'When mines are abandoned, it is sometimes a very short time indeed, perhaps a matter of days, when Mother Nature takes over,' a spokesman for British Coal said yesterday.
The soft rock where coal is found becomes almost malleable at the extremely high pressures of the deep mines on the closure list. Sides cave in, roofs buckle and floors heave up to block the horizontal roadways leading from the shaft to the seams.
In addition, turning off the pumps quickly leads to flooding and a build-up of noxious gases such as methane and carbon monoxide, which have to be removed if a pit is to be reopened.
All but four of the mines will be completely abandoned, which means machinery that can be salvaged is removed before filling in the vertical shaft with backfill material and plugging the opening with a concrete cap.
The four mines due for 'mothballing' - Wearmouth in Sunderland, Prince of Wales in Pontefract, Hatfield/Thorne in Stainforth and Maltby near Rotherham - will have a skeleton care- and-maintenance team to keep shafts and tunnels open and free of water and gases.
Experts in mining technology agree that it will take only a few years following abandonment, or several months for some mines, to effectively close the pits for good.
It would then be just as economical to sink new shafts and drive new tunnels as to try to reopen an abandoned pit.
Dr Mike Richards, senior lecturer in mine engineering at Nottingham University, said: 'You cannot recover old underground roadways that have closed up. You have to start again with new ones. It's much easier to start with virgin rock.'
The costs would make it uneconomical for a future government to reverse British Coal's decision. Dr Richards estimates that it takes between pounds 600 and pounds 1,200 to drive a horizontal roadway a metre (3ft), and between pounds 20,000 and pounds 40,000 to sink a shaft the same distance.
Opening up an abandoned pit could cost 'hundreds of millions of pounds', he said.
'There are very few examples in the UK of a disused mine being reopened.'Reuse content