Morphometry of large and small cones in the Virunga Volcanic Province, East-African Rift

Within the western branch of the East-African Rift Valley lies the Virunga Volcanic Province (VVP), shared by DRC, Rwanda and Uganda. A spatio-temporal assessment of the volcanic hazards presented by the eight large volcanoes and their small satellite volcanoes is essential in this region characterized by recurrent military conflicts and a high population density of ~one million people in the cities of Goma and Gisenyi. Using recent high-resolution satellite images (SPOT, Pléiades) and a newly-created 5 m resolution digital elevation model (TanDEM-X), completed with colonial-time reports and limited field observations, we have mapped lava flow edges, eruptive cones and fissures in a Geographical Information System. The base of the eight large volcanoes was outlined on an SRTM DEM at 30 m resolution at the break-in-slope using the NETVOLC algorithm [1] while the base of the >550 small edifices was outlined manually using the TanDEM-X DEM. Using these cone bases, a set of morphometric parameters was calculated as indicators of edifice morphology and contrasts in erosion grade using the MORVOLC algorithm [2]. The morphometry of the large VVP volcanoes indicates morphology types ranging from shield volcanoes to hybrid complexes and strato-cones. Additionally, some large VVP volcanoes appear more irregular than others and may represent edifices with older eruptive activity compared to the smoother edifices. Based upon morphological indicators such as the presence of flank breaches and the presence of multiple or overlapping craters, we propose a grouping of the satellite cones into 4 categories. Using the MORVOLC program a set of morphometric parameters was calculated to highlight systematic spatial variation in size or morphometric ratios of the cones. The eruptive cones display concentrations in clusters and alignments, some of which align with the regional tectonic orientations. The quantification of volcano edifice morphometry helps in this manner the understanding of spatial distribution of volcanic activity in the VVP, and hence the spatio-temporal assessment of future eruptive susceptibility. [1] Euillades et al. 2013, Computers & Geosciences, 56, 151-160 [2] Grosse et al. 2012, Geomorphology, 136, 114-131