Assessing the spatial dispersion of products of the fumarolic activity using remotely sensed snow color in an alpine environment

The sulfur-bearing volcanic gases SO₂ and H₂S have a direct impact on ecosystems and can endanger human health. Timely information regarding dispersion patterns of fumarolic gases is crucial for predicting potential impacts. However, real-time fixed-point observations are difficult in alpine areas where snow accumulation is seasonably variable, in addition to being potentially dangerous to on-the-ground observers. Thus, in this study we tested a novel technique using a colorimeter, digital camera, and an unmanned aerial vehicle (UAV) imagery to evaluate the dispersion of sulfur particles from fumarolic gas over a snow-covered location in the Tateyama Mountain Range, central Japan, from 2013 to 2015. Snow samples were collected at the depths ranging from 0 to 0.5 cm and the sulfur particle content was determined by X-ray fluorescence analysis. The dissolved ion concentrations in snow melt solutions were analyzed to clarify the contribution of Asian yellow dust (KOSA) to the snow surface color. RGB color images captured by the UAV were converted to CIE-Lab color space with three axes: X axis changed from red to green (a*), Y axis from yellow to blue (b*), and Z axis from white to black (L*). The color levels of green and yellow increased in the snow surface of fumarolic areas and showed a significant correlation with the densities of sulfur particles on the snow surface (r² = 0.853, P < 0.001). These results indicated that aerial images of snow surface color can be used for estimation of sulfur particle dispersion from fumarolic gases.