Heat flux in volcanic and geothermal areas: Methods, principles, applications and future directions

The measurement and assessment of heat flux in volcanic and geothermal areas are crucial to studying the thermodynamic process, locating the activity of a geothermal field, evaluating geothermal resources, and assessing volcanic hazards. Several methods exist for conducting heat flux measurements, including assessing the soil temperature gradient, thermal infrared remote sensing, ground calorimeter, and other direct calorimetric methods; as well as assessing soil CO2 flux, chloride inventory balance, eddy covariance, and other indirect calorimetric methods; and integrated methods from those mentioned above. Here, we review the history, basic principles, field operation procedures, suitability, and application of these heat flux measurement methods. The relationship between these direct and indirect calorimetric methods and the conduction, convection, advection, and radiation heat transfer mechanisms near the surface are also discussed. Characterization of the intensity of heat accumulation in volcanic and geothermal areas and its potential value for heat and mass transfer near the surface are also recommended. We suggest that the soil temperature gradient and soil CO2 flux methods are promising and representative heat flux measurement methods after comparative analysis of their advantages and disadvantages, accuracy of results, relationship with the heat transfer mechanism, characterization of heat accumulation intensity, convenient operation, clear principle, wide range of characterization, and abundant application scenarios. With the increasing demand for these technologies, heat flux measurement methods can be applied in unconventional volcanic and geothermal areas, such as polar regions, the moon, and large lakes. The results are beneficial to the targeting of geothermal resources, as well as revealing the mechanism of heat and mass transfer in the upper crust. & COPY; 2022 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.