Giordano, Guido

During the last 20 kyr, the Etna volcano has been characterized by almost continuous summit eruptions and by less frequent—yet definitely more destructive—flank eruptions issuing at <1,000 m asl altitudes and reaching the Ionian Sea. The chronological framework of pre‐historic (pre‐2,750 yr BP) flank eruptions is supported only by few radiometric and paleomagnetic ages. Here we paleomagnetically investigated 15 Holocene lava flows from SE Etna lower slopes and dated 12 of them. Paleomagnetic dating at Etna relies on best method pre‐requisites: European location where reference geomagnetic models are well defined, and detailed stratigraphic evidence is available. We sampled 45 sites (450 oriented cores) from lavas loosely constrained in the 19,000–2,000 yr BP age window. Ten eruptions yielded a minimum 40% refinement with respect to initial age constraints, with four lava flows achieving refinement up to 90%. We obtained 620–1,398 yr (998 yr on average) dating accuracy for three flows bracketed in relatively short (1,398–1,644 yr) independent age constraints. By contrast, five flows characterized by longer 6,567–7,439 yr initial age windows yielded multiple age solutions. Finally, four lava flows with 1,644–6,567 yr‐long initial age windows were tightly dated with 120–680 yr age ranges. We conclude that at volcanoes where best paleomagnetic dating prerequisite are fulfilled, singular solutions are expected for 30% of the analyzed flows and, significant refinements for the others. Seven kyr seems to represent an independent age window threshold length to get or not significant dating refinements.

Topography plays an important yet uncertain role in modulating the temporal and spatial evolution of the in- ternal structure of pyroclastic density currents (PDCs). Understanding such changes is critical to characterize PDC transport regimes and their hazard. Here we combine paleomagnetic data from PDC deposits of the 18 May 1980 Mt. St. Helens eruption with numerical outcomes to capture spatio-temporal temperature variations induced by topography. We show that emplacement temperatures along the northwest flank of the volcano are ≃ 100◦C colder than those recorded along the northeast flank in response to proximal topographic drops. We further report that such vertical drops lead to an initial transient regime where the PDC internal temperature, velocity, and concentration stratification is altered for periods of time that are proportional to the ratio between the drop height and the square root of the current thickness. The topographic control on PDC dynamics is attenuated moving away from the drops or when a stationary phase is attained. Collectively, our results highlight that topographic regions promoting the flow separation/reattachment process are associated with vigorous entrainment of ambient air in the lower portion of PDCs. Low temperature variability is observed in the absence of such topographic irregularities. Based on our findings, we propose a local sedimentation rate of ≃ 150 ± 100 mm s−1 for PDC deposits in a proximal reattachment region. This investigation demonstrates the importance of transient processes in PDC dynamics, introducing a new methodology to measure sedimentation rates, and highlighting that flow-topography feedbacks should be considered to assess hazards.

The 39.8-ka Campanian Ignimbrite was emplaced during a large caldera-forming eruption of Campi Flegrei near Naples, Italy. The ignimbrite is found up to 80 km from the caldera, and co-ignimbrite ash-fall deposits occur 3200 km away. The proximal and distal stratigraphy of the Campanian Ignimbrite has not been definitively correlated due to the dissimilar appearance of the proximal and distal deposits, a lack of medial exposures, and the inconsistency and heterogeneity of the proximal stratigraphy. Here, we document the majorelement glass-shard chemistry, matrix componentry, and lithic componentry of the proximal and distal stratigraphic sequences of the ignimbrite to attempt to correlate the units. The results of these disparate observations taken together suggest that the established stratigraphic units cannot be directly and uniquely correlated between the proximal and distal regions and that neither the proximal nor distal stratigraphy provides a record of the entire eruptive sequence. However, the characteristics studied can be used to demarcate eruptive phases that are connected to some of the defined units in the proximal and distal stratigraphy

