Mining subsidence; Surface displacement; Dendrogeomorphology; Larix decidua; Extreme rainfall; Upper Silesian Coal Basin

Tree-ring records from sites affected by underground mining provide valuable data on the long-term development of subsidence troughs. However, due to complexity of local conditions, it is unclear whether the surface displacements are actually the result of mining operations or shallow landslides caused by extreme rainfall. This paper compares surface movements at two nearby sites in the Upper Silesian Coal Basin (Central Europe) that have been affected by underground coal mining. Dendrogeomorphic data on subsidence-related movements were obtained from 360 increment cores (90 trees) of European larch (Larix decidua Mill.). Subsidence between 1966 and 2013 was calculated from the corresponding digital elevation models and the actual morphometric parameters of the sites were related to tree-ring records. The effect of precipitation on surface displacements was evaluated using logistic regression models incorporating rainfall data from a nearby meteorological station and dendrogeomorphic event years. The subsidence at the edges of subsidence troughs (study sites) between 1966 and 2013 reached 4–9 m, which is relatively low compared to nearby (5 km radius) directly undermined sites with subsidence up to 22 m. Most events were dated to the 1930s, 1970s, 1990s, and late 2000s with a peak of activity in 1973 and other noteworthy events in 1986, 1995, and 2009. Event years at the site with a flatter topography, and more waterlogged and clay soils are well explained by higher triennial precipitation and higher Simple daily intensity index, suggesting a possible influence of near-surface displacements on the chronology of recorded events, whereas the elevated site with step-block topography showed no relationship between precipitation extremes and event years. We concluded that not only the time of mining operation, but also the site-specific conditions are crucial for characterization of surface displacements in the forested post-mining landscape.