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.