Mining consequences | Coal mining causes the ground to give way

Mine damage like the one here in Bochum in 2000 was previously known from hard coal mining. Photo: dpa/Gero Breloer Gigantic excavators have turned the Rhenish mining area into a desert. For opencast brown coal mining, they tore even larger holes in the ground between Aachen, Mönchengladbach and Cologne. The operator of Europe's largest brown coal mine, RWE Power, is now attracting tourists to the edge of the mine with viewing platforms made of steel and glass. The communities of Hambach, Garzweiler and Inden affected by excavation have previously become famous in connection with protest actions.

It is scientifically proven that mining represents a radical intervention in nature and the environment. Two new studies from the Helmholtz Center for Georesearch in Potsdam (GFZ) show that the subsoil is being changed far beyond the actual pits. The lowering of the groundwater necessary for mining disrupts the hydrogeological balance and leads to compaction and large-scale subsidence of the soil. At the same time, existing geological faults can be reactivated slowly and without earthquakes, creating steps and fissures.

These are the central results of two studies recently published in the specialist magazines “Engineering Geology” and “Remote Sensing of Environment” under the direction and participation of the GFZ. “This slow fault creep due to the mining process can create local steps in the ground surface and cause deformation patterns that are clearly visible from space,” explains Mahdi Motagh from GFZ, who was involved in both studies.

The data from the European Ground Motion Service (EGMS) of the European earth observation program Copernicus played an important role in both studies. The EGMS covers the European continent and provides displacement measurements from natural and man-made ground movements. The basis for the second study by an international team was the radar data from the Sentinel-1 satellites of the Copernicus program. Its missions provide large-scale observations that are renewed every six days for every location on the continent.

»Drainage for opencast mining changes the hydrogeological balance.«

The studies point to a “clear mechanism.” “Drainage for opencast mining changes the hydrogeological balance, weakens the supporting structures in the subsurface and creates conditions for uneven subsidence and fault movements,” explains Marzieh Baes, GFZ expert for subsurface process modeling. In practice, this means that the impacts of mining do not end at the edge of the pit. They could spread into surrounding communities and affect buildings, roads and other infrastructure through various fault-related deformations.

However, the two studies did not capture deeper underground anthropogenic activities such as mine depth or tailings redistribution. “The inclusion of such data in future research could significantly improve the physical realism and completeness of the risk assessment,” emphasizes the GFZ.

The brown coal mining area between Aachen and Cologne is often shaken by weak earthquakes. However, it is unknown whether the ground faults could also have an impact on seismic activity. "We have not examined the connection between reactivation of faults caused by mining subsidence and seismicity," Modagh tells the "nd" and adds: "However, this needs to be investigated in future studies."

While the viewing platforms offer tourists a fascinating view of the open-cast mine, people in the region are concerned with future prospects. “Lignite mining at the Garzweiler open-cast mine is not yet finished, but structural change is underway,” says the website of the Garzweiler land sequence association’s website – true to the Cologne motto: “Nothing like it is.”

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