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71.
Induced sinkholes (catastrophic subsidence) are those caused or accelerated by human activities These sinkholes commonly result
from a water level decline due to pumpage Construction activities in a cone of depression greatly increases the likelihood
of sinkhole occurrence Almost all occur where cavities develop in unconsolidated deposits overlying solution openings in carbonate
rocks. Triggering mechanisms resulting from water level declines are (1) loss of buoyant support of the water, (2) increased
gradient and water velocity, (3) water-level fluctuations, and (4) induced recharge Construction activities triggering sinkhole
development include ditching, removing overburden, drilling, movement of heavy equipment, blasting and the diversion and impoundment
of drainage Triggering mechanisms include piping, saturation, and loading
Induced sinkholes resulting from human water development/management activities are most predictable in a youthful karst area
impacted by groundwater withdrawals Shape, depth, and timing of catastrophic subsidence can be predicted in general terms
Remote sensing techniques are used in prediction of locations of catastrophic subsidence. This provides a basis for design
and relocation of structures such as a gas pipeline, dam, or building Utilization of techniques and a case history of the
relocation of a pipeline are described 相似文献
72.
Benjamin D. Santer Karl E. Taylor Tom M. L. Wigley Joyce E. Penner Philip D. Jones Ulrich Cubasch 《Climate Dynamics》1995,12(2):77-100
It has been hypothesized recently that regional-scale cooling caused by anthropogenic sulfate aerosols may be partially obscuring
a warming signal associated with changes in greenhouse gas concentrations. Here we use results from model experiments in which
sulfate and carbon dioxide have been varied individually and in combination in order to test this hypothesis. We use centered
[R (t)] and uncentered [C (t)] pattern similarity statistics to compare observed time-evolving surface temperature change patterns with the model-predicted
equilibrium signal patterns. We show that in most cases, the C (t) statistic reduces to a measure of observed global-mean temperature changes, and is of limited use in attributing observed
climate changes to a specific causal mechanism. We therefore focus on R (t), which is a more useful statistic for discriminating between forcing mechanisms with different pattern signatures but similar
rates of global mean change. Our results indicate that over the last 50 years, the summer (JJA) and fall (SON) observed patterns
of near-surface temperature change show increasing similarity to the model-simulated response to combined sulfate aerosol/CO2 forcing. At least some of this increasing spatial congruence occurs in areas where the real world has cooled. To assess the
significance of the most recent trends in R (t) and C (t), we use data from multi-century control integrations performed with two different coupled atmosphere-ocean models, which
provide information on the statistical behavior of 'unforced' trends in the pattern correlation statistics. For the combined
sulfate aerosol/CO2 experiment, the 50-year R (t) trends for the JJA and SON signals are highly significant. Results are robust in that they do not depend on the choice of
control run used to estimate natural variability noise properties. The R (t) trends for the CO2-only signal are not significant in any season. C (t) trends for signals from both the CO2-only and combined forcing experiments are highly significant in all seasons and for all trend lengths (except for trends
over the last 10 years), indicating large global-mean changes relative to the two natural variability estimates used here.
The caveats regarding the signals and natural variability noise which form the basis of this study are numerous. Nevertheless,
we have provided first evidence that both the largest-scale (global-mean) and smaller-scale (spatial anomalies about the global
mean) components of a combined CO2/anthropogenic sulfate aerosol signal are identifiable in the observed near-surface air temperature data. If the coupled-model
noise estimates used here are realistic, we can be highly confident that the anthropogenic signal that we have identified
is distinctly different from internally generated natural variability noise. The fact that we have been able to detect the
detailed spatial signature in response to combined CO2 and sulfate aerosol forcing, but not in response to CO2 forcing alone, suggests that some of the regional-scale background noise (against which we were trying to detect a CO2-only signal) is in fact part of the signal of a sulfate aerosol effect on climate. The large effect of sulfate aerosols found
in this study demonstrates the importance of their inclusion in experiments designed to simulate past and future climate change.
Received: 10 November 1994 / Accepted: 19 July 1995 相似文献
73.
