Cover-collapse sinkholes in the 'Tournaisis' area, southern Belgium

摘要

In the Tournaisis area (southern Belgium), cover-collapse sinkholes have been reported since the beginning of thiscentury. In this area, the relatively flat lying carboniferouslimestone is overlain by an unconformable mesocenozoic cover.Recent research has shown that these sinkholes developed fromreactivated paleokarsts. The intensive pumping for domestic andindustrial water supply combined with the dewatering due to deeplimestone quarries operations resulted in the lowering ofgroundwater levels. This triggered the reactivation ofpaleokarstic systems and thus the occurrence of cover-collapsesinkholes. These sudden and unexpected collapses have alreadyhad major impacts in the region. In 1977, about thirty sinkholesopened up along the Escaut River downstream from the city ofTournai. As a consequence, the groundwater was polluted by anextensive loss of river water into the Carboniferous Aquifer.More recently, a house and industrial facilities were severelydamaged by such cover-collapse sinkholes. In this context, ageoharzard map would be a valuable tool as far as regionaldevelopment is concerned. This points at the importance todevelop methods to locate and characterize hidden paleokarsts. Astudy site has been chosen in an area where sinkholes have beenopening up for about ten years. A geophysical survey of the sitewhich included electrical resistance mapping of the area hasshown "weakness" lineaments. These lineaments are parallel to amain fault affecting the region.