A devastating geologic event in Indonesia may have helped defeat Napoleon

Nature

In 1815, a volcanic eruption in Indonesia sent shockwaves through history. It gave us science fiction. It gave us Dickensian Christmas (we’ll get to that in a bit). And now, it turns out it may also have played a role in the downfall of one of western history’s greatest generals, Emperor Napoleon Bonaparte.

Napoleon was brilliant, but when he marched onto the field at Waterloo, Belgium in June 1815, conditions were not in his favour. The French army was ill prepared for the pouring rain and thick mud, and historians believe those hostile weather conditions played an important part in Napoleon’s defeat.

And those weather conditions? Could very likely have been caused by the catastrophic eruption of Mount Tambora, which climaxed on 10 April 1815.

It was one of the most powerful volcanic eruptions in recorded history. It killed 100,000 people, and the vast amounts of ash its eruption column spewed 43 kilometres (27 miles) into the atmosphere shrouded the world, resulting in an event called the Year Without a Summer.

It was a dismal time. Small particles from the volcanic dust – particularly sulfur dioxide – blocked light from the Sun, causing a short-term cooling effect around the Northern Hemisphere. Crops failed, and many people died of starvation or cold in the year that followed the eruption.

In the summer of 1816, inclement weather kept a young Mary Shelley and her friends indoors in Geneva, where, desperate for something to do, they wrote stories. Shelley’s was the first draft of Frankenstein, arguably the first science fiction novel.

And Charles Dickens, born in 1812, and who grew up under the severe weather of Tambora, recreated those harsh conditions of his boyhood in A Christmas Carol, enshrining them in the collective consciousness.

The sulfur dioxide wouldn’t have reached Europe by the time of the Battle of Waterloo. But the eruption’s effects could still have been felt in Belgium as early as just two months after the eruption, according to planetary scientist Matthew Genge from Imperial College London.

He has discovered that electrified volcanic ash can reach and disrupt the electrical currents in the ionosphere at an altitude of over 50 kilometres (31 miles), the atmospheric level where clouds are formed.

When Tambora erupted, his paper suggests, the volcanic ash could have “short-circuited” the ionosphere, triggering cloud formation, which resulted in unusually high levels of rainfall.

“Previously, geologists thought that volcanic ash gets trapped in the lower atmosphere, because volcanic plumes rise buoyantly,” Genge said.

“My research, however, shows that ash can be shot into the upper atmosphere by electrical forces.”

Reliable weather data that can be used to evaluate this effect for the Tambora eruption are scarce, he notes in his paper. But Genge conducted a series of computer simulations that show that electrostatic levitation can lift volcanic particulates under 500 nanometres (0.0005 millimetres) as high as 100 kilometres, delivering charge into the atmosphere.

“Volcanic plumes and ash both can have negative electrical charges and thus the plume repels the ash, propelling it high in the atmosphere,” Genge explained.

“The effect works very much like the way two magnets are pushed away from each other if their poles match.”

And just a small amount of that ash would be sufficient to have an abrupt global effect on cloud formation.

Although Tambora data may be unavailable, there were other volcanic eruptions with enough data for Genge to cross-reference his findings. And they showed he may be onto something.

Almost immediately the eruption of Krakatoa in August 1883, global temperatures fell. During the eruption, rainfall declined – indicating the suppression of cloud formation.

And, after the eruption, there was an increase in the appearance of noctilucent clouds, which form in the ionosphere.

He also found reports of disturbances in the ionosphere after the 1991 eruption of Mount Pinatubo in the Philippines.

All these eruptions were huge. Krakatoa and Pinatubo were rated 6 on the Volcanic Explosivity Index, while Tambora was a 7 – the most recent 7 on record.

Although it may feel like volcanic activity around the world has been pretty intense recently, with an eruption in Vanuatu causing evacuations last month, Pinatubo remains the most recent 6.

(Italy’s Vesuvius was a 5 and Iceland’s Eyjafjallajökull, which disrupted air travel all over Europe for weeks in 2010, was a 4.)

Hopefully we’re not going to have a first-hand example to test out Genge’s theory – but it can perhaps help us understand history more fully.

“Victor Hugo in the novel Les Miserables said of the Battle of Waterloo: ‘an unseasonably clouded sky sufficed to bring about the collapse of a World’,” he said.

“Now we are a step closer to understanding Tambora’s part in the Battle from half a world away.”

The paper has been published in the journal Geology.

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