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991.
Grilli Stéphan T. Shelby Mike Kimmoun Olivier Dupont Guillaume Nicolsky Dmitry Ma Gangfeng Kirby James T. Shi Fengyan 《Natural Hazards》2017,86(1):353-391
Natural Hazards - We perform numerical simulations to assess how coastal tsunami hazard from submarine mass failures (SMFs) is affected by slide kinematics and rheology. Two types of two-layer SMF... 相似文献
992.
993.
Basin-wide Holocene environmental changes in the marginal area of the Asian monsoon,northwest China 总被引:1,自引:0,他引:1
In arid regions, because of spatial variability, using single climate records is difficult to reconstruct the past climate
change for the drainage basins. Holocene environmental records were collected from the upper, middle and lower regions of
the Shiyang River drainage basin in the marginal area of the Asian monsoon (northwest China). The main objective of this paper
was to compare the records from the terminal lake and the middle and upper reaches of the basin to study the basin-wide environmental
changes. During the early Holocene the vegetation was sparse, and the effective moisture was relatively low in the basin.
The Holocene Climatic Optimum started between 7.0 and 8.0 cal ka BP, during which the lake level reached the highest level
in the terminal lake; the vegetation density and the effective moisture reached the highest level during the Holocene in the
drainage basin. From 4.7 cal ka BP the terminal lake began to shrink, while the vegetation density decreased dramatically.
In the middle and upper regions of the drainage, the effective moisture began to decrease since 3.5 cal ka BP, and the arid
tendency was earlier in the terminal lake than it was in the middle and upper regions of the drainage basin. During the early
Holocene the relatively arid environment was affected by the gradually intensifying East Asian monsoon and the dry westerly
winds. The mid-Holocene Optimum benefited from the intensive East Asian monsoon and the humid westerly winds. Then, the East
Asian monsoon retreated since the late-Holocene. In the basin the arid tendency may be related to the retracting of the East
Asian monsoon. However, the intensifying acidification after 1.5 cal ka BP may be correlated to the increasing dryness of
the westerly winds. 相似文献
994.
Simulation of DNAPL infiltration and spreading behaviour in the saturated zone at varying flow velocities and alternating subsurface geometries 总被引:2,自引:1,他引:2
Katharina Erning Sibylle Grandel Andreas Dahmke Dirk Schäfer 《Environmental Earth Sciences》2012,65(4):1119-1131
The influence of varying groundwater flow velocities on DNAPL infiltration and spreading behaviour was investigated by multiphase
modelling using TMVOC and PetraSim. The multiphase models were calibrated by results of previously conducted laboratory experiments
for the complete spatio-temporal range of the experiments. The small scale 2D scenario modelling was applied to qualify and
quantify changes in position, architecture, geometry and dissolution of a TCE body in a fully saturated homogeneous sandy
medium. The applied flow velocities ranging from 0.05 up to 40.00 m/day exhibited that the DNAPL TCE is affected even at the
lowest flow velocity in its position, its size and its architecture. Additionally, several impermeable lenses with simple
geometry were assumed in the model, to investigate the influence of stratified subsoil. In the experimental set-ups, the DNAPL
body reacts more sensitive to the applied groundwater flow velocities than to the geometrical set-up of the scenarios. A possible
consequence can be the transportation and displacement of a DNAPL pool due to natural or anthropogenic induced high groundwater
flow velocities, as by Pump and Treat facilities, complicating site investigation process and planning of remediation activities. 相似文献
995.
Submersed aquatic vegetation (SAV) communities have undergone declines worldwide, exposing them to invasions from non-native
species. Over the past decade, the invasive species Hydrilla verticillata has been documented in several tributaries of the lower Chesapeake Bay, Virginia. We used annual aerial mapping surveys from
1998 to 2007, integrated with spatial analyses of water quality data, to analyze the patterns and rates of change of a H. verticillata-dominated SAV community and relate them to varying salinity and light conditions. Periods of declining SAV coverage corresponded
to periods where salinities exceeded 7 and early growing season (April to May) Secchi depths were <0.4 m. Increases were driven
by the expansion of H. verticillata along with several other species into the upper estuary, where some areas experienced an 80% increase in cover. Field investigations
revealed H. verticillata dominance to be limited to the upper estuary where total suspended solid concentrations during the early growing season were
<15 mg l−1 and salinity remained <3. The effect of poor early growing season water clarity on annual SAV growth highlights the importance
of water quality during this critical life stage. Periods of low clarity combined with periodic salinity intrusions may limit
the dominance of H. verticillata in these types of estuarine systems. This study shows the importance of the use of these types of biologically relevant episodic
events to supplement seasonal habitat requirements and also provides evidence for the potential important role of invasive
species in SAV community recovery. 相似文献
996.
