In January 1919, a steel storage tank in Boston's North End quietly held over two million gallons of molasses destined for rum and industrial alcohol production.
Neighbors had complained for years that the tank groaned, leaked, and sometimes wept dark syrup down its sides, but the company brushed off every warning as harmless.
On a warm afternoon, the tank ruptured with a roar heard for blocks, releasing a wave of molasses roughly fifteen feet high that surged through the streets at an estimated thirty-five miles per hour.
The flood killed twenty-one people and injured about one hundred fifty more, many of them trapped and suffocated beneath the thick, fast-moving molasses before rescuers could reach them.
Cleanup crews spent months scraping congealed molasses from buildings, streets, and even the harbor, which reportedly stayed brown and sticky for a considerable stretch of time.
Even now, more than a century later, longtime residents insist that on especially hot summer days a faint sweet smell of molasses still drifts through the North End's old streets.
Investigators later found the tank had been rushed into use, poorly tested, and never signed off by an engineer, a failure so glaring it helped push Massachusetts to require formal structural inspections.