Measured carbon dioxide emissions from Oldoinyo Lengai and the skewed distribution of passive volcanic fluxes

Airborne measurements of CO₂ released from Oldoinyo Lengai, the only carbonatite-erupting volcano in the world, reveal a CO₂ flux of 0.055 × 10¹² mol/yr. This flux is substantially smaller than that of Mount Etna (1 × 10¹² mol/yr), which accounts for over half of the global carbon flux attributed to subaerial volcanoes (1–2 × 10¹² mol/yr). We propose that the subaerial flux distribution may be a power-law distribution (fractal) rather than Gaussian. Fitting the limited available volcanic flux data to a fractal distribution yields a power-law exponent of <1. Although rigorous testing of the power-law nature of the flux distribution is impossible, the skewed nature of the distribution and low value of the power-law exponent suggest that simultaneous measurement of the 20 largest-flux volcanoes could yield an accurate assessment of the volcanic CO₂ flux. Summation over the power-law distribution predicts a maximum global subaerial passive volcanic flux of 2–3 × 10¹² mol/yr and 2–3 × 10¹¹ mol/yr for CO₂ and SO₂, respectively. Normalizing the emission flux by scaling per unit crater area (instead of per volcano) to investigate the extension of the power-law behavior to geothermal areas with lower gas fluxes yields a power-law exponent of ∼1 and predicts a subaerial volcanic-metamorphic CO₂ flux of 6 × 10¹² mol/yr.