Naples:life,death &
                Miracle contact:Jeff Matthews

 entry Apr 2010, update Nov 2018

Big Archie & Living on the Edge

The Archiflegrean Caldera is the area bounded         
by the red lines with wedges. The area shown         
  in the map is about 30 km/20 miles across.     
I have always known that the area is volcanically a bit “iffy.” After all, from my balcony (about where the word "Chiaia" (lower right) is, above "Bay of Naples" in this image) I can see Mt. Vesuvius way over to the east. It (Vesuvius, not my balcony), has been quiet, lo, these last 66 years. (And that’s just one 6 short of a hell of a volcano!) But that’s only the tip of the volcano. Vesuvius is a child (less than 20,000 years old) compared to the roaring land-forming engines that earlier produced almost everything else in this image: the Fuorigrotta Plain and everything to the west of the Posillipo hill until you get to Capo Miseno, Monte di Procida, and Cuma at the western end of the Gulf of Naples. There are still remnants (Monte di Procida is one) of the cataclysmic caldera collapse of the so-called Archiflegrean volcano or Caldera (also known as the Campanian Ignimbrite Eruption); it was a super-volcano that exploded 40,000 years ago, tearing the roof off itself, settling back to sea-level and below. Bits of the ancient volcano rim of Big Archie (my term of endearment) are very visible on the surface. As you go through the area, you go through Agnano, the Astroni, and other places, all parts of the Campi Flegrei, or Flegrean Fields. Flegrean means "fiery." They are remnant and extinct (probably) volcanoes from secondary eruptions from the so-called Second Flegrean Period (c. 20,000 ago). That second, smaller area is simply named the Flegrean Volcano (bounded by the black lines with wedges, centered on the town of Pozzuoli). One area, the Solfatara, is still wheezing if not active, but it could erupt, they say. The Flegrean Volcano produced the Posillipo hill, the slopes of which attracted the Greeks, then Romans and now a bunch of other optimists who never studied geology.

(See this page for a photograph shot from the NE rim
the Camaldoli convent across the entire Campi Flegrei to the remnant SW rim above Baia.)

update added Nov. 2018 -  See this link for the latest studies on the ominous "bulge beneath the bay."

A bit to the east, I (and thousands of others —photo, right) live on the northern slope of another earth-engine called the Chiaia volcano (again, right where that word, "Chiaia" is in the above image). It had not occurred to me before, but as I look from my balcony to the south, the postcard below me is a vast amphitheater, a semi-circle with the Egg Castle on the left and Mergellina on the right with that western end of the amphitheater extending out to a point called Cape Posillipo. The stage below me (photo, below) is at sea-level and Capri is dead ahead, a backdrop, 25 miles away. From the slopes of the ancient Chiaia crater, we all have great seats for whatever is to come. That original explosion was a piker compared to Big Archie of some eons earlier, but it did form what is now the Chiaia section of Naples and most of the Vomero hill above it.

From the sea, the Vomero hill above me seems to run over to the west and form a single long ridge with the Posillipo hill. That is deceptive. They do run together, after a fashion, but only because the Chiaia volcano came first, and then the smaller-than-Archie Flegrean volcano to the west blew and spat out the Posillipo hill partially on top of it.

All of this volcanic activity has made the area rich in yellow tuff, a sandstone, the ubiquitous building material in Naples. I am currently in the midst of translating a book about the subsoil of Naples. Co-translator, Larry Ray, writes this in his presentation of the translation for the Napoli Underground website:

...the tuff sandstone strata are honeycombed with hundreds and hundreds of gigantic manmade cavities where the durable sandstone had been quarried and brought to the surface to build palaces, villas and other buildings over the centuries. Additionally other voids included railroad tunnels, ancient Greek and Roman aqueducts and water reservoirs, long tunnels from the city's pneumatic mail and message network from the early 1900's, as well as elaborate network of ancient as well as operating sewer lines, gas lines and other similar cavities...
All of that is a cause for concern in construction around here. There is not an area in the city that is not undermined in some fashion or other. And maybe not even a building. We get earth slides and cave-ins frequently. I have learned to be as fatalistic about that as I am about volcanoes. My Chiaia explosion must have come from right where that rich guy’s yacht is anchored. If Chiaia goes “ka-blooey” (to use the geological term) again, he’s a goner. But, then, so am I.

added May 12, 2019
an interesting update, to say the least, is here.

