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51.
Heather M. N. Wright Chiara Lesti Raymond A. F. Cas Massimiliano Porreca José G. Viramonte Chris B. Folkes Guido Giordano 《Bulletin of Volcanology》2011,73(10):1567-1582
Columnar jointing is thought to occur primarily in lavas and welded pyroclastic flow deposits. However, the non-welded Cerro
Galán Ignimbrite at Paycuqui, Argentina, contains well-developed columnar joints that are instead due to high-temperature
vapor-phase alteration of the deposit, where devitrification and vapor-phase crystallization have increased the density and
cohesion of the upper half of the section. Thermal remanent magnetization analyses of entrained lithic clasts indicate high
emplacement temperatures, above 630°C, but the lack of welding textures indicates temperatures below the glass transition
temperature. In order to remain below the glass transition at 630°C, the minimum cooling rate prior to deposition was 3.0 × 10−3–8.5 × 10−2°C/min (depending on the experimental data used for comparison). Alternatively, if the deposit was emplaced above the glass
transition temperature, conductive cooling alone was insufficient to prevent welding. Crack patterns (average, 4.5 sides to
each polygon) and column diameters (average, 75 cm) are consistent with relatively rapid cooling, where advective heat loss
due to vapor fluxing increases cooling over simple conductive heat transfer. The presence of regularly spaced, complex radiating
joint patterns is consistent with fumarolic gas rise, where volatiles originated in the valley-confined drainage system below.
Joint spacing is a proxy for cooling rates and is controlled by depositional thickness/valley width. We suggest that the formation
of joints in high-temperature, non-welded deposits is aided by the presence of underlying external water, where vapor transfer
causes crystallization in pore spaces, densifies the deposit, and helps prevent welding. 相似文献
52.
Florian Kobierska Tobias Jonas Jan Magnusson Massimiliano Zappa Mathias Bavay Thomas Bosshard Frank Paul Stefano M. Bernasconi 《Applied Geochemistry》2011
A comprehensive hydrological modeling study in the drainage area of a hydropower reservoir in central Switzerland is presented. Two models were tested to reproduce the measured discharge dynamics: (1) a detailed energy-balance model (ALPINE3D) primarily designed for snow simulations; (2) a conceptual runoff model system (PREVAH), including a distributed temperature-index snow and ice melt model. Considerable effort was put into distributing available meteorological station data to the model grids as forcing data. The recent EU regional climate modeling initiative ENSEMBLES provided up-to-date climate predictions for two 30-a periods in mid and late 21st century. These were used to estimate evolutions in the water supply of the hydropower reservoir in response to expected climate changes. The simulations suggest a shift of spring peak-flow by almost two months for the end of the century. Warmer winter temperatures will cause higher winter base-flow. Due to glacier retreat, late-summer flow will decrease at the end of the century. 相似文献
53.
Direct, partitioned, and projected (conjugate gradient‐like) solution approaches are compared on unsymmetric indefinite systems arising from the finite element integration of coupled consolidation equations. The direct method is used in its most recent and computationally efficient implementations of the Harwell Software Library. The partitioned approach designed for coupled problems is especially attractive as it addresses two separate positive definite problems of a smaller size that can be solved by symmetric conjugate gradients. However, it may stagnate and when converging it does not prove competitive with a global projection method such as Bi‐CGSTAB, which may take full advantage of its flexibility in working on scaled and reordered equations, and thus may greatly improve its computational performance in terms of both robustness and convergence rate. The Bi‐CGSTAB superiority to the other approaches is discussed and demonstrated with a few representative examples in two‐dimensional (2‐D) and three‐dimensional (3‐D) coupled consolidation problems. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
54.
