On January 15, 1919, an industrial storage tank in Boston's North End catastrophically ruptured, releasing 2. 3 million gallons of sticky molasses into the city streets. The resulting wave was 25 feet high, killed 21 people, injured 150, and flattened buildings.
While a flood of syrup might sound slow, fluid dynamics explain why it was so shockingly fast and lethal. Molasses is a non-Newtonian fluid, specifically a shear-thinning liquid whose viscosity depends on applied stress and temperature. On the unseasonably warm 40-degree Fahrenheit day, the fermenting molasses inside the tank was warm and fluid.
When the structural failure occurred, the sudden release created immense pressure and gravity-driven shear force. Under high shear, the molasses behaved like a fast-moving, low-viscosity liquid, roaring through the streets at an initial speed of 35 miles per hour. However, as the wave spread and encountered the cold Boston ambient air, the fluid cooled rapidly.
Molasses experiences an exponential increase in viscosity as temperature drops. Within minutes, the fast-flowing wave transformed into a thick, inescapable, concrete-like trap. Rescuers struggled to swim or pull victims from the rapidly congealing sludge, turning what initially acted like a flash flood into a deadly physical trap due to non-Newtonian thermodynamics.