Poet John Greenleaf Whittier called it a “horror of great darkness … when men prayed and women wept.” At noon on May 19, 1780, the sky darkened to such an extent over coastal New England that citizens of Portland, Boston and Providence ate their midday meals by candlelight.
Night birds came out to sing, flowers folded their petals and animals behaved strangely. Many thought the Day of Judgment had come.
The sky returned to its normal blue hue the next day. All manner of explanations were discussed, from volcanic eruptions to celestial cataclysms. Now, researchers at the University of Missouri have traced the source of the darkness to forest fires 600 kilometers to the northwest.
Erin McMurry, research assistant in the MU College of Agriculture, Food and Natural Resources’ Tree Ring Laboratory, and colleagues base their conclusion on tree ring records from fire-damaged trees around North America. In the International Journal of Wildland Fire, the researchers report that 1780 was a big year for forest fires in eastern North America, due in part to drought around the Great Lakes.
New England’s noontime darkness, they found, most likely resulted from the smoke of fires that spanned at least 2000 square kilometers in southern Ontario. At one Ontario burn site, fire swept in just after distinctive wood tissue began forming early in the growing season, consistent with the timing of the darkness.
The researchers studied tree rings from the Algonquin Highlands of southern Ontario and many other locations. They found that a major fire had burned in 1780 affecting atmospheric conditions hundred of miles away. Large smoke columns were created and carried into the upper atmosphere.
“The patterns in tree rings tell a story,” said McMurry. “We think of tree rings as ecological artifacts. We know how to date the rings and create a chronology, so we can tell when there has been a fire or drought. This unlocks the history the tree has been holding for years.”
“A fire comes along and heat goes through the bark, killing the living tissue,” said Richard Guyette, director of the Tree Ring Lab and research associate professor of forestry in the MU School of Natural Resources. “A couple of years later, the bark falls off revealing the wood and an injury to the tree. When looking at the rings, you see a charcoal formation on the outside and a resin formation on the top that creates a dark spot.”
Limited ability for long-distance communication prevented colonists from knowing the cause of the darkness. It was dark in Maine and along the southern coast of New England with the greatest intensity occurring in northeast Massachusetts, southern New Hampshire and southwest Maine. In the midst of the Revolutionary War, Gen. George Washington noted the dark day in his diary while he was in New Jersey.
“This study was a unique opportunity to take historical accounts and combine them with modern technology and the physical historical evidence from the tree rings and solve a mystery with science,” McMurry said.