Ground fissures in the central Ethiopian Rift: insights on distribution, genesis and hazard

Ground fissuring is an endemic hazard along the East African Rift, rather common in the volcanic lacustrine deposits of Ethiopia and Kenya. Fissures reach lengths of kilometers and widths of several meters, menacing villages and infrastructures, locally taking the shape of coalescing holes. In this study, the phenomenon has been mapped over the Central Main Ethiopian Rift (CMER), based on field observation and remotely sensed images. Geophysical investigations (geoelectrical and seismic profiles) at two sites (Ziway and Muleti), have provided informative imaging of the underground across recent ruptures. No premonitory ground deformation has ever been reported before the opening of the fissures, whose strike corresponds to that of the widespread system of Late Quaternary faulting inside the Rift. However, while a structural control seems well established, a genetic correspondence of the two phenomena, as observed to the north in the NMER or locally in the western flank of the rift, cannot be proven. As well, no direct link with seismicity does exist. Heavy rains appear to trigger such linear collapses, as in 2016, but again a biunivocal relationship is not yet verified. Thus, this local source of serious hazard remains elusive and unpredictable, unless widespread, and expensive, geophysical and borehole investigations are carried out, possibly supported by high resolution remotely-sensed DinSAR monitoring, still to be proven effective though.