With a voracity unrivaled in Yellowstone since the early 1700s, eight huge fires burned nearly half the park’s 2.2 million acres (0.9 million hectares). The effort to fight the inferno brought more than 9,500 firefighters to Yellowstone, at one point, and cost the U.S. government more than 100 million dollars.

Extreme conditions arose when a severe drought continued into early summer, leaving most deadfall with less moisture than kiln-dried lumber. Although human carelessness touched off several fires, most were ignited by lightning and advanced as far as 14 miles (23 kilometers) a day, whipped by dry, gusty cold fronts.

Officials allowed several early fires to burn unsuppressed, following a 1972 U.S. Park Service policy that encourages fire’s natural role. The policy, dubbed “let it burn” by critics, is rooted in the idea that fires set by natural ignitions promote regrowth of diverse vegetation types of different ages, clean out deadfall and other quick-burning forest fuels, and burn firebreak corridors that reduce the risk of catastrophic fire spread. But prior to 1972, all fires had been fought vigorously, adding to an 86-year kindling buildup that exploded in the great fires of 1988.

Adapted from “Yellowstone: The Great Fires of 1988” in the February 1989 issue of NATIONAL GEOGRAPHIC.