann; A. Mazot; Travis B. Horton; D Gravley; B. Kennedy; C Oze

doi:10.1002/2014gc005327

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Soil CO2 emissions as a proxy for heat and mass flow assessment, Taupō Volcanic Zone, New Zealand

S. Bloomberg·Cynthia A. Werner·C.F. Rissmann·A. Mazot·Travis B. Horton·D Gravley·B. Kennedy·C Oze

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Abstract

The quantification of heat and mass flow between deep reservoirs and the surface is important for understanding magmatic and hydrothermal systems. Here, we use high-resolution measurement of carbon dioxide flux (φCO 2 ) and heat flow at the surface to characterize the mass (CO 2 and steam) and heat released to the atmosphere from two magma-hydrothermal systems. Our soil gas and heat flow surveys at Rotokawa and White Island in the Taupō Volcanic Zone, New Zealand, include over 3000 direct measurements of φCO 2 and soil temperature and 60 carbon isotopic values on soil gases. Carbon dioxide flux was separated into background and magmatic/hydrothermal populations based on the measured values and isotopic characterization. Total CO 2 emission rates (ΣCO 2 ) of 441 ± 84 t d −1 and 124 ± 18 t d −1 were calculated for Rotokawa (2.9 km 2 ) and for the crater floor at White Island (0.3 km 2 ), respectively. The total CO 2 emissions differ from previously published values by +386 t d −1 at Rotokawa and +25 t d −1 at White Island, demonstrating that earlier research underestimated emissions by 700% (Rotokawa) and 25% (White Island). These differences suggest that soil CO 2 emissions facilitate more robust estimates of the thermal energy and mass flux in geothermal systems than traditional approaches. Combining the magmatic/hydrothermal-sourced CO 2 emission (constrained using stable isotopes) with reservoir H 2 O:CO 2 mass ratios and the enthalpy of evaporation, the surface expression of thermal energy release for the Rotokawa hydrothermal system (226 MW t ) is 10 times greater than the White Island crater floor (22.5 MW t ).

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Source-reported bounding extent: -39.30029918615028° to -36.43896124085945° latitude; 175.14404296874997° to 177.978515625° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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S. Bloomberg, Cynthia A. Werner, C.F. Rissmann, A. Mazot, Travis B. Horton, D Gravley, B. Kennedy, C Oze. 2014-12-18. Soil CO2 emissions as a proxy for heat and mass flow assessment, Taupō Volcanic Zone, New Zealand. https://doi.org/10.1002/2014gc005327

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