Summary

Lignite opencast mining in western Germany leaves clear and measurable traces on the Earth’s surface – not only due to the excavation by coal excavators. New research findings from the Rhenish coalfields between Aachen and Cologne show that the drop in the groundwater level caused by opencast mining has triggered extensive ground subsidence. At the same time, it has reactivated pre-existing geological faults in a slow, aseismic manner. These movements are evident in some places on the surface as fault steps, uneven settlement and damage to roads, houses and other infrastructure.

The findings stem from two studies recently published in the specialist journals Engineering Geology and Remote Sensing of Environment, led by or involving the GFZ Helmholtz Centre for Geosciences. The studies combined satellite radar observations, field observations and spatial geo-analyses – covering aspects such as geography and hydrology – whilst also incorporating reports on damage to buildings. On this basis, the researchers have also proposed a framework for predicting susceptibility to subsidence and produced regional subsidence risk maps. These can contribute to the development of more resilient infrastructure and disaster risk management strategies.

Background: Land subsidence associated with mining

Land subsidence is becoming a widespread global geohazard. Downward or lateral movements of the Earth’s surface pose a significant risk to infrastructure – including buildings and underground utility lines – as well as to the environment and human safety. They can be of natural origin – triggered, for example, by soil compaction, limestone dissolution or tectonic activity. Increasingly, however, they are also caused by human activities, such as unsustainable groundwater extraction and rapid urbanisation – or by mining operations. The latter include not only the underground mining of hard coal, the effects of which are well known in the Ruhr region, for example, and which are frequently caused by the collapse of underground workings.

Land subsidence is also observed in the vicinity of opencast mines. The primary cause of this is the extensive dewatering measures required for safe coal extraction. Continuous groundwater extraction disrupts the hydrogeological balance. This can lead to compaction of the aquifer, and existing geological faults can be reactivated, resulting in the formation of steps and fissures.

New studies in the Rhenish opencast mining region

A research team from the GFZ Helmholtz Centre for Geosciences has examined the situation in the Rhenish mining region – Europe’s largest lignite-producing area, located in the densely populated federal state of North Rhine-Westphalia between the cities of Aachen and Cologne – in two studies. In particular, the three major opencast mining sites at Hambach, Garzweiler and Inden were examined. In addition to the large-scale opencast pits, the region is characterised by extensive deforestation, proximity to seismically active zones and documented slope instabilities within the pits.

In the first study, GFZ researchers M.Sc. Dibakar Kamalini Ritushree, Dr Marzieh Baes and Prof. Dr Mahdi Motagh identified the dominant factors influencing local ground subsidence and quantified their relative impact. On this basis, they also produced regional risk maps for ground subsidence.

To do this, they utilised a range of geospatial variables, including topographical data (slope and aspect derived from the Digital Elevation Model (DEM)), hydrological data (groundwater levels and river courses), geological data (lithological data, fault planes), remote sensing data (InSAR measurements) – ground motion data from the European Ground Motion Service (EGMS) and the Normalised Difference Vegetation Index (NDVI)) – as well as anthropogenic data (locations of mines). These were used to train machine learning models aimed at understanding the relative influence of each factor. To create a regional subsidence risk map, building damage reports from the state of North Rhine-Westphalia were also used for damage assessment.

Use of EGMS data on ground deformation from the European Copernicus Programme

Data from the European Ground Motion Service (EGMS) – a service of the European Earth observation programme Copernicus, launched in 2015 to systematically monitor ground deformation across Europe – played a key role in the investigations. The second study, published in the journal Remote Sensing of Environment, highlights a decade of data availability, using the Rhineland mining region as one example. The study was carried out by an international team of authors led by Dr Michele Crosetto from the Centre Tecnológic de Telecomunicacions de Catalunya, Castelldefels, Spain, with the participation of Prof. Dr Mahdi Motagh from the GFZ.

The study is based on radar data from the Sentinel-1 satellites. The EGMS covers the European continent and provides displacement measurements for both natural and anthropogenic ground movement phenomena, which are standardised and harmonised across Europe, transcending national borders. The Sentinel-1 missions provide large-scale observations that are updated every six days for every location on the continent. The data is made freely available, and there are corresponding visualisation platforms. Due to its characteristics, the EGMS represents one of the world’s most important initiatives of its kind, as the authors write.

Findings for opencast mining in the Rhineland and the significance of satellite data

The study, published in *Engineering Geology*, shows that opencast mining in the Rhineland not only lowers the water table and causes extensive ground subsidence, but also activates existing faults. “This slow fault creep caused by the mining process can create local steps in the ground surface and produce deformation patterns that are clearly visible from space,” explains Prof. Dr Mahdi Motagh, head of the working group  “Radar and optical remote sensing for geohazards” in GFZ Section 1.4 “Remote Sensing and Geoinformatics”.

