On June 18, 1815, in what is now Belgium, two armies of the Seventh Coalition – the British and the Prussian – met Napoleon's French forces at Waterloo. It proved to be a close call, but the continuous supply of Prussian troops, along with a failed final French attack, led to the Emperor’s defeat.
As it happens, the weather at the time was abysmal, with rain blanketing much of Europe, creating muddy, sticky terrain.
According to historians, this mud caused delays and problems for Napoleon’s forces. Although not the only factor, nor the most important, some have suggested that “Napoleon might indeed have won at Waterloo had the ground been dry” – and the world today would be a very different place if he did.
That’s where the new Geology paper, authored solely by Dr Matthew Genge, a geoscientist at Imperial College London, comes into it. He largely focused on the subject of ash being levitated up into the atmosphere for his work, but it’s the sole mention of the Battle of Waterloo at the end that’s understandably making headlines.
Enter, Tambora. This Indonesian volcano’s 1815 cataclysm may have taken place over many months, but its climactic blast on April 10 sent around 50 cubic kilometers (12 cubic miles) of fresh volcanic debris into the atmosphere.
There were pyroclastic flows, tsunamis, and large chunks of debris, all of which proved deadly. The ash veil also blanketed much of Indonesia, causing widespread crop failure. The United States Geological Survey (USGS) puts the casualties at 92,000, with the predominant cause of death listed as “starvation”.
Ultimately, though, it was the material that entered the stratosphere that proved to be a planetary game-changer.
Volcanic products can cause dramatic, temporary changes to the climate. Ash can darken the sky, and disrupt cloud formation. Sulfur dioxide gases can react with water and sunlight to form light-reflecting aerosols, and regions can suddenly cool down. Both can drift around the planet if they reach the stratosphere.
The Tambora eruption led to a global cooling of several degrees in 1816. Those in the Northern Hemisphere dubbed it The Year Without a Summer, one that featured, among other things, catastrophes around the world, from famines in Europe and China to monsoon-driven cholera spreads in India.
Tambora’s 1816 effects are well known, but it took several months for the gases and ash to spread across the world and make such horrific differences. How, then, could they affected the Battle of Waterloo, taking place in July of 1815?
Genge's suggestion is that ash could be pushed up into the ionosphere, the electrified and energetic part of the atmosphere that starts 80 kilometers (50 miles) above sea level.
Conventional wisdom suggests that ash can never reach this height because temperature changes in the stratosphere cancel out its natural buoyancy. However, it’s known that if you apply an electric field to certain tiny objects, they can levitate against the forces of gravity.
Volcanic ash, whose electrostatic properties are already known to generate lightning, can also be electrostatically levitated. Charged by sunlight, Genge told IFLScience that “it’s a big thing on asteroids and moons. In fact, the Apollo astronauts observed a horizon glow that came from dust levitated above the surface.”
In this case, the ash was negatively charged through jostling interactions with other ash particles. The overall negative charge of the eruption plume could then, theoretically, repel the ash to monumental heights.
Making some physical calculations, and assessing ionospheric disturbance signals from other colossal eruptions, Genge reasoned that fine volcanic ash could indeed be lifted into the ionosphere in this way. Putting all that charged ash up there would have caused a “short-circuit”, leading to a disruption of, then a minor spike in, cloud formation – and thereby causing more rain to fall.
This would have happened in the immediate aftermath of the April 10, 1815 blast. At the end of the paper, almost as an aside, it’s posited that this may have all played a role in the Battle of Waterloo.
Although it’s “difficult to say”, Genge opined that Tambora’s atmospheric tinkerings “may have serendipitously had a world-changing effect.”
It’s worth stressing that the hypothetical cloud spike merely correlated with the combat. It’s not possible to say if it directly had an effect on it, an obstacle that plenty of similar volcano-history mashup studies run into. Genge himself described the effect as “not very extreme”.
Even if we assume the well-reasoned electrostatic levitation effects in the paper hold water, at the end of the day, there’s considerable debate over which factors proved to be the most important in Napoleon’s defeat.
“Would Napoleon [have] won if it had been dry? Maybe, maybe not,” Genge added. “The Prussian army did arrive at the right time. With history, hindsight is a wonderful thing.”
His son happens to be a military historian. Asked for his opinion, he suggested that “Napoleon was ultimately doomed since you shouldn't try and fight most of Europe all at once.”