How Does The Boston Molasses Disaster of 1919 Work?

Imagine if a giant, wobbly cup of chocolate syrup exploded on your street, but instead of dripping down slowly, it rushed out like a heavy, sweet tsunami. That is basically what happened in Boston in 1919 when a massive tank filled with molasses burst open.

Deep underground, the Industrial Rail Company built a huge steel cylinder to store molasses, which is that thick, dark syrup you might put on pancakes. This tank was as tall as a three-story building and held 2.3 million gallons of liquid honey-colored goo. On January 15, 1919, the weather turned unusually warm for Boston. The sun heated up the metal tank, causing the molasses inside to expand and become more pressurized. Think of shaking a soda bottle until it feels tight; the pressure inside was just too much for the old rivets holding the steel plates together. Pop!

When the tank burst, about 2.3 million gallons of molasses rushed out at 35 miles per hour. It looked like a liquid glacier moving down Commercial Street. The wave was about 15 feet high and weighed thousands of tons. Because molasses is so heavy and sticky, it did not just flow; it crashed. It demolished houses, overturned streetcars, and drowned horses and dogs in the sludge. Rescue workers had to use buckets and hoses to wash people and animals free from the gooey trap.

People called it the "Boston Molasses Flood," but it was really a structural failure. The tank had been built quickly and the steel was thin. Heat combined with poor construction caused a catastrophic rupture. It reminds us that even big, strong things can fail if they get too hot or are put together hastily. The smell of sweet syrup lingered in Boston for years after the cleanup crew finally scraped the streets clean.