1,721,151 research outputs found
Caldera unrest prior to intense volcanism in Campi Flegrei (Italy) at 4.0 ka B.P.: Implications for caldera dynamics and future eruptive scenarios
No full textThe Campi Flegrei caldera is one of the highest risk
volcanic areas on the Earth. Our research documents a
150 year-long period of intense volcanism following less
than 200 years of repose after the Agnano-Monte Spina
Plinian eruption (4.1 ka). The new data show that the
renewal of volcanism was preceded by an uplift of a few
tens of meters, triggered by mafic refilling of reservoirs at
depths of 3 km or less. Our studies also indicate for the first
time the occurrence of contemporaneous eruptions from
at locations in different sectors of the caldera. These results
suggest that a future eruptive crisis will likely be preceded
by several meters of caldera-wide uplift in response to
magma movements at depth. The trend of uplift of the
caldera since 1969 may thus represent the unrest expected
before a renewal of volcanism within an interval of decades
to centuries. Citation: Isaia, R., P. Marianelli, and A. Sbrana
(2009), Caldera unrest prior to intense volcanism in Campi
Flegrei (Italy) at 4.0 ka B.P.: Implications for caldera dynamics
and future eruptive scenarios, Geophys. Res. Lett., 36, L21303
Turbulent boundary layer shear flows as an approximation of base surges at Campi Flegrei (Southern Italy)
No full textSmall-volume base-surge deposits of Astroni and Agnano-Monte Spina eruptions at Campi Flegrei consist of sets of beds formed by the passage of multiple pyroclastic density currents. Each set is made by a fining-upward sequence consisting, from base to top, of: (1) an inversely graded layer made of bombs and lapilli; (2) a finely laminated layer with wavy bedforms made of coarse ash and fine lapilli; (3) a structureless fine-ash bed. Lack of discontinuities at layer contacts allows us to hypothesize that each set of beds represents the passage of one pyroclastic density current. The sequence formed as a function of the decreasing particle transportation capability of the base surge during the waxing-sustained-waning phases of flowage. We make the simplifying assumptions that the flow, on passing from the deposition of the inversely graded layer to the deposition of the finely laminated layer, had low particle concentration, was quasi-steady and incompressible. By such assumptions, some of the equations that regulate sediment mechanics are applicable to the base surges of Campi Flegrei to reconstruct flow density and shear velocity in between the deposition of the two layers. Structural and textural features of deposits stress the importance of shear and turbulence during transportation and suggest that the turbulent boundary layer shear flow is a good approximation to such pyroclastic density currents. We used the Coles formula to reconstruct velocity as a function of flow height during the formation of the finely laminated layer of Astroni and Agnano-Monte Spina base surges. The methodology we used allows the reconstruction of flow parameters just at a particular point in time and space of base-surge evolution, and does not provide the complete picture of the flow history of pyroclastic density currents. Nevertheless, flow velocity and density data, as obtained with the proposed approach, point to dynamic pressure values that are compatible with those reported for similar currents on other volcanoes. We conclude therefore that the results obtained give approximate but helpful information on the nature of such hazardous events at Campi Flegrei
Simultaneous normal and reverse faulting in reactivating caldera faults: A detailed field structural analysis from Campi Flegrei (southern Italy)
No full textModels of volcanic collapses proposed in the literature rely on combining field examples with analogue and numerical modelling to connect superficial observables to sub-surface volcano-tectonic processes. However, the behaviour of such collapses in an already faulted and fractured medium needs to be better explored. We studied a complex array of normal and reverse faults within the central sector of the active Campi Flegrei caldera, where faults with centimeters-to-meters displacements are hosted in the La Pietra tuff (∼13.5 ka) and the overlying pyroclastic succession of the last ∼5.5 kyr. We analyzed the attitude, kinematics and throw of these structures, employing a UAV-based digital outcrop model. The analysis shows that antithetic normal and reverse faults form in the hanging wall of a pre-existing WNW striking, NNE-dipping master normal fault. Moving northward, the strike of the antithetic faults rotates from WNW to NNW directions, with the latter showing a right-lateral oblique component. The simultaneity and coherence of both kinematics and attitudes are verified by the throw analysis. We associated the formation of this array with the caldera-collapse phase of the Agnano-Monte Spina eruption (∼4.55 ka), which caused off-caldera faulting beyond the main collapsed area. Based on field data, we suggest that during peak caldera-forming phases, wider areas beyond the main caldera scarps can be involved in volcano-tectonic collapses in the presence of a pre-existing fault network and complex tapped reservoirs. This highlights the role of inherited structures in weakening the crust above the magma reservoir that can potentially increase the magnitude and duration of caldera-forming eruptions, as they may induce a broader roof rock subsidence, pressurizing wider regions of the sub-caldera magma system
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Statistical analysis of textural data from complex pyroclastic sequences: implications for fragmentation processes of the Agnano-Monte Spina Tephra (4.1 ka), Phlegraean Fields, southern Italy
No full textThe Agnano-Monte Spina eruption (4.1 ka) generated pyroclastic deposits with complex internal stratigraphy that reflects variations in eruptive style. To obtain constraints on the fragmentation processes, we analysed grain-size and scanning electron microscopy (SEM) data by means of multivariate statistical techniques of the cluster and factor analysis types. The results allow the identification of end-member deposits related to either pure magmatic activity, or pure phreato-magmatic activity. In addition, some deposits show evidence of the contemporaneous operation of both end-member fragmentation modes. The presence of the two contrasting fragmentation processes during the various phases of explosive activity is tentatively interpreted to be a function in inhomogeneities in gas exsolution processes within the magma column that feeds the eruption
Textural and rheological constraints on the fallout- PDCs transitions of the Agnano-Monte Spina eruption (Campi Flegrei, Italy)
No full textHolocene benthic foraminiferal and ostracod assemblages in a paleo-hydrothermal vent system of Campi Flegrei (Campania, south Italy)
Full text linkThe succession of the Late Quaternary La Starza terrace, located within the Campi Flegrei caldera, on the Tyrrhenian side of southern Italy, represents a well-known example of deposition under the combined influence of bathymetric and phys-ico-chemical variations due to volcanic activities. One hundred and seven samples collected in six outcrops and some tunnel excavation fronts, with an age between ~12 and ~4 k.y.a, comprise both barren and fossiliferous sediments. The latter contain siliceous and/or calcareous microfossil remains, including benthic foraminiferal and ostracod assemblages indicative of a marine paleodepth ranging from the upper infralittoral to the upper circalittoral zone, with phases of intense environmental stress typical of a hydrothermal system. A detailed reconstruction of the Holocene paleoenvironmental evolution of the succession is presented. The majority of foraminiferal and ostracod species is illustrated and brief taxonomic and ecological notes are given for each of them. © November 2018 Paleontological Society
THE CAMPANIAN IGNIMBRITE ERUPTION, HEINRICH EVENT 4, AND PALAEOLITHIC CHANGE IN EUROPE: A HIGH-RESOLUTION INVESTIGATION
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