Temporal cycles of karst denudation in northwest Georgia,U.S.A.

Time patterns of karst denudation in northwest Georgia (U.S.A.) were investigated at three spring sites for 12 months and at five stream sites for 10 years. Rainfall was evenly distributed and showed no significant seasonality. At the springs, as well as the streams, water hardness was largely controlled by discharge. At the springs, soil pCO₂ and water pH were strongly correlated (r + -0·69 to -0·83). Solute transport in spring waters was highly seasonal, with two conduit flow springs removing more limestone in the winter, and the diffuse flow spring removing more during the growing season. At the stream sites, most denudation occurred during the winter and spring seasons, and least during the summer. Fourier analysis showed that variations in denudation occur on deterministic (long-wave) as well as stochastic (shortwave) time scales. As contributing variables, discharge varied in short-wave and long-wave cycles, whereas soil pCO₂ showed only a long-wave cycle. The 12 month deterministic cycles were the most important, with changes in discharge taking precedence over soil pCO₂. Time series regression explains up to 69 per cent of changes in denudation through rain and soil pCO₂. Time cycles in available water are the key controlling factor of denudation, and amounts of available soil CO₂ may not be as important in the temporal patterns of karst downwearing as has been believed previously.     

矿区岩溶陷落柱探测中遥感与地理信息系统技术的应用研究

岩溶陷落柱是煤矿生产中严重的地质灾害之一。本文研究了陷落柱的遥感图像特征，从中提取了矿山环形和线性构造及热异常区，并结合实际地质，采矿资料，应用ＡＲＣ／ＩＮＦＯ地理信息系统进行多因素复合分析，预测陷落柱的可能分布区，进而实施探验证，结果表明，这种综合探测技术方案效果好，费用省。     

Case study of compaction grouting for foundation support in karst terrain: Earth and Marine Sciences Building,University of California at Santa Cruz

Sinkholes were discovered during initial construction of a new science building at the University of California, Santa Cruz campus. The occurrence of such classic karst features in California is typically uncommon, although sinkholes have frequently been encountered at the campus during previous construction projects. Subsequent to the sinkhole collapse, geologic and engineering investigations were conducted to determine the size and extent of the collapsed sinkholes and assess the potential for further failure. An exploratory compaction grouting program was developed and implemented in order to locate, fill, and plug voids and to densify loose soils beneath the structure. Eighty-one injection locations were drilled, totaling 1350 m (4429 ft), and 248.2 m³ (324.4 yd³) of low-slump grout was placed. Grout volumes and pressures were carefully monitored, and these data correlated well with lithology determined during grout pipe drilling. Permitted movement on the structure was kept well within the allowable 0.64 cm (0.25 in) using a combination of manometers and laser levels.     

Hydrogeologic investigations of contaminant movement in karst aquifers in the vicinity of a train derailment near Lewisburg,Tennessee

A train derailment near Lewisburg, Tennessee, in October 1990 prompted two series of groundwater investigations. The first was to determine the subsurface flow route of chloroform and styrene that sank into the underlying karst aquifer. The second was to determine the source of contamination for two nearby residential wells which were found to be contaminated with trichloroethylene (TCE). Water-sample analysis and a dye trace performed at the time of the train derailment indicated groundwater flow to Wilson Spring. A dam was constructed to contain the entire discharge from the spring so that it could be treated before being discharged into Big Rock Creek. Three springs and three water wells were contaminated with chloroform and styrene. Dye traces were performed to determine groundwater flow directions in the vicinities of the TCE-contaminated wells and in the vicinities of potential sources. At the train derailment, the chloroform and styrene sank into the Upper Ridley Karst Aquifer and pooled on top of the Lower Ridley Confining Layer. An exploratory well revealed a layer of chloroform (a Dense Non-Aqueous Phase Liquid DNAPL) on the bottom, a layer of groundwater in the middle, and a layer of styrene (a Light Non-Aqueous Phase Liquid LNAPL) on top. Groundwater with relatively low levels of chloroform and styrene in solution was carried by a small cave stream southeast along the strike to Wilson Spring. Chloroform product moved by gravity southwest down-dip along weathered bedding planes. Treatment of contaminated groundwater from Wilson Spring and recovery wells at the spill site has occurred continuously since October, 1990.     

