Ready.
Aim.
Fire.
You’re probably wondering why I’m in a
cold, dark room, repeatedly spilling molasses.
To answer that, we need to look back to when
this quiet Boston neighborhood was a bustling
mixture of waterfront industry, freight operators,
and tenement houses.
And 100 years ago, in January 1919, nothing
in the neighborhood stood taller than the
US Industrial Alcohol Company’s molasses
tank.
The molasses tank stood just behind where
I am now.
It would have stretched from me all the way
past home plate over there, and it would have
stood taller than these stadium lights.
The tank had been built in December 1915 to
store molasses that was then fermented into
ethanol, a key ingredient in manufacturing
munitions during World War 1.
But on January 15th, 1919, in the middle of
the lunch hour, the tank ruptured, disgorging
enough molasses to fill three-and-half Olympic-sized
swimming pools.
The results were devastating.
Buildings were smashed and flooded.
The Elevated Railway’s supports collapsed.
Twenty-one people were killed, and another
150 injured, many of them severely.
Despite contemporary theories of an explosion
– including the idea of a bomb placed by
unseen anarchists – evidence indicates the
tank wasn’t strong enough to withstand the
pressure of the nearly 15 meters of molasses
inside it.
When the steel cracked, the tank tore itself
apart.
And this is where we get back to spilling
molasses because I’ve spent the last several
years, along with colleagues at Harvard University,
exploring the fluid mechanics of this Boston
Molasses Flood.
You see, the Molasses Flood is an example
of a type of flow known as a gravity current.
It’s where a dense fluid – in this case,
molasses – spreads into a less dense one
– like air.
They’re pretty common, actually.
Avalanches, lava flows, mudslides, and even
the cold draft that sneaks under your door
are all gravity currents.
And since they were first described in the
1940s, scientists have developed models that
describe how these flows move.
When I first started reading about the Molasses
Flood, I saw estimates that the initial wave
of molasses moved more than 55 kilometers
per hour.
And so my first question was: is that realistic?
Could molasses actually move that fast?
Using those gravity current models, I calculated
how fast the molasses in the tank could have
moved, and, sure enough, the predicted speed
is about 55 kilometers per hour.
The key to this result is two-fold: molasses
is very heavy -- about one and a half times
denser than water.
And the level of molasses in the tank was
very high.
That combination of height and density meant
that the molasses had a lot of potential energy
– and that potential energy changed into
kinetic energy when released.
For the first 30 seconds or so, the molasses
would have been like a tsunami – a fast,
powerful, and unavoidable wave that devastated
everything in its path.
One eyewitness described it thus: “It looked
like a tidal wave, and I never thought of
molasses at the first of it.
It looked to me like boiling oil; hot oil.
It was curling like a wave at the seashore,
and looked frothy."
That’s pretty different from how we normally
picture molasses.
That’s pretty different from how we normally
picture molasses.
Molasses is really viscous – it resists
flowing – so that property should have affected
the Flood, too, right?
To test how molasses responds to deformation,
my collaborator Jordan Kennedy used a rheometer
to measure how the viscosity of molasses changes
with temperature.
What she found is that molasses’s viscosity
can change by a factor of 100 just over the
range of temperatures relevant to the Molasses
Flood.
That’s like the difference between beating
milk and beating a whole egg.
Except that molasses starts out a lot more
viscous than either of those.
That affected how the molasses spread after
the momentum of that initial wave gave way
to viscous seeping.
The molasses spread over several blocks, and
even where it was only inches deep, it posed
serious problems.
As day turned to night and the molasses cooled
further, it became harder to move, both for
rescue workers trying to remove rubble and
for the trapped victims who had to fight the
molasses in order to keep breathing.
At least one victim, firefighter George Layhe,
suffocated hours after the initial accident
when he no longer had the energy to fight
the cold molasses.
Much of what we know historically about the
disaster comes from the transcripts of the
hearing that followed.
My own research is continuing as I analyze
the testimony of hundreds of witnesses for
key facts that will help us further understand
the science of this accident.
In the meantime, it’s worth taking a moment
to appreciate the destructive potential behind
gravity currents.
We might not have huge, poorly constructed
molasses tanks in our neighborhoods, but we
do face the prospect of natural disasters,
whether they’re lava flows, avalanches,
or mudslides caused in the aftermath of wildfires.
The Boston Molasses Flood teaches us that,
under the right circumstances, even seemingly
harmless fluids can be deadly.
Hey guys, Nicole here!
I owe a big thank you to the collaborators,
friends, and library staff who’ve helped
me during this project.
It has been and continues to be a wild adventure.
If you want to learn more about the Molasses
Flood and other fluid dynamical oddities,
subscribe here on YouTube and check out the
main site at fyfluiddynamics.com.
This project, like all of FYFD, is primarily
reader and viewer supported, so if you’d
like to help out, become a patron over on
Patreon.
Thanks again and I’ll see you next time!
