Monte Nuovo Eruption Research Articles

Combined volcano-tectonic processes for the drowning of the Roman western coastal settlements at Campi Flegrei (southern Italy)

The active Campi Flegrei caldera in southern Italy has a remarkably long history of coexistence between volcanism and human settlements, and it is famous for its peculiar slow ground movement called bradyseism, i.e. episodes of inflation and deflation of the caldera floor due to magmatic and/or hydrothermal processes. This natural phenomenon has interacted with the civilization that inhabited this strategic and fertile area, especially in Roman times, when the sinking of the coast hindered the flourishment of Puteoli and Baiae coastal towns. The drowning of a large part of Republic-early Imperial Roman coastal buildings, west of the modern Pozzuoli town, is classically used to illustrate the bradyseism activity. In this paper, we investigate the spatial variability and the role of this phenomenon, demonstrating that the caldera deflation alone cannot account for the submersion of Roman facilities in the western sector where the harbour structures of Portus Iulius and luxury villas of the Baianus Lacus presently lie beneath sea level. On the contrary, the sinking of this area is mainly the result of the activity of volcano-tectonic faults. We restored the topography to 100 BCE using archaeological and high-resolution topographic data. Results show that the several metres of vertical displacement recorded in the Baia area in the last 2100 yr were mainly produced by the activity of normal faults and secondarily by caldera deflation, the former including the long-lived Baia Fault and the younger normal faults associated with the Monte Nuovo eruption at 1538 CE.Graphical

A gravitational origin for volcano-tectonic faults in the Campi Flegrei caldera (southern Italy) inferred from detailed field observations

Faults in volcanic areas can have different origins and can form due to several volcano-tectonic processes. In this work, by means of detailed field observations, we analysed a fault array cutting through a recent pyroclastic succession in the Campi Flegrei caldera of southern Italy to investigate its origin. Geometric and kinematic data indicate that the fault array consists of steeply dipping faults with both normal and reverse senses of movement. Displacement data suggest that these faults with opposed kinematics acted together , in agreement with what was previously described from analogue and numerical experiments for faults formed in response to gravitational collapses in volcanic areas. By integrating these results with considerations of the recent volcano-tectonic evolution of the Campi Flegrei caldera, we propose a model in which the studied fault array developed to accommodate a gravitational collapse triggered by an underground magma migration predating the 1538 CE historical Monte Nuovo eruption. This work is, to our knowledge, the first thorough field description of faults developed to accommodate gravitational collapses in volcanic areas.

A 3D imaging textural characterization of pyroclastic products from the 1538 AD Monte Nuovo eruption (Campi Flegrei, Italy)

The explosive volcanic event of the 1538 AD Monte Nuovo eruption (Volcanic Explosivity Index, VEI = 2) in the Campi Flegrei high-risk caldera (Italy) has a strategic significance in the framework of volcanology and volcanic hazard of caldera-forming magmatic systems. In fact, it represents the last and unique historical eruption of the highly populated Phlegraean restless-caldera, and its precursory and eruptive phenomena are well-known because they were described in detail by contemporaneous eyewitnesses.In this study, a set of samples representative of the complete stratigraphic sequence of the Monte Nuovo eruption was characterized using phase-contrast synchrotron radiation computed microtomography and quantitatively investigated through the development of a new protocol for 3D textural analysis of highly-vesiculated volcanic rocks. Previous studies of products from this eruption are available in the literature, mostly based on 2D imaging techniques, and thus provide a useful data set for comparison.The 3D textural measurements allow us to investigate the subvolcanic processes (mechanisms and timing of magma degassing) that occurred during magma ascent in the conduit for each stage of the eruption and their relationship with the variations in the eruptive style described in the contemporaneous accounts of the eruption. This information is fundamental for the definition of a volcanic eruption scenario for such low-VEI events, often recurrent in the history of the caldera, and is useful both for hazard assessment and emergency planning.

