The karst geomorphology of the Boukadir region (Chelif – Algeria)

In June 1988, in the region of Boukadir, northwestern Algeria, a large collapse 60 m in diameter and 35 m deep occurred in the National Road RN4. This region was not considered as strongly exposed to a geotechnical karst hazard. However, this collapse sinkhole suggests that there are large underground cavities under the Quaternary alluvium of the Boukadir plain, at an altitude near or lower than the present sea level. Geological analysis reveals that the Lithothamnium limestones outcropping on the northern Ouarsenis piedmont extend under the Quaternary alluvium. The surface karstic morphology is not spectacular because of the friable nature of this carbo nate platform, but a deep collapse sinkhole called “Bir Djeneb” or “Puits du Diable” was evidenced. The underground voids below the plain could be the result of the base level drop during the Messinian Salinity Crisis (MSC) which let an imprint on the marginal platforms of the Mediterranean Basin.