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1.
Using ALSM to map sinkholes in the urbanized covered karst of Pinellas County,Florida—1, methodological considerations 总被引：1，自引：0，他引：1
Larry D. Seale Lee J. Florea H. L. Vacher Robert Brinkmann 《Environmental Geology》2008,54(5):995-1005
Comparison of a database of interpreted sinkholes made using airborne laser swath mapping (ALSM) with databases of sinkholes
made from interpretation of aerial photographs reveals substantial disagreement. The discrepancies involve the location, number,
areas, and circularity of interpreted sinkholes. Methodological factors that contribute to the discrepancies include blockage
of ALSM laser returns in thick vegetation, multi-path reflections, and misrepresentation of the true extent of sinkholes.
Comparison of two ALSM-derived databases made (1) independently from versus (2) in combination with earlier air photo analysis
in undeveloped regions had the following result: one-fourth of the sinkholes interpreted by using the composite method were
missed by the independent analysis, and one-third of the sinkholes that were interpreted from the independent analysis were
not interpreted as sinkholes using the composite method. Subjective interpretation leads to a high level of uncertainty such
that the results of the remote sensing studies are suspect, if not invalid. 相似文献
2.
Development and morphometry of sinkholes in coastal plains of Apulia, southern Italy. Preliminary sinkhole susceptibility assessment 总被引：1，自引：0，他引：1
Evolution of coastlines in karst areas may be strongly controlled by dissolution processes which favour the development of surface and subsurface landforms. The generation of caves in these environments is commonly favoured by the mixing between fresh and brackish waters. The sinkholes resulting from the upward propagation of the caves may interfere with the anthropogenic environment and cause damage to human elements (property and activities). To highlight the often underestimated importance of karst phenomena in coastal areas, we have analyzed a coastal stretch of Apulia, in southern Italy. The study area, covering an extension of about 6 km2, is situated in the Ionian coast, and presents several interesting karst landforms that are generally connected to caves. Tens of sinkholes were mapped through field surveys, multi-year aerial-photographs (dating back to the 1940s) and archival research. We have performed a morphometric analysis of the sinkholes. The analysis describes the main parameters of the sinkholes (area, length, width, and depth), and the control exerted by the main discontinuity systems in the area. The detrimental effects derived from interaction between human environment and these karst landforms is also under consideration. A sinkhole susceptibility map, which may provide useful information for planners, developers and the insurance industry has eventually been produced through application of a decision tree model. 相似文献
3.
Sinkhole collapse is one of the main limitations on the development of karst areas, especially where bedrock is covered by
unconsolidated material. Studies of sinkhole formation have shown that sinkholes are likely to develop in cutter (enlarged
joint) zones as a result of subterranean erosion by flowing groundwater. Because of the irregular distribution of pinnacles
and cutters on the bedrock surface, uncertainties arise when "hit-or-miss" borehole drilling is used to locate potential collapse
sites. A high-resolution geophysical technique capable of depicting the details of the bedrock surface is essential for guiding
the drilling program. Dipole-dipole electrical resistivity tomography (ERT) was used to map the bedrock surface at a site
in southern Indiana where limestone is covered by about 9 m of clayey soils. Forty-nine transects were conducted over an area
of approximately 42,037 m2. The electrode spacing was 3 m. The length of the transects varied from 81 to 249 m. The tomographs were interpreted with
the aid of soil borings. The repeatability of ERT was evaluated by comparing the rock surface elevations interpreted from
pairs of transects where they crossed each other. The average difference was 2.4 m, with a maximum of 10 m. The discrepancy
between interpreted bedrock-surface elevations for a transect intersection may be caused by variations in the subsurface geology
normal to the transect. Averaging the elevation data interpreted from different transects improved the ERT results. A bedrock
surface map was generated using only the averaged elevation data at the transect junctions. The accuracy of the map was further
evaluated using data from four exploratory boreholes. The average difference between interpreted and actual bedrock surface-elevations
was less than 0.4 m. The map shows two large troughs in the limestone surface: one coinciding with an existing sinkhole basin,
while the other is in alignment with a small topographic valley. Because sinkholes were observed at the same elevation interval
in similar valleys in the vicinity, the delineated trough may have implications for future land use at the site.
Received: 4 January 1999 · Accepted: 8 March 1999 相似文献
4.
