Abstract :
[en] 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 in-
cludes 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 de-
formations. 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 Nyamu-
lagira 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.
