Integrative Natural History of Mount Vesuvius & the Gulf of Naples, Part 3: The Gran Cono Interior, and a Violation of Understandings | Campania, Italy
Taken along the summit rim trail of Mount Vesuvius. Looking at a portion of the interior of the Gran Cono crater.
When I was a child, my father spent hours, with Chicago Motor Club maps spread out before him, planning a family trip to the Pacific Northwest and the Cascade Range. In his own childhood he'd been to Crater Lake in Oregon and for good reason thought it the most beautiful place on Earth.
While in my early years we did get to many splendid places in the West, including the Yellowstone Caldera and the Canadian Rockies, we never quite made it all the way to the Cascade peaks that form the magnificent (and dangerous) continental volcanic arc a little inboard from the subducting Juan de Fuca Plate. As a matter of fact, I didn't get to them by myself until my middle adulthood, long after I'd been to the tops of Vesuvius, Etna, and Stromboli.
Of that Italian triad, Vesuvius was my first ascent. And it was the first place I'd ever visited that seemed to be chronologically unhitched from the landscape below and around it.
Whether they're currently erupting or not, the world's great volcanic summits invest one with the feeling that the planet itself is still very young and forming. It's an eerie thing to suddenly find oneself in an early chapter of the Earth's creation—the Hadean, perhaps, or the dawn of the Eoarchean, some 4 Ga before the birth of our species.
That makes it all the more ironic that the geology here is actually remarkably young. This fact is made abundantly clear in one of my main sources for this series, "Volcanic Evolution of the Somma-Vesuvius Complex (Italy)," Sbrana et al., Journal of Maps, January 2020.
If I'm interpreting one of that article's illustrations correctly, the upper portion of the crater wall shown in the photo above was almost all produced in the 1944 eruption, during the Allies' torturous advance up the Italian peninsula. Only the lowest quarter of the visible strata are older; and they just date to the period 1913-1930.
Incidentally, notice that I used the term strata for rock units that are obviously igneous. If you're someone who's taken a single geology course, perhaps as a 100-level science elective in college, you probably think that strata (synonymous with layers and beds) are the sole intellectual property of sedimentary rocks.
So it appears I'm violating a basic understanding uttered by countless Earth-science instructors. But it turns out that what they told you is something I call a beginner's truth—an educatively helpful fact that is partly abrogated as one gains additional experience.
It's true that a nice set of stacked beds is an excellent way to identify sedimentary rocks. But in composite volcanoes like Vesuvius, also known as stratovolcanoes for good reason, you'll see striking patterns of alternating layers, too. In this case, though, they're not made of sandstone, limestone, or some other clastic or chemically precipitated type. Instead, they're a succession of tephra (ash, lapilli, pumice, and other ejected particles) and lava flows that poured onto the surface while still in a liquid state.
In Part 1 of this set, I discussed the petrology and predominant rock types of Vesuvius' more recently erupted material. But in this post, instead of focusing on the arcanities of tephrite, phonolite, and their intergradations, let's just identify what beds are lava and which are the tephra.
Fortunately, this is one of the best places in the world to see the inner structure of a stratovolcano: the crater is about 500 m (1,640 ft) wide and 300 m (984 ft) deep. And its almost-vertical walls are nothing less than the opened pages of a geology textbook.
First of all, the sunlit, reddish-brown material blanketing the rim is mostly tephra. When you actually walk on it, it has a crunchy, granular to dusty texture.
Farther down the wall, in the shade, the tephra takes on a darker aspect. In contrast, the lava strata are lighter-toned and more massive (thicker). See how many different layers you can actually count. Each bed represents its own geologic story worthy of remembrance.
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 3: The Gran Cono Interior, and a Violation of Understandings | Campania, Italy
Taken along the summit rim trail of Mount Vesuvius. Looking at a portion of the interior of the Gran Cono crater.
When I was a child, my father spent hours, with Chicago Motor Club maps spread out before him, planning a family trip to the Pacific Northwest and the Cascade Range. In his own childhood he'd been to Crater Lake in Oregon and for good reason thought it the most beautiful place on Earth.
While in my early years we did get to many splendid places in the West, including the Yellowstone Caldera and the Canadian Rockies, we never quite made it all the way to the Cascade peaks that form the magnificent (and dangerous) continental volcanic arc a little inboard from the subducting Juan de Fuca Plate. As a matter of fact, I didn't get to them by myself until my middle adulthood, long after I'd been to the tops of Vesuvius, Etna, and Stromboli.
Of that Italian triad, Vesuvius was my first ascent. And it was the first place I'd ever visited that seemed to be chronologically unhitched from the landscape below and around it.
Whether they're currently erupting or not, the world's great volcanic summits invest one with the feeling that the planet itself is still very young and forming. It's an eerie thing to suddenly find oneself in an early chapter of the Earth's creation—the Hadean, perhaps, or the dawn of the Eoarchean, some 4 Ga before the birth of our species.
That makes it all the more ironic that the geology here is actually remarkably young. This fact is made abundantly clear in one of my main sources for this series, "Volcanic Evolution of the Somma-Vesuvius Complex (Italy)," Sbrana et al., Journal of Maps, January 2020.
If I'm interpreting one of that article's illustrations correctly, the upper portion of the crater wall shown in the photo above was almost all produced in the 1944 eruption, during the Allies' torturous advance up the Italian peninsula. Only the lowest quarter of the visible strata are older; and they just date to the period 1913-1930.
Incidentally, notice that I used the term strata for rock units that are obviously igneous. If you're someone who's taken a single geology course, perhaps as a 100-level science elective in college, you probably think that strata (synonymous with layers and beds) are the sole intellectual property of sedimentary rocks.
So it appears I'm violating a basic understanding uttered by countless Earth-science instructors. But it turns out that what they told you is something I call a beginner's truth—an educatively helpful fact that is partly abrogated as one gains additional experience.
It's true that a nice set of stacked beds is an excellent way to identify sedimentary rocks. But in composite volcanoes like Vesuvius, also known as stratovolcanoes for good reason, you'll see striking patterns of alternating layers, too. In this case, though, they're not made of sandstone, limestone, or some other clastic or chemically precipitated type. Instead, they're a succession of tephra (ash, lapilli, pumice, and other ejected particles) and lava flows that poured onto the surface while still in a liquid state.
In Part 1 of this set, I discussed the petrology and predominant rock types of Vesuvius' more recently erupted material. But in this post, instead of focusing on the arcanities of tephrite, phonolite, and their intergradations, let's just identify what beds are lava and which are the tephra.
Fortunately, this is one of the best places in the world to see the inner structure of a stratovolcano: the crater is about 500 m (1,640 ft) wide and 300 m (984 ft) deep. And its almost-vertical walls are nothing less than the opened pages of a geology textbook.
First of all, the sunlit, reddish-brown material blanketing the rim is mostly tephra. When you actually walk on it, it has a crunchy, granular to dusty texture.
Farther down the wall, in the shade, the tephra takes on a darker aspect. In contrast, the lava strata are lighter-toned and more massive (thicker). See how many different layers you can actually count. Each bed represents its own geologic story worthy of remembrance.
The other photos and descriptions of this series can be found in my Integrative Natural History of Mount Vesuvius & the Gulf of Naples album.