Volcanology and Archaeology for Better Understanding the History of Campi Flegrei: Post-NYT Bradyseisms and More Rapid Deformation

The Campi Flegrei volcanic district includes insular (Ischia and Procida Islands) and peninsular volcanic activity (Campi Flegrei volcanic field) with the link to older activity till Ponza Island. The history of this area has been studied in detail since the eruption of the Campanian Ignimbrite (CI, age: 39 ky BP, volume: 200 - 300 km3), which makes this one of the most powerful eruptions in Europe. In the Neapolitan Yellow Tuff (NYT: age: 15.0 ky BP, volume: 50 km3), another powerful eruption occurred. Activity younger than the NYT can be subdivided in three epochs which include 70 recognized ephemeral eruptions. The volume of these individual eruptions is between 0.4 and 1 km3 (DRE). Probably, the long-lasting magma reservoirs (i.e., CI and NYT) represent eruptions that are fed by deep magma reservoirs. In deep reservoirs (>10 km), magmas stagnate, differentiate and are probably modified by crustal components (Hercynian basement). The long-lasting reservoirs are also the ones that feed the ephemeral shallow magmatic system (2 - 5 km) that gave rise to the post-caldera magmatic epochs. However, the magmas of the post-caldera epochs are isotopically heterogeneous and made by several components (i.e., least evolved (as an example the Minopoli eruption, 9500 y BP), CI, and NYT components). Mixing between ephemeral shallow reservoirs occurs. Mixing of long lasting reservoirs also occurs; and also during explosive eruptions. The concentration of earthquakes and the deformation history suggest that Campi Flegrei could erupt again with an ephemeral eruption, especially if the uplift will reach 5 - 6 m like Monte Nuovo eruption, given existing uplift of 1970-72 and 1983-84.

Hydrothermal fluid venting in the offshore sector of Campi Flegrei caldera: A geochemical, geophysical, and volcanological study

AbstractThe ongoing unrest at the Campi Flegrei caldera (CFc) in southern Italy is prompting exploration of its poorly studied offshore sector. We report on a multidisciplinary investigation of the Secca delle Fumose (SdF), a submarine relief known since antiquity as the largest degassing structure of the offshore sector of CFc. We combined high‐resolution morphobathymetric and seismostratigraphic data with onshore geological information to propose that the present‐day SdF morphology and structure developed during the initial stages of the last CFc eruption at Monte Nuovo in AD 1538. We suggest that the SdF relief stands on the eastern uplifted border of a N‐S‐trending graben‐like structure formed during the shallow emplacement of the Monte Nuovo feeding dike. We also infer that the high‐angle bordering faults that generated the SdF relief now preferentially allow the ascent of hot brines (with an equilibrium temperature of 179°C), thereby sustaining hydrothermal degassing on the seafloor. Systematic vertical seawater profiling shows that hydrothermal seafloor venting generates a sizeable CO2, pH, and temperature anomaly in the overlying seawater column. Data for the seawater vertical profile can be used to estimate the CO2 and energy (heat) outputs from the SdF area at ∼50 tons/d (∼0.53 kg/s) and ∼80 MW, respectively. In view of the cause‐effect relationship with the Monte Nuovo eruption, and the substantial gas and energy outputs, we consider that the SdF hydrothermal system needs to be included in monitoring programs of the ongoing CFc unrest.

Constraining pre-eruptive magma conditions and unrest timescales during the Monte Nuovo eruption (1538 ad; Campi Flegrei, Southern Italy): integrating textural and CSD results from experimental and natural trachy-phonolites

