The Wave That Moved at 35 Miles an Hour
At half past noon on a mild January day, Boston's North End heard a sound like machine-gun fire — and then the street turned to syrup.
By the morning of January 15, 1919, the bitter cold that had gripped Boston for days had broken. Temperatures climbed past 40 degrees Fahrenheit, a welcome thaw in the North End, where dockworkers, teamsters, and children moved along Commercial Street near Keany Square as they did any other winter day. Looming over them was a steel tank belonging to the Purity Distilling Company: 50 feet tall, 90 feet across, holding as much as 2.3 million gallons of molasses, destined to be piped to an ethanol plant in Cambridge. The day before, a ship had unloaded a fresh, warmed batch of molasses into the tank, mixing with the older, colder syrup already inside.
Just before 12:30 in the afternoon, something inside the tank gave way. Witnesses felt the ground shake. There was a deep, machine-gun-like rattle as rivets shot from the steel plates, followed by a sound like a passing elevated train, or a thunderclap. The tank's walls tore open and collapsed outward.
What followed was not water but something far heavier — molasses is roughly 40 percent denser than water, and the sheer weight of 13,000 tons crashing down turned into a wave 25 feet high, surging through the streets at an estimated 35 miles per hour. The force was enough to bend steel panels against the girders of the Boston Elevated Railway's Atlantic Avenue structure and briefly lift a streetcar off its tracks.
Buildings near the tank were knocked clean off their foundations, crushed by the advancing wall of syrup. Within moments, several blocks stood flooded two to three feet deep in molasses. A truck was said to have been picked up by the rush of air the wave displaced and hurled into the harbor. People near the tank were reportedly thrown feet into the air by that same displaced air, with debris flung alongside them.
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