Answer: Molasses

It seems like something out of a bad horror movie, but it’s a quite real disaster that befell the citizens of Boston: a massive wave of molasses. On January 15th, 1919 a huge 2.3 million gallon (8,700 cubic meters) holding tank in a molasses factory burst catastrophically. The sudden release of the molasses (and the pressure in the tank) created a wave of tsunami like proportions; witnesses reported the wall-like wave of molasses was 30 feet tall.

Buildings close to the wave’s peak strength were completely destroyed with wreckage scattered fifty or more yards from the site. Secondary damage was wrought by the shards of the tank falling down (one such shard fell on a firehouse and crushed the building along with the three firemen inside). The total death toll was 21 citizens with another 150 injured.

“As slow as molasses in January” proved that even a trite truism can turn, under the right circumstances, into a disaster.