Hydrogen emissions from Erebus volcano, Antarctica

The continuous measurement of molecular hydrogen (H-2) emissions from passively degassing volcanoes has recently been made possible using a new generation of low-cost electrochemical sensors. We have used such sensors to measure H-2, along with SO2, H2O and CO2, in the gas and aerosol plume emitted from the phonolite lava lake at Erebus volcano, Antarctica. The measurements were made at the crater rim between December 2010 and January 2011. Combined with measurements of the long-term SO2 emission rate for Erebus, they indicate a characteristic H-2 flux of 0.03 kg s(-1) (2.8 Mg day(-1)). The observed H-2 content in the plume is consistent with previous estimates of redox conditions in the lava lake inferred from mineral compositions and the observed CO2/CO ratio in the gas plume (similar to 0.9 log units below the quartz-fayalite-magnetite buffer). These measurements suggest that H-2 does not combust at the surface of the lake, and that H-2 is kinetically inert in the gas/aerosol plume, retaining the signature of the high-temperature chemical equilibrium reached in the lava lake. We also observe a cyclical variation in the H-2/SO2 ratio with a period of similar to 10 min. These cycles correspond to oscillatory patterns of surface motion of the lava lake that have been interpreted as signs of a pulsatory magma supply at the top of the magmatic conduit.