Propagation and arrest of the May 2021 lateral dike intrusion at
Nyiragongo (D.R. Congo)
Abstract
On the 22nd of May 2021, although no alarming
precursory unrest had been reported, Nyiragongo volcano erupted and lava
flows threatened about 1 million of inhabitants living in the cities of
Goma (Democratic Republic of Congo) and Giseny (Rwanda). After January
1977 and January 2002, it was the beginning of the third historically
known flank eruption of Nyiragongo volcano and the first ever to be
recorded by dense measurements both on the ground and from space. In the
following days, seismic and geodetic data as well as fracture mapping
revealed the gradual southward propagation of a shallow dike from the
Nyiragongo edifice underlying below Goma airport on May 23-24, then Goma
and Gisenyi city centers on May 25-26 and finally below the northern
part of Lake Kivu on May 27. Southward migration of the associated
seismic swarm slowed down between May 27 and June 02. Micro seismicity
became more diffuse, progressively activating transverse tectonic
structures previously identified in the whole Lake Kivu basin. Here we
exploit ground based and remote sensing data as well as inversion and
physics-based models to fully characterize the dike sized, the dynamics
of dike propagation and its arrest against a structural lineament known
as the Nyabihu Fault. This work highlights the shallow origin of the
dike, the segmented dike propagation controlled by the interaction with
pre-existing fracture networks and the incremental crater collapse
associated with drainage which led to the disappearance of the world’s
largest long-living lava lake on top of Nyiragongo.