Use of LIDAR in landslide investigations: a review 总被引:13,自引:0,他引:13
Michel Jaboyedoff Thierry Oppikofer Antonio Abellán Marc-Henri Derron Alex Loye Richard Metzger Andrea Pedrazzini 《Natural Hazards》2012,61(1):5-28
This paper presents a short history of the appraisal of laser scanner technologies in geosciences used for imaging relief
by high-resolution digital elevation models (HRDEMs) or 3D models. A general overview of light detection and ranging (LIDAR)
techniques applied to landslides is given, followed by a review of different applications of LIDAR for landslide, rockfall
and debris-flow. These applications are classified as: (1) Detection and characterization of mass movements; (2) Hazard assessment
and susceptibility mapping; (3) Modelling; (4) Monitoring. This review emphasizes how LIDAR-derived HRDEMs can be used to
investigate any type of landslides. It is clear that such HRDEMs are not yet a common tool for landslides investigations,
but this technique has opened new domains of applications that still have to be developed. 相似文献
997.
Glaucony from the Cretaceous of the Sierra de Guadarrama (Central Spain) and its application in a sequence-stratigraphic context 总被引:1,自引:0,他引:1
Alessandro Amorosi Roberto Guidi Ramon Mas Elisa Falanga 《International Journal of Earth Sciences》2012,101(2):415-427
Detailed sedimentological and geochemical analyses of Upper Cretaceous glaucony-bearing deposits from the middle portion of the Castro de Fuentidueña Formation, in Central Spain, enable identification of a multiphase history of glaucony accumulation. Despite its relatively high maturity (K2O > 7%), glaucony from the transgressive subtidal sandstones has anomalously low concentration in the host rock (generally <10%), suggesting remobilization from a different source. The remarkable thickness of the glaucony-bearing horizons, concurrently with concentration of glaucony in laminae, small size, and high degree of roundness and sorting provide further evidence for an allochthonous origin of the green grains. In contrast, authigenic glaucony from the overlying offshore clays exhibits higher abundance (up to 45%) and lower maturity (K2O < 7%) and is interpreted to have formed in situ. Allochthonous glaucony originally developed in more distal areas during a prolonged period of sediment starvation. The green grains were then swept away from their place of origin and concentrated into tidal bars and channels within the upper transgressive systems tract of the third-order depositional sequence. Maximum concentration of autochthonous glaucony is recorded at the transition from tidal-influenced to offshore deposits: this glaucony, which is relatively less evolved due to lower time available for maturation, is interpreted to reflect the turnaround from transgressive to highstand conditions, marking the condensed section of the depositional sequence. As postulated by previous sequence-stratigraphic models, this study documents that allochthonous glaucony can be widespread throughout the transgressive systems tract (TST), while the condensed section (CS) typically hosts autochthonous glaucony. Contrary to the existing literature, however, this study shows that glaucony from the TST may be even more mature than glaucony from the CS, if enough time for maturation during transgression is allowed before the ultimate concentration of the green grains. Identification of spatial and temporal characteristics of glaucony, thus, is critical to a reliable sequence-stratigraphic interpretation of the glaucony-bearing deposits. 相似文献
998.
Transient release of Ni,Mn and Fe from mixed metal sulphides under oxidising and reducing conditions
C. Naylor W. Davison M. Motelica-Heino L. M. van der Heijdt G. A. van den Berg 《Environmental Earth Sciences》2012,65(7):2139-2146
The potential release of metals from anoxic sediments exposed to oxygen was investigated by using a synthetic preparation
of metal sulphides dominated by solid phase FeS. The technique of DGT (diffusive gradients in thin-films) was used to measure
sulphide and Fe, Mn and Ni in the anoxic metal-sulphide slurry, which had a pH of 6.4. Speciation calculations based on these
data showed there was moderate supersaturation with respect to amorphous FeS in the solution phase. Measurements made using
DGT with a range of diffusion layer thicknesses showed that when Fe, Mn and Ni are removed from solution there is fairly rapid
(minutes) release from the solid phase, that is reasonably well sustained. This presumed desorptive release will be responsible
for elevated concentrations of some metals in solution when sediments are resuspended. Oxidation of the slurry by bubbling
with air rapidly (hours) removed Fe, Mn and Ni from the pore water solution. While Fe concentrations in solution remained
low after the removal, Mn and Ni were transiently released. These results were consistent with initial rapid oxidation of
Fe(II) to oxyhydroxides, which remove Mn(II) and Ni by adsorption. The slower oxidation of FeS then releases Mn and Ni, but
these too are eventually removed by adsorption to iron oxyhydroxides. These data suggest that oxidation of metal sulphides
will contribute to the release of metals from sediment disturbed by dredging or remedial aeration, but it is likely to be
short lived, with complete removal within a day. 相似文献
999.
1000.
This paper analyzes the regional differences in dust weather and its relationship with climatic factors and vegetation cover,
using data at 27 observation stations in the Beijing-Tianjin Sand Source Region from 1960 to 2007. There was a decreasing
trend in dust weather in the southeast, which was correlated with wind and temperature. In contrast, in the northwest, the
number of dusty days did not decrease and was significantly correlated with precipitation and vegetation cover. These results
suggest that, in addition to the climate and underlying conditions, physical geographic conditions also influenced the frequency
of dust weather. 相似文献