Eddy covariance measurements of geothermal heat flux at Solfatara Volcano, Naples, Italy

Abstract

The first measurements of volcanic/hydrothermal water vapor and heat flux using eddy covariance (EC) were made at Solfatara crater, Italy, June 8–25, 2001. Deployment at six different locations within the crater allowed areas of focused gas venting to be variably included in the measured flux. Turbulent (EC) fluxes of water vapor varied between 680 and 11200g H2O m−2 d−1. Heat fluxes varied diurnally with the solar input, and the volcanic component of sensible heat ranged from ∼25 to 238W m−2. The highest measurements of both sensible and latent heat flux were made downwind of hot soil regions and degassing pools and during mid-day. The ratio of average volcanic heat (both latent and sensible) to CO2 flux resulted in an equivalent H2O/CO2 flux ratio of 2.2 by weight, which reflects the deep source H2O/CO2 gas ratio. The amount latent heat flux/evaporation was determined to be consistent both with what would be expected from the magnitude of CO2 fluxes and the fumarolic H2O/CO2 ratio, as well as with observed surface temperatures and wind speeds given a moist soil. This suggests that the water vapor that condenses in the shallow subsurface is remobilized at the soil–atmosphere interface through variable evaporation dependent on the deep heat flux and surface temperature. The results suggest that EC provides a quick and easy method to monitor average H2O/CO2 ratios continuously in volcanic regions, providing another important tool for volcanic hazards monitoring.