Morphological effects of local scouring in step–pool streams     

Francesco Comiti  Andrea Andreoli  Mario A. Lenzi 《地球表面变化过程与地形》2005,30(12):1567-1581

Step–pool morphology characterizes many high‐gradient streams in a variety of natural settings, but formative processes and evolutionary dynamics are still poorly understood. In this paper, natural step–pool geometry is compared with steep alluvial channels where grade‐control structures such as check‐dams and bed sills make the stream profile resemble a natural stepped stream. Along these channels, local scouring due to falling jets forms plunge pools under each structure, analogous to natural steps determining the formation of pools. In order to test the hypothesis that natural pools are analogous to pools formed below grade‐control works with respect to their dimensions, shape and formative dynamics, 37 natural pools and 73 artificial pools were surveyed in 10 mountain streams of the eastern Italian Alps. Pools below grade‐control works featured a transitional zone between the scour hole and the downstream sloping bed, marked by a depositional berm. When geometric parameters such as maximum pool depth, length and step–berm distances are normalized to the jet virtual energy, no statistically significant differences were detected between natural and artificial systems. These results lend support to an upstream‐forced cascade model for step–pool formation, where the energy of falling jets controls the geometry of the pools, and is therefore regarded as the most important scaling‐independent variable. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Practical application of fractal analysis: problems and solutions   总被引：2，自引：0，他引：2  

Guido Gonzato  Francesco Mulargia  & Warner Marzocchi 《Geophysical Journal International》1998,132(2):275-282

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Eruption style and petrology of a new carbonatitic suite from the Mt. Vulture Southern Italy/: The Monticchio Lakes Formation     

Francesco Stoppa  Claudia Principe 《Journal of Volcanology and Geothermal Research》1997,78(3-4)

The Monticchio Lakes Formation MLF is a newly identified carbonatite-melilitite tuff sequence which is exposed in the southwestern sector of the Vulture volcano. It is the youngest example ca. 0.13 m.y. of this type of volcanism in Italy, although other carbonatites of smaller volume, but with similar characteristics, have been discovered recently. This volcanic event occurred in isolation after a 0.35 m.y. period of inactivity at Vulture. The eruption produced two maar-type vents and formed tuff aprons mainly composed of dune beds of lapilli. Depositional features suggest that a dry surge mechanism, possibly triggered by CO₂ expansion, was dominant during tuff emplacement. The MLF event involved a mixture of carbonatite and melilitite liquids which were physically separated before the eruption. Abundant mantle xenoliths are direct evidence of the deep-seated origin of the parental magma and its high velocity of propagation towards the surface. Often, these nodules form the core of lapilli composed of concentric shells of melilitite andror porphyritic carbonatite. Coarse-ash beds alternate with lapilli beds and consist of abundant lumps and spherulae of very fine-grained calcite immersed in a welded, highly compacted carbonatite matrix. Porphyritic carbonatite shells of the lapilli and fine-grained spherulae of calcite in the tuff matrix suggest incipient crystallisation of a carbonatite liquid in subvolcanic conditions and eruption of carbonatite-spray droplets. Dark coloured juvenile fragments mainly consist of melilite, phlogopite, calcite, apatite, perovskite, and häuyne crystals in a carbonatite or melilitite matrix. The rocks have an extremely primitive, ultramafic composition with very high Mga) 85. and Cr and Ni content 1500 ppm-. The calcite contains high SrO, BaO and REE of up to 1.5 wt.%. Similar compositions are typical of primary, magmatic carbonates which are found in both intrusive and extrusive carbonatites. The high modal Sr-Ba-REE-rich calcite, the typical mineralogy, and the high amount of Sr-group elements identify the carbonate component as a carbonatite. The very high Mga, mantle debris and C, O, He isotope ratios in the range of mantle values indicate a near-primary character for the carbonatite which is distinctive of a restricted group of extrusive carbonatites only found in continental rift areas.  相似文献   

Enhancing the credibility of ecology: Is interdisciplinary research for land use planning useful?     

