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51.
Carolina Lauro Stella M. Moreiras Sebastian Junquera Ivan Vergara Rafael Toural Johannes Wolf Ruben Tutzer 《Environmental Earth Sciences》2017,76(5):213
The Central-West region of Argentina was seriously affected by a series of convective summer storms on January–February of 2013 generating many debris flows and rockfall in the Central Andes mountain regions. In particular, the unreported 8th February event caused the sad death of a 10-year-old child being completely ignored by society and local authorities. Despite this, meteorological conditions associated with this event and further episodes were rarely measured and determined mainly due to scarce meteorological stations in Andean mountain areas. In this paper, meteorological data from CMORPH algorithm and measurements of surrounding gauges were analyzed for estimating the triggering precipitation value of this event. As well, the particular debris flow channeled into the main branch of the Amarilla gully in the Agua Negra valley was geomorphologically described. The amount of precipitation associated with this debris flow was 5.5 and 13.2 mm accumulated previous to the event. This violent debris flow was generated in a talus zone in a periglacial environment located just below a covered rock glacier. However, the influence of the permafrost thawing in this process is not feasible. The altitude of the 0 °C isotherm was lower during the previous days of the event, and no monitoring on permafrost is available for this area. The volume of removed mass was estimated in 5 × 104 m3, and the mean velocity was 35 km/h. Boulders of 4 m diameter were found in the source area, while the deposit is up to 75% sandy with clasts that hardly exceed 10 cm in the alluvial fan distal part. Herein the main objective is to advice about the probable catastrophic impact of similar events in the future. These findings could be useful for hazard remediation, mitigation, and prevention plans for the Agua Negra international pass under construction. 相似文献
52.
Benjun Wu Clinton P. Conrad Arnauld Heuret Carolina Lithgow-Bertelloni Serge Lallemand 《Earth and Planetary Science Letters》2008,272(1-2):412-421
Although subducting slabs undergo a bending deformation that resists tectonic plate motions, the magnitude of this resistance is not known because of poor constraints on slab strength. However, because slab bending slows the relatively rapid motions of oceanic plates, observed plate motions constrain the importance of bending. We estimated the slab pull force and the bending resistance globally for 207 subduction zone transects using new measurements of the bending curvature determined from slab seismicity. Predicting plate motions using a global mantle flow model, we constrain the viscosity of the bending slab to be at most ~ 300 times more viscous than the upper mantle; stronger slabs are intolerably slowed by the bending deformation. Weaker slabs, however, cannot transmit a pull force sufficient to explain rapid trenchward plate motions unless slabs stretch faster than seismically observed rates of ~ 10− 15 s− 1. The constrained bending viscosity (~ 2 × 1023 Pa s) is larger than previous estimates that yielded similar or larger bending resistance (here ~ 25% of forces). This apparent discrepancy occurs because slabs bend more gently than previously thought, with an average radius of curvature of 390 km that permits subduction of strong slabs. This gentle bending may ultimately permit plate tectonics on Earth. 相似文献
53.
Phytoplankton and its relationships with physical and chemical variables were analysed over a 2-year period in Hueihue and Linao Bays (southern Chile). Samples were collected on a monthly basis from May 1991 to May 1993. The growth rate of a single stock of hatchery-produced oysters (Ostrea chilensis) distributed between these two bays was also monitored monthly. The growth rate of oysters maintained at Linao Bay (site associated with a fish farm) was significantly higher, at every depth, compared with the oysters maintained at Hueihue Bay. Temperature and salinity values and their annual fluctuations were similar at both locations, presenting higher variations at the surface (1 m) due to the influence of air temperature and local precipitation than at depth. However, significant differences in phytoplankton abundance and composition were found between the two locations. The phytoplankton community was characterized by high biomass values during spring and summer, the dominance of diatoms and an inverse relationship between temperature and species diversity. However, phytoplankton cell abundance, biovolume and chlorophyll a concentration were significantly higher at Linao at every depth sampled. Cell abundance ranged between 4.49 × 104 and 7.45 × 106 cells · l?1 in Hueihue and between 6.48 × 104 and 8.71 × 106 cells ·1?1 in Linao. The influence of temperature on chlorophyll a concentration was significant except at 8 m at both locations. The instantaneous oyster growth rate was found to be positively correlated with temperature, chlorophyll a concentration and particulate organic matter at both locations. A significant negative relationship between oyster growth and amount of particulate inorganic matter was found; this confirms the important role played by seston composition in oyster growth. The demonstration of variation in oyster growth rate associated with differences in food availability between the two locations provides insight into the ecological role played by fish farms in southern Chile. The results suggest a strong link between food availability and oyster growth. 相似文献
54.