Modern fluvial meander plains exhibit complex planform transformations in response to meander‐bend expansion, downstream migration and rotation. These transformations exert a fundamental control on lithology and reservoir properties, yet their stratigraphic record has been poorly evaluated in ancient examples due to the lack of extensive three‐dimensional exposures. Here, a unique exhumed meander plain exposed to the north of Scarborough (Yorkshire, UK) is analysed in terms of architecture and morphodynamics, with the aim of developing a comprehensive model of facies distribution. The studied outcrop comprises tidal platforms and adjacent cliffs, where the depositional architecture of un‐tilted deposits was assessed on planform and vertical sections, respectively. In its broader perspective, this study demonstrates the potential of architectural mapping of extensive planform exposures for the reconstruction of ancient fluvial morphodynamics. The studied exhumed meander plain is part of the Scalby Formation of the Ravenscar Group, and originally drained small coastal incised valleys within the Jurassic Cleveland Basin. The meander plain is subdivided into two storeys that contain in‐channel and overbank architectural elements. In‐channel elements comprise expansional and downstream‐migrating point bars, point‐bar tails and channel fills. Overbank elements comprise crevasse complexes, levées, floodplain fines and lake fills. The evolution of the point bars played a significant role in dictating preserved facies distributions, with high flood‐stage nucleation and accretion of meander scrolls later reworked during waning flood‐stages. At a larger scale, meander belt morphodynamics were also a function of valley confinement and contrasts in substrate erodibility. Progressive valley infilling decreased the valley confinement, promoting the upward transition from prevalently downstream migrating to expansional meander belts, a transition associated with enhanced preservation of overbank elements. Strikingly similar relations between valley confinement, meander‐bend transformations and overbank preservation are observed in small modern meandering streams such as the Beaver River of the Canadian prairies and the Powder River of Montana (USA). 相似文献
55.
Massimiliano Ghinassi Wojciech Nemec Mauro Aldinucci Slavomir Nehyba Volkan Özaksoy Francesco Fidolini 《Sedimentology》2014,61(4):952-977
The mode of channel‐bend transformation (i.e. expansion, translation, rotation or a combination thereof) has a direct bearing on the dimensions, shape, bedding architecture and connectivity of point‐bar sandstone bodies within a fluvial meander belt, but is generally difficult to recognize in vertical outcrops. This study demonstrates how the bend transformation mode and relative rate of channel‐floor aggradation can be deciphered from longitudinal outcrop sections aligned parallel to the meander‐belt axis, as a crucial methodological aid to the reconstruction of ancient fluvial systems and the development of outcrop analogue models for fluvial petroleum reservoirs. The study focuses on single‐storey and multi‐storey fluvial meander‐belt sandstone bodies in the Palaeogene piggyback Boyabat Basin of north‐central Turkey. The sandstone bodies are several hundred metres wide, 5 to 40 m thick and encased in muddy floodplain deposits. The individual channel‐belt storeys are 5 to 9 m thick and their transverse sections show lateral‐accretion bed packages representing point bars. Point bars in longitudinal sections are recognizable as broad mounds whose parts with downstream‐inclined, subhorizontal and upstream‐inclined bedding represent, respectively, the bar downstream, central and upstream parts. The inter‐bar channel thalweg is recognizable as the transition zone between adjacent point‐bar bedsets with opposing dip directions into or out of the outcrop section. The diverging or converging adjacent thalweg trajectories, or a trajectory migrating in up‐valley direction, indicate point‐bar broadening and hence channel‐bend expansion. A concurrent down‐valley migration of adjacent trajectories indicates channel‐bend translation. Bend rotation is recognizable from the replacement of a depositional riffle by an erosional pool zone or vice versa along the thalweg trajectory. The steepness of the thalweg trajectory reflects the relative rate of channel‐floor aggradation. This study discusses further how the late‐stage foreland tectonics, with its alternating pulses of uplift and subsidence and a progressive narrowing of the basin, has forced aggradation of fluvial channels and caused vertical stacking of meander belts. 相似文献
56.
