Ninety-seven years ago, on an unusually warm January day, millions of gallons of molasses flooded the streets of the North End after a massive tank collapsed in one of the most bizarre and iconic disasters in Boston's history. 

The Great Molasses Flood was a thick deluge, said to have peaked at a 40-foot-tall wave that moved at an estimated 35 miles per hour through the streets, killing 21 people, injuring about 150, buckling railroad tracks and damaging the surrounding neighborhood. It even tore the Engine 31 firehouse from its foundation.

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Witnesses described hearing what they thought were machine gun shots firing as the rivets of a poorly constructed 50 foot tall, 90 foot in diameter tank shattered and exploded due to internal temperature shifts. As the molasses spread out, the syrup spread at a 2 to 3 foot deep river that trapped people, dogs and horses in their tracks. 

“The substance itself gives the entire event an unusual, whimsical quality,” author Stephen Puleo wrote in his book “Dark Tide,” which recounts the stories of witnesses and survivors. 

The tank was known to leak from time to time. As a result, the United States Industrial Alcohol Company workers were said to have painted the tank to disguise the leaking liquids.

“The company tried to claim that Italian anarchists blew up the tank at first,” Bob Allison, Chair of the History Department at Suffolk University, said. “But it was inadequately constructed and maintained. Following the flood, stricter inspection protocol for gas tanks were introduced. There was a gas tank directly across the street where the playground is today. The initial thought was ‘these gas tanks aren’t dangerous in a dense neighborhood.’ A molasses tank explosion changed that attitude.”

The Scientific American described the wave as a unique body of liquid in motion. 

“A wave of molasses does not behave like a wave of water. Molasses is a non-Newtonian fluid, which means that its viscosity depends on the forces applied to it, as measured by shear rate.” 

That means that a thick substance like molasses does not want to move unless it is put into motion, much like squeezing toothpaste or extracting ketchup from the bottle. Because of this texture, it made for a nasty way to die and a burden to clean up. 

What followed became the basis of new inspection regulations and an increase in social tensions during a tumultuous time in American history. 

“There was a lot of suspicions that anarchist might have blown it up,” Allison said. “ It’s human nature, especially in times of heightened tension, to want to blame someone. You had labor unrest, the Boston Police strike, a real fear of communist for the first time, anarchist activities and the Spanish flu ravaging entire neighborhoods. And all of this going on right after World War I.”

Ultimately, one of the largest civil suits in Massachusetts history was filed against the United States Industrial Alcohol Company, who eventually paid $600,000 in out-of-court settlements and dished out about $7,000 per victim. 

Today, the area where the tanks were housed are playgrounds across the street from Copp’s Hill and across the bay from the Charlestown Navy Yards.