A coal seam fire in interior Alaska was suspected to have started the Rex Creek forest fire in the summer of 2009. With prevailing winds, the forest fire spread rapidly to the north and within eleven days it burned about 410 km(2) of boreal forest. Coal seam fires can go unnoticed and unreported when present in remote and inaccessible areas. However, they still pose a serious threat to the surroundings. We used summer-time thermal infrared images from 1999 through 2009 acquired by the Landsat satellite and, through the process of image stacking, identified a region where the surface persistently showed temperatures 5 degrees C to 14 degrees C higher than the background areas. Field validation confirmed that this thermal anomaly area corresponds to a previously undocumented shallow coal seam fire. Superimposing the boundary of the Rex Creek forest fire revealed that the coal seam fire was at the southern end of the burn area where the forest fire originated. Plotting the location of all lightning strikes during this period helped to rule out lightning as the cause of the forest fire. Coal fires and forest fires can have a complex and dynamic relationship, one being the possible cause of the other. A thorough inventory of all past and present known coal seam fire locations can help to update forest fire hazard maps. A detailed map of shallow coal seam areas can help to prioritize fire fighting operations in order to avoid the chance of starting a new coal seam fire. (C) 2010 Elsevier B.V. All rights reserved.