## 7 Conclusions  
The risks posed by sinkholes are becoming a particularly severe problem in urban areas and in spatial planning, where it is necessary to assess the suitability for development of areas at risk from sinkholes, or at a risk from a certain probability of the occurrence of sinkholes such as, for example, in the town of Inowroclaw. Geodetic and geophysical monitoring are then required, as is knowledge about the geological and hydrogeological background of the area. This combination of data provides knowledge about the conditions in which sinkholes are formed, and also the process of their formation, and may enable the assessment of the probability of their occurrence. The presented work highlights this problem and shows an example of geohazard monitoring. In 2018, the authors received a commission from the town authorities of Inowroclaw to assess the safety of the surface facilities for the town area with the aim of implementing a new division of the area of land in question into land development zones. The research carried out at that time allowed for the adoption of new solutions, which were less demanding in their terms related to the creation of new buildings. The problem of assessing ground surface movements in this specific area of old sinkholes and old drilling and shallow underground mining has remained unsolved so far. To make this task harder, the area which is the subject of the analysis presented here is an area without geodetic points. Soon, after our investigation started, LIDAR data were made public, which made it possible to indirectly assess ground surface movements. However, these data had to be compared to the situation from years ago. Such previous data included information obtained in the years 1978 (when heights of topographical of 1589 points were determined) and 1998 (2842 points). The distribution of heights was analyzed--the distribution of height changes, in particular. The analysis was performed for areal distribution and for the distribution of profile lines. Characteristics of terrain surface profiles and their changes in the above-mentioned time intervals were analyzed in light of geological data (the topography of the salt roof surface) and gravimetric data. Amongst the many conclusions that could be derived from this research, the most significant are as follows:  
Figure 13: The distribution of residual microgravity anomaly (red line) and height changes between 1978 and 2018 along the W4 profile line (blue line). 1. The surface topography changes (small hills and small valleys) of the area largely follow the morphological characteristic of the salt layer at the top of the dome. Furthermore, the distribution of these morphological elements at the terrain surface indicates their mutual connection with the characteristic of the determined height changes: the most elevated part of the roof of the salt layer clearly corresponds to increases in elevation of the terrain surface and positive height changes (uplifts). In turn, the lowered part of this roof corresponds to decreases in elevation of the terrain surface and negative height changes (subsidence). This observation leads to an understanding of the mechanism of the geological processes which control the ground surface topography and ground surface displacement. 2. Uplift is the dominant trend in the observed height changes in the period 1978-2018, and the average value of these changes is approximately 0.25 m. This value is higher than the error of the determined height change, and therefore should be considered significant. It was found that the annual changes determined on this basis amounted to approximately 6 mm/y. While the activity of the Inowroclaw diapir is the only instance of such activity in the European lowlands to which scientific studies have been devoted, the presented work is the first in which LIDAR data were used to describe diapir movements in the area of European Zechstein salt formation. 3.