Investigations of Nyamuragira and Nyiragongo volcanoes (Democratic Republic of the Congo) using InSAR
Cambridge, CB2 3EQ,
Nyamuragira and Nyiragongo are neighbouring volcanoes in the DRC, and are amongst the most active and dangerous in the world. Eleven ERS SAR scenes were obtained, spanning the period between June 1997 and January 2003, and were combined to form interferograms and associated coherence images. During this period, Nyamuragira erupted four times (in October 1998, February 2000, February 2001 and July 2002), and Nyiragongo erupted in January 2002.
The coherence images enabled mapping of the 2002 Nyiragongo, and the 1998 and 2001 Nyamuragira lava flows in finer detail than available in existing maps. Based on the mapped lava flow areas, and assumed flow thicknesses, the erupted volumes were estimated to be 22 × 106 m3, 71 × 106 m3 and 133 × 106 m3, for the 2002 Nyiragongo, and 1998 and 2001 Nyamuragira eruptions, respectively.
SRTM data were used to remove the topographic signal from the interferograms, revealing previously undetected volcanic deformation signals over both long (years) and short (weeks) time-scales. Both inflation and deflation were observed, with maximum deformation rates of 6 and 30 cm/yr recorded on Nyamuragira’s NE flanks, for long and short time-period interferograms, respectively. Deformation within Nyamuragira’s summit caldera and NE flow field, were interpreted to result from shallow magma transport, and to a lesser extent, lava flow cooling, compaction and flexuring. Inflation on the NW flanks of Nyamuragira was interpreted as a response to magma accumulation prior to the 2002 eruption.
This study shows that InSAR can provide insights into the behaviour of these otherwise little studied volcanoes, and can usefully support hazard assessment. The study also emphasises the value of InSAR, even when applied to densely vegetated volcanoes in the humid tropics.