VOLCANOLOGICAL EXCURSION TO CAMPI FLEGREI

(based on "Excursion Guide to Campi Flegrei", Campi Flegrei-Campania Felix; Giacomelli & Scandone, Liguori Ed., Naples, 1992)

The proposed excursion allows the most significant products of the Campi Flegrei volcanoes to be seen in a few hours. The excursion can be made by car, but some places can be reached with public transport takeng the Cumana railway to Terme station, one can walk to Pozzuoli and look at outcrops along the coast road. The Cumana railway can then be taken from Pozzuoli to Lucrino, to visit Averno Lake and, eventually, to climb Monte Nuovo. Again using the Cumana, one can reach Torre Gaveta and stop n. 12. The Solfatara crater is more easily reached using the "Metropolitana"railway, leaving the train at Pozzuoli station. The observation points are shown on the map with squares.

1) The excursion starts from Mergellina, going up along Via Orazio. An old quarry of Neapolitan Yellow Tuff is visible at the right after the first turn. The tuff has a structure with light cross-laminations. The Neapolitan Yellow Tuff is the product of the major eruption of Campi Flegrei occurred about 12,000 years ago, which caused caldera formation.

2) Proceeding along Via Petrarca, after about one kilometre from stop 1 and at a wide bend to the right, the Yellow Tuff is again visible below the road to the left. A vertical wall 40-50 m high, shows the stratification and the immersion toward the sea of the Yellow Tuff.

3) This stop is reached by proceeding along Via Petrarca until arriving at the road which goes to Coroglio. Here, one can stop after passing below a bridge and see the entire extent of the Campi Flegrei caldera. The Nisida islet is visible to the left; it is one of the volcanoes which was built up after caldera formation; Capo Miseno, Procida and Ischia are visible in the background. Pozzuoli can be seen at the midpoint along the Gulf, immediately before the lava-dome on which the Air Force Academy is built. To the right is the district of Naples called Fuorigrotta and with, in the background, the great crater of Astroni, which formed 3,700 years ago, and the Agnano depression. The Neapolitan Yellow Tuff is visible on the left along the road which goes down to Coroglio.

4) Go down to Coroglio and take Via Napoli. At the Cumana station of Terme the typical products of several pyroclastic flows and surges are visible on the wall in front of the sea. The products have a ruddy to yellowish colour and have sand-wave laminations; they belong to the eruption of Monte Spina which occurred 4,200 years ago.

5) About one km beyond the previous outcrop is the lava dome of "Accademia". The lavas visible to the right have a dense and lithoidal aspect in the upper part of the dome and are fragmented toward the lower part because of cooling during emplacement. The dome is one of the few examples of lava eruption at Campi Flegrei and was formed by the slow extrusion of a viscous magma depleted in gas.

6) Before entering Pozzuoli, a shore is visible to the left. This shore formed between 1982-84, during the last episode of ground inflation. Previously, the sea had reached the side of the old road flanking the buildings. Rione Terra is visible in the background. It was the old town and, built on a hill of Neapolitan Yellow Tuff, was evacuated in 1970.

7) The "Serapeo" is in the centre of Pozzuoli, a few tens of metres on the right, beyond the ticket offices for the ferries. The Serapeo or Macellum was a roman market built in the II century B.C. It was slowly submerged by the subsidence of the ground and as early as in the I century A.D., it was necessary to rebuild a new floor. In the IX century A.D., the coastal area of Pozzuoli was reportedly submerged by one fathom of water. The holes left by marine molluscs on the three bigger columns testify a submersion of about 10 metres below sea-level. The movement of the ground changed direction sometime before 1538, the date of the eruption of Monte Nuovo. A 6-metre uplift is reported to have occurred in the two days before the eruption. Subsidence took place again after the eruption and continued until 1970 when the movement of the ground reversed. Between 1970 and 1984, a maximum inflation of 320 centimetres was measured by repeated levellings made by the Osservatorio Vesuviano. Since 1985 the ground has again been deflating.

8) Take the coastal road to Arcofelice; the marine terrace of "La Starza" is visible on the right. It is a rock wall 40 m high, which borders the road and is composed entirely of alternating marine and volcanic products. It was raised to the present height between 10,000 and 5000 years ago, probably as a result of a shallow magmatic intrusion.

9) Upon reaching Arco Felice, proceed toward Lake Lucrino. A road to the right, immediately before the lake, goes toward Lake Averno. The Averno lake is the crater of a volcano formed 3700 years ago within an older volcano named Archiaverno. The products of the Averno eruption consists of a basal pumice deposit overlain by pyroclastic flow deposits. The Averno was considered by the Greeks and Romans to be the entrance to Hell, because of the abundant fumes rising from it. The name, in Greek, means "with no birds", because they were killed on flying into the gases. Monte Nuovo is visible to the right of the lake, toward the sea. It is the cone produced by the last eruption of Campi Flegrei, in 1538. In the background, there is the so-called temple of Apollo, which was not destroyed by the low-energy eruption of 1538. However, the eruption did cause the destruction of a small village called Tripergole.

