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371.
372.
A note on 10Be‐derived mean erosion rates in catchments with heterogeneous lithology: examples from the western Central Andes 下载免费PDF全文
Sebastien Carretier Vincent Regard Riccardo Vassallo Joseph Martinod Frederic Christophoul Eric Gayer Laurence Audin Christelle Lagane 《地球表面变化过程与地形》2015,40(13):1719-1729
Millennial catchment–mean erosion rates derived from terrestrial cosmogenic nuclides are generally based on the assumption that the lithologies of the parent rock each contain the same proportion of quartz. This is not always true for large catchments, in particular at the edge of mountainous plateaus where quartz‐rich basement rocks may adjoin sedimentary or volcano‐sedimentary rocks with low quartz content. The western Central Andes is an example of this type of situation. Different quartz contents may be taken into account by weighting the TCN production rates in the catchment. We recall the underlying theory and show that weighting the TCN production rate may also lead to bias in the case of a spatial correlation between erosion rate and lithology. We illustrate the difference between weighted and unweighted erosion rates for seven catchments (16 samples) in southern Peru and northern Chile and show variations up to a factor of 2 between both approaches. In this dataset, calculated erosion rates considering only granitoid outcrops are better correlated with catchment mean slopes than those obtained without taking into account the geological heterogeneity of the drained watershed. This dataset analysis demonstrates that weighting erosion rates by relative proportions of quartz is necessary to evaluate the uncertainties for calculated catchment–mean erosion rates and may reveal the correlation with geomorphic parameters. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
373.
G. Moreels J. Clairemidi M. Faivre D. Pautet F. Rubio da Costa P. Rousselot J.W. Meriwether G.A. Lehmacher E. Vidal J.L. Chau G. Monnet 《Experimental Astronomy》2008,22(1-2):87-107
The emission of the upper atmosphere introduces an additional variable component into observations of astronomical objects in the NIR 700–3,000 nm range. The subtraction of this component is not easy because it varies during the night by as much as 100% and it is not homogeneous over the sky. A program aimed at measuring and understanding the main characteristics of the atmospheric NIR emission was undertaken. A 512?×?512 CCD camera equipped with a RG780/2 mm filter is used to obtain images of the sky in a 36°?×?36° field of view. The intensities of a given star and of the nearby region devoid of star in a 439 arcmin2 area are monitored during periods of time of several hours. The sky intensity measured in the 754–900 nm bandpass, reduced to zenith and zero airmass is comprised between mag20 and mag18.5 per arcsecond2. A diminution by a factor of two during the night is frequently observed. Intensity fluctuations having an amplitude of 15% and periods of 5–40 min are present in the images with a structure of regularly spaced stripes. The fluctuations of the NIR sky background intensity are due to (1) the chemical evolution of the upper atmosphere composition during the night and (2) dynamical processes such as tides with periods of 3–6 h or gravity waves with periods of several tens of minutes. We suggest that a monitoring of the sky background intensity could be set up when quantitative observations of astronomical objects require exposure times longer than ~10 min. The publication is illustrated with several video films accessible on the web site http://www.obs-besancon.fr/nirsky/. Enter username: nirsky and password: skynir. 相似文献
374.
C. Bonadonna R. Cioni A. Costa T. Druitt J. Phillips L. Pioli D. Andronico A. Harris S. Scollo O. Bachmann G. Bagheri S. Biass F. Brogi K. Cashman L. Dominguez T. Dürig O. Galland G. Giordano M. Gudmundsson M. Hort A. Höskuldsson B. Houghton J.C. Komorowski U. Küppers G. Lacanna J.L. Le Pennec G. Macedonio M. Manga I. Manzella M. de’ Michieli Vitturi A. Neri M. Pistolesi M. Polacci M. Ripepe E. Rossi B. Scheu R. Sulpizio B. Tripoli S. Valade G. Valentine C. Vidal N. Wallenstein 《Bulletin of Volcanology》2016,78(11):84
375.
Vidal Javier Marcé Rafael Serra Teresa Colomer Jordi Rueda Francisco Casamitjana Xavier 《Aquatic Sciences - Research Across Boundaries》2012,74(2):315-327
The local response of the phytoplankton community to river inflow processes was investigated with modeling and field analyses
in a long and narrow, stratified reservoir in mid-summer. The river water had high concentrations of phosphorus and nitrogen
(ammonium and nitrate) and temperature had large variations at diurnal scales. As a consequence of the large variation in
river temperature, the level of neutral buoyancy (the depth where the river water spreads laterally in the reservoir) oscillated
between the surface (overflows) during the day, and the depth of the metalimnion (interflows) during the night. The reservoir
remained strongly stratified, which favoured the presence of cyanobacteria. It is shown that under these conditions, nutrient-rich
river water injected during overflows into the surface layers promoted the occurrence of localized algal blooms in the zones
where the overflow mixed with the quiescent water of the reservoir. A series of hydrodynamic simulations of the reservoir
were conducted both with synthetic and realistic forcing to assess the importance of river temperatures and wind-driven hydrodynamics
for algal blooms. The simulations confirmed that the river inflow was the main forcing mechanism generating the localized
bloom. 相似文献
376.
