In northern part of Upper Silesia Coal Basin, where Triassic deposits overlay Carboniferous strata, difficult conditions of ground surface exist in regard to extraction of shallow meal ore deposits in Triassic and coal in Carboniferous strata. Ground surface over remnants of shallow ore metal mining is endangered by discontinuous deformations, especially in a form of sinkholes. On most of the area mining works are completed, although the risk of sinkholes occurrence is still significant due to high dynamics of ground waters movement in permeable carbonate rocks, supported by drainage of active and closed coal mines as well as presence of old void and current mining works.
New mining operations undertaken in Bytom trough assume use of mining system that minimises rock mass movements to avoids development of deformation in Triassic overburden and maximal protection of ground surface. However, from the point of view of hydrogeological phenomena, previous and current mining activity influences accelerated, in relation to natural conditions, processes of erosion and karst development. It results from physical and chemical properties of carbonate rocks as well as increased flow of ground waters generated by drainage of the rock mass. In many cases drainage of mines cannot be seen as temporary process until completion of mining activities. It will be permanently necessary for a reason of drainage of urbanised terrains subsided in results of excessive mining operation, in result of which erosion and karst process will continue. Presence of voids and loose zones in shallow layers of carbonate rocks as well as flooding of rock environment may observed using geophysical measurements, from which the most useful is electrical resistivity method. This method allows, between other, selection of flooded (low resistivity anomalies) and dry (highly resistive anomalies), eventually containing rocks of low permeability, areas.
As an illustration of theoretical considerations two examples of measurements have been discussed : an area in Piekary Śląskie, where coal mine extraction took place, and in area of Czeladź, where metal ores do not exist. Conducted measurements, aimed on determination of the risk of sinkholes arise on the ground surface over Triassic foundation undermined by coal mine extraction, confirm strong relation between hydrogeological conditions, which occur in Triassic formations and predisposition for sinkhole occurrence.