In detail, the AI-supported data analysis allows for a more precise quantification of the driving factors behind ground subsidence: distance from mines is the dominant predictive variable, followed by changes in the groundwater level. Geological factors such as distance from faults and lithology show a moderate influence, whilst hydrological factors such as distance from a river are less significant. Terrain and land-cover variables such as vegetation contribute only minimally.

The second study, published in “Remote Sensing of Environment”, shows that the European Ground Motion Service (EGMS), which is based on freely available Sentinel-1 radar data, can capture the deformation patterns around the Hambach mine in remarkable detail. The satellite results were independently verified using high-resolution TerraSAR-X data from Germany, confirming that the observed deformation is real, spatially extensive and locally severe.

Taken together, the two studies show that satellite monitoring can not only reveal where the ground is subsiding, but also how geological structures in the subsurface influence the nature of the deformation[UD1] [UD2] .

The research points to a clear mechanism: “Drainage for opencast mining alters the hydrogeological balance, weakens the supporting structures in the subsurface and creates conditions for uneven subsidence and fault movements,” explains Dr Marzieh Baes, a researcher in GFZ Section 4.5 “Subsurface Process Modelling”. In practice, this means that the effects of mining do not end at the edge of the pit. They can spread outwards into the surrounding communities and, through varying settlements and fault-induced deformation, affect buildings, roads and other infrastructure.

Damage patterns are not random

The most important finding is that the damage pattern is not random. The studies show that proximity to mines and changes in groundwater are the strongest predictors of ground subsidence, whilst existing faults concentrate the deformation in specific locations.

“Geospatial analyses are essential for identifying where ground deformation is most likely to occur and for supporting reliable risk and vulnerability assessments in the region. Our findings show that the zones of highest risk are where active ground subsidence coincides with exposed infrastructure and settlements, particularly around the mines and along fault zones,” says M.Sc. Dibakar Kamalini Ritushree, a PhD student in GFZ Section 1.4 “Remote Sensing and Geoinformatics”, who led the study published in *Engineering Geology*. In other words, the ground does not simply subside in the same way everywhere; instead, the deformation is influenced by the geological structure of the region. This makes some areas more vulnerable than others, even if they lie outside the mine itself.

Mapping vulnerability and risk of ground subsidence

The current research has significance beyond the field of geology. This is because it demonstrates that satellite-based monitoring and the insights it provides into the direction and significance of various influencing factors can offer authorities, engineers and planners a means of early warning. 

To this end, the researchers have produced regional hazard maps and, based on these, regional subsidence risk maps.

On this basis, targeted measures for monitoring, containment and risk mitigation can be implemented, thereby contributing to the development of more resilient infrastructure and disaster management strategies. 

The study also highlights that the impacts of opencast mining in Germany are not only ecological but also structural and societal in nature, with consequences that may persist long after mining operations have ceased.

Outlook

The current study did not take into account deeper underground and ground-based measurements, such as borehole and levelling data, nor detailed anthropogenic underground processes such as mine depth, the geometry of ore extraction and the redistribution of waste rock. The inclusion of such data in future research could significantly improve the physical realism and completeness of the hazard assessment.

With regard to the EGMS data, the team of authors proposes gradually expanding the European Ground Motion Service to provide global coverage. This would represent a significant contribution by Europe to the Sendai Framework for Disaster Risk Reduction. A roadmap for this has been outlined, as have technological advancements, both in satellite radar technology – for example, through the use of so-called L-band data – and in the integration of new big data analysis tools. 

Project information:

The research was carried out as part of the SARKI4 Tagebaufolgen project financed via Bundesministerium für Wirtschaft und Energie (BMWE) in Germany. 

Original publications

• Ritushree, D.K., Baes, M. and Motagh, M., 2026. Hydrological and tectonic linkage to subsidence risk in the Rhineland coalfields, Germany: Integrating machine learning with remote sensing and geospatial data. Engineering Geology, p.108751. https://doi.org/10.1016/j.enggeo.2026.108751

   

• Crosetto, M., Cuevas-González, M., Mróz, M.S., Moldestad, D.A., Raspini, F., Casagli, N., Bateson, L., Novellino, A., Motagh, M., Guerrieri, L. and Comerci, V., European Ground Motion Service: A Decade of Sentinel-1 Observations. Remote Sensing of Environment, Volume 339, 2026, 115389. https://doi.org/10.1016/j.rse.2026.115389