About 30 minutes after noon on Jan. 15, 1919, a five-story tall tank nearly full of molasses in Boston’s North End burst without warning, popping its rivets like a zipper. A sable wave 25 feet high and 160 feet wide coursed down a hill and then through city streets at 30 miles per hour, producing what survivors described as an ominous hissing or sucking sound. The molasses—more than 2 million gallons of it—swept away people, horses, and railroad cars, leveling stout brick walls and buckling an elevated train track just seconds after one train full of passengers had passed by and moments before another came around the bend.