The Yellowstone fires of 1988 collectively formed the largest wildfire in the recorded history of Yellowstone National Park in the United States. Starting as many smaller individual fires, the flames quickly spread out of control due to drought conditions and increasing winds, combining into one large conflagration which burned for several months. The fires almost destroyed two major visitor destinations and, on September 8, 1988, the entire park closed to all non-emergency personnel for the first time in its history. In an average year, approximately 21 fires are ignited in Yellowstone by lightning. About 75% of fires in Yellowstone never reach more than 0.1 hectares (0.25 acres) in size