Cave development in the Qatar peninsula: insights on their origin and associated geohazards

Abstract

The geology of the State of Qatar comprises large spans of carbonate rocks at the surface and evaporitic rocks at shallow depth, and a number karst features (depressions, caves) spread across the country that may cause challenges during land development or infrastructure construction. The government of Qatar has identified that existing geodatabases and geological and hydrogeological maps require improvement to mitigate this risk. In this framework, a thorough assessment of the karst geohazard has been performed including a karst features survey, geologic study of karstification, and an assessment of associated ground subsidence related to karst. The main findings indicate the existence of two types of caves: one corresponding to shallow subsurface dissolution caves developed under phreatic conditions in the past and truncated by erosion at a later stage, the other corresponding to large roof collapse caves originating at depth (intrastratal karst). These latter caves are systematically located on the edge of large depressions. In agreement with the existing literature, it is proposed that the depressions and collapse caves are part of a same collapse/sagging process caused by loss of material at depth (e.g., dissolution of evaporites, compaction of weathered dolostone, or incremental collapse of coalesced relict caves). To extract the karst collapse depressions among the large number of depressions mapped using a recent (2017) LiDAR DTM dataset, it is hypothesized that the karst depressions shall have the same geometrical characteristics (width, length, area, depth) than the few ones containing a roof collapse cave. This results in the identification and mapping of 3537 karst depressions spread across the entire Qatar peninsula. Presently, these karst features seem mostly inactive and thus inherited  from a geoclimatic context, which was more favorable to karstification. Under the present geoclimatic conditions, the karst subsidence geohazard appears to be generally low, as caves are inherited, and ongoing karstification processes are limited. However, this geohazard is present across large spans of the territory and any future land development shall include plans and strategies to consider the presence of karstified rocks in the subsurface and ensure that karst is not reactivated by human activity.