Mapping the Spatial Distribution of CO2 release from Kīlauea Volcano, Hawaii, USA

Abstract:

Kīlauea Volcano is a large emitter of volcanic CO₂ with emission rates ranging from 7500-30,000 t/d. However, Kīlauea presents a challenging situation for CO₂ emission rate measurement in that the main source of SO₂ is the active vent in Halema’uma’u Crater, whereas CO₂ emits mainly from a large (> 1km²) diffuse region east of the vent. Previous researchers recognized this issue and advocated for the use of a plume-integrated concentration ratio paired with the SO₂ emission to determine CO₂ emission rates; however, this worked best prior to the opening of the summit vent in 2008, or when SO₂emission was still diffuse as opposed to focused degassing from the vent.

We used two techniques to study the spatial distribution and temporal variability of CO₂ release from the summit caldera in July, 2014. Eddy covariance measurements made at 14 locations in the area of diffuse emission resulted in elevated fluxes that generally ranged from 500 to > 5000 g/m²d, or typical of other volcanic and hydrothermal areas worldwide. MultiGas measurements of the CO₂ and SO₂ concentration in air at 1-m above the ground identified approximately seven areas of elevated area of CO₂ degassing in the caldera. The CO₂ concentrations in air were spatially well correlated to approximately 100 m and displayed anisotropy that was consistent with the measured wind direction. Areas of highest CO₂ concentration correlated with the areas of highest flux using the eddy covariance method and were found near the middle of the caldera approximately 1 km NE of the active vent. This area overlies the inferred location of the shallow summit reservoir, and is characterized by linear fractures with adhered sublimate deposits at the surface. A few of the fractures are visibly fuming, but much of the degassing in the area is not apparent. Future work includes monitoring the fluxes in this area over time, and attempting to quantify emission rates from the areas of measured flux.