We present crystallization experiments representing a broad range of growth conditions of alkali feldspar and sodalite in a trachy-phonolite magma composition during later stages of evolution. Our results include (i) textural data and mineral assemblages of synthetic samples; (ii) feldspar nucleation kinetics and growth rate estimates; and (iii) textural data, mineral abundances, and crystal size distribution measurements on samples representative of the Monte Nuovo eruption (1538 ad), the last eruption of Campi Flegrei, Southern Italy. Experiments reproduced the texture and feldspar content of natural products indicating that kinetic data can provide insights into processes within the volcanic system shortly before and during this small-magnitude eruption and, particularly, about magma ascent timescale. We suggest that the groundmass crystallization of Monte Nuovo magma started between 4 and 7 km depth (∼100–200 MPa) at a temperature between 825 and 840 °C (close to the liquidus of alkali feldspar). The crystallization kinetics of alkali feldspar and the absence of sodalite in most of the natural samples indicate that magma ascent rate increased in the shallow part of the conduit from about 3 km depth to the quenching level (possibly fragmentation point; ∼30 MPa), during the first phases of the eruption. The crystallization time of the magma requires that it ascended from pre-eruptive storage to the quenching level in several hours to a few days. We also observe that a small decrease in pressure can induce a dramatic increase in crystallinity, with associated rheological changes, leading to changes in the eruption style, and such changes could occur on timescales of hours to several days. The products from the later phases of the Monte Nuovo eruption are more crystalline and contain sodalite in response to the decrease in magma ascent rate, which in turn allowed for more degassing during ascent, resulting in more time spent at very shallow depths.

Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption.

Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common.

Rheological properties of magma from the 1538 eruption of Monte Nuovo (Phlegrean Fields, Italy): An experimental study

The rheology of natural, partially crystallized samples from Monte Nuovo (1538 AD) eruption have been investigated using a high temperature, high pressure internally heated pressure vessel. Within the temperature interval of investigation the samples exhibited Newtonian rheology at deformation strain rates up to 10 − 4 s − 1 . At higher strain rates a decrease of viscosity with increasing strain rate (shear thinning), eventually terminating in a sudden viscosity drop (stress weakening), was observed. Stress weakening occurred at higher applied strain rates and stresses with increasing temperature. The microstructural analyses of the samples revealed that stress weakening resulted from strain localization, which occurred in brittle and viscous regimes at the lowest and highest temperatures investigated respectively. The different rheological behaviors of the investigated material is likely responsible for the changes in the dynamics of magma ascent within the volcanic conduit during the eruption of Monte Nuovo volcano. We infer that the occurrence of syn-eruptive decompression driven crystallization, observed in previous studies, induced strong variations in the rheological properties of magma, which in turn was responsible for the changes of eruptive style observed during the Monte Nuovo eruption.

Magma ascent and eruptive processes from textural and compositional features of Monte Nuovo pyroclastic products, Campi Flegrei, Italy

Geochemical and textural studies were carried out on alkaline products of the AD 1538 Monte Nuovo eruption. Due to the integration of the volcanological study with eyewitness reports, the dynamics and timing of each phase of the eruption and the volume of emitted magmas are known in detail. On this basis, unique in Campi Flegrei, the relations between magma chamber mechanisms, eruptive styles, magma ascent dynamics and volatile exsolution processes have been explored. Glass and phenocryst compositions indicate that the erupted magma has a homogeneous phono-trachytic composition. Textures and compositions of phenocrysts indicate that they crystallised at equilibrium with the melt in the magma chamber, likely as a mushy boundary layer along the chamber wall, where the temperature was below the liquidus temperature of the crystal free-chamber core. The estimated crystallisation temperature is 850±40°C. The magma phase relations in Petrogeny’s Residua System suggest that phenocryst crystallisation occurred at \(\text{P}_{\text{H}_2 \text{O}}\) between 100 and 200 MPa, corresponding to depths ranging from 3 to 8 km. The microlite composition and their close genetic relations with vesicles indicate that groundmass crystallisation occurred during the eruption as a consequence of magma degassing and vesiculation induced by decompression during its ascent toward the surface. Crystal size distributions reveal that microlites grew in two stages of undercooling that we define as: (1) magma migration onset upward from the chamber and (2) magma rising through the conduit to the surface, possibly lasting tens of days and few days, respectively. These results provide information on the physical conditions that characterise pre- and syn-eruptive processes, which may be useful in order to define eruptive scenarios and to evaluate short-term precursors. Furthermore, the collected data provide for the first time information on degassing-induced crystallisation during the eruption of a highly evolved alkaline magma.

