Publicaties

Nobile, A.,  d'Oreye, N.,  Smets, B.,  Geirsson, H. & Kervyn, F. 2017. ‘Deep and Shallow Magma Plumbing system interactions at Nyamulagira volcano, Central Africa, revealed by high temporal resolution InSAR time series and GPS’. IAVCEI Scientific Assembly 2017. Book of abstracts.

Conference abstract

Analyzing ground deformations associated with volcanic eruptions contributes to understand the mechanisms of magma emplacement and characterize the magma plumbing systems. In regions where in-situ deformation measurements are limited or impossible, because of geographical, economical or political reasons, InSAR may provides crucial information about the surface deformation. 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, is characterized by cycle of short-lived flank eruptions (sometimes accompanied with intracrateral activity) every 1-4 yr, and less frequent long-lived eruptions usually emitting larger volumes of lava from eruptive vents most of the time located >8km from the central caldera. The 2011-2012 Nyamulagira eruption, which lasted from November 6 2011 to April 2012, is one of these long-lived events, which are usually also characterized by longer repose time. SAR images from different satellites (Envisat, COSMO SkyMed, Terrasar-X and Radarsat) allowed measuring pre-, co and post-eruptive ground displacements associated with the eruption. Ground deformation time series obtained with the short revisiting time COSMO SkyMed satellite allowed detecting a very fast (one day) magmatic intrusion below the eastern flank two days prior to the eruption onset. It also allowed the detection of the subsequent intrusion that brought the magma up to the two eruptive vents located 11km ENE from the caldera. We assessed source parameters and the mechanisms of magma emplacement using analytical models jointly inverting two interferograms in ascending and descending orbits that cover the intrusive period. We tested different type of sources to find the most suitable one for this eruption, given the observed deformation and the volcanotectonic context. Considering also the few geophysical (seismic and GPS) data available 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 contrasts with classical flank eruptions, which commonly involve the shallow plumbing system only.