55.
Adjustments in channel morphology due to land‐use changes and check dam installation in mountain torrents of Calabria (southern Italy) 下载免费PDF全文
Diego Fortugno Carolina Boix‐Fayos Giuseppe Bombino Pietro Denisi Juan Manuel Quiñonero Rubio Vincenzo Tamburino Demetrio Antonio Zema 《地球表面变化过程与地形》2017,42(14):2469-2483
In Mediterranean semi‐arid conditions, the availability of studies monitoring channel adjustments as a response to reforestation and check dams over representative observation periods, could help develop new management strategies. This investigation is an integrated approach assessing the adjustments of channel morphology in a typical torrent of southern Italy after land‐use changes and check dam construction across a period of about 60 years. A statistical analysis of historical rainfall records, an analysis of land‐use changes in the catchment area and a geomorphological mapping of channel adjustments were carried out and combined with field surveys of bed surface grain‐size over a 5‐km reach including 14 check dams. The analysis of the historical rainfall records showed a slight decrease in the amount and erosivity of precipitation. Mapping of land‐use changes highlighted a general increase of vegetal coverage on the slopes adjacent to the monitored reaches. Together with the check dam network installation, this increase could have induced a reduction in water and sediment supply. The different erosional and depositional forms and adjustments showed a general narrowing between consecutive check dams together with local modifications detected upstream (bed aggradation and cross‐section expansion together with low‐flow realignments) and downstream (local incision) of the installed check dams. Changes in the torrent bends were also detected as a response to erosional and depositional processes with different intensities. The study highlighted: the efficiency of check dams against the disrupting power of intense floods by stabilizing the active channel and the influence of reforestation in increasing hillslope protection from erosion and disconnectivity of water and sediment flows towards the active channel. Only slight management interventions (for instance, the conversion of the existing check dams into open structures) are suggested, in order to mobilize the residual sediment avoiding further generalized incision of the active channel and coast line erosion. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
56.
Bizat Ruhama, an Early Pleistocene site located in the southern coastal plain of Israel, has yielded a single archaeological horizon dating to the Matuyama chron. Recent technological and zooarchaeological studies suggest evidence of near in situ hominin occupations taking place in a semiarid climatic setting. Such an archaeological context is rare for the Early Pleistocene and must be corroborated through reconstruction of site formation processes. This paper offers a microstratigraphic view of the site based on results from a micromorphological and granulometric study aimed at reconstructing site formation processes. Results show that the bone and lithic specimens were deposited near their excavated provenience, in a depressed, seasonally waterlogged area, and were subsequently slightly displaced and buried by surface sediment. We infer that the Bizat Ruhama deposit represents one or a few hominin occupations taking place on the surface of an undulating inter‐dune depression under a semiarid Mediterranean climate. © 2010 Wiley Periodicals, Inc. 相似文献
57.
Mercury levels of Audouin's gull are amongst the highest for Mediterranean seabirds, and have been mainly attributed to its piscivorous habits in these naturally Hg rich waters. Moreover, two additional factors could enhance its mercury intake: the consumption of discarded fish (which attain higher concentrations) and/or feeding in areas receiving Hg anthropogenic inputs. In order to differentiate the relevance of both sources we analysed Hg and stable isotopes of chick feathers from different breeding locations in western Mediterranean: one in its northern part (Ebro Delta) and two southern (Chafarinas Isl. and Alborán Isl.). The results from stable isotopes indicate that consumption of discards is higher at Alborán Isl., followed by the Ebro Delta and Chafarinas Isl. Thus, the higher mercury levels found in the Ebro Delta cannot be explained uniquely by the contribution of discarded fish to diet, but local pollution caused by the river Ebro waters accounts for Hg differences observed. 相似文献
58.
