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Retrospect: January 15, 1919: Boston Molasses Flood

Caption: U.S. Weather Bureau Synoptic Weather Map for 8:00 a.m. EST, January 15, 1919. Five days after the passage of a cold front that brought the coldest air of the season to the Boston area, temperatures had warmed significantly, possibly contributing to the rupture of a large tank of molasses that left 21 people dead and another 150 injured.

Caption: U.S. Weather Bureau Synoptic Weather Map for 8:00 a.m. EST, January 15, 1919. Five days after the passage of a cold front that brought the coldest air of the season to the Boston area, temperatures had warmed significantly, possibly contributing to the rupture of a large tank of molasses that left 21 people dead and another 150 injured.

It has been described as “America's most fascinating and surreal disaster.” On January 15, 1919, a 58-foot-high tank filled with more than 2 million gallons of molasses burst in Boston's North End, creating a literal flood of the gooey substance, with waves as high as 50 feet by some accounts that crushed everything in its path. When it was over, 21 people were killed, another 150 were injured, 20 city horses lay dead, and six wooden buildings had been destroyed.

While the exact cause of the disaster has never been conclusively established, several factors may have contributed. Among them was the cold weather in Boston during the second week of January and the subsequent rise in temperature that took place in the days preceding the disaster, which may have contributed to fermentation of the molasses and increased the internal pressure of the tank. Although January 1919 had not begun as a particularly cold month in Boston—the high temperature of 59°F on the first two days of the month was well above normal—a cold wave gripped the city by mid-month. A short blurb that ran in the Boston Daily Globe on Thursday, January 9, read, “‘Thursday rain or snow’ was the prediction of the Weather Man last night. On Friday, he said, there will be colder weather.”

The high temperature of 41°F on the 9th gave way to some of the coldest temperatures of the season by the next morning, when the low dipped down to 8°F with the passage of a cold front that also brought southwest winds gusting to 34 mph. “When the mercury dropped toward the bottom of the thermometer yesterday morning and remained stationary at 8 degrees above zero between 8:15 and 8:30,” read a report in the next day's Daily Globe, “the coldest weather of the winter was recorded at the Boston Weather Bureau.”

By Saturday the 11th, the cold air mass settled in “for an extended visit,” as the Daily Globe put it. Although there had been a “promise of mild weather yesterday morning, with a bright sun overhead,” the newspaper reported on the 12th, that by 9 a.m. there was a “sudden change that sent the mercury tumbling fast. From 36 at 9 o'clock yesterday morning it had fallen 20 degrees by 2 in the afternoon, and continued to drop each hour, until at 10 o'clock last night it registered only 7 above at the Weather Bureau.” In fact, the mercury dipped down to as low as two degrees above zero by the morning of the 12th with a “piercing cold making itself felt even under the heaviest clothing.”

Bostonians seemed to take the cold weather in stride. “There was just enough sting in the air yesterday to make outdoor sports enjoyable,” the Daily Globe reported on Monday the 13th. There was also a report of a young woman who “set a new fashion in skating costumes … by appearing on the Charles River in a bathing suit” (which she apparently wore “under a walking skirt and a substantial sweater”).

After three days of frigid temperatures, warmer weather was set to return to Boston, but with it, ultimately, came disaster. The Monthly Meteorological Notes section of the Monthly Record of Observations from the Boston Weather Bureau office stated that “Although the temperature averaged near the normal during the first thirteen days of the month, the remaining eighteen days were all above normal, the excess being more than eleven degrees each day on the average.”

The Daily Globe's forecast on Monday the 13th called for “cloudy and much warmer conditions” through Tuesday, when the high temperature at the official Weather Bureau thermometer, located at the old U.S. Post Office building, reached 46°F. That morning, crews from the ship Miliero had finished pumping half a million gallons of molasses—still warm after being in the ship's hold—into the tank on Commercial Street, where it mixed with the much colder molasses that was already there. This mixture, as described by author Stephen Puleo in his book Dark Tide: The Great Boston Molasses Flood of 1919, produced “a bubbling churn that vibrated against the tank's walls. The men on the Commercial street wharf heard those walls groaning, had heard them groan many times before, usually immediately following a delivery, but it is unlikely that they knew that when the warm and cold molasses mix, the reaction triggers a fermentation process that produces gas. And in a near-full tank, that gas increases the pressure against the steel walls.” The warm spell would continue for the next several days, with the high reaching 50°F by the 17th.

By the morning of the 15th it was cloudy with a temperature of 39°F. At noon the sun had come out and it had warmed to 40.5°F, an increase of nearly 39 degrees over the previous two- and- a- half days—“practically a heat wave,” as Puleo describes it. It's possible that this increase in temperature could have contributed to the fermentation process or otherwise increased the pressure inside the tank—perhaps pushing it beyond the breaking point. About half an hour later, the bottom of the giant molasses tank gave way, sending the flood of the sticky substance flowing down Boston's North End at an estimated speed of 35 mph.

“A dull, muffled roar gave but an instant's warning before the top of the tank was blown into the air,” read a description published in The New York Times. “Two million gallons of molasses rushed over the streets and converted into a sticky mass the wreckage of several small buildings which had been smashed by the force of the explosion.”

The deaths and damage wrought by the molasses flood created a legal nightmare. The approximately 125 lawsuits that followed lingered over a period of six years, with some 3,000 witnesses taking the stand to testify to various aspects of the incident. While prosecutors pointed to faulty construction of the tank and neglect of basic safety rules, attorneys with U.S. Industrial Alcohol, the company that owned the distilling company that operated the tank, claimed that anarchists had sabotaged it for political purposes. In the end, the company was found negligent, having ignored basic safety factors in the construction and maintenance of the tank, and ultimately paid more than $600,000 to the plaintiffs (the equivalent of more than $7 million today).

Nearly a century after it occurred, the Boston Molasses Flood remains but a curious historical footnote in the city's great legacy. To what extent weather may have been a factor in this dark chapter in Boston's history may never be known, but, as it turns out, weather remains a part of the legend of the disaster even to this day. Local lore claims that on sweltering hot summer days, you can still smell the sweet scent of molasses flowing through the air while strolling along the Boston waterfront.

Contributing Editor SEAN POTTER is a New Yorkbased Certified Consulting Meteorologist (CCM), Certified Broadcast Meteorologist (CBM), and science writer with an interest in weather history.

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