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 (φCO₂) and heat flow at the surface to characterize the mass (CO₂ 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 φCO₂ 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 CO₂ emission rates (ΣCO₂) of 441 ± 84 t d⁻¹ and 124 ± 18 t d⁻¹ were calculated for Rotokawa (2.9 km²) and for the crater floor at White Island (0.3 km²), respectively. The total CO₂ 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 CO₂ emissions facilitate more robust estimates of the thermal energy and mass flux in geothermal systems than traditional approaches. Combining the magmatic/hydrothermal‐sourced CO₂ emission (constrained using stable isotopes) with reservoir H₂O:CO₂ 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).

From April 2010 to February 2011, CO₂ flux surveys were performed on Lake Rotomahana, New Zealand. The area has been hydrothermally active with fumaroles and sublacustrine hydrothermal activity before and since the eruption of Mt Tarawera in 1886. The total CO₂ emission from the lake calculated by sequential Gaussian simulation is 549 ± 72 t d⁻¹. Two different mechanisms of degassing, diffusion through the water‐air interface and bubbling, are distinguished using a graphical statistical approach. The carbon dioxide budget calculated for the lake confirms that the main source of CO₂ to the atmosphere is by diffusion covering 94.5% of the lake area (mean CO₂ flux 25 g m⁻² d⁻¹) and to a lesser extent, bubbling (mean CO₂ flux 1297 g m⁻² d⁻¹). Mapping of the CO₂ flux over the entire lake, including over lake floor vents detected during the survey, correlates with eruption craters formed during the 1886 eruption. These surveys also follow regional tectonic patterns present in the southeastern sector of Lake Rotomahana suggesting a deep magmatic source (∼10 km) for CO₂ and different pathways for the gas to escape to the surface. The values of δ¹³C_CO2 (−2.88 and −2.39‰) confirm the magmatic origin of CO₂.

El flujo de dióxido de carbono fue medido en marzo de 2007 en la superficie del lago del Volcán El Chichón, México, usando el método de la cámara de acumulación flotante. Los resultados de 162 medidas y la aplicación del método estadístico estándar, desarrollado para estos estudios, demuestran que la tasa de emisión total de CO2 del lago cratérico es relativamente alta. La tasa de emisión total calculada con simulación secuencial Gaussiana fue de 164 ± 9.5 t.d-1 para el área de superficie del lago de 138, 000 m2. Se proponen dos mecanismos diferentes de desgasificación (por difusión a través de la interfase agua-aire y por burbujas) después de usar el método estadístico gráfico (GSA). Los flujos más altos fueron observados a lo largo de trazas de fallas deducidas. Una desgasificación alta también fue observada a lo largo de lineamentos que concuerdan con fallas que afectan el basamento de la región. Si se considera que el flujo promedio de CO2 comprendiera todo el fondo del cráter (308,000 m2) se tendría una emisión total del cráter del Volcán El Chichón de por lo menos 370 t.d-1. Este flujo sería cinco veces más alto que el del lago volcánico de Kelud, Indonesia y similar al flujo de CO2 de otros volcanes activos con desgasificación pasiva en el mundo.