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Fisher, Richard V
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Fisher, Richard V
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Fisher, R. V.
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- PublicationRestrictedThe Agnano–Monte Spina eruption 4100 years BP/ in the restless Campi Flegrei caldera Italy(1999)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;de Vita, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Orsi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Civetta, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Carandente, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;D’Antonio, M.; Dipartimento di Geofisica e Vulcanologia, L. go San Marcellino, 10-80138 Naples, Italy ;Deino, A.; Institute of Human Origin, Berkeley, CA, USA ;di Cesare, T.; Dipartimento di Geofisica e Vulcanologia, L. go San Marcellino, 10-80138 Naples, Italy ;Di Vito, M. A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Fisher, R.V.; Department of Geological Sciences, UniÍersity of California, Santa Barbara, CA, USA ;Isaia, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Marotta, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Necco, A.; Dipartimento di Geofisica e Vulcanologia, L. go San Marcellino, 10-80138 Naples, Italy ;Ort, M.; Department of EnÍironmental Sciences and Geology, Northern Arizona UniÍersity, Flagstaff, AZ, USA ;Pappalardo, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Piochi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Southon, J.; LiÍermore National Laboratory, LiÍermore, CA, USA; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The Agnano–Monte Spina tephra AMST , dated at 4100 years BP by Arr Ar and C AMS techniques, is the product of the highest-magnitude eruption in the Campi Flegrei caldera CFc. during its last epoch of activity 4800–3800 years BP.. The sequence alternates magmatic and phreatomagmatic pyroclastic-fallout, -flow and -surge beds and bedsets. Two main pumice-fallout deposits with variable easterly-to-northeasterly dispersal axes are about 10 cm thick at 42 km from the vent area. High particle concentration pyroclastic currents were confined to the caldera depression; lower concentration flows overtopped the morphological boundary of the caldera and traveled at least 15 km over the surrounding plain. The unit is subdivided into six members, named A through F in stratigraphic sequence, based upon their sedimentological characteristics. Isopachs and isopleths maps suggest a vent location in the Agnano plain. A volcano-tectonic collapse begun during the course of the eruption, took place along the faults of the northeastern sector of the resurgent block within the CFc, and generated the Agnano plain. The early erupted trachytic magma had a homogeneous alkali–trachytic composition, whereas later-erupted magma shows small-scale hetereogeneities. Trace elements and Sr-isotope compositions, indicate that two isotopically distinct magmas, one alkali–trachytic and the other trachytic, were tapped and partially mixed during the eruption. The small volume 1.2 km3 DRE. of erupted magma and the structural position of the vent suggest that the eruption was fed by a dyke intruded along a normal fault in the sector of the resurgent block under a tensional stress regime. q1999 Elsevier Science B.V. All rights reserved285 20 - PublicationRestrictedAnisotropy of magnetic susceptibility studies of depositional processes in the Campanian Ignimbrite, Italy(2003)
; ; ; ; ; ; ; The late Pleistocene trachytic Campanian Ignimbrite underlies much of the Campanian Plain near Naples, Italy, and occurs in valleys in the mountainous area surrounding the plain out to about 80 km from its source, the Campi Flegrei caldera. At sites within 15 km of the Campi Flegrei, anisotropy of magnetic susceptibility (AMS) principal directions indicate that, in the absence of significant topography, deposition came from a flow moving in a roughly radial direction. AMS studies of the more distal ignimbrite reveal downhill and/or downvalley flow directions prior to deposition, even where these directions are at high angles to a generally radial transport direction from the vent. On the flanks of Roccamonfina Volcano, flow was directly downhill, as if the source of the ignimbrite was the summit of the volcano. In most localities, the ignimbrite consists of a single massive deposit. In a few localities in the Apennine Mountains, however, the confluence of multiple drainage systems off mountains resulted in multiple local flow units that cannot be correlated between valleys. A detailed study of the ignimbrite in the flat Titerno River valley near Massa shows that the AMS fabrics are not due to late-stage creeping during deposition or compaction. Well-defined, but non-parallel AMS fabrics from vertical and lateral sections in the Massa area are best explained by the merging of gravity currents flowing down the valley and steep valley sides to form a single aggradational deposit. Clast compositions and AMS axes at Mondragone indicate that the pyroclastic flow encountered the Monte Massico massif and was partially blocked, so that flow during deposition was toward the Campi Flegrei. Similar AMS data from sites along the edge of the Campanian Plain indicate back-flow off the first ridge of the Apennine Mountains reached at least 5 km from their base. The Campanian Ignimbrite was deposited from a density-stratified pyroclastic flow. The depositional system consisted of the lower, denser portion of the current, and was controlled by topography. The grouping of the AMS axes is interpreted to indicate that deposition occurred under laminar flow conditions.92 2 - PublicationRestrictedGeochemical zoning, mingling, eruptive dynamics and depositional processes — the Campanian Ignimbrite, Campi Flegrei caldera, Italy(1997)
