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1.
F. Marcolini G. Bigazzi F. P. Bonadonna E. Centamore R. Cioni G. Zanchetta 《第四纪科学杂志》2003,18(6):545-556
The stratigraphical context of two Middle Pleistocene fossiliferous palaeosols from Central Italy (Abruzzo and Tuscany) have been studied. Small mammals and molluscs occur in both palaeosols, which are covered by tephra layers that were analysed using an interdisciplinary approach. Application of fission‐track dating to apatites separated from the Case Picconetto tephra (Pescara, Abruzzo), yielded an age of 0.48 ± 0.04 Ma, indistinguishable from those previously determined for the Campani Quarry (Lower Valdarno, Tuscany) (0.46 ± 0.05 Ma and 0.48 ± 0.05 Ma). Geochemical and petrographic investigations indicate that these tephra originated from different volcanoes, the Alban Hills Volcanic Complex and the Vico Volcano (Latium) respectively. Small mammal and mollusc assemblages indicate different palaeoclimatic and palaeoenvironmental conditions for the Case Picconetto and Campani Quarry palaeosols. Warm and humid conditions can be inferred for the Campani Quarry site, whereas open and cold conditions can be inferred for Case Picconetto. On the basis of faunal data, fission‐track dates and attribution of tephra to specific volcanic eruptions, we suggest a correlation of these faunas with marine oxygen isotope stage 14 (Case Picconetto) and with marine oxygen isotope stage 11 (Campani Quarry), respectively. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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Claudio Arias Giulio Bigazzi Francescopaolo Bonadonna Karl Brunnacker Brigitte Urban 《Quaternary Science Reviews》1984,3(1):73-89
Biostratigraphic and palaeomagnetic research has been carried out on selected profiles in North-Western Germany and Central Italy in order to correlate Plio-Pleistocene sections.Around the Réunion subchronozone, vegetation in the Valle Ricca was dominated by a mountain forest type pointing to cool climatic conditions. In the Lower Rhine Basin vegetation had a slightly warmer character, but was also dominated strongly by a mountain type of forest vegetation, characteristic of cooler summers and higher precipitation than at present.Two warmer periods have been determined in the Central Italian profiles; the youngest around the Olduvai reversal, should correspond to the youngest Tiglian beds of the Lower Rhine Basin.Deposits older than the Réunion subzone have not been found in the Valle Ricca. In the Lower Rhine Basin, on the other hand, the Gauss-Matuyama boundary is located between the uppermost Pliocene, the Reuverian C and the Praetiglian. 相似文献
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Physical parameters of explosive eruptions are typically derived from tephra deposits. However, the characterization of a
given eruption relies strongly on the quality of the dataset used, the strategy chosen to obtain and process field data and
the particular model considered to derive eruptive parameters. As a result, eruptive parameters are typically affected by
a certain level of uncertainty and should not be considered as absolute values. Unfortunately, such uncertainty is difficult
to assess because it depends on several factors and propagates from field sampling to the application and interpretation of
dispersal models. Characterization of explosive eruptions is made even more difficult when tephra deposits are poorly exposed
and only medial data are available. In this paper, we present a quantitative assessment of the uncertainty associated with
the characterization of tephra deposits generated by the two largest eruptions of the last 2,000 years of Cotopaxi volcano,
Ecuador. In particular, we have investigated the effects of the determination of the maximum clast on the compilation of isopleth
maps, and, therefore, on the characterization of plume height. We have also compared the results obtained from the application
of different models for the determination of both plume height and erupted volume and for the eruption classification. Finally,
we have investigated the uncertainty propagation into the calculation of mass eruption rate and eruption duration. We have
found that for our case study, the determination of plume height from isopleth maps is more sensitive to the averaging techniques
used to define the maximum clast than to the choice of dispersal models used (i.e. models of Carey and Sparks 1986; Pyle 1989) and that even the application of the same dispersal model can result in plume height discrepancies if different isopleth
lines are used (i.e. model of Carey and Sparks 1986). However, the uncertainties associated with the determination of erupted mass, and, as a result, of the eruption duration,
are larger than the uncertainties associated with the determination of plume height. Mass eruption rate is also associated
with larger uncertainties than the determination of plume height because it is related to the fourth power of plume height.
