On the night before Napoleon Bonaparte was defeated at the 1815 Battle of Waterloo, heavy rains fell in the area where the seminal conflict was fought. According to some theories, Napoleon, worried that the mud would bog down his soldiers and artillery, delayed the advance of his troops until the ground was dry—a fateful decision that gave the opposing Prussian and British forces time to unite and deliver a final, crushing blow to Napoleon’s army.
Now, as Mindy Weisberger reports for Live Science, a new study posits that the inclement weather that may have led to Napoleon’s demise can be traced back several months before the battle, to the eruption of a volcano in Indonesia.
The new study conducted by Matthew J. Genge, an earth scientist at Imperial College London, does not focus primarily on the battle of Waterloo. Instead, Genge set out to show that volcanic ash can be ejected as high as the ionosphere, as he explains in the journal Geology.
Previously, geologists believed that volcanic plumes are propelled by buoyancy into the stratosphere, up to 31 miles above the Earth’s surface—but no higher than that. Genge, however, used computer modeling to show that electrostatic forces can lift ash all the way up to the ionosphere, between 50 to 600 miles above the Earth’s surface. In a statement, Genge explains that “volcanic plumes and ash both can have negative electrical charges and thus the plume repels the ash, propelling it high in the atmosphere. The effect works very much like the way two magnets are pushed away from each other if their poles match.”
When electrically charged particles reach the ionosphere, Genge adds, they can disrupt the climate by causing cloud formation and, ultimately, rain. This got Genge thinking about the 1815 Battle of Waterloo. In April of that year, around two months before the famed June battle, Mount Tambora on Indonesia’s Sumbawa Island underwent a catastrophic eruption. Around 10,000 people on the island were killed, and debris from the volcano blocked out the sun and plunged the Northern hemisphere into a period of unseasonable coolness.
But the chill would not have happened right away; as Genge writes in the new study, it took months before sulfate aerosols from the eruption reached Europe. Indeed, it was 1816—not 1815, when the eruption occurred—that was known as “the year without a summer.” Cloud formation caused by the levitation of ash into the ionosphere, however, could have had a more immediate effect, bringing stormy clouds to Europe—and, perhaps, to the battlefield of Waterloo.
British weather records from 1815 do, in fact, note that the summer of that year was unusually rainy. And Genge puts forth other evidence to suggest that volcanic eruptions can lead to unusual cloud formations shortly after they occur. In late August of 1833, another Indonesian volcano, Krakatau, erupted forcefully. In early September, observers in England recorded the presence of strange, luminous clouds, which, according to Genge, “strongly resemble” Polar mesospheric clouds—a type of cloud that forms up to 53 miles above the Earth’s surface. The presence of these clouds shortly after Krakatau “could suggest the presence of volcanic ash” high above the stratosphere.
Of course, even if the Tambora eruption brought about inclement weather, it is far from certain that stormy skies caused Napoleon’s defeat. As a 2005 paper in the Royal Meteorological Society notes, both sides of the conflict had to contend with the same weather conditions. And many other factors—including ill-advised tactical decisions—were at play. “Napoleon might indeed have won at Waterloo had the ground been dry,” the authors of that study write. “He might also have won had he outflanked the enemy rather than launch a bold frontal assault.”
Genge’s Napoleon theory is just that—a theory. But his research does suggest that volcanic ash can travel higher than climate experts previously thought, entering the upper atmosphere and, perhaps, causing short-term changes in the weather.