10) Proceed toward Baia; the products of the volcanoes of Mofete and Baia are visible immediately before the village of Baia. Here, you can visit the Roman thermal baths, which were possibly part of the Imperial House of the Caesars. The Fondi di Baia craters are visible after the second turn on the road toward the Aragonese castle, going in the general direction of Bacoli. They belong to the later period of activity of Campi Flegrei and formed approximately 8,000 and 5,000 years ago. Upon reaching Bacoli, turn to the right toward Monte di Procida and follow the road which goes up hill. At the top of the hill, stop at the view points to the left of the road. The volcano Capo Miseno is visible to the right and, immediately below, can be seen the Porto Miseno volcano with the small peninsula of Punta Pennata. The port of Miseno was the site of the Roman fleet at the time of the 79 A.D. eruption of Vesuvius, and it was from here that Pliny the Elder sailed to the rescue of the endangered people.

11) Proceed toward Monte di Procida and go down to Acquamorta beach. Here the products of the older activity of Campi Flegrei and Procida are exposed. The scoria deposits belonging to the San Martino lava dome can be seen at the far end of the beach on the right. They are covered by pumice-fall deposits of eruptions from Ischia. An horizon of alternating grey ashes and black lapilli marks the products of Fiumicello. The eruptive center of the Fiumicello Formation is on Procida island and the products are widely distributed on Procida and Monte di Procida; the typical facies on Procida are those of a base surge deposit found in the Fiumicello locality, whereas the same formation outcrops on Monte di Procida as a fall deposit with alternating grey ash and black lapilli. The age of the paleosol underlying this deposit is 31,700 years. On top of the Fiumicello formation it is possible to see some paleosol alternating with pumice-fall deposits. The lower pumice-fall belongs to the basal layer of the S. Martino pyroclastic flow, not visible on this side of Monte di Procida, but which makes up the small islet visible in the background. A sequence of ash deposits lies immediately below the Museum Breccia formation, which pinches out on the side of a paleo-valley. The thickness and character of the Museum-Breccia is better seen on the other side of the beach, where it immediately overlies a paleosol. The age of this formation is approximately 18,000 years. The Museum Breccia deposit is made up by an agglomerate of lithic blocks of sedimentary and volcanic rocks, pumices, obsidians and is thought to be the result of a violent explosive eruption. The products of Torregaveta and the Neapolitan Yellow Tuff overlie the Museum Breccia. The general stratigraphic sequences of this area are shown in fig.

12) Go back to Monte di Procida and proceed toward Fusaro. The road is always flanked to the left by the products of the Neapolitan Yellow Tuff; take the last road to the left when the products do not any longer border the road. The big cliff facing the sea shows the contact between the Neapolitan Yellow Tuff (as shown in the sketch) and the underlaying formations of Torregaveta (14,000 years), the Museum Breccia, etc. Looking to the North, the products of the Neapolitan Yellow Tuff still preserve the original stratification, climbing a hill now eroded by the sea.

13) In the background you can observe the hill of Cuma with its archeological excavations of the first Greek colony of Southern Italy. You can reach the excavations following the coastal road which borders Lake Fusaro.

14) On the way back to Naples do not take the "Tangenziale", but follow the Domiziana road. Along the road you can see on the left the Anfiteatrum Flavius and, after 1 kilometer, the Solfatara volcano. Solfatara is privately owned and a ticket must be purchased to enter. The site belongs to the last phase of activity in Campi Flegrei (4,500-3,500 years ago) and is still the site of significant fumarolic activity. Solfatara crater is made up of a sequence of pyroclastic deposits: at the base is a phreato-magmatic breccia overlain by pyroclastic-flow deposits, mostly altered by fumarolic activity. These products cover the so-called Accademia dome, which had been emplaced previously. Many lava pieces belonging to the dome can be found in the basal breccia. The temperature of some fumaroles and the reducing capacity of gases are monitored as part of the volcanic surveillance of Campi Flegrei. During the recent seismic crisis between 1983-1985, the area below the Solfatara was shaken by the most energetic earthquakes occurring during the seismic swarm (magnitude 4+). The Solfatara has also been the area of an abnormal horizontal stretching. Cracks are still visible on the floor of the crater. A new fumarolic vent with pressurized steam opened in December 1984 on the north-eastern part of the crater floor.


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