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The Onano explosive eruption of the Latera Volcanic Complex (Vulsini Volcanoes, Quaternary potassic Roman Comagmatic Region, Italy) provides an interesting example of multiple changes of eruptive style that were concomitant with a late phase of collapse of the polygenetic Latera Caldera. This paper reports a reconstruction of the event based on field analysis, laboratory studies of grain size and density of juvenile clasts, and re-interpretation of available subsurface geology data. The Onano eruption took place in a structurally weak area, corresponding to a carbonate substrate high bordered by the pre-existing Latera caldera and Bolsena volcano-tectonic depression, which controlled the ascent and eruption of a shoshonitic-phonotephritic magma through intersecting rim fault systems. Temporal changes of magma vesiculation, fragmentation and discharge rate, and consequent eruptive dynamics, were strongly controlled by pressure evolution in the magma chamber and changing vent geometry. Initially, pumice-rich pyroclastic flows were emplaced, followed by spatter- and lithic-rich flows and fallout from energetic fire-fountaining. The decline of magma pressure due to the partial evacuation of the magma chamber induced trapdoor collapse of the chamber roof, which involved part of the pre-existing caldera and external volcano slopes and eventually led to the present-day caldera. The widening of the vent system and the emplacement of the main pyroclastic flow and associated co-ignimbrite lag breccia marked the eruption climax. A sudden drop of the confining pressure, which is attributed to a pseudo-rigid behaviour of the magma chamber wall rocks during a phase of rapid magma drainage, led to extensive magma vesiculation and fragmentation. The disruption of the magma chamber roof and waning magma pressure in the late eruption stage favoured the explosive interaction of residual magma with groundwater from the confined carbonate aquifer. Pulsating hydrostatic and magma pressures produced alternating hydromagmatic pyroclastic surges, strombolian fallout and spatter flows. 相似文献
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Danilo R. Velis 《Mathematical Geology》2007,39(4):409-417
Stationary segments in well log sequences can be automatically detected by searching for change points in the data. These
change points, which correspond to abrupt changes in the statistical nature of the underlying process, can be identified by
analysing the probability density functions of two adjacent sub-samples as they move along the data sequence. A statistical
test is used to set a significance level of the probability that the two distributions are the same, thus providing a means
to decide how many segments comprise the data by keeping those change points that yield low probabilities. Data from the Ocean
Drilling Program were analysed, where a high correlation between the available core-log lithology interpretation and the statistical
segmentation was observed. Results show that the proposed algorithm can be used as an auxiliary tool in the analysis and interpretation
of geophysical log data for the identification of lithology units and sequences. 相似文献
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An incentive mechanism for reducing emissions from conversion of intact and non-intact forests 总被引:1,自引:0,他引:1
Danilo Mollicone Frédéric Achard Sandro Federici Hugh D. Eva Giacomo Grassi Alan Belward Frank Raes Günther Seufert Hans-Jürgen Stibig Giorgio Matteucci Ernst-Detlef Schulze 《Climatic change》2007,83(4):477-493
This paper presents a new accounting mechanism in the context of the UNFCCC issue on reducing emissions from deforestation
in developing countries, including technical options for determining baselines of forest conversions. This proposal builds
on the recent scientific achievements related to the estimation of tropical deforestation rates and to the assessment of ‘intact’
forest areas. The distinction between ‘intact’ and ‘non intact’ forests used here arises from experience with satellite-based
deforestation measurements and allows accounting for carbon losses from forest degradation. The proposed accounting system
would use forest area conversion rates as input data. An optimal technical solution to set baselines would be to use historical
average figures during the time period from 1990 to 2005. The system introduces two different schemes to account for preserved
carbon: one for countries with high forest conversion rates where the desired outcome would be a reduction in their rates,
and another for countries with low rates. A ‘global’ baseline rate would be used to discriminate between these two country
categories (high and low rates). For the hypothetical accounting period 2013–2017 and considering 72% of the total tropical
forest domain for which data are available, the scenario of a 10% reduction of the high rates and of the preservation of low
rates would result in approximately 1.6 billion tCO2 of avoided emissions. The resulting benefits of this reduction would be shared between those high-rate countries which reduced
deforestation and those low-rate countries which did not increase their deforestation over an agreed threshold (e.g., half
of “global” baseline rate). 相似文献
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Simona Petrosino Paola Cusano Mario La Rocca Danilo Galluzzo Justo Orozco-Rojas Mauricio Bretón Jesus Ibáñez Edoardo Del Pezzo 《Bulletin of Volcanology》2011,73(7):887-898
This paper presents an analysis of seismicity associated with the volcanic activity of Volcàn de Colima (México) and recorded
in the period November 2005–April 2006 during a field survey by the Istituto Nazionale di Geofisica e Vulcanologia (INGV)–Osservatorio
Vesuviano, the Observatorio Vulcanologico de Colima of Colima University and the Instituto Andaluz de Geofisica, University
of Granada. Three different types of volcanic earthquakes have been identified on the basis of their spectral properties:
Type A (0.3–1 Hz), Type B (1–5 Hz) and Type C (3–4 Hz). Results of polarization analysis applied to Type A events show a predominance
of radial motion, indicating that the wavefield comprises compressional waves (P) and shear waves polarized in the vertical
plane (SV), while the signal always begins with a negative polarity. Type A, B and C earthquakes have been located using both
a flat layered model and a 3D model including topography. Hypocentre distributions indicate that the source of Type A signals
is very shallow and confined to a small volume lying about 1 km below the crater. In contrast, the source of Type B and C
events is significantly deeper, with most hypocentres located in a volume of about 1 km3 centred at 2.5–3 km depth. A cluster analysis based on the cross-correlation among the waveforms of different events recorded
at the same station was applied to Type A earthquakes. Only two clusters, which include only a small percentage of events
were found, indicating that earthquake families were uncommon during the period of our survey. 相似文献
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Carmela Freda Mario Gaeta Biagio Giaccio Fabrizio Marra Danilo M. Palladino Piergiorgio Scarlato Gianluca Sottili 《Bulletin of Volcanology》2011,73(3):241-256
Generally, the intensity and magnitude of explosive volcanic activity increase in parallel with SiO2 content. Pyroclastic-flow-forming eruptions in the Colli Albani ultrapotassic volcanic district (Italy) represent the most
striking exception on a global scale, with volumes on the order of tens of cubic kilometres and K-foiditic compositions (SiO2 even <42 wt.%). Here, we reconstruct the pre-eruptive scenario and event dynamics of the ~456 ka Pozzolane Rosse (PR) eruption,
the largest mafic explosive event of the Colli Albani district. In particular, we focus on the driving mechanisms for the
unusually explosive eruption of a low-viscosity, mafic magma. Geologic, petrographic and geochemical data with mass balance
calculations, supported by experimental data for Colli Albani magma compositions, provide evidence for significant ingestion
of carbonate wall rocks by the Pozzolane Rosse K-foiditic magma. Moreover, the scattered occurrence of cored bombs in Pozzolane
Rosse pyroclastic-flow deposits records carbonate entrainment even at the eruptive time scale, as also tested quantitatively
by thermal modelling of magma–carbonate interaction and carbonate assimilation experiments. We suggest that the addition of
free CO2 from decarbonation of country rocks was the major factor controlling magma explosivity. High CO2 activity in the volatile component, coupled with magma depressurisation, produced extensive leucite crystallisation at short
time scales, resulting in a dramatic increase in magma viscosity and volatile pressurisation, which was manifested a change
of eruptive dynamics from early effusion to the Pozzolane Rosse's highly explosive eruption climax. 相似文献
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