## 2 Geoenvironmental Setting
Ignorance of geological and hydrogeological conditions resulted in a violation of the natural water regime. In the next stage (years 1878-1907), underground mining was started (southern area of the deposit), which was carried out in the roof part of the deposit (salt and gypsum exploitation), but brine was still being pumped by several shafts. This stage was completed when numerous sinkholes appeared at the ground surface and the underground excavations flooded and collapsed (1907). However, the economic pressure exerted by various chemical companies forced the continuation of mining exploitation. A new approach was applied: in the time interval of 1923-1941, a system of boreholes was constructed for the brine extraction [18]. Although the method of extraction (borehole mining) was modern for those times, there was no plan to expand the mining fields due to the limited possibilities for developing this exploitation. Therefore, the concept of exploitation in the conditions of an underground mine operating in an orderly and rational manner that would not threaten structures on the surface was relinquished. The decision to build such a mine in the southern part of the deposit was made as early as 1924. After ten years of preparatory work, which involved drilling a shaft and building a network of drifts, mining with a room and pillar system began in the depth range of 479-637 m in the new and modern Solno mine. The total volume of all the mining chambers (1500) amounted to 16 mln m\({}^{3}\). The subsidence process caused by salt mining in the Solno mine created a subsidence basin with a maximum depth of 35 cm [4; 18]. This period of mining activity in Inowroclaw lasted until 1986, when the planned liquidation of the mine took place and mining workings were finally flooded in 1991 [4; 18]. The Solno Salt Mine, the last company operating in Inowroclaw, was closed down and regular measurements of ground displacements were stopped. Thus, the history of mining in Inowroclaw ended. Surface deformations above the salt dome, in the form of sinkholes occurring in the town, were recorded even before the start of any mining operations, i.e., before 1871 [13; 18]. There are no reliable data on these sinkholes from that time, apart from the documenting of their location. After the catastrophic flooding of the first mine in 1907, sinkholes were formed mainly in the northern group, and from 1917 there was an increase in surface subsidence in the southern part of the dome [13]. These sinkholes usually have a circular or elongated shape with significant dimensions and usually almost vertical walls. The last sinkhole occurred in 2004, in the western part, and it was well documented. Thus, occurrence of sinkholes should be considered as a \"genetic\" feature of this area, because their cause is salt karst and voids associated with this phenomenon and is created in the dissolution process occurring in the cap of the salt dome. Contemporary Studies on Deformations Induced by Old Mining and by the Natural Movements of the Salt Dome  
Movement of the rock substance deep into the rock medium, which is induced by mining or by natural geological processes, causes an effect called deformation. Deformation characteristics depend on many factors (geological, hydrogeological, mining, etc.). The concept of ground deformation can be related to the geological substrate or to the terrain surface. When connected with the terrain surface, the concept of deformation refers to geometrical changes in the topographical relief, while deformation of rock mass is a concept which usually refers to changes in the physical properties of the rock medium. They cause observable changes at the ground surface which may be determined via surveying methods. On the other hand, geophysical surveys are able to recognize and identify deformations occurring in the geological substrate that may also develop and be revealed on the ground surface in the future.