Changes in eruptive style during the A.D. 1538 Monte Nuovo eruption (Phlegrean Fields, Italy): the role of syn-eruptive crystallization

The Monte Nuovo eruption is the most recent event that occurred at Phlegrean Fields (Italy) and lasted from 29 September to 6 October 1538. It was characterized by 2 days of quasi-sustained phreatomagmatic activity generating pumice-bearing pyroclastic density currents and forming a 130-m-high tuff cone (Lower Member deposits). The activity resumed after a pause of 2 days with two discrete Vulcanian explosions that emplaced radially distributed, scoria-bearing pyroclastic flows (Upper Member deposits). The juvenile products of Lower and Upper Members are, respectively, phenocryst-poor, light-coloured pumice and dark scoria fragments with K-phonolitic bulk compositions, identical in terms of both major and trace elements. Groundmass is formed by variable proportions of K-feldspar and glass, along with minor sodalite and Fe-Ti oxide present in the most crystallized samples. Investigations of groundmass compositions and textures were performed to assess the mechanisms of magma ascent, degassing and fragmentation along the conduit and implications for the eruptive dynamics. In pumice of the Lower Member groundmass crystal content increases from 13 to 28 vol% from the base to the top of the sequence. Products of the Upper Member consist of clasts with a groundmass crystal content between 30 and 40 vol% and of totally crystallized fragments. Crystal size distributions of groundmass feldspars shift from a single population at the base of the Lower Member to a double population in the remaining part of the sequence. The average size of both populations regularly increases from the Lower to the Upper Member. Crystal number density increases by two orders of magnitude from the Lower to the Upper Member, suggesting that nucleation dominated during the second phase of the eruption. The overall morphological, compositional and textural data suggest that the juvenile components of the Monte Nuovo eruption are likely to record variations of the magma properties within the conduit. The different textures of pumice clasts from the Lower Member possibly reflect horizontal gradients of the physical properties (P, T) of the ascending magma column, while scoriae from the second phase are thought to result from the disruption of a slowly rising plug crystallizing in response to degassing. In particular, crystal size distribution data point to syn-eruptive degassing-induced crystallization as responsible for the transition in eruptive style from the first to the second phase of the eruption. This mechanism not only has been proved to profoundly affect the dynamics of dome-forming calc-alkaline eruptions, but may also have a strong influence in driving the eruption dynamics of alkaline magmas of intermediate to evolved compositions.

The viscosity of trachytes, and comparison with basalts, phonolites, and rhyolites

The viscosity of natural liquids representative of the glassy portion of pumice collected from the deposits of the Campanian Ignimbrite (IGC) and Monte Nuovo (MNV) eruption of Phlegrean Fields has been measured in the temperature range from 1770 K down to the glass transition, and for a dissolved water content range from dry to nearly 4 wt.%. Measurements were performed by a combination of techniques involving concentric cylinder and micropenetration apparatuses, depending on the specific viscosity range. These measurements, together with those made on samples from the Agnano Monte Spina (AMS) eruption of Phlegrean Fields presented in a companion paper, represent the first viscosity determinations for natural trachytic liquids. Liquid viscosities have been parameterized by means of a modified VFT equation that allows the calculation of viscosity as a function of temperature and water content. Calculated viscosities are compared with those pertaining to natural liquids of phonolitic, rhyolitic, and trachybasaltic composition, showing that trachytes are intermediate between rhyolites and phonolites, consistent with the dominant eruptive style associated with the different magma compositions (mainly explosive for rhyolites and trachytes, either explosive or effusive for phonolites, mainly effusive for basalts). Compositional diversity among the analyzed trachytes corresponds to liquid viscosity differences of one to two orders of magnitude, with higher viscosities approaching that of rhyolite at the same temperature–water content conditions. All hydrous natural trachytes and phonolites become indistinguishable when isokom temperatures (i.e., temperatures corresponding to the same viscosity) are plotted versus a compositional parameter given by the molar ratio on an element basis (Si+Al)/(Na+K+H). In contrast, rhyolitic and basaltic liquids display distinct trends, with the more fragile basaltic liquids crossing the curves pertaining to all other compositions.