This paper illustrates the main characteristics of the newly developed landslide model r.massmov, which is based on the shallow water equations, and is capable of simulating the landslide propagation over complex topographies. The model is the result of the reimplementation of the MassMov2D into the free and open-source GRASS GIS with a series of enhancements aiming at allowing its possible integration into innovative early warning monitoring systems and specifically into Web processing services. These improvements, finalized at significantly reducing computational times, include the introduction of a new automatic stopping criterion, fluidization process algorithm, and the parallel computing. Moreover, the results of multi-spatial resolution analysis conducted on a real case study located in the southern Switzerland are presented. In particular, this analysis, composed by a sensitivity analysis and calibration process, allowed to evaluate the model capabilities in simulating the phenomenon at different input data resolution. The results illustrate that the introduced modifications lead to important reductions in the computational time (more than 90 % faster) and that, using the lower dataset resolution capable of guaranteeing reliable results, the model can be run in about 1 s instead of the 3.5 h required by previous model with not optimized dataset resolution. Aside, the results of the research are a series of new GRASS GIS modules for conducting sensitivity analysis and for calibration. The latter integrates the automated calibration program “UCODE” with any GRASS raster module. Finally, the research workflow presented in this paper illustrates a best practice in applying r.massmov in real case applications. 相似文献
57.
Fodde Iosto Feng Jinglang Vasile Massimiliano 《Celestial Mechanics and Dynamical Astronomy》2022,134(5):1-22
Celestial Mechanics and Dynamical Astronomy - Ballistic capture orbits offer safer Mars injection at longer transfer time. However, the search for such an extremely rare event is a computationally... 相似文献
58.
Massimiliano Tardio Francesca Sangiorgi Henk Brinkhuis Maria Letizia Filippi Marco Cantonati André F. Lotter 《Journal of Paleolimnology》2006,36(3):315-318
This paper documents the discovery of peridinioid organic walled dinoflagellate cysts in Holocene sediments of the freshwater, low-alkalinity, high mountain Lake Nero di Cornisello (Adamello mountain range, Trentino, Italy). Among the three main cyst morphotypes found in the samples, the dominant one is acavate, with a smooth and light brown colored wall, with a clear conical shape, elongated with a pointy to rounded end in the antapical-ventral part, with the epicyst broader than the hypocyst and displays a typical peridinioid archeopyle. Comparison with data available in literature, besides pointing out the general scarcity of observations on dinocysts in lakes sediments, suggested a strong morphological similarity with the marine genus Brigantedinium. This finding pinpoints the need for more detailed studies on cysts in freshwater environments offering a new tool for paleoenvironmental interpretations. 相似文献
59.
Giada Frenzilli Raffaella Bocchetti Massimiliano Pagliarecci Marco Nigro Francesca Annarumma Vittoria Scarcelli Daniele Fattorini Francesco Regoli 《Marine environmental research》2004,58(2-5):609
Harbours can be considered as model environments for developing and validating field monitoring procedures and to investigate mechanistic relationships between different biological responses. In this study several biomarkers were investigated in marine mussels caged for 4 weeks (June–July 2001) into an industrialized harbour of NW Italy. Organisms were collected at different time-intervals to better characterize the sensitivity, temporal variations and interactions of analysed responses. Besides single antioxidants the total oxyradical scavenging capacity (TOSC) assay was used to analyse the capability of the whole antioxidant system to neutralize specific forms of radicals: these data were further integrated by measurement of DNA integrity, oxidized bases and the impairment of lysosomal membrane stability in haemocytes. Results showed a biphasic trend for single antioxidants and TOSC, with an increase during the first 2 weeks of exposure to the polluted site followed by a progressive decrease up to a severe depletion in the final part of the experiment. 相似文献
60.
We present CCD B and V light curves,obtained in the year 2006,and a photometric solution of the low-mass ratio contact binary ASAS 021209+2708.3. With our data we were able to determine six new times of minimum light and refine the orbital period of the system to 0.3181963 days.The light curves are analyzed using the 2003 version of the Wilson-Devinney program and the analysis was performed with and without adding a spot on the surface of one star because the light curves appear to exhibit a typical O’Conne... 相似文献