; ; ; ; ; ; ; ; ; ; ; The Campanian Ignimbrite (CI) is a large-volume trachytic tuff erupted at 37 ka from the Campi Flegrei and composed of a fallout deposit overlain by ignimbrite. The ignimbrite was spread over an area of about 30,000 km2 including the Campanian Plain and the Apennine Mountains, with ridges over 1000 m a.s.l. The pumice fragments of the CI range in composition from trachyte to phonolitic-trachyte (DI = 75-90). They do not show any systematic compositional variation with stratigraphic height, but the analyzed sections can be divided into three groups on the basis of chemical composition of pumices. Least-evolved pumices (DI = 75-83) occur in the ignimbrite in the central sector of the Campanian Plain up to 30 km from the vent, while the most-differentiated pumices (DI = 88-90) characterize the cogenetic fallout deposit and the ignimbrite in the western sector of the Campanian Plain, on the Tyrrhenian scarp of the Apennines between Caserta and Mt. Maggiore, on Roccamonfina volcano, and on the Sorrento Peninsula, up to 50 km from the source. Pumice fragments of intermediate composition (DI = 84-87) occur in the ignimbrite on the Apennine Mountains and Roccamonfina volcano, up to 65 km from the vent. In one exposure at Mondragone, at the base of a calcareous ridge, an ignimbrite with pumices of most-evolved composition is overlain by an ignimbrite with pumices of intermediate composition. The observed compositional variation between most-and least-evolved ignimbrite was generated in part by crystal-liquid fractionation, although other magmatic processes such as syn-eruptive mingling between most-and least-evolved magmas accounts for the mineralogical disequilibria and for the bimodality of the glass compositions in the intermediate-composition rocks. Pumice Sr-isotope ratios are positively correlated with degree of differentiation. Feldspar crystals separated from pumices of different compositions have a homogeneous Sr-isotope composition similar to that of the least-evolved pumices. Interaction between fluids and strongly fractionated Sr-poor less-dense magma can account for these isotopic features. Geochemical, mineralogic, stratigraphic and volcanologic data, together with the stratigraphic relations between most-, intermediate-and least-evolved ignimbrite as detected at Mondragone and from bore-hole drillings suggest that: (1) the CI magmatic system was composed of two distinct magma layers - the upper layer was more differentiated and homogeneous in composition, while the deeper was less evolved and slightly zoned; and (2) the CI was mostly emplaced in three main pulses of pyroclastic flows that tapped the chamber at variable levels and with distinct withdrawal dynamics. The eruption began with emission of the most differentiated magma, which gave rise to the fallout deposit. It continued with generation of expanded, turbulent pyroclastic flows that reached the Sorrento Peninsula in the southeast and Roccamonfina volcano in the northwest. These flows, whose thickness was greater than the overtopped relief, were able to travel over the water of the bay of Naples. Subsequently an intermediate-composition magma resulting from mingling of different portions of the magma chamber generated similar flows that spread radially and traveled not less than 65 km from the vent. During the last pulse the least-evolved magma was tapped and generated flows that spread within the Campanian Plain. Variation in eruptive dynamics and composition of magma during the course of the eruption likely reflected variations of both geometry of vent and plumbing system, and efficiency of water/magma interaction, which in turns affected the dynamics of the magma chamber and the withdrawal mechanism, and resulted from the dynamics of the caldera collapse.88 3 - PublicationRestrictedTiming of magma extraction during the Campanian Ignimbrite eruption (Campi Flegrei Caldera)(2002)
; ; ; ; ; ; ; ;Pappalardo, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Civetta, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;de Vita, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Di vito, M. A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Orsi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Carandente, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Fisher, R. V.; Department of Geological Sciences, University of California, Santa Barbara, CA 93106, USA; ; ; ; ; ; A core drilled within the northern part of the city of Napoli has offered the unique opportunity to observe in one single sequence the superposition of the four pyroclastic flow units emplaced during the Campanian Ignimbrite (CI) eruption. Such a stratigraphic succession has never been encountered before in natural or in man made exposures. Therefore the CI sequence was reconstructed only on the basis of stratigraphic correlations and compositional data (in literature). The occurrence of four superposed CI flows, together with all the data available (in literature) allowed us to better constrain the chemical stratigraphy of the deposit and the compositional structure of the CI magma chamber. The CI magma chamber includes two cogenetic magma layers, separated by a compositional gap. The upper magma layer was contaminated by interaction with radiogenic fluids. The two magma layers were extruded either individually or simultaneously during the course of the eruption. In the latter case they produced a hybrid magma. But no evidence of input of new geochemically and isotopically distinct magma batches just prior or during the eruption has been found. Comparison with the exposed CI deposits has permitted reconstruction of variable eruption phases and related magma withdrawal and caldera collapse episodes. The eruption was likely to have began with phreatomagmatic explosions followed by the formation of a sustained plinian eruption column fed by the simultaneous extraction from both magma layers. Towards the end of this phase the upward migration of the fragmentation surface and the decrease in magma eruption rate and/or activation of fractures formed an unstable pulsating column that was fed only by the most-evolved magma layer. This plinian phase was followed by the collapse of the eruption column and the beginning of caldera formation. At this stage expanded pyroclastic flows fed by the upper magma layer in the chamber generated. During the following major caldera collapse episode, the maximum mass discharge rate was reached and both magma layers were tapped, generating expanded pyroclastic flows. Towards the end of the eruption, only the deeper and less differentiated magma layer was tapped producing more concentrated pyroclastic flows that traveled short distances.188 16