Campanian Ignimbrite eruption

The Campanian Ignimbrite eruption (CI, also CI Super-eruption) was a major volcanic eruption in the Mediterranean during the late Quaternary, classified 7 on the Volcanic Explosivity Index (VEI).[1][2] The event has been attributed to the Archiflegreo volcano, the 12-by-15-kilometre-wide (7.5 mi × 9.3 mi) caldera of the Phlegraean Fields, located 20 km (12 mi) west of Mount Vesuvius under the western outskirts of the city of Naples and the Gulf of Pozzuoli, Italy.[3] Estimates of the date and magnitude of the eruption(s), 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.[4]

Campanian Ignimbrite eruption
VolcanoPhlegraean Fields
Dateca. 37,000 to 38,000 BCE
TypePlinian eruption
LocationNaples, Campania, Italy
40.827°N 14.139°E / 40.827; 14.139
VEI7
Phlegraean Fields is located in Italy
Phlegraean Fields
Phlegraean Fields
Location of eruption

The most recent results by radiocarbon and argon–argon dating are, respectively, 39 220 to 39 705 calendar year BP[5] and 39850±140 year BP.[6] The estimated eruptive volume in dense-rock equivalent (DRE) is in the range of 181–265 km3 (43–64 cu mi),[1] and tephra has dispersed over an area of around 3,000,000 km2 (1,200,000 sq mi), commonly referred to as the ash horizon Y-5.[7][8] 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.[9]

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.[10] 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 (fire) and imber (shower)) and -ite. It means the deposits that form as a result of a pyroclastic eruption.[11]

Background
Main article: Phlegraean Fields
Solfatara Pozzuoli

The Phlegraean Fields (Italian: Campi Flegrei "burning fields"[lower-alpha 1])[12] caldera is a nested structure with a diameter of around 12 km × 15 km (7.5 mi × 9.3 mi).[13] 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.[14]

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.[15]
  • During the Second Period, the smaller Neapolitan Yellow Tuff eruption (Neapolitan Yellow Tuff or NYT) took place around 15,000 years ago.
  • Eruptions of the Third Period occurred during three intervals between 15,000–9,500 years ago, 8,600–8,200 years ago and from 4,800 to 3,800 years ago.[16]

The structure's magma chamber remains active as there apparently are solfataras, hot springs, gas emissions and frequent episodes of large-scale up- and downlift ground deformation (Bradyseism) do occur.[17][18]

In 2008 it was discovered that the Phlegraean Fields and Mount Vesuvius have a common magma chamber at a depth of 10 km (6.2 mi).[19]

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.[20]

In 2016 Italian Volcanologists announced plans to drill a probe 3 km (1.9 mi) deep into the Phlegraean Fields several years after the 2008 Campi Flegrei Deep Drilling Project which had aimed to drill a 3.5 km (2.2 mi) diagonal borehole in order to bring up rock samples and install seismic equipment. The project was suspended in 2010 due to safety problems.[21]

Eruptive sequence
Diagram of a Plinian eruption. (key: 1. Ash plume; 2. Magma conduit; 3. Volcanic ash rain; 4. Layers of lava and ash; 5. Stratum; 6. Magma chamber)

The CI eruption has been interpreted as the largest volcanic eruption of the past 200,000 years in Europe.[22] The eruption started with an intense Plinian phase, succeeded by a sequence of voluminous pyroclastic density currents with co-ignimbrite plumes.[8][23] Both phases generated high eruptive columns, culminating in the widespread deposition of the Y-5 layer.[7][23][24]

Plinian phase

The distribution of basal Plinian fallout strongly suggests that the onset of the eruption occurred in the northeastern sector of Campi Flegrei.[25] This phase is supplied by the uppermost, most evolved trachytic magma of the chamber.[26][27]

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 29 km (18 mi) and then peaked at 39 km (24 mi), and during the latest stage, the top of the plume waned to 26 km (16 mi). The entire Plinian eruption lasted about 20 hours and emitted 7.8 km3 (1.9 cu mi) of magma.[25] Another attempt at reconstruction by numerical simulation shows a different Plinian process. The eruptive column rose to 44 km (27 mi), and the entire phase was completed within 4 hours with a magma volume of 23 km3 (5.5 cu mi).[8]

