Over two centuries ago, the French army under the command of Emperor Napoleon Bonaparte was defeated by a British-led Allied army. The events of the famous Battle of Waterloo changed the course of European history, but if a new study is anything to go by, a natural calamity also contributed to Napoleon’s loss.

Historians have long suggested that rains and muddy conditions at the battlefield helped the Allied army defeat the French. But, the cause of these conditions, according to the study, was a volcano that erupted two months before the battle took place on June 18, 1815.

The thunderous eruption of Mount Tambora, located in the northern part of Indonesia’s Sumbawa island, ejected huge amounts of volcanic matter and killed nearly 100,000 people. It was so powerful that Earth witnessed a year without summer in 1816.

Most of the climatic changes occurring during this period are attributed to the volcanic ash and dust that rose into the sky, and researchers from Imperial College London believe the same factors created the rainy and muddy conditions contributing to Napoleon’s defeat.

They ran a series of experiments and found that electrostatic forces can hurl huge plumes of volcanic ash 62 miles up into the atmosphere, much higher than previously thought. At such levels, electrically charged volcanic ash could easily ‘short circuit’ the electric current of the ionosphere, forming a cloud cover big enough to make it rain heavily across Europe.

“Previously, geologists thought that volcanic ash gets trapped in the lower atmosphere because volcanic plumes rise buoyantly,” Matthew Genge, the lead author of the study, said in a statement. “My research, however, shows that ash can be shot into the upper atmosphere by electrical forces."

To prove this theory, Genge and his team ran a series of simulations aimed at witnessing the behavior of charged volcanic ash, essentially how far it could levitate. The work revealed that charged particles smaller than 0.2 millionths of a meter could go into the ionosphere.

"Volcanic plumes and ash both can have negative electrical charges and thus the plume repels the ash, propelling it high in the atmosphere,” Genge added. “The effect works very much like the way two magnets are pushed away from each other if their poles match."

As weather records for the year 1815 are scant, the researchers verified the finding by taking another volcanic eruption into account – the explosion of Krakatoa caldera in 1883 and Mount Pinatubo in 1991.

The rainfall data and shining cloud formation in the wake of these volcanoes indicated the impact of charged volcanic ash rising into the ionosphere. The researchers believe gaining more insight into these rare, luminous clouds could be the key to confirm the theory.

The study titled “Electrostatic levitation of volcanic ash into the ionosphere and its abrupt effect on climate” was published Aug. 21 in the journal Geology.