Campanian Ignimbrite eruption
The Campanian Ignimbrite eruption was a major volcanic eruption in the Mediterranean during the late Quaternary, classified 7 on the Volcanic Explosivity Index. The event has been attributed to the Archiflegreo volcano, the caldera of the Phlegraean Fields, located west of Mount Vesuvius under the western outskirts of the city of Naples and the Gulf of Pozzuoli, Italy. It was the largest explosive volcanic event in Europe in the past 200,000 years, and the largest eruption of Campi Fleigrei caldera.
Estimates of the date and magnitude of the eruption, and the amount of ejected material have varied considerably during several centuries the site has been studied. This applies to most significant volcanic events that originated in the Campanian Plain, as it is one of the most complex volcanic structures in the world. However, continued research, advancing methods, and accumulation of volcanological, geochronological, and geochemical data have improved the dates' accuracy.
The most recent results by radiocarbon and argon–argon dating are, respectively, 39,220 to 39,705 calendar year BP and year BP. The estimated eruptive volume in dense-rock equivalent is in the range of, and tephra has dispersed over an area of around, commonly referred to as the ash horizon Y-5. The accuracy of these numbers is of significance for marine geologists, climatologists, palaeontologists, paleo-anthropologists and researchers of related fields as the event coincides with a number of global and local phenomena, such as widespread discontinuities in archaeological sequences, climatic oscillations and biocultural modifications.
Etymology
The term Campanian refers to the Campanian volcanic arc located mostly but not exclusively in the region of Campania in southern Italy that stretches over a subduction zone created by the convergence of the African and Eurasian plates. It should not be confused with the Late Cretaceous stage Campanian.The word ignimbrite was coined by New Zealand geologist Patrick Marshall from Latin ignis and imber ) and -ite. It means the deposits that form as a result of a pyroclastic eruption.
Background
The Phlegraean Fields caldera is a nested structure with a diameter of around. It is composed of the older Campanian Ignimbrite caldera, the younger Neapolitan Yellow Tuff caldera and widely scattered sub-aerial and submarine vents from which the most recent eruptions have originated. The Fields sit upon a Pliocene – Quaternary Extensional domain with faults, that run North-East to South-West and North-West to South-East from the margin of the Apennine thrust belt. The sequence of deformation has been subdivided into three periods.Phlegraean Periods
- The First Period, which includes the Campanian Ignimbrite Eruption, was the most decisive era in the Phlegraean Fields' geologic history. Beginning more than 40,000 years ago as the external caldera formed, subsequent caldera collapses and repeated volcanic activity took place within a limited area.
- During the Second Period, the smaller Neapolitan Yellow Tuff eruption took place around 15,000 years ago.
- Eruptions of the Third Period occurred during three intervals between 15,000 and 9,500 years ago, 8,600–8,200 years ago and from 4,800 to 3,800 years ago.
In 2008 it was discovered that the Phlegraean Fields and Mount Vesuvius have a common magma chamber at a depth of.
The region's volcanic nature has been recognized since Antiquity, investigated and studied for many centuries. Methodical scientific research began in the late 19th century. The yellow tuff stone was extensively quarried for centuries, which left large underground cavities that served as aqueducts and cisterns for the collection of rain water.
In 2016 Italian Volcanologists announced plans to drill a probe deep into the Phlegraean Fields several years after the 2008 Campi Flegrei Deep Drilling Project which had aimed to drill a diagonal borehole in order to bring up rock samples and install seismic equipment. The project was suspended in 2010 due to safety problems.
