The eruptions of the Nyiragongo volcano documented respectively on January 10, 1977, January 10, 2002 and May 21, 2021 were all fissural on its flanks characterized by the opening of the invoices followed by the effusion of very fluid lava flows.
hese fractures are more important on its southern flank. They are divided into three categories including the emissive fractures of the newly formed flows, the old fractures reopened or reactivated by the new eruption which are in certain places emissive and those formed by the seismicity comes after the eruption of volcano. Emissive fractures are very wide and deep, fractures and cracks resulting from seismic activity are narrow and non-emissive.
The old fractures (formed by the eruptions before 1977) were mapped by Thonnard, those of 2002 by Jean Christophe Komorowky of IPGP France and the Deformation service currently Department of Geodesy and the map of new fractures which has been updated by the team of the Department of Geodesy of volcanological observatory of goma.
These open fractures further north on the flank of the volcano enter a volcanic cone through a single wide and deep opening exiting it on the other side through a network of parallel fractures, which emit lava and are in some places covered by lava flows that come upstream.
The post-eruptive activity of the 2021 eruption, like the other two previous ones, was accompanied by strong seismicity, the epicentres of which were located in the east of the city of Goma and the western part of the city of Gisenyi (Rwanda) then in Lake Kivu. The fractures opened during this activity are oriented North-South like most of the others open to the North on the southern flank of Nyiragongo but have many branches, especially at the epicentres of the earthquakes.