Eastern Kentucky news outletsare reportingthat Arch Coal will lay off 500 miners across the region. This is only the latest wave of layoffs in the coal industry, but so far, the largest. Earlier this month, Alpha Natural Resources announced it would close four Eastern Kentucky mines, but that only resulted in 150 total layoffs. There are numerous factors contributing to the current weak market for coal--the main ones are a warm winter, where people didn't use as much energy and record-low natural gas prices. With new federal pollution regulations on the horizon, power plants are finding it more cost-effective to cut back or abandon coal entirely.And in the most recent data from the Energy Information Administration, coal's share of the nation's energy had dropped to only 34 percent.UPDATE 2:13pm: In addition to the 500 layoffs planned in Kentucky, the Lexington Herald-Leader is reporting an additional 250 coal miners in West Virginia will be affected.UPDATE 5:23 pm: Here's a link to Alpha's announcement. It quotes Arch CEO John Eaves: