A rock avalanche deposit was investigated in order to understand the chronological evolution of geological hazards and to evaluate the interaction of the triggering geodynamic processes in the valley Val Viola, Italian Alps. The deposit is situated west of the Alpe Dosdé, in a permafrost area with deep-seated gravitational deformations (DSGD) along a tectonic line. Based on its geomorphologic context, the rock avalanche was first interpreted as a result of slope stress release without exact timing. This hypothesis was tested by measuring the 10Be exposure date of quartz from one boulder from the rock avalanche. The age of 7430±460 years places the event in the early Holocene. The timing of the last deglaciation was constrained using the inner late glacial moraine of a moraine doublet in the valley Alpe Dosdé situated at an altitude between 2140 and 2120 m a.s.l. west of the rock avalanche. The 10Be concentrations of quartz yield minimum exposure ages of 11,480±670 and 10,850±820 years. Different proposals for potential triggering factors of the rock avalanche include (a) melting of the local valley glacier and slope stress release in the Val Viola, likely to play a minor role as trigger, because of the time delay between the deglaciation and the rock avalanche event. More likely are (b) enhanced crustal seismicity induced by post-glacial regional isostatic glacial rebound coupled with tectonic stress or/and (c) climate conditions with higher temperatures around 7430±460 years, resulting in an upwards movement of the permafrost limit and destabilization of the rock walls. 相似文献
Strontium sorption to amorphous silica and goethite was measured as a function of pH and dissolved strontium and carbonate
concentrations at 25°C. Strontium sorption gradually increases from 0 to 100% from pH 6 to 10 for both phases and requires
multiple outer-sphere surface complexes to fit the data. All data are modeled using the triple layer model and the site-occupancy
standard state; unless stated otherwise all strontium complexes are mononuclear. Strontium sorption to amorphous silica in
the presence and absence of dissolved carbonate can be fit with tetradentate Sr2+ and SrOH+ complexes on the β-plane and a monodentate Sr2+complex on the diffuse plane to account for strontium sorption at low ionic strength. Strontium sorption to goethite in the
absence of dissolved carbonate can be fit with monodentate and tetradentate SrOH+ complexes and a tetradentate binuclear Sr2+ species on the β-plane. The binuclear complex is needed to account for enhanced sorption at hgh strontium surface loadings. In the presence
of dissolved carbonate additional monodentate Sr2+ and SrOH+ carbonate surface complexes on the β-plane are needed to fit strontium sorption to goethite. Modeling strontium sorption as outer-sphere complexes is consistent
with quantitative analysis of extended X-ray absorption fine structure (EXAFS) on selected sorption samples that show a single
first shell of oxygen atoms around strontium indicating hydrated surface complexes at the amorphous silica and goethite surfaces. 相似文献
Despite the widely acknowledged threat posed by invasive species in coastal estuaries, there are substantial gaps at the intersection
of science and policy that are impeding invasive species management. In the face of pressing management needs in coastal and
estuarine environments, we advocate that introduced species should receive the kind of management effort dedicated, for example,
to reducing pollution. We support our argument with some examples of economic costs of estuarine and coastal introduced species
and a summary of recent evidence for the ecological costs. We highlight some of the issues that either thwart or facilitate
the successful marriage between science and management of introduced species, including the regulatory framework for management.
We use the available information on coastal eradication programs, including case histories of the programs for Caulerpa taxifolia and Spartina alterniflora (and hybrids) in the western USA, to indicate the feasibility of managing introduced species and to help point out how management
and science can improve the outcome. We close with a research agenda that focuses primarily on science that will really assist
with invasive species management and reflects our own experience and the opinions of managers directly involved with this
issue. 相似文献
3He/4He ratios have been measured for olivine and clinopyroxene phenocrysts in 7–15 m.y. old basaltic lavas from the island of St. Helena. Magmatic helium was effectively resolved from post-eruptive radiogenic helium by employing various extraction techniques, includingin vacuo crushing, and stepwise heating or fusion of the powders following crushing. The inherited3He/4He ratio at St. Helena is 4.3–5.9 RA. Helium isotope disequilibrium is present within the phenocrysts, with lower3He/4He upon heating and fusion of the powders following crushing, due to radiogenic ingrowth or to -particle implantation from the surrounding(U + Th)-rich lavas.
A single crushing analysis for clinopyroxene in a basalt from Tubuaii gave3He/4He= 7.1 RA.3He/4He ratios at St. Helena and Tubuaii (HIMU hotspots characterized by radiogenic Pb isotope signatures) are similar to3He/4He ratios previously measured at Tristan da Cunha and Gough Island (EM hotspots characterized by low206Pb/204Pb). Overall, the HeSrPb isotope systematics at these islands are consistent with a mantle origin as contiguous, heterogeneous materials, such as recycled crust and/or lithosphere.3He/4He ratios at HIMU hotspots are similar to mantle xenoliths which display nearly the entire range of Pb isotope compositions found at ocean islands, and are only slightly less than values found in mid-ocean ridge basalts (7–9 RA). This suggests that the recycled materials were injected into the mantle within the last 109 yrs. 相似文献
Monitoring of crater lake chemistry during the recent decline and disappearance of the crater lake of Poás Volcano revealed that large variations in SO4/Cl, F/Cl, and Mg/Cl ratios were caused by the enhanced release of HCl vapor from the lake surface due to increasing lake temperature and solution acidity. Variation in the concentration of polythionic acids (H2SxO6, x=4–6) was the most reliable predictor of renewed phreatic eruptive activity at the volcano, exhibiting sharp decreases three months prior to the initiation of phreatic eruptions in June 1987. Polythionic acids may offer a direct indicator of changing subsurface magmatic activity whereas chloride-based element ratios may be influenced by surface volatilization of HCl and subsequent recycling of acidic fluids in crater lake volcanoes. 相似文献
To obtain clues about how coastal primary production might be affected by interannual and interdecadal changes in climate, we studied marine laminated sediments from the center of the Santa Barbara Basin. We report here a large decrease in the flux of diatoms between the periods 1954–1972 and 1973–1986, by a factor of five, and sustained reductions from 1973 to 1978 by a factor of ten below the pre-1972 period. Planktonic foraminifera flux shows a consistent trend of decrease with lowest values from 1981 to 1984. On the whole, the 1954–1972 period is considerably cooler than the 1973–1986 period, over the entire North Pacific. The decrease in biological production in this coastal system is accompanied by an overall intensification of the Aleutian Low in the North Pacific over the past 14 years, providing for a weakening of the California Current, and an overall reduction of mixing and upwelling. The possibility that the low coastal production could provide positive feedback to global warming through reduction of CO2-uptake, and its relation to the greenhouse effect is considered. On a shorter time-scale, the effects of El Niño phenomena are clearly seen in the sediments of this basin, as decreases in total diatom flux and increases in the relative abundance of certain warm-water diatoms. 相似文献
AbstractUrban heat islands result from human modification of land surfaces. Snow cover reduces heating due to its reflectivity; however, urban snow is quickly plowed, thus altering surface radiative properties. The goal of this study was to evaluate the extent to which municipal snow removal affects the magnitude of solar input associated with changes in the radiation balance. Incoming and reflected shortwave radiation, surface radiating temperature, air temperature, and snow depth were measured with portable devices at eight sites in Syracuse, New York. Sites were classified as cleared, undisturbed, or snow piles. Measurements were taken following fresh snowfall, and continuing until snow had melted. A HOBO weather station provided hourly baseline conditions. Longevity of snow varied across snow site types, with greater persistence when in piles and on open areas. Albedo was reduced and surface temperatures were higher over cleared areas. The difference between absorbed energy due to clearing was quantified using an albedo regression model for undisturbed sites and comparing these to average reflectivity of cleared surfaces. The magnitude difference over the study period ranged from 841 million to 1670 million MJ. Snow plowing is therefore a significant source of additional energy that enhances the winter urban heat island. 相似文献