Geoelectric structure of the Ein Gedi sinkhole occurrence site at the Dead Sea shore in Israel 总被引：2，自引：0，他引：2
Hazardous sinkholes started to appear in alluvial fans and unconsolidated sediments along the western Dead Sea coast in 1990. Since then hundreds of sinkholes have appeared from north to south along the shoreline. The Electrical Resistivity Tomography (ERT) method was used to achieve a better understanding of the subsurface geoelectric structure at the sinkhole development sites, taking into account that electric parameters (such as resistivity or conductivity) are very sensitive to formation properties and their variations in time. Fifteen image lines were surveyed at the Ein Gedi area during a period of active sinkhole development (in 2001–2002) over an area of 300 × 550 m2. Resistivity cross-sections and maps were constructed from 2-D linear surveys. The process of sinkhole formation in the surveyed area is located in a strip 50–70 m wide and 300–500 m long, extending approximately in a north–south direction. The sinkholes are arranged along a tortuous line within this strip. On resistivity maps and sections this U-shaped zone appears as an alternation of high resistivity anomalies of 350–1000 Ωm (at sinkhole group locations) with narrow background resistivity zones of 50–100 Ωm. The large size of resistivity anomalies (250 × 300 m2), which are considerably greater than those of the sinkholes, form one of the features of the sinkhole sites in the Ein Gedi area. The anomalies continue down to the water table or even deeper (maximum of 25–35 m depth). A low resistivity layer of 1–8 Ωm underlies them. The combined analysis of the image results and other geophysical data shows that high resistivity anomalies are associated with the decompaction of the soil mass at the sinkhole development sites and surrounding areas. Recent studies have shown that sinkholes in the Ein Gedi area are developing along the salt western edge located at a depth of 50 m. The subsurface high resistivity anomaly conforms to the sinkhole line (and salt boundary). They are presumably located above the great dissolution caverns at the salt edge. The heterogeneity of the resistivity structure within the high resistivity anomaly (seen in both lateral and vertical planes) confirms that a disintegration of internal formation structure takes place. Away from the sinkhole sites the subsurface resistivity distribution is homogeneous. 相似文献
5.
Sinkhole hazards along the eastern Dead Sea shoreline area, Jordan: a geological and geotechnical consideration 总被引：2，自引：0，他引：2
For the last four decades, the level of the Dead Sea has been subjected to continual variation which, among other important
factors, has led to the occurrence of much subsidence and many sinkholes in the southern Dead Sea area. Sinkhole activities
occurred repetitively and were observed in open farms, across roads, near dwellings and near an existing factory, thus causing
a serious threat to the locals and farmers of the area and their properties. This paper presents the main results from detailed
geological and geotechnical studies of this area. Aerial photo interpretation and borehole drilling aided these studies. Parallel
geophysical investigations (vertical electrical sounding and seismic refraction) and hydrological and hydrogeological studies
were made by others in the same area to also investigate this phenomenon. It was found that sinkholes are aligned to and follow
old water channels and are concentrated parallel to the recent shoreline of the Dead Sea. The development of subsurface cavities
is associated mainly with the variation in the level of the Dead Sea over the four past decades, the presence of regional
salt intrusion under the surface of salt beds, the fluctuation of the water table and continuous dissolution and the active
tectonism of the area. Moreover, this work showed that the area is still under active sinkhole hazards and other parts of
the area will be inevitably affected by sinkholes in the future.No practical engineering solution to this problem is feasible.
Received: 1 July 1999 / Accepted: 11 October 1999 相似文献
6.
7.
A genetic classification of sinkholes illustrated from evaporite paleokarst exposures in Spain 总被引：2，自引：0，他引：2
This contribution analyses the processes involved in the generation of sinkholes from the study of paleokarst features exposed
in four Spanish Tertiary basins. Bedrock strata are subhorizontal evaporites, and in three of the basins they include halite
and glauberite in the subsurface. Our studies suggest that formation of dolines in these areas results from a wider range
of subsidence processes than those included in the most recently published sinkhole classifications; a new genetic classification
of sinkholes applicable to both carbonate and evaporite karst areas is thus proposed. With the exception of solution dolines,
it defines the main sinkhole types by use of two terms that refer to the material affected by downward gravitational movements
(cover, bedrock or caprock) and the main type of process involved (collapse, suffosion or sagging). Sinkholes that result
from the combination of several subsidence processes and affect more than one type of material are described by combinations
of the different terms with the dominant material or process followed by the secondary one (e.g. bedrock sagging and collapse
sinkhole). The mechanism of collapse includes any brittle gravitational deformation of cover and bedrock material, such as
upward stoping of cavities by roof failure, development of well-defined failure planes and rock brecciation. Suffosion is
the downward migration of cover deposits through dissolutional conduits accompanied with ductile settling. Sagging is the
ductile flexure of sediments caused by differential corrosional lowering of the rockhead or interstratal karstification of
the soluble bedrock. The paleokarsts we analysed suggest that the sagging mechanism (not included in previous genetic classifications)
plays an important role in the generation of sinkholes in evaporites. Moreover, collapse processes are more significant in
extent and rate in areas underlain by evaporites than in carbonate karst, primarily due to the greater solubility of the evaporites
and the lower mechanical strength and ductile rheology of gypsum and salt rocks. 相似文献
8.
