The 2021 Nyiragongo (DR Congo) eruptive crisis monitored by multi-sensor satellite remote sensing data

The 2021 Nyiragongo (DR Congo) eruption started on 22 May 2021, nineteen years after the last effusive eruption of 2002. The lava flows erupted from three vents, one East of the summit area and two along the southern slope, and produced two lava flows, the western of which inundated part of the Goma city, causing serious damages to population, buildings and infrastructures and stopped only at ~1 km from the Goma international Airport. Here we process a variety of satellite imagery, including visible, infrared and radar data, mapping the pre-eruptive phase, the evolution of the eruption and the post-eruptive phase. Most of the remote sensing data were acquired in the framework of Virunga Geohazards Supersite, which is part of the GEO-GSNL (Geohazard Supersite and National Laboratories) initiative. In particular we analysed: (i) Sentinel 1 (European Space Agency, ESA) and (ii) COSMOSkymed, CSK (Italian Space Agency, ASI) data providing displacement time-series and eruptive source model; (iii) Visible Infrared Imaging Radiometer Suite, VIIRS ( NASA/NOAA Suomi National Polar-orbiting Partnership) data at 375 m spatial resolution to provide thermal maps; (iv) different Pleiades (AIRBUS) triplets, at 0.5 m spatial resolution, to update the topography of the volcano.

Pre-eruptive 2020-2021 InSAR (Interferometric Synthetic Aperture Radar) analysis from Sentinel-1 and high resolution CSK data show a deflation of the summit area of Nyiragongo and Nyamuragira volcanoes amounting to few cm/yr Line of Sight (LOS). The syn-eruptive InSAR data evidence surface deformation of 70 cm LOS located South of Nyiragongo, in a wide area including the city of Goma and Lake Kivu. Modelling of the InSAR syn-eruptive data show a sub-vertical dike located from South Nyiragongo reaching Lake Kivu. The top depth is 1.5 km from the surface, and the volume variation is slightly less than 0.2 km3. Post-eruptive Sentinel-1 and CSK data showed deflation of the summit area of Nyiragongo, negative LOS surface deformation at Goma and lava cooling.

VIIRS data allowed us to see an increase in the size and temperature of the lava lake a few months before the eruption, and provided a first image of the erupted lava flow on 22 May 2021 at 22:47 GMT. Thanks to Pleiades imagery we could retrieve the lava flow area and by using a pre-eruptive topography we also provided an estimation of the erupted volumes.

Results highlight how the synergic use of multi-source, multi-temporal satellite imagery, along with innovative and automatic processing techniques, may be adopted for real-time hazard estimates in an operational environment especially in remote volcanoes with limited terrestrial networks.

This contribution is supported by the GEO-GSNL initiative and the H2020 Reliance project (grant agreement 101017501).