The dislocation process of the points located on a surface in the area that was under the influence of underground mining was observed in a small time scale. It exhibited highly irregular behaviour (e.g. the observed points during the time their vertical subsidence oscilated in a random way). In the paper is analysed vertical subsidence of three points. The results of the analysis show in an evident way that the nature of the observed irregularities is inherently random. Thus the observed phenomen proves that the underlying mechanism which rules the formation process of the post mining subsidence is of the purely random nature.