James Andrew Griffiths Fangfang Zhu Faith Ka Shun Chan David Laurence Higgitt 《地学前缘(英文版)》2019,10(2):363-372
Urban drainage systems in coastal cities in SE China are characterized by often complex canal and sluicegate systems that are designed to safely drain pluvial flooding whilst preventing tidal inundation.However, the risk of coastal flooding in the region is expected to increase over the next 50-100 years, as urban areas continue to expand and sea-levels are expected to rise. To assess the impact of projected sealevel rise on this type of urban drainage system, a one-dimensional model and decision support tool was developed. The model indicated that although sea-level rise represents a significant challenge, flood probability will continue to be most influenced by rainfall. Events that are significant enough to cause flooding will most likely be minimally impacted by changes to the tidal frame. However, it was found that a sea-level rise of up to 1.2 m by 2010 would result in increased drainage times and higher volumes of over-topping when flooding occurs. 相似文献
377.
José M. Mirás‐Avalos Antonio Paz‐González Jorge Dafonte‐Dafonte Eva Vidal‐Vázquez Montserrat Valcárcel‐Armesto 《地球表面变化过程与地形》2009,34(15):2087-2095
Knowledge of soil loss rates by water erosion under given climate, soil, topography, and management conditions is important for establishing soil conservation schemes. In Galicia, a region with Atlantic climatic conditions in Spain, field observations over the last decade indicate that interrill, rill and ephemeral gully erosion may be an important sediment source. The aim of this work was to assess concentrated erosion rates, describe types of rills and ephemeral gullies and determine their origin, evolution and importance as sediment sources. Soil surface state and concentrated flow erosion were surveyed on medium textured soils, developed over basic schists of the Ordenes Complex series (Coruña province, Spain) from 1997 to 2006. Soil surface state was characterized by crust development, tillage features and roughness degree. Soil erosion rate was directly measured in the field. Concentrated flow erosion took place mainly on seedbeds and recently tilled surfaces in late spring and by autumn or early winter. During the study period, erosion rates were highly variable and the following situations could be distinguished: (a) no incision or limited rill incision, i.e. below 2 Mg ha?1 year?1; (b) generalized rill and ephemeral gully incision in the class of mean values between 2·5 and 6·25 Mg ha?1 year?1, this was the most common erosion pattern; and (c) heavy erosion as observed during an extremely wet winter period, between October 2000 and February 2001, with erosion figures that may be about ten orders of magnitude higher, up to 55–60 Mg ha?1 year?1. Therefore, low values of soil losses are dominant, but also large values of rill and ephemeral gully erosion occurred during the study period. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
378.
M. B. Benito M. Navarro F. Vidal J. Gaspar-Escribano M. J. García-Rodríguez J. M. Martínez-Solares 《Bulletin of Earthquake Engineering》2010,8(4):739-766
A probabilistic seismic hazard assessment of Andalusia (Southern Spain) in terms of peak ground acceleration, PGA, and spectral
accelerations, SA(T), is presented in this paper. In contrast to most of the previous studies in the region, which were performed
for PGA, making use of Intensity-to-PGA relationships, hazard was here calculated in terms of magnitude, using published spectral
ground-motion models. Moreover, we considered different ground-motion models for the Atlantic sources, since the attenuation
of those motions seems to be slower, as evidenced in the case of the extensive macroseismic areas of earthquakes like those
occurred in the years 1755, 1969 and 2007. A comprehensive review of the seismic catalogue and of the seismogenic models proposed
for the region was carried out, including those for Northern Africa, which is part of the influence area. Hazard calculations
were performed following the Probabilistic Seismic Hazard Assessment (PSHA) methodology using a logic tree, which accounts
for six different seismic source zonings and five different ground-motion attenuation relationships. Hazard maps in terms
of PGA and SA (0.2 s) and SA (1 s) and coefficient of variation (COV) maps, for the 475-year return period were first obtained
in rock sites. A geotechnical classification and amplification factors were proposed and new hazard maps including local effects
were represented, showing PGA values ranging from 24 to 370 cm/s2 for the whole Andalusian territory, with the highest expected values (PGA > 300 cm/s2) in some parts of the Granada Province and in the town of Vélez Málaga. Lowest values (PGA < 50 cm/s2) correspond to some towns of the Huelva and Córdoba provinces. The inclusion of soil effects provides a more detailed picture
of the actual hazard the region is subjected to. 相似文献
379.
