Integrative Natural History of Mount Vesuvius & the Gulf of Naples, Part 2: What's in a Name? | Campania, Italy
Facing more or less northward. Taken along the trail leading to the summit of Vesuvius.
Everyone knows that it was Mount Vesuvius that buried Pompeii, Herculaneum, and other ancient communities in AD 79. And everyone happens to be wrong, at least if one adheres to modern geologic and geographic jargon. In current terminology, it wasn't Vesuvius that wreaked that havoc, but the famous volcano's long-lived predecessor, Mount Somma.
According to an excellent paper and accompanying geologic map, "Volcanic Evolution of the Somma-Vesuvius Complex (Italy)" (Sbrana et al., Journal of Maps, January 2020), Mount Somma assembled itself as a major stratovolcano from about 44 ky to 22 ky ago. And then, from 22 ky to AD 79, it suffered a number of Plinian eruptions, each of which resulted in the collapse of its central cone and the formation of a caldera.
Whenever italicized terms begin to proliferate, it's time to stop and provide some definitions. Let's do this in tabular form:
Plinian eruption: named for that prolific letter-writer, Pliny the Younger, whose uncle (you guessed it—Pliny the Elder) was ancient Rome's foremost naturalist and seeker after the odd and curious. See the comments section of Part 1 for more on this dynamic duo.
Because Pliny the Younger did a superb job of describing the AD 79 event, that type of highly violent and destructive eruption now bears his name. As a great mass of pyroclastic material is shot high into the atmosphere, it forms a mushroom cloud that eventually suffers gravitational collapse and falls onto and buries surrounding terrain. So much of the underlying magma chamber is emptied in a short time that the volcano caves in under its own weight. The result is a
Caldera. Essentially this is just a very big crater that has formed due to the process of magma-chamber collapse described above.
So what is Vesuvius? It's the newer stratovolcano that has risen atop the Somma caldera since the 1600s AD. The latest alterations and additions to its Gran Cono summit and its downslope lava flows were made during its most recent major eruption, in 1944.
But this is very confusing if you happen to be a Classics scholar and you read the famous letter of Pliny the Younger concerning the AD 79 eruption (Epistulae 6.16) in the original Latin. You'll come upon this passage detailing the aforesaid eruption:
Nubes incertum procul intuentibus ex quo monte; Vesuvium fuisse postea cognitum est
My own crude translation of this is, "A cloud that came from a mountain not identifiable from this far away, but which was later understood to be Vesuvius." Hmm. This shows that what we now call Mount Somma the ancients called Vesuvius. Uffa!
So perhaps it's best to be a little vague, tolerant, and adjustable. Let's just use the term found in the article title cited above, "the Somma-Vesuvius Complex." In fact, I'm going to get even more sciency and abbreviate it to the SVC. How cool is that?
In this shot, the SVC can be categorized as:
- Vesuvius Gran Cono slope (angle of repose of about 30 degrees from horizontal): the dark portion at lower left, foreground;
- Somma caldera floor, with considerable tree growth;
- Somma caldera rim.
The rim is of special interest because it reveals classic stratovolcano composition (alternating layers of tephra and lava) as well as striking examples of dikes. The dikes resemble narrow, vertical walls projecting radially outward from the rim. In fact, they're former fissures or feeder channels for volcanic vents. Some of the magma they contained solidified within them, and created flat-sided bodies of rock considerably more resistant than the pyroclastic material around them.
The other photos and descriptions of this series can be found in my Integrative Natural History of Mount Vesuvius & the Gulf of Naples album.
Integrative Natural History of Mount Vesuvius & the Gulf of Naples, Part 2: What's in a Name? | Campania, Italy
Facing more or less northward. Taken along the trail leading to the summit of Vesuvius.
Everyone knows that it was Mount Vesuvius that buried Pompeii, Herculaneum, and other ancient communities in AD 79. And everyone happens to be wrong, at least if one adheres to modern geologic and geographic jargon. In current terminology, it wasn't Vesuvius that wreaked that havoc, but the famous volcano's long-lived predecessor, Mount Somma.
According to an excellent paper and accompanying geologic map, "Volcanic Evolution of the Somma-Vesuvius Complex (Italy)" (Sbrana et al., Journal of Maps, January 2020), Mount Somma assembled itself as a major stratovolcano from about 44 ky to 22 ky ago. And then, from 22 ky to AD 79, it suffered a number of Plinian eruptions, each of which resulted in the collapse of its central cone and the formation of a caldera.
Whenever italicized terms begin to proliferate, it's time to stop and provide some definitions. Let's do this in tabular form:
Plinian eruption: named for that prolific letter-writer, Pliny the Younger, whose uncle (you guessed it—Pliny the Elder) was ancient Rome's foremost naturalist and seeker after the odd and curious. See the comments section of Part 1 for more on this dynamic duo.
Because Pliny the Younger did a superb job of describing the AD 79 event, that type of highly violent and destructive eruption now bears his name. As a great mass of pyroclastic material is shot high into the atmosphere, it forms a mushroom cloud that eventually suffers gravitational collapse and falls onto and buries surrounding terrain. So much of the underlying magma chamber is emptied in a short time that the volcano caves in under its own weight. The result is a
Caldera. Essentially this is just a very big crater that has formed due to the process of magma-chamber collapse described above.
So what is Vesuvius? It's the newer stratovolcano that has risen atop the Somma caldera since the 1600s AD. The latest alterations and additions to its Gran Cono summit and its downslope lava flows were made during its most recent major eruption, in 1944.
But this is very confusing if you happen to be a Classics scholar and you read the famous letter of Pliny the Younger concerning the AD 79 eruption (Epistulae 6.16) in the original Latin. You'll come upon this passage detailing the aforesaid eruption:
Nubes incertum procul intuentibus ex quo monte; Vesuvium fuisse postea cognitum est
My own crude translation of this is, "A cloud that came from a mountain not identifiable from this far away, but which was later understood to be Vesuvius." Hmm. This shows that what we now call Mount Somma the ancients called Vesuvius. Uffa!
So perhaps it's best to be a little vague, tolerant, and adjustable. Let's just use the term found in the article title cited above, "the Somma-Vesuvius Complex." In fact, I'm going to get even more sciency and abbreviate it to the SVC. How cool is that?
In this shot, the SVC can be categorized as:
- Vesuvius Gran Cono slope (angle of repose of about 30 degrees from horizontal): the dark portion at lower left, foreground;
- Somma caldera floor, with considerable tree growth;
- Somma caldera rim.
The rim is of special interest because it reveals classic stratovolcano composition (alternating layers of tephra and lava) as well as striking examples of dikes. The dikes resemble narrow, vertical walls projecting radially outward from the rim. In fact, they're former fissures or feeder channels for volcanic vents. Some of the magma they contained solidified within them, and created flat-sided bodies of rock considerably more resistant than the pyroclastic material around them.
The other photos and descriptions of this series can be found in my Integrative Natural History of Mount Vesuvius & the Gulf of Naples album.