Great Molasses Flood
The aftermath of the disasterWikiCommons

Back on January 15, 1919, a large molasses storage tank burst (about 8.7 million litres, or 2.3 million gallons), and a wave of molasses rushed through the streets of the North End of Boston, Massachusetts at an estimated 35 miles per hour (56 kilometers per hour), killing 21 and injuring 150.

Known as the Great Molasses Flood, also known as the Boston Molasses Disaster or the Great Boston Molasses Flood, occurred on January 15, 1919, , in the United States.

According to Science Alert, the strength of this molasses wave – which was, at the time, America's favourite sweetener and a key ingredient for rum production – was so strong, it reportedly ripped a fire station from its foundations, smashed several freight cars, and even came close to derailing a train.

Despite the damage, no one had been able to figure out how or why the wave became so powerful, but a team of students from Harvard University are finally uncovering clues as to what happened that chilly January day.

"It's a ridiculous thing to imagine, a tsunami of molasses drowning the North End of Boston, but then you look at the pictures," the students' professor, Shmuel Rubinstein, told The New York Times.

According to the Times, at a meeting of the American Physical Society this month, a team of scientists and students presented what may be a key piece of the century-old puzzle.

They concluded that when a shipment of molasses newly arrived from the Caribbean met the cold winter air of Massachusetts, the conditions were ripe for a calamity to descend upon the city.

How the Boston Post described the incident back in 1919

"Molasses, waist deep, covered the street and swirled and bubbled about the wreckage ... Here and there struggled a form‍ —‌ whether it was animal or human being was impossible to tell. Only an upheaval, a thrashing about in the sticky mass, showed where any life was ... Horses died like so many flies on sticky fly-paper. The more they struggled, the deeper in the mess they were ensnared. Human beings‍ —‌ men and women‍ —‌ suffered likewise."

By studying the effects of cold weather on molasses, the researchers determined that the disaster was more fatal in the winter than it would have been during a warmer season.

The syrup moved quickly enough to cover several blocks within seconds and thickened into a harder goo as it cooled, slowing down the wave but also hindering rescue efforts, the New York Times reported.

According to Gizmodo, Harvard students used modern knowledge of fluid dynamics to analyse this century-old case. They started by performing experiments on corn syrup in a walk-in refrigerator. This environment allowed them to simulate how the molasses would have behaved in a Boston winter. The students were able to apply the data they gathered to models of a flood over the North End of Boston. They found that the results were a close match to the historical accounts of what occurred in the Great Molasses Flood.

Great Boston Molasses disaster
The molasses tank seen here some time before the disasterWikiCommons

One thing that the scientific data confirms is the speed at which the molasses moved. People claimed the initial wave was hurtling forward at 56km per hour. This led many to believe it was propelled by an explosion. But the Harvard team's calculations showed that speed would be possible on its own.

Nicole Sharp is an aerospace engineer and science communications expert who acted as an adviser on the project. She tells the Times, "It's an interesting result and it's something that wasn't possible back then. Nobody had worked out those actual equations until decades after the accident."

When the molasses was delivered two days before the spill, it was heated in order to make it easier to transfer. Sharp says that the molasses was probably still four of five degrees warmer than the outside air when the disaster struck. The students determined that as the molasses flowed around victims it quickly trapped them as its viscosity raised in the cool air, Gizmodo reported.

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