BICTEL/e - ULg
Serveur institutionnel des thèses de doctorat

• modeling
• volcano
• InSAR
• Natron
• Nyamulagira
• Nyiragongo
• time-series
• East African Rift
• Kivu

Two active volcanic areas situated in immature portions of the East African Rift System (EARS): the Lake Kivu (Dem. Rep. of Congo) and Lake Natron, Tanzania) regions, which are located in the western and eastern branch, respectively, are still poorly known.

Both areas indeed lack of ground-based networks, due to security problems or difficult field accessibility. The Lake Kivu area includes two volcanoes erupting frequently: the Nyamulagira and Nyiragongo volcanoes. The SAR database covering these volcanoes includes data from JERS, ERS-1&2, ENVISAT, ALOS, RADARSAT-1&2 satellites back from year 1996. SAR Interferometry (InSAR) is thus applied to study the ground deformations. MT-InSAR approaches, such as the ”StaMPS” method, are used to give us new complementary information to better constrain the previous established eruption models, or gain new insights on eruptions missed by the conventional InSAR, as well as on magmatic and tectonic activity. When enough constrains are available, the ground

displacements are modeled using a 3D-Mixed Boundary Elements Method combined with a neighborhood algorithm. Hence, the 1996, 2002, 2004 and 2010 eruptions of Nyamulagira are modeled. The modeling results, coupled with the StaMPS MT-InSAR results, bring new insights concerning the magma plumbing system of this poorly known volcano

and its eruptive mechanisms. The collapse of the eastern flank of Nyamulagira, along the NNW-trend fractures network linking Nyamulagira and Nyiragongo volcanoes, can also

be identified. InSAR also captures the ground displacements associated with the January 2002 Nyiragongo eruption. The modeling of this major event evidences a deep magma intrusion beneath the Lake Kivu. Such intrusions should be taken into account for hazard

assessment. The magma could indeed finds its way to the Lake Kivu floor, as evidenced by the presence of several old phreato-magmatic cones, and causes a lake overturn. The low dikes overpressures found in the North Kivu and Lake Natron areas indicate that, although the rift is considered as immature, the rift extension is driven by the supply of magma from depth, rather than by the tectonics. A new criterion to identify the rifting stage is found to be the stress state. In the southern part of the rift, tectonic activity dominates, indicating

that the tectonics is probably driving the rift opening there.

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