How Earthquakes and Weather Contributed to the Black Death


By Dorsey Armstrong, Ph.D.Purdue University

In the Middle Ages, according to the medical faculty at the University of Paris, what contributed to the Black Death was that the air everyone breathe became infected by noxious vapors and spread about through gusts of wind. They suggested poisonous air from places like swamps, lakes, and unburied or unburned corpses probably contributed to the epidemic.

Image of a swamp.
According to the medical faculty at the University of Paris, the poisonous air from swamps had some link to the Black Death. (Image: Abbie Warnock-Matthews/Shutterstock)

Corpses Didn’t Just Smell

Any medieval person who had had any experience with warfare or surviving a siege of a city knew that having corpses lying around was not conducive to the continued health of the population. 

This is why there were so many mass graves during the plague—it might have been easier to simply leave the dead where they fell, or inside their homes, but enough civic leaders recognized the threat to sanitation if this were permitted to happen. 

Image of a medieval graveyard.
Most people who had been to war knew that besides the smell, it was highly likely that people in close proximity of corpses would become sick. (Image: Baloncici/Shutterstock)

Those people who were willing to take on the job of transporting and burying corpses were able to command very high wages during the plague years. While most medieval people believed that they were affected by astrology, some scholars of the day completely discounted these planetary conjunctions and eclipse explanations.

Plague from Under the Earth

Although the Paris medical faculty did believe the plague had to do with astronomy, in addition to the planetary issue, they added:

Another possible cause of corruption, which needs to be borne in mind, is the escape of the rottenness trapped in the center of the Earth as a result of earthquakes—something which has indeed recently occurred.

Some scholars felt quite strongly that this was the whole answer right there. In a chronicle from Germany, one scribe makes the argument that astrological conjunctions happen all the time, and there’s not usually a plague occurring in the aftermath.

But what’s less common are earthquakes, and the scribe finds this the most plausible explanation, on the following grounds:

When air that is full of vapors and earthy fumes is enclosed and shut up for a long time in the prison of the Earth, it becomes so corrupted that it constitutes a potent poison to men. This is especially marked in caverns or deep inside the Earth as is often seen in the case of wells that have been unused for a long time. For when such wells are opened in order to be cleaned out it often happens that the first man to enter is suffocated, and sometimes in turn those who follow him.

This is a transcript from the video series The Black Death: The World’s Most Devastating PlagueWatch it now, on Wondrium.

Earthquakes Might Have Contributed to the Black Death

The anonymous chronicler notes that “it is a matter of scientific fact” that earthquakes are caused when noxious fumes build up inside the Earth and finally burst out, and that there was an earthquake in Germany on St. Paul’s day in 1347, and after this, numerous people began to die from exposure to these vapors and fumes, which were then spread by storms, wind, and lightning. 

Also, this cause makes more sense because the planets should affect everyone on Earth the same, but from his own experience, the poor were being struck down much more quickly and in greater numbers than the rich. He has an answer for this, however. 

The chronicler argues that this is because the higher classes consume rich food and drink, which makes them hot, and “what is inside them leaves no room for such fumes and blocks their entry”. Still, even they won’t be able to avoid it forever, he concedes.

Learn more about literary responses to the Black Death.

Strange Weather Transported Miasma

So, while many medieval experts disagreed on the source, they did agree on the fact that there was some sort of bad air that served as the means by which the infection was transmitted, and they even came up with a name for it, which we still use today—miasma.

Making the outbreak and the spread of miasma that much worse, according to almost every expert, was the fact that for the last few years, the weather across Europe had been really unpredictable. 

The Paris medical faculty affirmed that last winter was not as cold as it should have been, with a great deal of rain; the spring windy and latterly wet. Summer was late, not as hot as it should have been, and extremely wet—the weather was very changeable from day to day and hour to hour. Autumn, too, was very rainy and misty.

Learn more about the economics of the Black Death.

The Non-Scientific Explanation

Image of rain pouring on the sea with mountains in the background.
The winters leading up to the plague outbreak were unusually warm, so the infection season was extended. (Image: Kotenko Oleksandr/Shutterstock)

When there are a series of earthquakes followed by pestilential disease, it’s pretty hard for the medieval mind not to see a connection. But it’s interesting to note the way in which the scientific explanations—planets, earthquakes, eclipses, weather—are able to stand right alongside a belief that the Black Death was also a punishment from God. 

The weather also probably played a role in that the winters leading up to the plague outbreak were unusually warm, as the Paris medical faculty observed. The black rat flea usually goes into hibernation in the winter, but if the weather was unseasonably warm, some of the fleas might not have hibernated, which means that what might be called the infection season was extended. And, of course, the idea that infected air from unburied corpses might be a contributing factor is absolutely correct.

Common Questions about How Earthquakes and Weather Contributed to the Black Death

Q: How did scholars in the Middle Ages view the relationship between earthquakes and the Black Death?

They believed that noxious fumes were trapped beneath the Earth, which eventually got released, leading to earthquakes. These fumes were then spread by storms, wind, and lightning, contributing to the Black Death.

Q: What is miasma?

Many medieval experts agreed on the fact that there was some sort of bad air that served as the means by which the infection was transmitted. They called this miasma.

Q: What effect did bad weather have on the Black Death?

Because of the strange weather before the plague arrived, people thought this contributed to the Black Death, but it was not in the way they quite thought. Some unusually warm winters might have meant that some of the black rat fleas, which usually go into hibernation in the winter, had not hibernated, extending the infection season.

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