Eruptive sequence
The CI eruption has been interpreted as the largest volcanic eruption of the past 200,000 years in Europe. The eruption started with an intense Plinian phase, succeeded by a sequence of voluminous pyroclastic density currents with co-ignimbrite plumes. Both phases generated high eruptive columns, culminating in the widespread deposition of the Y-5 layer.Plinian phase
The distribution of basal Plinian fallout strongly suggests that the onset of the eruption occurred in the northeastern sector of Campi Flegrei. This phase is supplied by the uppermost, most evolved trachytic magma of the chamber.A detailed attempt to reconstruct this phase through direct field measurements recognized the evolution of the Plinian column through five units of fall deposits. The eruption first reached a column height of and then peaked at, and during the latest stage, the top of the plume waned to. The entire Plinian eruption lasted about 20 hours and emitted of magma. Another attempt at reconstruction by numerical simulation shows a different Plinian process. The eruptive column rose to, and the entire phase was completed within 4 hours with a magma volume of.
Plinian tephra is present in deposits to distances of at least and between and constitutes 35–45% of the Y-5 deposit.
Ignimbrite phase
The Plinian phase was followed by six main units of impressive pyroclastic density currents spreading over an area of and managing to surmount mountain ridges up to, extinguishing all life within a radius of about.The collapse of Plinian column due to an increase of the mass eruption rate produced the first ignimbrite unit, the Unconsolidated Stratified Ash Flow. Subsequently, the eruption advances into the climactic stage, generating three ignimbrite units, namely the voluminous Welded Grey Ignimbrite, Coarse Pumice Flow, and Lower Pumice Flow Unit. Collectively, these three units constitute the bulk of the CI eruption. The Y-5 co-ignimbrite ash dispersals to the southeast and northeast within of Campi Flegrei are associated with these first four units of pyroclastic density currents. After the eruption of the first four units, the majority of the CI magma had been expelled, resulting in the collapse of the caldera. The collapse triggered a new phase of eruption of Breccia/Spatter Unit and Upper Pumice Flow Unit. The magma was sourced from the lowermost, less evolved portions of the chamber. These two units represented the last stage of eruption and were only emplaced as very proximal deposits along the caldera rim. Most of the ultra-distal dispersal > was associated with this stage.
Calculations of exposed and inferred thickness and area of pyroclastic density currents yield a total ignimbrite volume of of magma. Consequently, the DRE volume of co-ignimbrite ash based on vitric loss method falls in the range of DRE. The overall magma volume expelled during this phase amounts to.
Numerical simulation obtained a lower estimate of DRE for co-ignimbrite ash.
Global impact
The Ar/Ar age of the CI eruption has been determined to year BP. The 14C age of charred wood embedded in Welded Grey Ignimbrite has been calibrated to 39,220—39,705 year BP. The two ages of the CI eruption disagree on a scale of centuries, suggesting that the dating uncertainties of Ar/Ar or 14C are underestimated. Nonetheless, the temporal proximity of CI eruption, Middle to Upper Paleolithic transition, Neanderthal disappearance, and the onset of Heinrich event 4 drew considerable scholarly attention.Relation with Heinrich event 4
In climatostratigraphy, the CI eruption occurred near the onset of a millennial-scale cold stadial that encompassed HE-4. Francesco G. Fedele and his team postulated that the volcanic winter of the CI eruption triggered HE-4, which saw the summer sea surface temperature plummeting by 3–6 °C along the Iberian margin and by 5 °C in the westernmost Mediterranean. However, this connection has been refuted by high-resolution paleoclimate records, which clearly indicate that the Y-5 layer postdates the onset of HE-4 by 700–800 years.Volcanic winter hypothesis
Petrological studies show that the magma of the CI eruption contained 50–250 million tones of sulfur dioxide and is expected to have caused a severe volcanic winter on top of already cool climate of HE-4 by injecting stratospheric sulfur aerosols. Simulations of the CI eruption by the Community [Earth System Model] find that temperature anomalies in Western Europe reach –2 °C to –4 °C during the year following the eruption, and the peak cooling and acid deposition lasted one to two years.To assess the volcanic winter using climate proxies, significant effort has been invested in directly detecting the sulfate signal of the CI eruption in polar ice cores, but these attempts have turned out to be fruitless. Several large sulfate peaks occurring near the onset of HE-4 have been tentatively attributed to the CI eruption, but it requires a well-characterized tephra find in the ice cores to ensure that the sulfate peak is indeed associated with the CI.