Magmatic inflation, miniature dyke intrusion and prolonged torrential rainfall led to the emergence of the 2018 aseismic fissure in Kenya

In March 2018, a large fissure closely parallel to the eastern rift belt of the East African Rift (EAR) system in Kenya emerged across the highway near Mai Mahiu town. It raises the possibility of rift tectonics aided by subsurface erosion. A thorough investigation was made based on remote sensing-based lineament analysis, land surface deformation by spaceborne geodetic techniques, and rainfall pattern vs denudational processes in the affected area in relation to local geology to adjudge the cause of the aseismic fissure. By conventional and advanced differential interferometric SAR (DInSAR and ADInSAR) and GNSS data analyses aided by the knowledge of generalised rift direction obtained from remote-sensing based lineament analysis, we inferred miniature dike intrusion and reactivation of pre-existing fault in a transiently elevated extensional regime. Episodic magmatic inflation in the Mt Longonot volcano and sudden increase in hydrological loading due to prolonged torrential rainfall led to the elevated extension and fracturing of the magma chamber, which prompted to miniature dyke intrusion along the pre-existing NNW-SSE fault, reactivation of faults and fractures and subtle rifting on SW dipping normal fault. Further, internal erosion in porous and permeable sandy soil and volcaniclastic deposits led to cavity formation along the reactivated weak plane, which finally led to the emergence of the ground fissure. In this paper, we presented our observations on volcano movements (due to magmatic inflation), reactivation of the pre-existing fault(s)/fracture(s) and, finally, their linkage with the formation of the surface fissure in an area with favourable geomorphology, rock and soil properties for internal erosion during heavy torrential rainfall.