Francesco di Castri  Malcolm Hadley 《GeoJournal》1986,13(4):299-325

Interdisciplinary approaches involving inputs from both the natural and social sciences represent one operational and social response to the complexity of today's environmental and land use problems. The resulting amalgam can be useful to both science and society, given the right mix of ingredients. Important steps in the planning and conduct of interdisciplinary research include problem indentification; definition of a precise scientific theme derived from the social demand; choice of relevant disciplines; selection of study area and spatial scale; ensuring that the project is adaptable to changing circumstances; obtaining the involvement of scientists, planners and local people; developing a continuum of actions from basic and applied research through to training and information diffusion; early and explicit definition of the criteria for evaluation. Though interdisciplinary approaches have shown their worth, they founder easily. Obstacles include the behavioural and psychological characteristics of individual scientists, differences in scientific method, and bottlenecks of a more administrative, institutional, political and financial nature.The views expressed are those of the authors and not necessarily those of the authors' employers.  相似文献   

Enhancing the credibility of ecology: Can research be made more comparable and predictive?     

Francesco di Castri  Malcolm Hadley 《GeoJournal》1985,11(4):321-338

A sounder theoretical basis for extrapolation and prediction, typologies of what is and what is not comparable, and representative natural areas for long-term field research are three geographically-based ingredients of comparative research in ecology. Two types of conceptual model allow assessment of the effects of phylogenesis and environment on ecosystem structure and functioning. The first is based on fixing of genetic variables and study of biological performance along a gradient of environmental conditions — an approach of sequential analysis of environmental gradients. The second is based on fixing of environmental variables and comparison of performance of different phylogenetic stocks in non-contiguous geographical areas — an approach entailing matching of disjunct ecological analogues. The two approaches are important complements in examining hypotheses of convergent and divergent evolution, in helping to define what really can be compared in comparative ecological research, and in contributing to ecology becoming a more predictive and credible science.  相似文献   

Geological features and landslide mechanisms of an unstable coastal slope (Petacciato, Italy)     

Francesco Fiorillo 《Engineering Geology》2003,67(3-4):255-267

On the basis of geological and geomorphological surveys, landslide phenomena are analysed on a slope along a stretch of the Adriatic coast, near Petacciato (Molise, Italy).

Locally, a blue clay sequence of Pleistocene outcrops, stratified with silty-sandy layers; bedding dips 3–8°NE and the slope has a similar attitude. This sequence evolves upwards to sands and conglomerates, with thickness of up to 40 m, on which the built-up area is located.

Several episodes of landslide reactivation occurred in the past century, involving the zone between the built-up area and the sea, along a coastal slope of over 2000 m long and 200 m high. Important roads and railway lines have been heavily damaged as well as the town itself.

The typology of the movement is a rotational–translational slide; the displacement reaches tens of centimetres at each reactivation episode along the entire coastal slope, extending well beyond the shore line.

Detailed studies already exists, but different mechanism failures have been proposed to explain the landslide phenomena. In this study, a new failure mechanism is proposed, (sudden spreading of Terzaghi, K., Peck, R.B., 1948. Soil Mechanics in Engineering Practice. Wiley and Sons New York) and analytical approaches have been adopted to evaluate the slope stability, based on the geotechnical and monitoring data and the geometrical and geological features of the slope.  相似文献   

Natural hexavalent chromium in groundwaters interacting with ophiolitic rocks   总被引：2，自引：0，他引：2  

Donatella Fantoni  Gianpiero Brozzo  Marco Canepa  Francesco Cipolli  Luigi Marini  Giulio Ottonello  Marino Zuccolini 《Environmental Geology》2002,42(8):871-882

Thirty of the 58 groundwaters sampled in September-October 2000 in the study area (La Spezia Province, Italy) have Mg-HCO₃ to Ca-HCO₃ composition, undetectable Cr(III) contents, and virtually equal concentrations of total dissolved Cr and Cr(VI). Therefore, dissolved Cr is present in toto as Cr(VI), with concentrations of 5-73 ppb. These values are above the maximum permissible level for drinking waters (5 ppb). Local ophiolites, especially serpentinites and ultramafites, are Cr-rich and represent a Cr source for groundwaters. However, since Cr is present as Cr(III) in rock-forming minerals, its release to the aqueous solution requires oxidation of Cr(III) to Cr(VI). This can be performed by different electron acceptors, including Mn oxides, H₂O₂, gaseous O₂, and perhaps Fe(III) oxyhydroxides. Based on this evidence and due to the absence of anthropogenic Cr sources, the comparatively high Cr(VI) concentrations measured in the waters of the study area are attributed to natural pollution.  相似文献   

