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What Did 2.3 Million Gallons Of Molasses Do To Boston Harbor?04:53
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Wreckage under elevated train tracks from the molasses disaster (Courtesy of "The Great Molasses Flood," by  Deborah Kops)
Wreckage under elevated train tracks from the molasses disaster (Courtesy of "The Great Molasses Flood," by Deborah Kops)

The Great Molasses Flood of 1919 is the stuff of legends. It started with a hiss, a boom and a low rumble that eyewitnesses likened to an earthquake. Then a 15-foot wave tore through the streets at 35 miles per hour, on Jan. 15.

The molasses flooded underground cellars, enveloped and suffocated humans and horses alike, and, as The Boston Post reported the following day, “crushed” buildings like they were made of “eggshells.”

After the wave receded, parts of the North End were submerged in pools of molasses said to be thigh-high. A group of sailors and local firefighters descended on the area, working alongside residents to save people caught in the gluey sludge.

Some firemen tried to blast the molasses off the street with municipal water while others tried to sop up the mess with sand. Neither method worked well, particularly as the hours passed and the molasses congealed. By the following day, newspapers reported that firemen had turned to the waters of Boston Harbor for help. The briny liquid cut through the hardened molasses, allowing it to be washed away.

The Great Molasses Flood of 1919 unleashed 2.3 million gallons of molasses, most of which ended up in Boston Harbor, says Stephen Puleo, author of "Dark Tide: The Great Boston Molasses Flood of 1919." There was reportedly so much molasses in the harbor that the water turned brown.

“Residents commented that it remained brown for weeks before it finally begins to dilute,” Puleo says. Some testified that it persisted for two-and-a-half months.

In 1919, Boston had seven newspapers. In colorful, and often horrifying descriptions, they documented the event and its aftermath. They told stories of people whose cellars flooded with molasses, and devoted entire columns to the deceased. Reporters wrote about the mayor’s call to investigate the explosion, and more than one paper talked about pig farmers from Billerica who came to the North End with buckets, hoping to take advantage of the free food.

But amid the coverage of the catastrophe, no one documented any environmental impacts, nor does it seem anyone questioned the decision to dump the molasses in the harbor, Puleo says. And why would they? At the time of the flood, most people considered the ocean an infinite trash can, able to wash away any manner of pollution.

With the advent of hindsight, we now know that a lot of early industrial waste management plans were far more harmful and destructive than people realized at the time. Recall that Boston discharged raw sewage into the ocean until the mid-20th century.

Exactly what 2.3 million gallons of molasses did to the Boston Harbor ecosystem is hard to say, but if a more recent molasses spill in Hawaii is any indication, the results could have been devastating.

In September 2013, a faulty underwater pipe leaked 233,000 gallons of molasses into Honolulu Harbor. It created a feast for bacteria.

As the bacteria feed, grow and reproduce, they suck oxygen out of the water. In Honolulu, this meant that within a day, dead fish were floating to the surface. And as a scuba diver with Hawaii News Now documented, the scene on the harbor floor was also gruesome.

“There wasn’t a whole lot that could be done for cleanup of the spill itself because molasses is very soluble, so it mixed into the water,” says Grieg Steward, professor of oceanography at the University of Hawaii. “It’s not like with an oil spill where a lot of this material is floating at the surface and can be scooped off.”

He says the most officials could do was remove the dead fish while they waited for the tides to disperse the molasses. Honolulu Harbor took months to fully recover. And that spill was one-tenth the size of the 1919 Boston flood.

The ruins of a tank containing 2 1/2 million gallons of molasses lie in a heap after an eruption that hurled trucks against buildings and crumpled houses in the North End of Boston, on Jan. 15, 1919. The disaster took 21 lives and injured 40. (AP)
The ruins of a tank containing 2 1/2 million gallons of molasses lie in a heap after an eruption that hurled trucks against buildings and crumpled houses in the North End of Boston, on Jan. 15, 1919. The disaster took 21 lives and injured 40. (AP)

So was the impact as catastrophic here? Hard to say, says Jennifer Bowen, professor of marine science at Northeastern University. For starters, the water here in January was substantially cooler. Bacteria would have consumed the molasses more slowly, making it less likely that they depleted such a substantial portion of the oxygen.

“The actual impact would depend on how much of the molasses persisted in the water until the water warmed back up, and how much of it just got diluted and washed out to sea,” she says. But the fact that the water stayed brown for months suggests to Bowen that some sort of increased bacterial feeding could have happened as the temperature rose.

Had a substantial amount of molasses persisted come summer, Boston Harbor might have gone the same way as Honolulu Harbor, she says.

“The bacteria would start taking up the sugar, and all of the oxygen would go away. And that would have the consequence of killing anything that can’t move out of the way of the area,” Bowen says.

Surely that would have been reported in the newspapers.

While speculating about other potential environmental impacts, Bowen wonders how the molasses affected certain plants and animals.

In 1919, the shallow waters of Boston Harbor still had substantial eelgrass meadows that supported a complex ecosystem. If the molasses blocked sunlight for too long, the eelgrass wouldn’t be able photosynthesize and could eventually die.

“The long-term consequences for the eelgrass would depend on how long the water stayed dark,” she says. (Much of the eelgrass died in the 1930s as a wasting disease decimated the meadows.)

The molasses would also have changed the viscosity of the water, making it thicker and harder for animals to swim. Bowen wonders what impact a coating of molasses on the skin or scales of some creatures might have caused.

One hundred years later, we don’t know — and may never know — the true extent of the environmental damage from the Great Molasses Flood of 1919. But one thing is certain: We are incredibly lucky it didn’t happen in the summertime.

This segment aired on January 15, 2019.

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Miriam Wasser Twitter Reporter, EarthWhile
Miriam Wasser is a reporter for WBUR's environmental vertical.

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