A swelly is a geological anomaly where the roof and floor of a coal seam diverge, creating a sudden, localized thickening of the coal bed. These formations often result from ancient stream channels or uneven compaction in the peat swamp. While they yield extra tonnage, they can disrupt the planned mining height and complicate roof control.
Heard on the job
The continuous miner just hit a swelly, so we've an extra three feet of top coal to cut before we reach the sandstone roof.
Also heard as
- swell
Do not mix it up with
- Nip-out: A swelly is a sudden thickening of the seam, while a nip-out is a sudden thinning or disappearance.