Remote Sensing based investigation of secondary mining deformation processes in a postglacial landscape of the Muzakow Arch Geopark (Western Poland) – preliminary results

The area of the present day Muzalkow Arch Geopark located on the border of Poland and Germany was subjected to a long term mining of lignite and other rock raw materials that ceased in the 70’ties of the 20^th Century. The present-day geomorphological landscape of the research area is characterised by numerous and differentiated forms of anthropogenic origin (e.g. artificial lakes, subsidence troughs, sink holes, waste heaps) associated with underground and subsequently opencast mining of lignite in complex geological and tectonic conditions that result from glaciotectonic processes of subsequent stages of accumulation and weathering. It is thought that the area is presently subjected to geodynamic processes associated with weathering of exposed areas (lignite outcrops and waste heaps), destruction of shallow underground workings (subsidence troughs, sink holes) and changing hydrogeological conditions of the rock mass. The scale of these secondary deformations is presently unknown and these processes pose a threat the present day tourist development of the area, such as: sudden development of discontinuous terrain deformations, slope instability, flooding and subsequent dying of vegetation, etc.
Geodetic surveying and remote sensing (terrestrial, aerial and satellite) observations have been employed, apart from other in-situ investigations (geophysical and geological prospecting), to study the processes in one of the former coal mining fields in the geopark.
In this study preliminary results of selected geodetic field investigations, i.e. terrestrial laser scanning of a sink hole that showed on the surface in Autumn 2019 and UAV photogrammetric monitoring of an artificial waste rock tips have been reported. It has been found, based on mapping of old mining maps in GIS, that the sink hole is directly related to old shallow underground workings. Maximum depth of the analysed sink hole below ground level is  5.5 m and volume of subsidence is 35 m³. The location is being monitored to check if the geometry changes in time.
Whereas, comparison of digital elevation models of the investigated waste heap (one of three measured so far) showed development of gully erosion and downward movement of the weathered material. The deposition of material at the bottom of the heap averaged over a dozen cm and maximum of over 50 cm for a half year Summer period (from 15.05.2020 to 07.11.2020).
The presented results constitute a first approximation of 3D mapping and modelling the post-mining deformations in glaciotectonic landscape and constitute part of an ongoing research project financed from the Polish National Science Centre OPUS funds (no 2019/33/B/ST10/02975).