Formation mechanism of ground fissures in the Kenyan Rift: tectonics, sediments, and erosion

The East African rift system (EARS) is the most famous continental rift valley on earth, and its ground fissure disasters have been receiving increasing attention. Kenya is located in the middle of the EARS, and its widespread ground fissures have damaged infrastructure, threatened community safety, and restricted urban and rural planning. In the study area, field mapping revealed 85 ground fissures of different scales. The morphology of ground fissures comprises mainly linear, broken lines and arcs, and their lengths range from tens of meters to several kilometers. Ground fissures can extend in all directions, with the dominant strikes being NE, NW, and NNW. Ground fissures are dominated by horizontal tension, and there are no offsets on the two opposite walls. The morphology of ground fissures on the profile is mainly linear and trumpet-like, ranging from young to old fissures. Field investigations, geophysical exploration, and geotechnical testing indicated that ground fissures in the Kenyan Rift are controlled by tectonic activity, stratigraphic lithology, and erosion. The origin and formation of ground fissures can be divided into three stages: Stage I, where tectonic activity forms rock fractures in the crust that are prototypes of ground fissures; Stage II involving formation of rainfall-controlled ceiling collapses and underground voids; and Stage III, involving expansion and connection of ceiling collapses and underground voids, and formation of ground fissures. The study of ground fissures in the Kenyan Rift fills the gaps in ground fissure research and supports local community development and safety.