Cas De M’rara, Bas Sahara, Sud-est Algerien

Résumé: Sahara is known by its stability on the tectonic, seismic and volcanic level. M’rara is a Saharan area threatened by several natural risks such as subsidence, soil collapses and sink-holes. Reduce natural hazards is a critical need for spatial planning of land use. View the lack of geological and hydrogeological studies in the region, has forced us to study a diagnosis, which might provide valuable information on the various collapses are a constant danger in the region and also identify the causes that contributed to the formation of the latter. Among sinkhole damage noted in studied zone are cited the cracking of the water tower, the slope of the electric poles and the losses of irrigation water. We noted the existence of four collapses of considerable size aligned according to the direction NW-SE which coincides with the itinerary of Retem Wadi. The surface geology shows Plio-Quaternary continental formations of lithology varying between sands, conglomerates, clay, limestone and gypsum. The latter two facies are subject to dissolution following the attacks of erosive water. The origin of these anomalies is related to the presence of a karst in Eocene limestone and gypsum in association with water circulation in the overlying formations without forgetting the torrential dynamics of water flowing in Retem wadi.

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