Assessing aquatic macrophyte community change through the integration of palaeolimnological and historical data at Loch Leven,Scotland 总被引:1,自引:0,他引:1
Jorge Salgado Carl Sayer Laurence Carvalho Thomas Davidson Iain Gunn 《Journal of Paleolimnology》2010,43(1):191-204
Submerged macrophytes have a critical role in lake ecosystems affecting nutrient cycling, sediment stability, and community
composition across multiple trophic levels. Consequently temporal changes in the composition of submerged plant populations
can have profound ecological implications and key significance from the perspective of lake conservation. By focusing on macro-remains
of aquatic macrophytes and extensive historical plant records spanning the last approximately 180 years, this study seeks
to evaluate a combined historical-palaeolimnological approach for establishing pre-disturbance macrophytes communities in
Loch Leven, Kinross, Scotland and to provide new information regarding temporal trends in its macrophyte vegetation as well
as potential drivers of change. Some 81% of the species historically recorded for the core site (east side of St. Serf’s Island)
were found as macro-remains. Potamogeton taxa were underrepresented, whereas remains of Elatine hexandra, a small species never recorded historically were found. The core sequence showed good agreement with known floristic changes
including an early (pre- ca. 1850) loss of Isoetes lacustris and Lobelia
dortmanna and a more recent (post-1910) shift to dominance by Potamogeton and Chara taxa associated with eutrophic conditions. A clear pattern in the relationship between macrofossil principal component analysis
(PCA) and loss on ignition suggested a key control of sediment conditions on macrophyte community structure. In particular
the major macrophyte community change of the mid-nineteenth century was concurrent with a substantial increase in organic
matter, likely linked to a historic lake lowering (early 1830s) which would have beached the former gravel-sand shoreline
leading to a much siltier lake littoral. Although recent monitoring data show signs of ecological recovery our study illustrates
that Loch Leven remains a long way from its reference state as a lake with characteristic soft-water macrophytes. To achieve
a full recovery, sediment properties would need to change in addition to nutrient reduction. Consequently restoration strategies
will need to compromise between the desirability of achieving the pre-disturbance state and what is feasible and practicable.
Our study shows the clear potential role of a combined palaeolimnological-historical approach for informing lake management
decisions. 相似文献
380.
Long-term monitoring of a large deep-seated landslide (La Clapiere,South-East French Alps): initial study 总被引:1,自引:1,他引:0
Edouard Palis Thomas Lebourg Emmanuel Tric Jean-Philippe Malet Maurin Vidal 《Landslides》2017,14(1):155-170
The large-scale deformation of high mountain slopes finds its origin in many phenomena (inherent parameters, external stresses) with very different time constants (instantaneous to geological scale). Gravitational effect, tectonic forces and water infiltration are generally the principal causes of slope instability. However, it can be very difficult to distinguish which cause is dominant and which are their respective effects. To gain a better understanding of the complex processes taking place during the evolution of an unstable slope and separate the causes responsible of the landslide dynamic, an observational study based on geodetic, meteorological, seismological and electrical data has been performed on the La Clapière rockslide (Southern French Alps). This deep-seated landslide (DSL) is known for many years as one of the largest and fastest rock slide in Europe (60 million m3 of highly weathered metamorphic material, moving at 1 to 3 m year?1). The set-up of the “Observatoire Multidisciplinaire des Instabilités de Versants” (OMIV, http://omiv.osug.fr) in 2011 has allowed the production and availability of an important and original data set over several years of accurate monitoring. Thus, for the first time, the long-term study of geodetic data permitted us to highlight acceleration phases in the general movement of the landslide that affect its dynamic. These modifications are associated with variations of the velocity by a factor 3 to 6. The characterization of the origin of these variations was possible due to the comparison with meteorological, electrical and seismological data. Based on these various signals, we were able to establish correlations and contributions of meteorological water infiltration in the dynamic evolution of the La Clapière slope. We determine several response times to the meteorological stress for seismic endogenous events (mainly rockfalls), the resistivity of the ground (quasi-instantaneous) and the kinematics of the slope (from 2 weeks to 2.5 months). Moreover, our results strongly suggest the existence of rainfall threshold of 3.5?±?1 mm day?1 from which the number of seismic endogenous events is highly increased. 相似文献