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The Solfatara, by Michel Wutky (1739 - 1723), an Austrian landscape painter.
Here is an overview of the geology of the Bay of Naples. This entry deals specifically with recent geological concerns about the area of the Campi Flegrei (or Phlegrei). Since the entire Naples area is tightly interwoven, you will find a lot of repetition, but more recent information may be new to you. As an intro, know that there is a "volcanic explosivity index" (VEI). It is a relative measure of the explosiveness of volcanic eruptions, using various indicators to tell you what this or that eruption was about. It tells you how much BULK (ejecta and pyroclastic material) there was in an eruption, HOW HIGH the eruptive cloud rose, and with what FREQUENCY the volcano has erupted in the past. It uses easy terms, from "gentle" to "mega-colossal". The scale is open-ended with the largest eruptions in history given a magnitude of 8. A value of 0 is for non-explosive eruptions. They eject almost nothing. If you're in the parking lot, wipe your windshield afterwards. At that other end,  8 is a mega-colossal explosive eruption and can eject enough pyroclastic (volcanic) substance to have a cloud column height of over 20 km (66,000 ft). The scale is logarithmic, with each interval on the scale a tenfold increase in ejecta. Thousands of years may pass between one 7 or 8 VEI and another one at the same spot.
Eruptiom of Vesuvius seen from the Bay of Naples, also by Michel Wutke     
Our "Campanian volcanic arc" includes a number of active, dormant, and extinct volcanoes centered on the Bay of Naples and includes Mount Vesuvius (painting, right), an active volcano that last erupted in 1944, and the Phlegrean Fields, a huge, ancient caldera (crater) containing the western area of Naples. The Campi Flegrei are a group of many extinct craters, evidence of ancient eruptions; however, also included in this area is Solfatara (painting above), a shallow volcanic crater still giving off jets of sulfur fumes and, thus, still active. Solfatara is the thrust of this entry. I am ignoring the big picture —we are sitting on a super-volcano (similar to Yellowstone in the U.S.) If that goes, your smart-phone will suddenly get very stupid.
"Solfatara" is really a generic term. Ours is just one of many in the world. They feature fumaroles (or fumeroles), vents in the surface of the Earth that emit hot volcanic gases and vapors without any accompanying liquids or solids. Fumaroles are features of the late stages of volcanic activity but can also precede an eruption and, indeed, have been used to predict  eruptions. Most fumaroles die down within a few days or weeks of the end of an eruption, but a few have great staying power, lasting for decades or longer. An area containing fumaroles is known as a "fumarole field". Our Solfatara is such a field. Most of the vapor coming out of fumaroles is steam, formed by the circulation of groundwater through heated rock. This typically goes along with volcanic gases given off by magma cooling deep below the surface. These volcanic gases include sulfur compounds, such as various sulfur oxides and hydrogen sulfide, hydrogen chloride, hydrogen fluoride, and other gases. Fumaroles that emit significant sulfur compounds are thus a solfatara.

Volcanic deposits showing eruptions in what would one day be the Phlegrean Fields have been dated to 315,000; 205,000; 157,000; and 18,000  years ago. The Phlegrean Fields are the Naples districts of Agnano and Fuorigrotta, the area of Pozzuoli, Bacoli, Monte di Procida, Quarto, and the Phlegrean Islands (Ischia, Procida and its tiny satellite island of Vivara).
The gated entrance to our Solfatara is near Pozzuoli.