The rates of uptake of the heavy metals zinc and cadmium from solution were measured in the caridean decapod crustacean Palaemon elegans. When radioactively-labelled zinc and cadmium were present together with both at dissolved concentrations of 20 μg l−1, the rate of zinc uptake by the decapod decreased and the rate of cadmium uptake increased in comparison with the uptake rates of each metal in single metal exposures of 20 μg l−1. This effect can be interpreted as a result of competition between the two metals for uptake routes. The rate of zinc uptake by individual P. elegans is positively linearly correlated with the rate of cadmium uptake. Thus, some individuals have inherently higher metal uptake rates than others, although such uptake rates are also greatly affected by the stage in the moult cycle. 相似文献
74.
75.
76.
The existence of detachment surfaces or décollement zones beneath folded rocks of the Valley and Ridge and Plateau provinces of the Appalachians has been recognized as an important condition of folding. Large folds at the border between the two provinces resulted primarily from repetition of strata by thrusting of blocks over ramp faults that connect detachement surfaces at different horizons. Some investigators have suggested that folds in the Plateau province of Pennsylvania were produced by splay faults arising from detachment surfaces, but field observations and theoretical analyses by Sherwin and by Wiltschko & Chapple suggest that the folds are a result of buckling of multilayered rocks above a décollement. An exception may be the Burning Springs anticline in West Virginia, which appears to have formed at the termination of a detachment surface.Investigation of the translation of an homogenous, viscous material above a flat detachment surface that terminates laterally indicates that the termination produces a broad, low-amplitude anticline in passive layering as a result of thickening induced by a gradient of shear stresses in the vertical direction. This thickening above the termination of a detachment is a mechanism of folding. If the viscous fluid contained mechanical layering, the fold would become amplified by buckling. Computations of stresses in the material indicate that minor faults should be generated first near the termination of the flat detachment surface. The Burning Springs anticline probably was initiated by termination of a detachment surface and subsequently amplified by buckling. 相似文献
77.
Mo and W have been determined in five CRPG and eight ANRT geochemical reference samples by spectrophotometric - zinc dithiol procedures. Although data are lacking for adequate comparisons on most samples, our data for tungsten in GIT-IWG MA-N and GIT-IWG BE-N are very near the presently proposed values. 相似文献
78.
79.
I. Camilo Higuera-Díaz Philip J. Carpenter Michael D. Thompson 《Environmental Geology》2007,53(4):805-812
Karst aquifers are highly susceptible to contamination, with numerous points of entry for contaminants through recharge features
such as sinkholes, swallow holes and solutionally enlarged fractures. These recharge features may be filled or obscured at
the surface, requiring the use of geophysical or remote sensing techniques for their identification. This study uses seismic
refraction data collected at the Ft. Campbell Army Airfield (CAAF), Kentucky, USA, to test the hypothesis that refraction
tomography is a useful tool for imaging bedrock depressions beneath thick overburden (greater than 20 m of unconsolidated
sediment). Southeast of the main taxiway of CAAF seismic velocity tomograms imaged a bedrock low, possibly a closed depression,
at a depth of 25 m that had been earlier identified through delay-time analysis of the same refraction data. Tomography suggests
the bedrock low is about 250-m wide by 10-m deep at its widest point. High rates of contaminant vapor extraction over the
western extension of this feature suggest a high concentration of contaminants above, and within, this filled bedrock low,
the base of which may contain solutionally enlarged fractures (i.e. karst conduits) that could funnel these contaminants to
the upper or lower bedrock aquifers. This study thus demonstrates the viability of seismic refraction tomography as a tool
for identification of filled sinkholes and bedrock depressions in karst areas. 相似文献
80.
Recent developments in long term landform evolution modelling have created a new demand for quantitative salt weathering data, and in particular data describing the size distribution of the weathered rock fragments. To enable future development of rock breakdown models for use in landscape evolution and soil production models, laboratory work was undertaken to extend existing schist/salt weathering fragmentation studies to include an examination of the breakdown of sub‐millimetre quartz chlorite schist particles in a seasonally wet tropical climate. Laser particle sizing was used to assess the impact of different experimental procedures on the resulting particle size distribution. The results reveal that salt weathering under a range of realistic simulated tropical wet season conditions produces a significant degree of schist particle breakdown. The fragmentation of the schist is characterized by splitting of the larger fragments into mid‐sized product with finer material produced, possibly from the breakdown of mid‐sized fragments when weathering is more advanced. Salinity, the salt addition method and temperature were all found to affect weathering rates. Subtle differences in mineralogy also produce variations in weathering patterns and rates. It is also shown that an increase in drying temperature leads to accelerated weathering rates, however, the geometry of the fracture process is not significantly affected. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献