In active volcanic environments magmas that ascend within the conduit and erupt at the surface as lava flows experience physico-chemical perturbations related to temperature changes and variable degrees of deformation. We have conducted experimental investigations to examine the concurrent effects of undercooling and stirring on the crystallization kinetics of a leucite-bearing phonotephrite from Somma-Vesuvius (Italy). Two sets of undercooling experiments have been carried out within the same temperature range of 1300–1150 °C. The first set involved classical static undercooling (SU) experiments with no stirring applied to the melt, while the second set involved dynamic undercooling (DU) experiments with a shear strain rate of 1 s−1 applied. By comparing SU and DU results with previous data from literature obtained using the same experimental approach, we observe that the degree of crystallization and the textural evolution of leucite and clinopyroxene progress upon the effect of melt stirring by shortening the incubation time. As a result, the solidification process is markedly enhanced in DU experiments, accompanied by a substantial increase in the crystal nucleation density and growth rate. Thermorheological modeling indicates that stirring-induced crystallization increases the melt viscosity by a factor of ∼1.5–4.5 depending on the system temperature. At a given temperature, mass transport can therefore produce higher crystallinity and higher viscosity magmatic suspensions than static crystallization conditions. We document that if subsequent cooling occurs, the existing crystal cargo in such suspensions may promote the onset of non-Newtonian rheological response, causing a transition from homogeneous viscous flow to shear localization and magma/lava rupture.

The destructive (Mw 3.9) earthquake of 21 August 2017 re-opened the question on where magma resides at the Ischia island volcano. The peculiar complexity of the seismic source initiated the debate on the involvement of fluid-related processes, but the magmatic origin of the event remains uncertain. Here we use ground displacement and broadband seismic data to investigate the magmatic system of Ischia volcano, where progressive underplating of mafic material at mid-crustal depth feeds the deep structures, which are characterized by exceptionally high seismic velocity and are connected with a shallow crystal mush. Although no direct evidence of large molten volumes was found, strong anisotropy suggests that the crystal mush is pervaded by magma-intruded dykes. We propose that the 2017 event was due to a negative tensile deformation caused by depressurization of supercritical fluids along a shallow southwest (SW-)-dipping fault defined by receiver functions (RFs) data, which acted as a valve regulating the overpressure of deep magmatic fluids.

The Roccamonfina volcano is located within the Garigliano Graben (southern Apennines, Italy) and has been active throughout the Middle-Late Pleistocene. Along its polyphase volcanic history (630–55 ka), including several caldera-forming eruptions (385–230 ka), several effusive/mildly explosive monogenetic events occurred along the volcano slopes, within the summit caldera, and along the graben-bounding carbonate reliefs. In this paper, we present a multidisciplinary study of a mafic magmatic feeder dike intruded within the Meso-Tertiary carbonates and overlying Lower Pleistocene breccias of Mt Cesima, northeast of the Roccamonfina volcano. We performed a stratigraphic and structural survey of the area and petrographic analyses on several samples of the dike. Results indicate that a ∼1 km long fissure fed an eruption that also emplaced a Strombolian pyroclastic sequence. Petrological data show that an open-system mafic recharge fueled the tephritic magma that fed the eruption, whereas no evidence of significant pre/syn-eruptive assimilation of carbonate has been identified. Stratigraphic and petrological data do not allow to firmly constrain the timing of the eruption, which could belong both to the pre-Brown Leucitic Tuff (>354 ka) and to the post-White Trachytic Tuffs (<230 ka) epochs of activity of the Roccamonfina volcano. Structural data show that the dike is broadly oriented E-W and changes direction toward NE-SW in correspondence with a pre-existing fault damage zone. We suggest that magma was intruded during an N-S trending extensional event in the Middle Pleistocene, whose prolonged activity resulted in regional uplift and exhumation of regional significance.

Despite their protracted periods of inactivity, long-dormant volcanoes may be highly hazardous, as their reactivation can be characterized by violent explosive eruptions. An example of such volcanoes is the Colli Albani caldera, onto which deposits Rome Capital City is built, Italy. Its last volcanic activity was characterized by voluminous maar-forming phreatomagmatic eruptions dated between 36 and 25ka, but the volcano has produced several maar lake overflows during the Holocene till historical times. Presently, Colli Albani is affected by recurrent seismic events, anomalous heat flow, ground uplifts, hydrothermal circulation and gas emissions. For these reasons, the Italian Civil Protection has recently listed Colli Albani among the ten active volcanoes of Italy, but products for the evaluation of its volcanic hazards lacking. This work presents the first study on vent opening susceptibility mapping at Colli Albani. We explore the potential of an available geological dataset for building, through geographic information system analysis, an index that classifies areas at different vents opening susceptibility (low, moderate and high). Such result highlights as a solid geological mapping is a prerequisite for the volcanic hazard assessment, especially in remote or poorly studied long-dormant volcanoes such as caldera systems where the location of new vents could occur in different volcano sectors.

