Speculative Fact #228: Yellowstone Volcano

Researching a means to produce a post-apocalyptic setting in the United States?
 While scientists agree that another eruption at Yellowstone  is very unlikely, its last outburst about 640,000 years ago was sufficient to cover North America in a blanket of ash (roughly 1000 cubic kilometers). Winds would carry ash through the air for days, being thickest in the northwest but reaching either coast.
            Your protagonists might witness a devastating and truly awesome sight before their struggle for survival begins.

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