The U.S. coal industry is in shambles, and the casualties are mounting. There are bankruptcies, mothballed power plants, and most dramatically, unemployed miners.

Since 2011, when coal prices began an unrelenting slide, cash-strapped companies have cut almost 10,000 jobs a year. That's a pace of downsizing not seen since highly productive mining machinery (pdf) proliferated in the 1980s and early 1990s, shrinking the need for manpower.

his time, though, U.S. coal production is going down, not up. China's slowing imports of the fuel are one reason. A bigger one is the boom in cheap natural gas, which has taken market share from coal at power plants and will probably keep doing so.

"The shale revolution has driven natural-gas prices so low that it makes sense for utilities to switch fuels," William Foiles and Andrew Cosgrove, Bloomberg Intelligence analysts, said in a recent note. "More coal miners will likely find themselves out of work."