This review summarizes what the volcanology community has learned thus far from studying the deposits of pyroclastic currents (PCs) from the 1980 eruption sequence at Mount St. Helens. The review includes mass flow events during the May 18 eruption, including the lateral blast, the afternoon column collapse and boil-over PC activity, and some aspects of the debris avalanche. We also include a summary of PCs generated in the smaller eruptions following the climactic May 18 event. Our objective is to summarize the state of our understanding of PC transport and emplacement mechanisms from the combination of field and laboratory observations, granular flow experiments, and numerical modeling techniques. Specifically, we couple deposit characteristics, experiments, and numerical modeling techniques to critically address the problems of (1) constraining conditions in the flow boundary zone at the time of deposition; (2) the influence of substrate roughness and topography on PC behavior; (3) the prevalence, causes, and consequences of substrate erosion by PCs; and (4) the reconstruction of PC transportation and sedimentation processes from a combination of geophysical and sedimentological observations. We conclude by providing opportunities for future research as our field, experimental, and numerical research techniques advance.

We present a multidisciplinary study based on Differential Scanning Calorimetry (DSC), paleomagnetic analysis, and numerical modeling to gain information on the timescales of syn- and post-depositional ductile deformation of the strongly welded and rheomorphic Green Tuff ignimbrite (GT; Pantelleria, Italy). DSC measurements allow the determination of glass fictive temperatures (Tf; i.e., the parameter accounting for the cooling dependence of glass structure and properties). Using a T -based f geospeedometry procedure, we infer the cooling rate (qc) experienced by the glassy phases in different lithofacies within the GT formation. Glass shards from the basal pumice fall deposit record a fast qc of ∼10°C/s. In contrast, the ignimbrite body returns slow qc values depending on the stratigraphic position and lithofacies (basal/upper vitrophyres, fiamme-rich and rheomorphic layers), ranging from ∼10−2 to ∼10−6 °C/s. Moreover, paleomagnetic analyses of the natural remanent magnetization of ignimbrite matrix and embedded lithic clasts indicate an emplacement temperature higher than 550–600°C. By integrating calorimetric and paleomagnetic datasets, we constrain a conductive cooling model, describing the ignimbrite's temperature-time-viscosity (T–t–η) evolution from the eruptive temperature to below Tf. Outcomes suggest that the upper and basal vitrophyres deformed and quenched over hours, indicating that the entire GT underwent intense syn-depositional ductile deformation. Furthermore, the central body remained above T for a much longer timespan (>1 month), enabling post-emplacement rheomorphic flow. Lastly, we discuss the critical role of mechanisms such as shear heating and retrograde solubility of volatiles, in locally controlling the rheological behavior of the GT.

The peninsular and insular Italy are punctuated by Quaternary volcanoes and their rocks constitute an important aliquot of the Italian Quaternary sedimentary successions. Also away from volcanoes itself, volcanic ash layers are a common and frequent feature of the Quaternary records, which provide us with potential relevant stratigraphic and chronological markers at service of a wide array of the Quaternary science issues. In this paper, a broad representation of the Italian volcanological community has joined to provide an updated comprehensive state of art of the Italian Quaternary volcanism. The eruptive history, style and dynamics and, in some cases, the hazard assessment of about thirty Quaternary volcanoes, from the northernmost Mt. Amiata, in Tuscany, to the southernmost Pantelleria, in Sicily Channel, are here reviewed in the light of the substantial improving of the conceptual models, methodological approaches and the overall knowledge made in the last decades in the volcanological field study. We hope that the prest review can represent an useful and agile document summarising the knowledege on the Italian volcanism at the service of the Quaternary community operating in central Mediterranean area.