Chinchaga fire

The Chinchaga fire, also known as the Wisp fire or the Chinchaga River fire, was a forest fire that burned in northern British Columbia and Alberta in the summer and early fall of 1950. With a final size of between 1,400,000 hectares (3,500,000 acres) and 1,700,000 hectares (4,200,000 acres), it is the single largest recorded fire in North American history. The fire was allowed to burn freely, a result of local forest management policy and the lack of settlements in the region. The Chinchaga fire produced large amounts of smoke, creating the "1950 Great Smoke Pall", observed across eastern North America and Europe. As the existence of the massive fire was not well-publicized, and the smoke was mostly in the upper atmosphere and could not be smelled, there was much speculation about the atmospheric haze and its provenance. The Chinchaga firestorm's "historic smoke pall" caused "observations of blue suns and moons in the United States and Europe." It was the biggest firestorm documented in North America—3,500,000 acres of forest burned in northern Alberta and British Columbia—created the world’s largest smoke layer in the atmosphere."

The spring of 1950 saw drought conditions develop in the boreal regions of northern Canada, especially in the watershed of the Chinchaga River. The region has a mix of black spruce, lodgepole pine and deciduous forests, giving way to muskeg in lower areas. Few people lived in the area in 1950.

Sources vary on the source of the fire but agree it was caused by human activity; one version faults an Imperial Oil surveying crew with starting a small blaze to protect their horses from biting insects. Other sources theorize that slash burning from agricultural clearing could have been the initial spark. The blaze started on 1 June 1950 and continued to burn throughout the summer and early fall until the end of October. The ignition point was north of Fort St. John, British Columbia, and the fire burned north-eastward nearly to Keg River, Alberta.

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