This severe underground hazard consists of a petrified tree trunk standing vertically in the shale or sandstone strata directly above a coal seam. Because the fossil is surrounded by a slick layer of coal or clay, it has no structural bond with the surrounding roof rock. When the coal beneath it is mined out, the massive stone cylinder can drop instantly, often with fatal results.
Set two extra roof bolts right there, I don't trust the look of that kettle bottom.
Also heard as
- cauldron bottom
- bell
Do not mix it up with
- Cauldron bottom: They refer to the exact same hazard, though kettle bottom is more common in Appalachian coalfields.
Related terms
Cauldron bottom
A heavy, bell-shaped mass of rock prone to falling from a coal mine roof.
Roof
The layer of rock located immediately above an underground excavation or mineral seam.
Roofbolt
A long steel rod anchored into the ceiling of an underground excavation to prevent rockfalls.
Bump
A violent, sudden release of stress in underground rock strata that causes a physical shockwave.