The sudden closure of the Nairobi-Nakuru highway after a sinkhole emerged at the Eveready Roundabout in Nakuru City drew national attention to the rare but extremely hazardous phenomenon of sinkholes. On Thursday, the Kenya National Highways Authority (KeNHA) announced that the stretch had been deemed safe for use after engineers initially responded to the sudden formation of a sinkhole which temporarily rendered the route impassable. But what exactly are sinkholes and how do they come about? Scientifically, sinkholes are defined as depressions in the ground which are caused by the collapse of a surface layer, often taking place with little to no warning. Sinkholes can range in size from a few feet to several meters in depth and width.
The sudden nature of their occurrence inevitably poses serious risk to infrastructure and vehicles. Motorists stranded in traffic on the Nairobi-Nakuru Highway on Thursday, September 4, 2025.
Photo KeNHA What Causes Sinkholes While some sinkholes are at times triggered by man-made activities such as drilling, mining or broken water pipes, more often than not, these depressions naturally occur due to underlying geological conditions. In some parts of Kenya, particularly in regions like the Rift Valley, the earth's subsurface consists of limestone, volcanic ash and other soluble rocks.
Over time, these materials can slowly be eroded by movement of groundwater, leading to the formation of underground voids. When the surface layer gets overwhelmed and can no longer support its own weight, it collapses into the underlying cavities, creating a sinkhole. Notably, the Nakuru - Eldoret highway, which traverses geologically active regions of the Rift Valley, is quite susceptible to sinkhole formations due to underlying sedimentary rock formations. In the Wednesday evening case, KeNHA cited the behaviour of the pyroduct upstream, a term which refers to natural conduits formed by past volcanic activity, as a possible contributing factor. During the rainy season especially, these underground tubes can weaken over time since increased water flow accelerates erosion. In urban areas, poor drainage system can exacerbate the issue of sinkholes since it allows water to accumulate, increasing pressure on soil. Besides natural phenomenon, human activity can also indirectly lead to sink holes.
