BOSTON (CBS) – Tuesday was the 100th anniversary of Boston’s Great Molasses Flood. A molasses flood might sound like a bad joke, but on January 15th, 1919, it was all too real. The destruction was enormous, and so were the human costs.

“This is the site of the great molasses flood,” says Mike Manning, standing in Langone Park on Commercial St. in the North End. Manning is the chair of the Friends of the Boston Harborwalk and will lead a molasses flood tour this weekend.

There’s a baseball field there now, but 100 years ago a tank four stories tall rose from the ground. “The tank here, filled with 2.3-million gallons of molasses, ruptured and then collapsed. The collapse sent a wave of molasses traveling about 35 miles per hour in all directions,” he explains. “It knocked buildings off their foundations, and it actually bent the vertical uprights supporting the Boston elevated railway.”

Twenty-one people died, smothered by the wave of molasses. Another 150 were injured. “The weight of the molasses was actually 26 million pounds, or about 13 million tons,” he says.

And when the badly designed and poorly constructed tank burst, the force was incredible. “The molasses flowed as far as Charter St. towards North Station, all the way to the harbor’s edge, and then to Copp’s Hill Terrace, to a depth of 2 to 3 feet,” he says.

That’s hard to imagine looking at the park that’s there now, but the headlines of the day blared the news. “In the middle of a warm winter day, out of the blue, disaster struck,” Manning says.

After the molasses flood, building codes were changed in hopes of preventing the shoddy work that lead to the tank collapse.

For more information, check out the definitive book about the flood, “Dark Tide: The Great Boston Molasses Flood of 1919” by local author Stephen Puleo. Thanks to Puleo, the Boston Public Library’s Leslie Jones Collection and the Boston Fire Dept. Archives for the still photos of the aftermath of the flood.