Plinian tephra is present in deposits to distances of at least 1,400 km (870 mi) and between 130 km (81 mi) and 900 km (560 mi) constitutes 35–45% of the Y-5 deposit.[24]

Ignimbrite phase

The Plinian phase was followed by six main units of impressive pyroclastic density currents spreading over an area of 30,000 km2 (12,000 sq mi) and managing to surmount mountain ridges up to 1,000-metre-high (3,300 ft), extinguishing all life within a radius of about 100 km (62 mi).[28][26][27][29][30]

The collapse of Plinian column due to an increase of the mass eruption rate produced the first ignimbrite unit, the Unconsolidated Stratified Ash Flow.[31][27] 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.[27] The Y-5 co-ignimbrite ash dispersals to the southeast and northeast within 1,000 km (620 mi) of Campi Flegrei are associated with these first four units of pyroclastic density currents.[32]

Ignimbrite

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.[26][27] Most of the ultra-distal dispersal > 1,500 km (930 mi) was associated with this stage.[32]

Calculations of exposed and inferred thickness and area of pyroclastic density currents yield a total ignimbrite volume of 60–83 km3 (14–20 cu mi) of magma. Consequently, the DRE volume of co-ignimbrite ash based on vitric loss method falls in the range of 116–155 km3 (28–37 cu mi). As a result, the overall magma volume expelled during this phase amounts to 179–243 km3 (43–58 cu mi) DRE.[1]

Numerical simulation obtained a lower estimate of 62 km3 (15 cu mi) DRE for co-ignimbrite ash.[8]

Global impact
Graphic of deposit dispersal during the eruption

The event's recent dating at 39,280±110 years ago draws considerable scholarly attention as it marks a time interval characterized by biocultural modifications in western Eurasia and widespread discontinuities in archaeological sequences, such as the Middle to Upper Palaeolithic transition. At several archaeological sites of South-eastern Europe, the ash separates the cultural layers containing Middle Palaeolithic and/or Earliest Upper Palaeolithic assemblages from the layers in which Upper Palaeolithic industries occur. At some sites the CI tephra deposit coincides with a long interruption of paleo-human occupation.

Effect on climate

The climatic importance of the eruption was tested in a three-dimensional sectional aerosol model that simulated the global aerosol cloud under glacial conditions. Black et al. (2015)[33] calculate that up to 450 million kilograms (990 million pounds) of sulphur dioxide would have been accumulated into the atmosphere, driving down temperatures at least by 1–2 degrees Celsius (1.8–3.6 degrees Fahrenheit) for a period of 2–3 years.[33]

Archaeology

Many archaeological sites in south-eastern Europe keep evidence of eruption. Kostyonki–Borshchyovo archaeological complex which is about 40,000 years old was found to have a layer of sediment ash.

Effect on living organisms

Sulphur dioxide and chloride emissions caused acidic rains, fluorine-laden particles become incorporated into plant matter, potentially inducing dental fluorosis, replete with eye, lung and organ damage in animal populations.[34]

Neanderthal demise
Further information: Neanderthal extinction

The eruption coincided also with the final decline of the Neanderthal in Europe. The environmental stress associated with the CI may have contributed to the extinction of the Neanderthals in combination with societal upheaval in the Paleolithic era. The notion remains contested; nonetheless, sources admit that although the CI would have affected both modern humans and Neanderthals equally, the assumed capacity of modern humans for resilience and ingenuity over and above that of Neanderthals could have allowed modern humans to recover more quickly at Neanderthals' expense.[35][36]

See also

Footnotes
  1. The term Campi Flegrei   is mixed Latin and ancient Greek, indicating that the volcanic nature of the area has been well known in antiquity.

References
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  2. Mastrolorenzo, Giuseppe; Palladino, Danilo M.; Pappalardo, Lucia; Rossano, Sergio (5 March 2016). "Probabilistic-Numerical assessment of pyroclastic current hazard at Campi Flegrei and Naples city: Multi-VEI scenarios as a tool for full-scale risk management – VEI 7 Campanian Ignimbrite extreme event". PLOS ONE. 12 (10): e0185756. arXiv:1603.01747. Bibcode:2017PLoSO..1285756M. doi:10.1371/journal.pone.0185756. PMC 5636126. PMID 29020018.
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