Satellite remote sensing enables continuous multiyear observations of volcanic activity in remote settings. Anatahan (Mariana Islands) is a remote volcano in the western North Pacific. Available ground-based measurements of sulphur dioxide (SO2) gas emissions at Anatahan place it among thelargest volcanic SO2 sources worldwide. These ground-based measurements, however, are restricted to eruptive intervals. Anatahan's activity since 2003 has been dominated temporally by prolonged periods of quiescence. Using 10 years of satellite observations from OMI, AIRS, SCIAMACHY, and GOME-2, we report highly variable SO2 emissions within and between eruptive and quiescent intervals at Anatahan. We find close correspondence between levels of activity reported at the volcano and levels of SO2 emissions detected from space. Eruptive SO2 emission rates have a mean value of ∼6400 t d−1, but frequently are in excess of 20,000 t d−1. Conversely, SO2 emissions during quiescent intervals are below the detection limit of space-based sensors and therefore are not likely to exceed ∼300 t d−1. We show that while Anatahan occupies a quiescent state for 85% of the past 10 years, only ∼15% of total SO2 emissions over this interval occur during quiescence, with the remaining ∼85% released in short duration but intense syn-eruptive degassing. We propose that the integration of multiyear satellite data sets and activity histories are a powerful complement to targeted ground-based campaign measurements in better describing the long-term degassing behavior of remote volcanoes.
