Volcano-tectonic deformation and lava flow subsidence modelling using InSAR data at Nyamuragira Volcano, D.R. Congo

The rift volcano Nyamuragira in D.R. Congo regularly produces large- volume lava flows resulting from flank fissure eruptions. The eruptions are usually fed by near-vertical dykes whose orientation and location are controlled by local and regional stress. Fissuring occasionally occurs within the summit caldera, but dyke emplacement and fissuring is usually confined to the flanks along preferential zones of weakness which radiate away from the 2 x 2.2 km caldera. Space-borne Synthetic Aperture Radar Interferometry (InSAR) was used to measure eo-eruptive and inter-eruptive surface deformation at the volcano between 1996 and 2010 (8 eruptions). The largest line-of-sight (LOS) displacement due to dyke emplacement (42 cm) was recorded during the 2002 eruption. Previously unreported displacements have been measured for the 1998, 2001 and 2004 eruptions. Numerical modelling of the 2006 and 2010 eruptive events was tried. The . orientation and size of the dykes is, however, poorly constrained, and the nature of subsurface connectivity with the caldera is not known. Both dykes were emplaced on the southern flank and are aligned with a NNW-trending fracture zone running between Nyamuragira and nearby Nyiragongo. Two methods using regression analyses on time-series data were devised to model and remove lava flow subsidence signals from interferograms. Subsidence signals> 3cm/year have been measured and are a function of time and lava thickness. Linear rate subsidence models were found to be appropriate for most lava flows. Detailed mapping of the recent lava flows of Nyamuragira has also better constrained their location and spatial extent. By stacking interferograms we obtained mean deformation maps of the volcano revealing inter-eruptive deformation: 1. Uplift within the Eastern Pit Crater and inflation of the summit prior to the 2010 eruption; 2. Post- eruptive deflation centred on the 2010 eruption site; 3. Long-period subsidence beneath the Western Crater and rifring of the caldera and 1 immediate flanks; 4. Long-period subsidence centred on the 2006 eruptive vent thought to be associated with visco-elastic relaxation of a cooling magma body; 5. Similar subsidence fields centred on the 1998 and 2002 eruptive vents; 6. Anomalous subsidence associated with the 1991-93 lava flow; 7. The existence of an apparently stable, fault-bounded, and dyke- resistant block of Precambrian crust beneath the NW flank of the volcano, probably related to the Western Border Fault.EThOS - Electronic Theses Online ServiceGBUnited Kingdo