Radon and carbon dioxide around remote Himalayan thermal springs

Abstract

AbstractRadon-222 and carbon dioxide (CO2) emissions were studied around four remote Nepalese thermal springs near the Main Central Thrust: Timure and Chilime in the upper Trisuli Valley, central Nepal; and Sulighad and Tarakot in Lower Dolpo, western Nepal. A total of 279 radon fluxes and 670 CO2fluxes were measured on the ground, complemented by radon concentration measurements in soil and water, and assisted by thermal infrared imaging. In Lower Dolpo, mean radon fluxes ranging from 270×10−3to 450×10−3Bq m−2s−1, radon concentration in water greater than 100 Bq l−1, low mean CO2fluxes (18–32 g m−2day−1), and integrated radon and CO2discharges of 70–180 Bq s−1and (2.3–3.8)×10−3mol s−1, respectively, suggest shallow-water-dominated transport with simultaneous radon and CO2degassing from the hydrothermal water. In the upper Trisuli Valley, mean radon fluxes ranging from 140×10−3to 570×10−3Bq m−2s−1, larger mean CO2fluxes that range from 430 to 2930 g m−2day−1, radon concentration in water of less than 6 Bq l−1, and integrated radon and CO2discharges of 290–840 Bq s−1and (390–830)×10−3mol s−1, respectively, indicate fast gas-dominated transport of deep metamorphic-origin CO2charged in radon along a fault network. Radon can thus give precious information on the gas transport properties of the shallow continental crust.