The Great Molasses Flood of 1919 in Boston killed 21 people and injured 150 more. A storage tank filled with 2,300,000 gallons of Molasses burst flooding the street at 35 mph. (A 2016 Harvard study concluded that the speed given in the original articles were credible.)

“Molasses, waist deep, covered the street and swirled and bubbled about the wreckage …. Here and there struggled a form—whether it was animal or human being was impossible to tell. Only an upheaval, a thrashing about in the sticky mass, showed where any life was …. Horses died like so many flies on sticky fly-paper. The more they struggled, the deeper in the mess they were ensnared. Human beings—men and women—suffered likewise.” – Boston Post

The cause is unknown but potentially due to a poorly constructed tank, warmer weather increasing the pressure inside, and/or a fatigue crack near a manhole cover.

Cleanup took weeks in the immediate area. They used salt water and sand to clean up the harbor, which was brown for 6 months. But the molasses had been tracked everywhere in the Greater Boston area and the suburbs and took months to clean up.

The smell remained for decades and some say they can still smell the molasses on hot, summer days.