What are volcanoes? A medieval answer

An explanation of volcanoes and why they erupt from a medieval scientist. 

Volcanoes have long captivated human interest, with their awe-inspiring power and potential danger prompting centuries of inquiry into their origins. Among the early scholars delving into the mysteries of volcanic activity was Albertus Magnus (c.1200-1280), a German friar and later bishop renowned for his extensive scholarly contributions spanning diverse subjects from zoology to metaphysics. Revered as the patron saint of natural scientists, Albertus advocated for empirical investigation and experimentation as essential tools for understanding the natural world.

In the mid-thirteenth century, Albertus penned On the Causes of the Properties of the Elements, a seminal work exploring the nature of the earth. Within this treatise, he tackled fundamental questions such as the formation of mountains and valleys, attributing their creation to seismic activity, notably earthquakes. Drawing upon the insights of his predecessors, Albertus embarked on his own analysis, culminating in a discussion of volcanoes towards the conclusion of his book.


Illustration of Mount Etna as observed by the author in 1637. From Athanasius Kircher’s Mundus Subterraneus, 1664.

Albertus Magnus notably singled out Mount Etna, the renowned volcano located in Sicily, as a focal point for his examination of volcanic phenomena.

There is a volcano like it in many places. For there was one that was in the province of Swabia that burned for many years from the fire that shepherds made on it and then later it was extinct, as in our times Etna is almost completely extinct. And similarly there is a burning mountain near Liege, and when the rain trickles down upon its edges, smoke rises from it as if from a furnace. 


Albert proposed that the generation of subterranean fires beneath the earth’s surface required the combination of two specific materials: sulfur and naphtha. He elucidated that sulfur, a mineral abundantly present within the earth, served as one of the essential components in this process:

For sulfur burns underground easily either from the movement of the earth’s vapor, as fire is generated in a cloud, or from the motion and friction of the wind that has entered the ground through certain hollows, or even from the fact that the heat pressed into the ground by the sun’s rays is concentrated on one place by the surrounding cold, and then it kindles the materials found in that place.

Then he describes the second material, which was used in medieval warfare to cause fires:

For naphtha is a kind of pitch that is found in Persia, which has a glutinous and vicious fattiness that is very sticky and is somewhat like the lees of oil. When it is mixed together with sulfur, it becomes inflammable, and its fires adhered in an amazing fashion to whatever it is thrown against, and it can only be extinguished if the whole is covered at the same time.


Albert postulated that the interaction of sulfur and naphtha not only generated subterranean fires but also contributed to the formation of hot springs, where these materials would perpetually heat the water. In his view, the presence of water was insufficient to extinguish these fires. Additionally, Albert suggested that this combination of materials, when occurring on land, would give rise to the phenomenon of volcanoes:

For the material cause it that earth is sulfurous and mixed with oily naphtha, and the efficient cause is a vapor that is distributed in the ground and is unable to emerge. And because the sea water obstructs the ground’s pores and openings, for this reason it burns more quickly near the sea than it does elsewhere, and it burns as long as the matter has not been consumed, and it may burn for many years or perpetually if it happens that the matter is continuously replenished. And because a great deal of naphtha has been absorbed by certain rocks, when they are burned they remain very porous and light and float on the water, as pumice does.

Albert the Great’s book On the Causes of the Properties of the Elements, has been translated by Irven Resnick and published by Marquette University Press.


Top Image: Eruption of a volcano, from Conrad Lycosthenes’s Prodigiorvm ac ostentorvm chronicon