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by ibgames

EARTHDATE: January 15, 2017

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REAL LIFE NEWS: WHY THE BOSTON MOLASSES FLOOD WAS SO DEADLY

by Hazed

I have mentioned the Boston molasses flood before – it’s a disaster that fascinates me, just like the London beer flood and a recent French wine deluge.

Now scientists have figured out why the molasses flood was so very deadly.

The flood happened in January 1915. A storage tank in Boston ruptured and a wave of molasses more than 15 feet high swept through the streets, destroying buildings and killing 21 people and several horses.

But how could a sticky, slow-moving substance such as molasses cause such widespread devastation?

Two scientists teamed up to examine as much data as they could find about the molasses flood, the city and the weather conditions on that day. They looked at newspaper articles, old city maps and weather reports. Nicole Sharp, an aerospace engineer with an interest in fluid dynamics and Jordan Kennedy from Harvard University ran experiments on how molasses flows under various conditions. Then they plugged all the data into computer models.

Their conclusions show that molasses is a fluid which flows more easily in response to applied stress. The technical name is a non-Newtonian fluid. Think of the way ketchup won’t come out of the bottle, unless you shake it vigorously – then it flows out nicely onto your chips. (For more info on non-Newtonian fluids, read this Wikipedia article.)

But molasses changes its behaviour when it is cold; if the temperature drops it behaves more like a classic fluid. In particular, its viscosity increases dramatically in cold conditions. Sharp explained that when they tested molasses in a cold room, “It took several minutes just to pour 48 millilitres into a graduated cylinder,” Sharp says. There’s a reason for the adage ‘Slow as molasses in January’.

So what made the molasses flood, which happened in January, move so fast? The answer is gravity currents. These take effect when a dense fluid (molasses) spreads horizontally into a less dense fluid (air). The density of the molasses alone would account for the speed of its initial spread. “Basically, you got bowled over by a tidal wave of molasses,” says Sharp, likening the effect to a sticky-sweet tsunami made of a substance 1.5 times as dense and several thousand times more viscous than water.

The molasses in the tank was slightly warmer than the surrounding air, but once it poured out of the ruptured tank and spread, it cooled quickly, making it more viscous.

Victims were left waist-deep in the goo, which behaved like quicksand – the more they thrashed about the more deeply they were trapped.

A classic case of too much of a good thing being really bad for you!

Source: https://www.newscientist.com/article/2114116-incredible-physics-behind-the-deadly-1919-boston-molasses-flood/

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