It is inferred that at the incipient stages of development, subsidence forms such as the ones shown above and below evolved on a very small scale either as cones, shallow depressions, or as irregular lines or holes that expanded in diameter and depth by time. Observation of the excavation process of the 20+ pits indicate that walls around the smallest of depressions in sandy profiles would collapse in generally circular fashion and thus lead to diameter expansion. For subsidence to proceed, disruption of the hydrostatic load must have taken place in situ or somewhere nearby. This must have been facilitated by a locally weak, heterogeneous sand profile. Sunken sand appears to have been accommodated at depth and subsequently compacted.

Tazerbo is a small village in southeast Libya. However, it assumes special importance in the framework of the Man-Made River Project, an ambitious plan that was undertaken to transfer groundwater from the depth of the desert to coastal metropolitan areas. East of Tazerbo is the Tazerbo Water Field (TWF), out of which a conveyance pipeline carries the pumped groundwater to the north.

Late in 2006, the area north of the TWF, part of the sand plain of the Great Sahara, experienced a phenomenon unknown to occur in desert regions whereby several forms of land subsidence began to develop. As the phenomenon was thought to threaten the safety of the water field and constructions around it, a multi-prong study was carried out in order to determine causes of such subsidence.

Land subsidence occurred mostly as circular forms of different diameters and depths of a few centimeters to a few meters. Morphology of these forms varied from gentle slopes to vertical or sub-vertical walls.

The study involved an initial ground survey followed by an extensive examination of the upper 5-10 meters below the sandy surface via bore holing and excavation. The soft cores extracted from the boreholes were subjected to engineering tests in geotech labs, whereas the sand sections exposed in the pits were measured on the spot and their lithologies were carefully recorded.

The study led to several conclusions as factors that led to subsidence, most important of which are: the initial permeation of the area north of the well field by water flushed due to well testing during the initial stages of development of the TWF, and lithological heterogeneities of the sandy-rocky nature of the upper few meters above bedrock. Structural heterogeneities such as faulting are not thought to have contributed to development of subsidence.