The ground beneath Karaganda
Beneath the city of Karaganda, Kazakhstan, lies a vast and unseen network of abandoned mine shafts and tunnels, a result of its past as a major coal producer for the Soviet Union. This subterranean labyrinth is now causing the ground surface to slowly give way. Buildings, roads, and infrastructure across an area of 50 square kilometers are sinking at rates up to 5 centimeters per year. This gradual, widespread sinking, known as subsidence, is caused by the collapse of underground voids left by more than a century of mining.
The Karaganda Coal Basin, one of the largest in Central Asia, has been exploited since the mid-19th century. Industrial-scale operations began in the 1930s, turning Karaganda into the USSR's "third coal base". The geology of the basin features multiple coal-bearing strata from the Carboniferous and Permian periods, with some seams several meters thick. Mining methods, particularly in the early decades, left behind a honeycomb of passages. As groundwater re-enters these abandoned workings and support pillars degrade, the rock layers above lose their structural integrity and begin to settle, a process that propagates all the way to the surface. The total length of these mine workings was estimated at approximately 490,000 meters in 2022.
This slow-motion collapse threatens the urban environment. An estimated 10,000 buildings sit atop this unstable ground. Catastrophic sinkholes are one potential danger, but the more common issue is differential settlement, where one part of a structure sinks faster than another. This uneven movement can crack foundations, break utility lines, and render buildings unsafe over time. The problem is compounded by the fact that many of the oldest and most dangerous mine workings are poorly mapped, making it difficult to predict exactly where the next major surface deformation will occur.
Watching the city sink from space
Scientists are not blind to the problem; they are watching Karaganda sink from orbit. A remote sensing technique called Interferometric Synthetic Aperture Radar (InSAR) is the main tool for monitoring the subsidence. Satellites, such as the European Space Agency's Sentinel-1, repeatedly bounce radar signals off the city's surface. By comparing the phase of the radar waves from consecutive passes, InSAR can detect vertical ground movements with sub-centimeter accuracy. This technology produces detailed deformation maps that show hotspots of sinking, allowing for a city-wide assessment of the risk.
The data from InSAR is unambiguous. It confirms the steady subsidence across large portions of the city, correlating directly with the locations of known underground mining operations. In some active mining zones, cumulative subsidence has been measured at over 600 millimeters (60 cm) over just a few years. This high-precision, large-scale monitoring provides information for urban planners and civil engineers working to mitigate the danger. By identifying the areas sinking most rapidly, authorities can prioritize inspections, reinforce vulnerable structures, and plan future development on more stable ground. The continuous stream of data from space offers the best available method for managing the geologic hazard from Karaganda's industrial past.