Publicaties

Geirsson, H.,  d'Oreye, N.,  Nobile, A.,  Smets, B. & Kervyn, F. 2017. ‘Volcano-tectonic deformation in the Kivu Region, Central Africa, observed by continuous GNSS observations of the Kivu Geodetic Network (KivuGNet) and InSAR time series analysis’. IAVCEI Scientific Assembly 2017. Book of abstracts.

Conference abstract

The Kivu Region in Central Africa is in the western branch of the East African Rift, where the Nubia plate and the Victoria micro-plate are diverging by approximately 2-3 mm/yr. Two closely spaced and frequently active volcanoes, Nyiragongo and Nyamulagira, are located at the plate boundary. Nyamulagira is a volcanic shield volcano in formation, while Nyiragongo is more known for its persistent large lava lake. Since 2009 the KivuGNet (Kivu Geodetic Network), comprised of now 15 continuously operating GNSS stations, has been tasked with monitoring deformation in the area. The subtle gradual plate motion is superimposed by co-eruptive deformation from the 2010 and 2011-2012 eruptions of Nyamulagira, and deformation from the Mw5.8 August 7, 2015 Katana earthquake at the western border of Lake Kivu. Importantly, the GPS data also show an ongoing deformation signal, which is most readily explained by long-term magma accumulation under the volcanic region. We use the GNSS and InSAR time series analysis (MSBAS) of the deformation signals to constrain and compare source parameters of simplistic elastic models for the different time periods. Although not well constrained, most of the time periods indicate the presence of a deep (deeper than approximately 10 km) magmatic source centered approximately under Nyamulagira or to the southeast of Nyamulagira, that inflates between eruptions and deflates during eruptions. Both the 2011-12 co-eruptive and inter-eruptive deformation fields show a horizontal asymmetry which may be modelled as an ellipsoidal-shaped source striking roughly along the Nyamulagira-Nyiragongo "transform" zone. The total volume changes of these deeper parts of the magmatic system are uncertain and highly dependent on the depth of the source, however, given that the inflation and deflation sources are the same, the source has (in 2017) recaptured less than half of the deflation that occurred during the 2011-2012 eruption.