A 2009 journal article said that inflation of the caldera center near Pozzuoli might mean an eruption within decades. In 2012 the International Continental Scientific Drilling Program planned to drill 3.5 kilometers (11,000 feet) below the earth's surface near Pompeii to monitor the massive molten rock chamber below and provide early warning of an eruption of Vesuvius. Local scientists were worried that such drilling might itself cause an eruption or earthquake, so in 2010 the Naples city council halted that drilling. Program scientists then said the drilling was no different from industrial drilling in the area, so the mayor allowed the project to go forward. A study from the National Institute of Geophysics and Volcanology (INGV) shows that the volcanic unrest of the Campi Flegrei caldera from January 2012 to June 2013 had shown rapid ground uplift of about 11 cm (4 in), with a peak rate of about 3 cm (1 in) per month during that period. It added that from 1985 to 2011 ground uplift was mostly linked to the caldera's "hydrothermal system" (the action of hot water beneath the surface that changes the distribution of minerals, but that this relation broke down in 2012. The driving mechanism of ground uplift changed to
—and is now— a periodic build-up of magma within a flat sill-shaped magma reservoir about 3,000 m (9,843 ft) in depth, 500 m (1,640 ft) south of the port of Pozzuoli. In December 2016, activity became so high that they feared an eruption. In May 2017 a new study by University College London and the Vesuvius Observatory published in Nature Communications said that an eruption might be closer than previously thought. (We are back to talking about the Solfatara volcano, not Vesuvius. That was just to relax you a bit.) The study found that the geographic unrest since the 1950s has a cumulative effect, causing a build-up of energy in the crust and making Solfatara volcano more susceptible to eruption. On 21 August 2017 there was a magnitude 4 earthquake on the western edge of the Campi Flegrei. Two people were killed and many more injured in Casamicciola on the northern coast of the island of Ischia, south of the epicener. A February 2020 status report said the "inflation around Pozzuoli has continued at steady rates with a maximum average of 0.7 cm per month since July 2017." Gas emissions and fumarole temperatures did not change significantly. On April 26, 2020, a moderate earthquake swarm hit the Campi Flegrei caldera, 34 quakes ranging from magnitude 0 to 3.1 with the swarm centered around Pozzuoli. The strongest quake in that series was a 3.1.  That was the strongest one in the caldera going back to the last major period of unrest and rapid uplift in 1982-1984. However, no new fumaroles were reported. In its weekly bulletin of April 6, 2021, the INGV reported that part of the Campi Flegrei had an average uplift rate of 13mm per month +/- 2mm. The strongest quake since March, 2021 was 2.2, and their station measured 72.5cm of uplift since January 2011.


Fumaroles break down rock around the vent, and active fumaroles are a hazard due to their emission of hot, poisonous gases. On Sept. 13 2017, a fatal accident at Solfatara occurred when an 11-year-old boy fell into a hole in the ground; his parents fell in as well when they rushed to save him. All three suffocated quickly from the concentrations of carbon dioxide and hydrogen sulfide that build up just below the surface. The hole was not more than 3 or 4 meters deep (10 to 12 feet). Documentaries on the Solfatara drill it into you: This is an active volcano and a dangerous one! This is not an amusement park, not a fun fair, not "Volcano World." This is smack on top of the old Campanian Ignimbrite eruption. Do not take it lightly. It has enough power down there to put Vesuvius to shame. Litigation is still going on. The boy had not wandered off a marked trail. The ground just gave way, according to an eye-witness.
   The consensus is that while Campi Flegrei has seen more unrest lately, an eruption in the area is unlikely to happen in
the near future. Though a large-scale eruption like the one that occurred 39,000 years ago is very unlikely, a new
caldera-forming eruption (that is, another Solfatara), in the area is possible. Given the unrest at the port of Pozzuoli, it is likely that the next eruption will be in that region of the caldera. Their ads say they are open again. Have a nice day.

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