On January 15, 1919, 2.3 million gallons of molasses flooded the North End of Boston, killing 21 people and injuring more than 100. Faulty construction caused the tragedy — leaving a lasting impact on Boston and the United States.

On Jan. 15, 1919, a tank that contained more than 2 million gallons of molasses ruptured, killing 21 people and injuring more than 100 others. It destroyed buildings, killed animals and coated everything in the vicinity of the tank with a suffocating and hard-to-remove layer of the sticky substance.

The anniversary of Boston's Great Molasses Flood of 1919 offers a bizarre, if grim, annual reminder of a freak accident in the city's North End. And one researcher suggests that looking back at the waterfront incident offers lessons for its future.