Eruption classification is also affected by data processing. In particular, uncertainties associated with the compilation
of isopleth maps affect the eruption classification proposed by Pyle (1989), whereas the VEI classification is affected by the uncertainties resulting from the determination of erupted mass. Finally,
we have found that analytical and empirical models should be used together for a more reliable characterization of explosive
eruptions. In fact, explosive eruptions would be characterized better by a range of parameters instead of absolute values
for erupted mass, plume height, mass eruption rate and eruption duration. A standardization of field sampling would also reduce
the uncertainties associated with eruption characterization. 相似文献
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We present a comprehensive probabilistic hazard assessment for tephra fallout of Cotopaxi volcano (Ecuador), a quiescent but active stratovolcano known for its highly explosive behaviour. First, we developed a set of possible eruptive scenarios based on thorough field investigations, literature studies and using the Global Volcanism Program (GVP) database. Five eruption scenarios were identified, including two based on large pre-historical sub-Plinian/Plinian eruptions with eruptive parameters constrained from field investigations (One Eruption Scenario; OES) and three Eruption Range Scenarios (ERS) based on the Volcanic Explosivity Index (VEI) classification, for which eruptive parameters (i.e. erupted volume, plume height and median grainsize) were stochastically sampled within boundaries defined by VEI 3, 4 and 5. Second, the modelling was performed using the advection-diffusion model TEPHRA2 in combination with wind profiles from the NOAA NCEP/NCAR Reanalysis 1 database. We performed 1,000 runs for each eruption scenario, stochastically sampling a wind profile (OES and ERS) and a set of eruptive parameters (ERS only) at each run. Using the conditional probabilities of occurrence of eruption of VEI 3, 4 and 5 calculated from the GVP catalogue, we assessed the probability of tephra accumulation in a given time window. Based on the GVP database, a simple Poisson model shows that an eruption of VEI???3 has a 36?% probability of occurrence in the next 10?years. Finally, the hazard assessment was compiled based on three different outputs, including (i) probability maps for a given tephra accumulation, (ii) isomass maps for a given probability value and (iii) hazard curves for a given location. We conclude that the area west of Cotopaxi is exposed to light to severe tephra fallout for the smallest eruption magnitude considered (i.e. VEI 3). This area comprises a main communication axis (Panamerican Highway) topographically constrained at the bottom of the Interandean Valley, as well as the capital Quito and the town of Latacunga. In a companion paper, Biass et?al. (this volume) propose a method for a rapid risk assessment for tephra fallout using global and easily accessible data and the hazard assessment described here. 相似文献
6.
New physical characterization of the Fontana Lapilli basaltic Plinian eruption,Nicaragua 总被引：1，自引：1，他引：0
The Fontana Lapilli deposit was erupted in the late Pleistocene from a vent, or multiple vents, located near Masaya volcano
(Nicaragua) and is the product of one of the largest basaltic Plinian eruptions studied so far. This eruption evolved from
an initial sequence of fluctuating fountain-like events and moderately explosive pulses to a sustained Plinian episode depositing
fall beds of highly vesicular basaltic-andesite scoria (SiO2 > 53 wt%). Samples show unimodal grain size distribution and a moderate sorting that are uniform in time. The juvenile component
predominates (> 96 wt%) and consists of vesicular clasts with both sub-angular and fluidal, elongated shapes. We obtain a
maximum plume height of 32 km and an associated mass eruption rate of 1.4 × 108 kg s−1 for the Plinian phase. Estimates of erupted volume are strongly sensitive to the technique used for the calculation and to
the distribution of field data. Our best estimate for the erupted volume of the majority of the climactic Plinian phase is
between 2.9 and 3.8 km3 and was obtained by applying a power-law fitting technique with different integration limits. The estimated eruption duration
varies between 4 and 6 h. Marine-core data confirm that the tephra thinning is better fitted by a power-law than by an exponential
trend. 相似文献
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G. Bigazzi O. Giuliani F. P. Bonadonna C. Ghezzo F. Rita F. Radicati Di Brozolo 《Bulletin of Volcanology》1981,44(3):455-465
K/Ar and fission track age measurements were performed on lava samples of Monte Amiata volcano (Central Italy) which is formed by a sequence of lava flows and lava domes ranging in composition from trachybasalts to high-SiO2 quartzlatites. The ages obtained, except for the oldest volcanic products, range from 290,000 to 180,000 years. Excess40Ar was found in some mineral separates, especially biotite, causing apparent rather old ages. The correct ages were calculated by means of K/Ar isochrons, and were found to be very similar to the ages calculated on sanidine separates. The volcanic activity that built up the outcropping Monte Amiata units seems to have lasted a relatively short time. 相似文献
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Lo?c Vanderkluysen Andrew J. L. Harris Karim Kelfoun Costanza Bonadonna Maurizio Ripepe 《Bulletin of Volcanology》2012,74(8):1849-1858
We collected thermal infrared video of two explosive eruptions at Stromboli in June 2008 and manually traced the trajectories of 95 particles launched during two eruptions. We found that 10–15?% of the analyzed trajectories deviated from predicted curves due to collisions, causing one particle to travel horizontally more than twice as far as expected. Furthermore, we observed an oscillatory cooling behavior for the airborne pyroclasts, with a median period of 0.46?s. Measured cooling was typically much faster than model-predicted cooling with discrepancies of up to 40?% between measured cooling and theoretical modeling. We interpret the measured cooling curves as resulting from the spinning and twisting and tearing of particles during travel: the periodic re-exposing of the hotter core of the pyroclasts to the atmosphere may cause the observed oscillations, and the spinning may accelerate cooling by enhancing convective heat transfer. Current volcanic trajectory and cooling models do not account for projectile collisions, spinning, or tearing and can thus severely underestimate the maximum landing distance and cooling rates of large pyroclasts. 相似文献