Gas emission and ground temperature measurements at Puhimau thermal area, Kilauea Volcano, Hawaii

Puhimau thermal area, located in the upper East Rift Zone of K?lauea Volcano, Hawai`i formed around 1936 when heat and gases migrated to the surface following a magma intrusion. As of April 2020, the area is about 0.2 km2 in size with regions of steaming ground. The site may be valuable for monitoring changes in gas and heat emissions related to movement of magma down the rift zone. On November 4-5, 2019 we used the accumulation chamber method and thermocouple probes to make 164 measurements of soil CO2 flux and temperature (20 cm depth) at 30-m spacing on a 0.2 km2 grid. Three gas samples were collected from areas of steaming ground on November 5-6, 2019 and analyzed for bulk chemical and carbon isotope (d13C-CO2) compositions. These data were used to characterize the spatial extent and distribution of volcanic CO2 emissions and thermal ground and estimate the total CO2 emission rate from the area. Measured soil CO2 fluxes and temperatures ranged from 4.3 to 5880.0 g m-2 d-1 and 19.3 to 94.0 oC, respectively. Gas samples contained mostly air components, with CO2 concentrations ranging from 3.7 to 10.0 vol.%. The d13C-CO2 value of the gas with the greatest amount of CO2 was -2.71 0/00.