Bulk atmospheric deposition of major cations (Na, K, Ca, Mg) and anions (Cl, F, SO4) were measured at 15 sites around an active volcano, Mount Etna, from 2001 to 2003. Their composition indicates several natural
sources, among which deposition of plume-derived volcanogenic gas compounds is prevalent for F, Cl and S. Plume-derived acidic
compounds are also responsible for the prevailing acidic composition of the samples collected on the summit of the volcano
(pH in the 2.45–5.57 range). Cation species have complex origin, including deposition of plume volcanogenic ash and aerosols
and soil-dust wind re-suspension of either volcanic or carbonate sedimentary rocks.
Variation of the deposition rates during the March 2001–March 2003 period, coupled with previous measurements from 1997 to
2000 (Appl Geochem 16:985–1000, 2001), were compared with the variation of SO2 flux, volcanic activity and rainfall. The deposition rate was mainly controlled by rainfall. Commonly, about 0.1–0.9% of
HF, HCl and SO2 emitted by the summit crater's plume were deposited around the volcano. We estimate that ∼2 Gg of volcanogenic sulphur were
deposited over the Etnean area during the 2002–2003 flank eruption, at an average rate of ∼24 Mg day−1 which is two orders of magnitude higher than that typical of quiescent degassing phases. 相似文献
We exploit observations at 1.25 mm with the ESO–SEST telescope of a southern galaxy sample, selected from the IRAS PSC and complete to S 60=2 Jy, to derive the FIR and mm luminosity functions and the conditional probability distributions of FIR and mm luminosity of galaxies. The reliability of these estimates is ensured by the good observed correlation of the far-infrared and mm emissions. This detailed knowledge of the millimetric properties of galaxies is used to simulate the extragalactic sub-mm sky (background intensity, small-scale anisotropy signals and discrete source statistics), which is the target of a variety of ground-based and space observatories. We find, in particular, that a recent tentative detection of a sub-mm background would require, if confirmed, strong evolution with cosmic time of the galaxy long-wavelength emissivity. We finally discuss ways to test such evolution with present and forthcoming facilities: while emphasizing the difficulty of achieving this with large mm telescopes on the ground (because of the poor atmospheric conditions of current sub-mm sites), we mention an interesting opportunity with the long-wavelength camera on ISO . Preliminary results of deep surveys, both from space and from the ground, seem indeed to require excess emission in the past by dusty galaxies with respect to no-evolution predictions. 相似文献
A better understanding of genesis and palaeoenvironmental setting of the Scisti silicei Formation (Lagonegro units, southern Italy) was achieved by means of geochemical analysis integrated with new stratigraphic information. Data show that major and trace element geochemistry of ancient clay-rich beds and banded cherts add new insights into the Mesozoic evolution of the Lagonegro basin. Sedimentary contributions to Jurassic shales sampled during this study were mainly derived from two major sources: (i) a dominant terrigenous fine-grained component, having affinity with average upper continental crust that had not undergone intense weathering and (ii) biogenic siliceous material. The latter component occurs in clay-rich layers from the “basal member” of the Scisti silicei Formation.
Composition varies up section and accounts for changes in the detrital supply due to bathymetric oscillations. The compositional variations from the basal to the overlying member are consistent with a distal source passing in time to a more “proximal” source, as indicated by sharp changes in the concentrations of detrital elements (Ti, Zr and Nb). It is likely that increased detrital input occurred through turbidity current deposition. Finally, the chemical features of the clay-rich layers from the upper cherty portion of the studied succession imply a progressive deepening of the basin.
The lack of any mafic and hydrothermal contributions in the Jurassic shales as well as the continental nature of detrital input suggests that the Lagonegro basin was located between two carbonate platforms, in accordance with the classical restoration of the African–Apulian palaeomargin. Thus, the basin acted as a preferential sink connected to the African cratonic areas through a southern entry point. 相似文献
Our understanding of sedimentation in alluvial basins is best for very short and very long time‐scales (those of bedforms to bars and basinwide deposition, respectively). Between these end members, the intermediate time‐scales of stratigraphic assembly are especially hard to constrain with field data. We address these ‘mesoscale’ fluvial dynamics with data from an experimental alluvial system in a basin with a subsiding floor. Observations of experimental deposition over a range of time‐scales illustrate two important properties of alluvial systems. First, ephemeral flows are disproportionately important in basin filling. Lack of correlation between flow occupation and sedimentation indicates that channelized flows serve mainly as conduits for sediment, while most deposition occurs via short‐lived unchannelized flow events. Second, there is a characteristic time required for individual depositional events to average to basin‐scale stratal patterns. This time can be scaled in terms of the time required for a single channel‐depth of aggradation, and in this form is constant through a four‐fold variation of experimental subsidence rate. 相似文献
Landslide risk of the Campanian carbonate slopes covered by pyroclastic deposits is mainly connected with the occurrence of
high-velocity debris avalanches and debris flows. Analyses show that flows initiate as small translational slides in the pyroclastics.
The failure process is controlled by the interaction of both natural and human-induced factors. Geomorphological settings
play a decisive role in locating the source failures. Therefore, the crucial aspects in landslide hazard and risk assessment
are: (a) recognise the geomorphological control factors, (b) determine parameters defining landslide intensity (velocity,
volume, depth of deposit) and (c) predict landslide runout distance. An approach combining geomorphology and numerical analysis
has been adopted in the work reported here. Potential future landslide intensity scenarios are simulated predicting the runout
behaviour of potential instabilities by using a dynamic model previously calibrated by back-analysing observed events of similar
scale and type. The selected area is a sector of the Avella Mountains having the same geomorphological environment as the
1998 Sarno landslides (Campania, Southern Italy). 相似文献