Cyclic degassing of Erebus volcano, Antarctica

Abstract

Field observations have previously identified rapid cyclic changes in the behaviour of the lava lake of Erebus volcano. In order to understand more fully the nature and origins of these cycles, we present here a wavelet-based frequency analysis of time series measurements of gas emissions from the lava lake, obtained by open-path Fourier transform infrared spectroscopy. This reveals (i) a cyclic change in total gas column amount, a likely proxy for gas flux, with a period of about 10 min, and (ii) a similarly phased cyclic change in proportions of volcanic gases, which can be explained in terms of chemical equilibria and pressure-dependent solubilities. Notably, the wavelet analysis shows a persistent periodicity in the CO 2 /CO ratio and strong periodicity in H 2 O and SO 2 degassing. The ‘peaks’ of the cycles, defined by maxima in H 2 O and SO 2 column amounts, coincide with high CO 2 /CO ratios and proportionally smaller increases in column amounts of CO 2, CO, and OCS. We interpret the cycles to arise from recharge of the lake by intermittent pulses of magma from shallow depths, which degas H 2 O at low pressure, combined with a background gas flux that is decoupled from this very shallow magma degassing.