贵州洪家渡电站水库诱发地震前期研究

本文通过地质构造背景、岩溶条件、光弹模拟实验分析,对洪家渡水库可能存在的诱震条件进行研究。在归纳云贵岩溶地区水库地震诱震条件的基础上,用水库地震类比的方法,对洪家渡水库地震进行预测。研究结果认为,洪家渡水库在蓄水至设计水位的1—5年内可能诱发地震。     

Autogenic and allogenic denudation in carbonate karst by the multiple basin method: An example from Svartisen,North Norway

In carbonate karst basins, adequate denudation rates are difficult to estimate when there are allogenic inputs. It is shown that the common practice of correcting for allogenic input by Corbel's modified formula leads to erroneous results unless the karst ratio is very high. When choosing small basins that are subsets of each other, assumptions of hydrologic and lithologic uniformity may be satisfied. Then the autogenic and allogenic components of the denudation may be calculated by a linear model of uniform mixing. The model was tested in a subarctic stripe karst in North Norway, yielding an autogenic denudation rate of 32.5 ± 10.2 mm ka^?1. The mean annual runoff is 2600 mm. The result is supported by independent denudation rates from comparable areas, micro-erosion meter data as well as the total post-glacial corrosion deduced from pedestal and vein heights.     

Geoelectrical investigations by means of resistivity methods in karst areas in Romania

The applicability of resistivity methods to ground water investigations is well recognized. As water-saturated rock formations have a lower electrical resistivity than dry ones, an electrical resistivity survey should result in low resistivity anomalies. Normally, such anomalies are interpreted to indicate areas of potentially significant ground water flows. In karst areas, however, interpretation may not be as straightforward: for example, large electrically conductive domains can represent water bearing zones, whose fluid-permeability may be poor; alternatively, fast flow conduits, which may be unsaturated, occur as slender objects, and not as clear anomalous features. In order to deal with such extreme heterogeneities, resistivity investigations require some specific adjustments. One example is the so-called “mise à la masse” method. In Romania, it was used to trace the cold karst water inflows that detrimentally affected the commercial exploitation of a thermal spring, Hercules at Baile Herculane. Conventional geoelectrical approaches––such as using resistivity highs to detect air-filled cave passages, are proved to be less efficient in the considered karst investigations.     

Assessment of suffosion-related hazards in karst areas using GIS technology

This paper describes an application of the geographic information system (GIS) technology to a ground stability assessment in the karst area of Dzerzhinsk, Russia. In the stability analysis, the groundwater level changes in the karst aquifer could cause suffosion sinkholes when the gravitational force was greater than the soil strength. The GIS technology was used to combine various data and to delineate the zones of potential gravitational collapse and suffosion collapse in the area.

Chemical and geological control of spring water in Eastern Guaniguanico mountain range, Pinar del Rìo, Cuba

Flows of different hierarchy, which travel through limestone, schist, sandstone and ultra-basic rocks, with ages from the Paleocene to the Jurassic, at Sierra del Rosario, Pinar del Río, Cuba, were characterized. The waters were sampled from 1984 until 2004 and the data were statistically processed by means of chemical equilibrium and physico-chemical models, under a flow system view of interpretation. Results demonstrate that the physico-chemical properties of the water are controlled by water–rock interaction resulting from residence time since rainwater infiltrate and the path it follows to the discharge zone and the type of aquifer material the different groundwater flows are in contact with. Geochemical indices allow the definition of the different types of flow (local, intermediate, regional) to be characterized, permitting a further definition of the different flow systems and rock type involved, as well as its use for water supply and medical use. The main geochemical processes which control the chemical composition acquisitions mode are: congruent dissolution of calcite, dolomite, and halite; incongruent dissolution of plagioclase and microcline minerals; pyrite oxidation, sulphate reduction, and silica dissolution at the surface or silica precipitation at deep saturation and circulation zones.     

Temporal–spatial variability of soil fertility in karst region: a case study of Xiaojiang watershed Yunnan

By sampling in the field and analyzing the soil samples in the laboratory in 1982 and 2005 the soil fertility data were obtained. Through application of geo-statistics combined with GIS, the temporal–spatial variability of the pH, organic matter, total nitrogen, total phosphorus and total potassium in soil of Xiaojiang watershed from 1982 to 2005 were analyzed. Results showed that: (1) the pH value and total potassium in soil showed an increasing trend, but the organic matter, total nitrogen and the total phosphorus in soil declined in the past 20 years in Xiaojiang watershed, (2) the parameters fitted by semivariogram models for fertility indices changed significantly in the past 20 years and (3) the result estimated by ordinary Kriging indicated the spatial pattern of the soil fertility indices changed significantly in the past 20 years. The soil pH increased in the east and southeast, but decreased in the middle of the watershed. The organic content of the soil matter decreased in the east, southeast and southwest, but increased in the northeast and middle of the watershed. The total nitrogen content of the soil decreased in the east, but increased in the middle of watershed. The total phosphorus content of the soil decreased in the whole watershed. The total potassium content of the soil increased in the southwest and southeast, but decreased in the middle of the watershed and (4) the change of land use and soil management measures was the main driving force of variability of soil properties.