Undermined area (old mining)

An undermined area is a place where minerals were mined or explored underground in the past, from medieval ore mining to 20th-century coal mines. The Czech Geological Survey (ČGS) records it in its Undermined Areas database, which according to ČGS flags land where collapses or other hazards from underground voids may occur. Individual mine workings are recorded separately.

Old mine workings

The Czech Mining Act (Section 35) defines an old mine working as an abandoned underground working whose original operator and legal successor do not exist or are unknown; an abandoned quarry after mining of reserved minerals also counts. The register of old mine workings is kept by ČGS on behalf of the Ministry of the Environment. Anyone who discovers an old mine working or its effects on the surface must report it to the ministry without delay. Securing or removing workings that threaten a legally protected public interest is arranged by the Ministry of the Environment to the extent necessary.

How to read it

• An undermined area nearby does not automatically mean a problem. It depends on the depth and age of the workings, the type of mining and whether the house stands directly above them.
• The boundary on the map is only a guide. For a specific building, an expert assessment is what counts.
• Data from the register of old mine workings are also provided to planning authorities, so undermining may be reflected in the zoning plan.

What it means for a buyer

When buying a house or plot in an undermined area, ask the building authority whether special conditions apply to construction there, and check walls for cracks. Cracks and ground subsidence can also have other causes, such as slope instability. Undermined areas and mine workings are publicly available in the ČGS map services.