A friend in Cross Lanes called me a few years back because a crack had opened across her garage slab overnight, wide enough to slide a nickel into edge-on, running straight through the slab, across the threshold, and a few inches into the driveway apron before stopping. Ordinary settlement cracking doesn’t usually do that. A call to the state and a look at old mine maps confirmed what we both suspected: a worked-out coal seam sat under that street, and the ground above it had let go, slowly enough that nobody heard it happen.
How subsidence cracking is different from ordinary settling
Most slab cracking I’ve seen over the years, in our own driveway included, comes from a localized soft spot or a poorly compacted trench under a corner, showing up as a crack a few feet long with maybe a quarter inch of vertical offset. Mine subsidence tends to look different because the ground movement underneath is much larger in area, so the cracking often runs in a rough line or band across a whole slab, sometimes continuing into the sidewalk, the yard, or a neighbor’s property in the same alignment. It can also happen two ways: a gradual sag over months or years as old workings compress slowly, or a sudden, localized collapse where the ground drops abruptly over a former mine entry or a shallow pillar that finally failed. My friend’s garage crack came with a noticeable step, maybe half an inch, which isn’t something I associate with ordinary settlement.
What the crack pattern usually tells you
A subsidence-related crack is often wider than a typical shrinkage crack, sometimes a half inch or more where a normal control joint might show hairline separation, and it tends to run through multiple separate pours rather than stopping at a joint the way settlement cracking often does. If the crack continues in a straight or gently curving line past the slab edge into the yard or street, that continuity across different materials is a strong hint that whatever moved is happening well below the surface. A crack confined to one slab, following the joint layout and stopping at the edges, is far more likely to be an ordinary base or subgrade issue.
West Virginia’s mine subsidence insurance
Because so much of the state sits over historic underground coal workings, West Virginia has a dedicated mine subsidence insurance program that homeowners can add to a standard policy, separate from flood coverage and separate from ordinary homeowner’s insurance, which typically excludes this kind of ground movement entirely. I won’t walk through the specific terms here, since they’ve changed over the years and I’d rather send you to your own agent or the state insurance office than get a detail wrong, but if you own a house near a mapped historic mining area, it’s worth a call to ask whether your policy has it.
What to do the day you notice it
Before anyone touches the concrete, document what you’re seeing. Photograph the crack with a ruler in frame so the width is legible later, mark both ends with a pencil line and the date, and check whether the same crack line continues into the yard, the street, or a neighbor’s lot. If you suspect subsidence rather than ordinary settling, most states with significant mining history, West Virginia included, have an office that fields subsidence reports and can tell you whether there are known workings mapped under your address. That report matters for insurance, and for figuring out whether the ground is still actively moving or has settled into a new stable position, which is a very different repair situation.
Why you don’t repair the slab until the ground has stopped moving
This is the part where I stop pretending to be qualified to make the call myself. Patching or replacing a slab over ground that’s still subsiding is a good way to spend money twice, because a new pour will crack again on the same alignment if the movement underneath hasn’t finished. Whether a subsidence event is done moving or still active is a judgment for a geotechnical engineer, sometimes working from mine maps and sometimes from monitoring the crack over months, not something a homeowner or a concrete crew can reliably determine by eye. The U.S. Geological Survey has background material on subsidence hazards over historic mining areas, though the specific determination for your property comes from a state mine records office or a hired engineer. Reading the crack pattern itself is a separate skill worth having regardless of cause, and this piece on reading a driveway crack goes into that in more detail.
Frequently asked questions
How is mine subsidence cracking different from normal settlement cracking? Subsidence cracks tend to be wider, sometimes with a visible step or offset, and often continue in a straight or curving line across multiple structures or into the yard, while ordinary settlement cracking is usually confined to one slab and follows its joint pattern.
Does homeowner’s insurance cover mine subsidence damage? Typically not automatically; West Virginia offers a separate mine subsidence insurance program that can be added to a standard policy, and it’s worth confirming directly with your insurer or agent whether you have it.
Should you repair a slab right after noticing subsidence damage? Not until it’s clear the ground has stopped moving; a slab repaired or replaced while subsidence is still active is likely to crack again along the same line, so confirming stability first is worth the wait.