Abstract

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.

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