Modeling of recent volcanic episodes at Phlegrean Fields (Italy): geochemical variations and ground deformation

The Phlegrean Fields is an active caldera structure, located on the periphery of Naples (Italy). After the last eruptive event (the Monte Nuovo eruption in 1538), periodic episodes of unrest have characterized the evolution of this volcanic district, involving seismic activity and slow ground motion (bradyseism). During these episodes of unrest, some remarkable changes have also affected the composition of the hydrothermal fluids discharged at La Solfatara fumarolic field. These unrest phenomena result from the complex interaction between magma chamber, hydrothermal fluid circulation, and country rocks undergoing thermal and mechanical stresses. In order to make an effective hazard assessment in such a densely populated area as the Phlegrean Fields, we must first reach a better understanding of the mechanism driving bradyseismic activity and determine the relation between ground deformation and hydrothermal fluid circulation. In this work, we present some results of numerical modeling of both the hydrothermal fluid circulation at La Solfatara, and of its effects on rock deformation. The modeling results show that periods of intensified magmatic degassing can explain many features of the recent crises of unrest at Phlegrean Fields.

Hazard assessment during caldera unrest at the Campi Flegrei, Italy: a contribution from gravity–height gradients

Hazard assessment and risk mitigation at restless calderas is only possible with adequate geophysical monitoring. We show here how detailed long-term micro-gravity and deformation surveys may contribute to hazard assessment at the Campi Flegrei caldera (CFc) in Italy by evaluating gravity–height change (Δ g/Δ h) gradients obtained during ground inflation and deflation between 1981 and 2001. Such gradients provide a framework from which to assess the likelihood and type of volcanic eruptions. Our new analysis of unrest at the CFc allows us to separate ‘noise’ during the gravity survey from the signal of deep-seated magmatic processes. This facilitates identification of the dynamics within the magma reservoir beneath the CFc. We found that magma replenishment during rapid uplift between 1982 and 1984 was insufficient, probably by one to two orders of magnitude, to trigger an eruption similar to the 1538 Monte Nuovo eruption, the most recent volcanic eruption within the CFc. Furthermore, our interpretation of Δ g/Δ h gradients for the ongoing period of deflation since 1984 suggests that eruptive volcanic activity is not imminent. Short periods of minor inflation associated with large gravity changes since 1981 are interpreted to reflect noise, which to some degree is probably due to sub-surface mass/density changes within shallow hydrothermal systems beneath the CFc, indicating no risk of eruptive volcanic activity. We propose that monitoring Δ g/Δ h gradients at restless calderas is essential as a caldera develops from a state of unrest to a state where volcanic eruptions have to be anticipated. Adoption of this method for the several tens of restless calderas world-wide will provide early warning of changes in or increase of activity at these supervolcanoes.

Active deformation and volcanism offshore Campi Flegrei, Italy: new data from high-resolution seismic reflection profiles

The interpretation of high-resolution seismic reflection profiles permitted the identification of many geologic features in the inner shelf of Pozzuoli Bay. This area corresponds to the offshore of Campi Flegrei: a classically active volcanic area that experienced earthquakes and meter-scale vertical ground uplift before the 1538 Monte Nuovo eruption and in the period from 1970 to 1985. The detected undersea features include two small debris flows that are located in a submarine valley in the western part of Pozzuoli Bay. They may be the result of a pyroclastic flow and a pyroclastic surge that entered the sea. The younger debris flow in the uppermost marine deposits of Pozzuoli Bay formed during the 1538 Monte Nuovo eruption, and the older debris flow during the 3.8 ka-old Averno eruption. Other features detected by our survey are an undersea 8 m-high and 1 km-wide cryptodome, corresponding to a near-surface intrusion, located off Pozzuoli, that warped post-4 ka marine deposits. The interpretation of the cryptodome is based on seismic facies analysis, deformation geometry and correspondence to a magnetic high. It is suggested that this undersea dome formed during the uplift phases associated with the 1538 Monte Nuovo eruption and the two more recent bradyseismic crises of 1970–1972 and 1982–1984. Surface-breaking faults (with maximum vertical offset of 1 m) were recognized in very shallow waters near the coast of Pozzuoli. It is suggested that some of these faults were active during the 1982–1984 bradyseismic earthquake sequence.