(NEWSER) – Nearly a century after what researchers call a "tsunami of molasses" descended on Boston, Harvard physicists say that fluid dynamics equations that hadn't yet been written now explain why the disaster proved so deadly—and that the cold weather is partly to blame. In January of 1919, 2.3 million gallons of molasses burst out of an enormous holding tank in Boston's North End, and a wave described as 40 feet high covered the waterfront at an astonishing 35 miles per hour, leveling buildings, toppling cars, and drowning people and horses in its wake, reports the New York Times. (In all, 21 people were killed and 150 injured.) Scientists announced at an American Physical Society meeting this month that the goo moved quickly at first but then hardened as it cooled, which slowed the wave but also attempts to rescue the dozens of people stuck.

"For the first 30 to 60 seconds or so, according to our calculations, that wave would have moved a lot like a tsunami, if you could imagine that," aerospace engineer Nicole Sharp tells the CBC. But then the viscous nature of molasses would have come into play, turning the fast-moving wave into something more like a "seeping." People in its path had little chance to escape. Sharp says she initially couldn't fathom the speed. But "I realized that because the molasses is one and a half times denser than water and there was so much of it in this tank, in fact, fluid dynamics and the physics equations predict that it would move at speeds that are ... totally in line with what the historical record says." Unfortunately for those nearby, it was the perfect, sticky storm. (Earlier this year, a worker died in a molasses tank in the US.)