Phlegraean Fields - Geological Phases

Geological Phases

Three geological phases or periods are recognised and distinguished.

• The First Phlegraean Period. It is thought that the eruption of the Archiflegreo volcano occurred about 39.28 ± 0.11 ka. The dating of the Campanian Ignimbrite (CI) eruption to ~37,000 calendar years B.P. draws attention to the coincidence of this volcanic catastrophe and the suite of coeval, Late Pleistocene biocultural changes that occurred within and outside the Mediterranean region. These included the Middle to Upper Paleolithic cultural transition and the replacement of Neanderthal populations by anatomically modern Homo sapiens, a subject of sustained debate. No less than 150 km3 of magma were extruded in the CI eruption, the signal of which can be detected in Greenland ice cores. As widespread discontinuities in archaeological sequences are observed at or following the CI event, a significant interference with ongoing human processes in Mediterranean Europe is hypothesized. Abstract (older estimate ~37,000 years ago), erupting about 200 cubic kilometres (48 cu mi) of magma (500 cubic kilometres (120 cu mi) bulk volume) to produce the Campanian Ignimbrite. New research led by Liubov Vitalievna Golovanova and Vladimir Borisovich Doronichev of the ANO Laboratory of Prehistory in St. Petersburg, Russia, supports the hypothesis that these eruptions drove Neanderthals to extinction and cleared the way for modern humans to thrive in Europe and Asia. The area is characterised by banks of piperno and pipernoid grey tuff at Camaldoli hill, like in the northern and western ridge of Mount Cumae; other referable deep products are those found at Monte di Procida, recognizable in the cliffs of its coast.

• The Second Phlegraean Period. Between the 35,000-10,500 years ago, it is characterized by the yellow tuff that constitutes the rests of an immense underwater volcano (having a diameter of ca. 15 kilometres (9.3 mi) and Pozzuoli to its center) Approximately 12,000 years ago the last major eruption occurred, forming a smaller caldera inside the main one, centered on the town of Pozzuoli. This event produced the Neopolitan yellow tuff, referring to the characteristic yellow rocks there.

• The Third Phlegraean Period. Dated between 8,000 – 500 years ago, it is characterized by white pozzolana, the material that forms the majority of volcanos in Flegrei Fields. Broadly speaking, it can be said there was an initial activity to the south-west in the zone of Bacoli and Baiae (10.000-8.000 years ago); an intermediate activity in an area centred between Pozzuoli, Spaccata Mountain and Agnano (8.000-3.900 years ago); and a more recent activity, moved towards the west to form Lake Avernus and Monte Nuovo (New Mountain) (3,800–500 years ago).

Volcanic deposit indicating possible eruption dated Ar at 315, 205, 157 and 18.0 kya

The caldera, which now is essentially at ground level, is accessible on foot. It contains a large number of fumaroles, from which steam can be seen issuing, and over 150 pools of boiling mud at last count. Several subsidiary cones and tuff craters lie within the caldera. One of these craters is filled by Lake Avernus. In 1538, an eight-day eruption in the area deposited enough material to create a new hill, Monte Nuovo. It has risen about 2 metres (7 ft) from ground level since 1970. It is a volcano capable of producing VEI 7 eruptions, as large as that of Tambora in 1815. At present, the Campi Flegrei area comprises the Naples districts of Agnano and Fuorigrotta, the area of Pozzuoli, Bacoli, Monte di Procida, Quarto, the Phlegrean Islands (Ischia, Procida and Vivara).

A 2009 journal article stated that inflation of the caldera centre in the vicinity of Pozzuoli might presage an eruptive event within decades. In 2012 the International Continental Scientific Drilling Programme planned to drill 3.5 km (2.2 miles) below the earth's surface near Pompeii intending to monitor the massive molten rock chamber below in order to provide early warning of any eruption. Local scientists are worried that such drilling itself could initiate an eruption or earthquake. In 2010 the Naples city council had prevented the drilling project. Programme scientsts said the drilling was no different than industrial drilling in the area. The newly elected mayor allowed the project to go forward. A Reuters article emphasized that the area could produce a "super volcano" that might kill millions.