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Short Summary
Main recommendation: Treat abandoned underground mines, especially room-and-pillar coal mines, as a long-term subsidence risk that can cause sinkholes and broad ground sinking years or decades after mining ends, and manage that risk through prediction, monitoring, and repair. The video explains that these collapses are often unpredictable, hard to trace to a responsible party, and not covered by standard property insurance.
Key Points
- Mining moved underground because surface mining becomes costly and environmentally damaging as overburden (the soil and rock above the material) gets thicker.
- Room-and-pillar mining leaves columns of material to hold up the roof, and these pillars often have thin safety margins because companies left only as much as they thought they could get away with.
- Early mines were poorly mapped and abandoned without maintenance, and records of their locations and condition were often lost as companies dissolved or were acquired.
- Water is a major driver of collapse: flooding after abandonment can dissolve soluble minerals like gypsum and limestone, soften materials, and erode soil into voids.
- Subsidence can appear as a sudden sinkhole directly above a mine, or as slower, broader sinking over a wide area, and it can extend sideways from the mine, with deeper mines producing wider effects.
- Property owners often have limited recourse because surface and mineral rights can be split between different owners, the responsible company may be gone, and typical property insurance excludes mine subsidence.
Details Worth Noting
- Concrete instructions: The video gives no step-by-step homeowner instructions. Its actionable guidance for managing subsidence is for engineers and mining operators: predict subsidence using past mining data, geotechnical data, simplified relationships, and detailed numerical modeling; measure results with instruments such as inclinometers and extensometers placed above underground mines; and repair damage by filling and grading subsided land, retrofitting buildings before extraction, backfilling sinkholes with layered materials (large at the bottom, small at the top) to act as a filter, and stabilizing large voids with grout or polyurethane foam.
- Eight US states that had the most extensive coal mining have government-subsidized subsidence insurance pools, and in a few of those states, this insurance is required to own property.
- The federal US government collects a fee from coal mines that goes into a fund for reclamation of mines abandoned before 1977, when the federal mining act took effect; that act also required modern mines to prevent subsidence or control its effects.
- Longwall mining, a modern method, intentionally lets the roof collapse behind supports, so surface subsidence is described as practically inevitable with that method.
- Examples cited include a sinkhole on I-80 near Wharton, New Jersey (December 2024, recurring in February and March 2025), linked to old underground iron mines, and a 2024 sinkhole in a sports complex in Alton, Illinois, caused by collapse in an active underground aggregate mine.
Bottom Line
Abandoned and modern underground mines can keep threatening the surface for decades, so the practical lesson is that subsidence risk needs ongoing prediction, monitoring, and funded repair rather than assuming the ground is safe once extraction stops.
