Eruptive and passive degassing of sulphur dioxide at Nyragongo volcano 1 ERUPTIVE AND PASSIVE DEGASSING OF SULPHUR DIOXIDE AT NYIRAGONGO VOLCANO ( D . R . CONGO ) : THE 17 JANUARY 2002 ERUPTION AND ITS AFTERMATH

The Total Ozone Mapping Spectrometer (toms) instrument aboard the Earth Probe (ep) satellite observed SO 2 emissions during the 17 January 2002 effusive eruption of Nyiragongo (D. R. Congo). A total of 9.3 ± 2.8 kilotons (kt) of SO 2 was measured by ep toms at 1108 local time on 17 January, in a plume that rose close to the tropopause (~14-17 km) according to brightness temperatures derived from Moderate Resolution Imaging Spectroradiometer (modis) data. Available data indicate that the eruption onset and the start of plume emission were not coincident, supporting a regional tectonic trigger for the eruption. Eruptive SO 2 fluxes for the initial 2-3 hours of activity average ~850-1700 kg s. Total SO2 production for the ≤ 24 hours of eruptive activity is highly dependent on the duration of plume emission and the source of the SO 2 , which are poorly constrained, but it is estimated to be 15-48 kt. Available evidence, while limited, suggests that degassing during the 2002 eruption did not differ substantially from that during the similar 10 January 1977 lava lake drainage event. Renewed, vigorous SO2 emissions from Nyiragongo’s rejuvenated lava lake were detected by EP TOMS beginning on 7 October 2002 and continuing until the time of writing. Between 7 October 2002 and 17 November 2003 ep toms detected a total of ~2 Mt SO 2 in plumes from the volcano that typically extended west across D. R. Congo. Extrapolation of this figure to account for data gaps indicates a possible total SO2 emission of 6.9 ± 2.1 Megatons (Mt) at an average of ~16 kt day-1 (~185 kg s-1). The sulphur content of magmas supplying the observed SO 2 flux is currently unknown, but reasonable bounds on the volume of magma degassed in this period are 0.4-3.4 km3. Accommodation of this degassed magma in the fracture system developed during the January 2002 eruption seems likely, although the total fracture space ultimately available for endogenous intrusion is poorly known. Based on known eruptive gas compositions, fluxes of CO 2 and HF from Nyiragongo may be higher than the SO 2 flux. Acta Vulcanologica · Vol. 14 (1-2) · 2002: 00-00

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