Publications

Nobile, A.,  Smets , B.,  d'Oreye, N.,  Geirsson, H.,  Samsonov, S. & Kervyn, F. 2017. ‘InSAR and GPS ground deformation measurements to characterize the Nyamulagira magma plumbing system during the 2011-2012 volcanic eruption’. Fringe. Book of abstracts.

Conference abstract

Volcanic eruptions are the ultimate surface expressions of magma movements at depth. Analyzing ground deformations associated with volcanic eruptions contributes to understand the mechanisms of magma emplacement and characterize the magma plumbing systems. InSAR is a particularly well-suited tool to measure ground displacement in areas that are difficult to access because of geographical, economical or political reasons, and/or where little or no ground-based monitoring systems are available. This is the case of Nyamulagira, an active shield volcano with a central caldera, located in the eastern part of the Democratic Republic of Congo along the western branch of the East African Rift System. Nyamulagira shows a particular eruptive cycle characterized by short-lived flank eruptions (sometimes accompanied with intracrateral activity) every 1-4 years, and less frequent long-lived eruptions usually emitting larger volumes of lava from eruptive vents located >8 km from the central caldera. The 2011-2012 Nyamulagira eruption is one of that last type. This eruption began on November 6 2011 and ended in late April 2012. In the present study we use InSAR data from various satellite (Envisat, COSMO SkyMed, Terrasar-X and Radarsat) to measure pre-, co and post-eruptive ground displacement associated with the Nyamulagira 2011-2012 eruption. In particular ground deformation time series obtained with the short revisiting time COSMO SkyMed satellites allowed us to detect a very fast (one day) magmatic intrusion below the Eastern flank of the caldera two days prior to the eruption. It also allowed the detection of the subsequent intrusion that brought the magma up to the two eruptive vents located 11 km ENE from the caldera. To evaluate the source parameters and the mechanisms of magma emplacement we used analytical models jointly inverting two interferferograms (COSMO SkyMed in descending orbit and Envisat in ascending orbit) that cover the intrusive period. We tested different type of sources to find the most suitable for this eruption given the observed deformation and the volcano-tectonic context. Considering also the few geophysical (seismic and GPS) data available for this area during the eruptive period, our analysis suggest that the eruption is a complex sequence of a deflation of a shallow magma chamber (~3km below the caldera) that fed a sill intrusion toward the ENE direction that twisted into a dyke and brought the magma up to the surface. Furthermore, GPS, InSAR and seismic datasets suggest the presence of a deep magmatic source that possibly fed the shallower magmatic system. This mechanism, involving a deep source for this large eruption, contrasts with the usual shallow plumbing system identified during the classical flank eruptions.