Ana Carolina Ruiz-Fernández José Luis Marrugo-Negrete Roberth Paternina-Uribe Libia Hascibe Pérez-Bernal 《Estuaries and Coasts》2011,34(6):1117-1128
With the aim of evaluating temporal changes in sedimentation and organic carbon (Corg) supplied over the last ~100 years, a sediment core was collected at Soledad Lagoon, a costal ecosystem surrounded by mangroves,
located in the Cispatá Estuary (Caribbean coast of Colombia). The core sediments were characterized by low concentrations
of calcium carbonate (0.2–2.9%), organic matter (3–8%), total nitrogen (0.11–0.38%), and total phosphorus (0.19–0.65 mg g−1). Fe and Al concentrations ranged from 4% to 5%, and Mn from 356 to 1,047 μg g−1. The 210Pb-derived sediment and mass accumulation rates were 1.54 ± 0.18 mm year−1 and 0.08 ± 0.01 g cm−2 year−1, respectively. The sediment core did not provide evidence of human impact, such as enhancement of primary production or nutrient
enrichment, which may result from recent land uses changes or climate change. The Corg fluxes estimated for Soledad Lagoon core lay in the higher side of carbon fluxes to coastal ecosystems (314–409 g m−2 year−1) and the relatively high Corg preservation observed (~45%) indicate that these lagoon sediments has been a net and efficient sink of Corg during the last century, which corroborate the importance of mangrove areas as important sites for carbon burial and therefore,
long-term sequestration of Corg. 相似文献
59.
Michel Michaelovitch de Mahiques Samara Cazzoli y Goya Maria Carolina da Silva Nogueira de Matos Rodrigo Augusto Udenal de Oliveira Bianca Sung Mi Kim Paulo Alves de Lima Ferreira Rubens Cesar Lopes Figueira Marcia Caruso Bícego 《国际泥沙研究》2021,36(2):317-327
The current study aims to do a comparative analysis of the results obtained with two End-Member(EM)grain-size modeling techniques(AnalySize and BasEMMA)and the Environmental Sensitive Grain-Size(ESGS)modeling for sediment samples collected in the mudbelts of the southern Brazilian shelf.The methods were compared using grain-size data from the south Brazilian shelf,and the results are discussed here.It is the first time that the concept of ESGS,in its present form,is utilized outside China.The results show that despite its relative ease of use,the ESGS is not fully comparable to the EM analyses,and only two grain-size ESGS classes were recognized as analogous to EMs.The comparison of the AnalySize and BasEMMA procedures also revealed significant differences between the techniques.A comparative analysis between the two EM techniques revealed advantages in the BasEMMA,especially in the better correlation of the end-members with the original grain size distribution.The analysis of the geographical distribution of the EM abundances allowed point sources of sandy populations to be recognized as well as the contribution of the Rio de la Plata as a source of silty sediments to be inferred. 相似文献
60.
Social,environmental and health vulnerability to climate change in the Brazilian Northeastern Region
Ulisses E. C. Confalonieri Anna Carolina L. Lima Isabela Brito Ana Flávia Quintão 《Climatic change》2014,127(1):123-137
A regional vulnerability study in relation to the projected patterns of climate change (A2 and B2 scenarios) was developed for the Brazilian Northeastern region. An aggregated Vulnerability Index was constructed for each of the nine States of the region, based on the following information: population projections; climate-induced migration scenarios; disease trends; desertification rates; economic projections (GDP and employment) and projections for health care costs. The results obtained shall subsidize public policies for the protection of the human population from the projected impacts of regional changes in climate patterns. 相似文献