Adjacency selection in Markov Random Fields for high spatial resolution hyperspectral data     

Francesco Lagona 《Journal of Geographical Systems》2002,4(1):53-68

 Markov Random Fields, implemented for the analysis of remote sensing images, capture the natural spatial dependence between band wavelengths taken at each pixel, through a suitable adjacency relationship between pixels, to be defined a priori. In most cases several adjacency definitions seem viable and a model selection problem arises. A BIC-penalized Pseudo-Likelihood criterion is suggested which combines good distributional properties and computational feasibility for analysis of high spatial resolution hyperspectral images. Its performance is compared with that of the BIC-penalized Likelihood criterion for detecting spatial structures in a high spatial resolution hyperspectral image for the Lamar area in Yellowstone National Park. Received: 9 March 2001 / Accepted: 2 August 2001  相似文献   

Fluid circulation at Stromboli volcano (Aeolian Islands, Italy) from self-potential and CO₂ surveys     

Anthony Finizola  Francesco Sortino  Jean-Franois Lnat  Mariano Valenza 《Journal of Volcanology and Geothermal Research》2002,116(1-2)

This work addresses the study of fluid circulation of the Stromboli island using a dense coverage of self-potential (SP) and soil CO₂ data. A marked difference exists between the northern flank and the other flanks of the island. The northern flank exhibits (1) a typical negative SP/altitude gradient not observed on the other flanks, and (2) higher levels of CO₂. The general SP pattern suggests that the northern flank is composed of porous layers through which vadose water flows down to a basal water table, in contrast to the other flanks where impermeable layers impede the vertical flow of vadose water. In the Sciara del Fuoco and Rina Grande–Le Schicciole landslide complexes, breccias of shallow gliding planes may constitute such impermeable layers whereas elsewhere, poorly permeable, fine-grained pyroclastites or altered lava flows may be present. This general model of the flanks also explains the main CO₂ patterns: concentration of CO₂ at the surface is high on the porous north flank and lower on the other flanks where impermeable layers can block the upward CO₂ flux. The active upper part of the island is underlain by a well-defined hydrothermal system bounded by short-wavelength negative SP anomalies and high peaks of CO₂. These boundaries coincide with faults limiting ancient collapses of calderas, craters and flank landslides. The hydrothermal system is not homogeneous but composed of three main subsystems and of a fourth minor one and is not centered on the active craters. The latter are located near its border. This divergence between the location of the active craters and the extent of the hydrothermal system suggests that the internal heat sources may not be limited to sources below the active craters. If the heat source strictly corresponds to intrusions at depth around the active conduits, the geometry of the hydrothermal subsystems must be strongly controlled by heterogeneities within the edifice such as craters, caldera walls or gliding planes of flank collapse, as suggested by the correspondence between SP–CO₂ anomalies and structural limits. The inner zone of the hydrothermal subsystems is characterized by positive SP anomalies, indicating upward movements of fluids, and by very low values of CO₂ emanation. This pattern suggests that the hydrothermal zone becomes self-sealed at depth, thus creating a barrier to the CO₂ flux. In this hypothesis, the observed hydrothermal system is a shallow one and it involves mostly convection of infiltrated meteoric water above the sealed zone. Finally, on the base of CO₂ degassing measurements, we present evidence for the presence of two regional faults, oriented N41° and N64°, and decoupled from the volcanic structures.  相似文献   

Morphological methods and dynamic modelling in landslide hazard assessment of the Campania Apennine carbonate slope   总被引：2，自引：2，他引：0  

Paola Revellino  Francesco M. Guadagno  Oldrich Hungr 《Landslides》2008,5(1):59-70

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