The formation of sinkholes in karst mining areas in China and some methods of prevention 总被引：2，自引：0，他引：2
Zhou Wanfang 《Environmental Geology》1997,31(1-2):50-58
Mining of coal, lead and zinc, gold, and iron ore deposits in karst areas has been closely associated with sinkholes in China.
Surface collapse causes an increase in mine water drainage and the possibility of major water inflow from karst aquifers,
which threatens the environment in mining areas and endangers mine safety. The origin of such sinkholes is analyzed quantitatively
in this paper and a combination of factors including soil weight, buoyancy, suffosion process and vacuum suction can contribute
to surface subsidence. The key measures to prevent sinkholes in mining areas are to control the amount of mine drainage, reduce
water-level fluctuation, seal off karst conduits and subsurface cavities in the overlying soil, prevent water inflow, and
to increase gas pressure in the karst conduits.
Received: 2 May 1996 · Accepted: 29 July 1996 相似文献
9.
Subsidence hazard avoidance based on geomorphological mapping in the Ebro River valley mantled evaporite karst terrain (NE Spain) 总被引：1，自引：6，他引：1
F. Gutiérrez-Santolalla M. Gutiérrez-Elorza C. Marín C. Maldonado P. L. Younger 《Environmental Geology》2005,48(3):370-383
In the valley of the Ebro River to the southeast of the city of Zaragoza (NE Spain), the dissolution of evaporite sediments (gypsum, halite and Na-sulphates) which underlie alluvial deposits gives rise to numerous sinkholes. These sinkholes are a potential hazard to human safety, particularly where they develop in a catastrophic way. Even slow-developing sinkholes are problematic, as they damage urban and agricultural infrastructure, necessitating costly repairs and vigilant maintenance. To assist in developing avoidance strategies for these hazards, the factors controlling sinkhole occurrence have been assessed using geomorphological maps produced from aerial photographs for 1956 and 1981. Important controls on sinkhole development are found to include underlying geological structure (manifest in preferred orientations of sinkholes on the azimuths N130-150E and N30-40E), and the presence of glauberite in the groundwater flow path, which apparently promotes accelerated gypsum dissolution. Perhaps surprisingly, alluvium thickness does not appear to significantly correlate with the density of sinkholes on the floodplain in this area. The maps for 1956 and 1981 reveal that both human activity and natural processes can serve to obscure the true density of sinkhole development. For instance, a large number of sinkholes which were conspicuous in 1956 have since been back-filled by farmers. In the most fluvially active zone of the Ebro valley (the meander belt), the relatively low density of sinkholes compared with adjoining zones suggests that subsidence is being masked by morpho-sedimentary dynamic processes (aggradation and erosion). Careful geomorphological mapping for different time periods yields a much more accurate impression of the frequency of sinkhole development than would be gained from surveying currently visible sinkholes in the area of interest. 相似文献
10.
Damien Closson 《Environmental Geology》2005,47(2):290-301
For about four decades, the Dead Sea (DS) level and the surrounding water table has been dropping dramatically. At least from the eighties, the direct vicinity of the Lisan Peninsula (LP), Jordan, has been facing high rates of subsidence and sinkhole hazards. Between 2000 and 2002, the Arab Potash Company (APC) lost two salt evaporation ponds resulting in a loss of $70 million. In the fertile plain of Ghor al Haditha (GAH), three deep and wide bowl-shaped subsidence areas threaten human activities and infrastructures. Over the part of the Lisan Peninsula that emerged before the 1960s, relict fossil sinkholes occurred everywhere, whereas new collapses constantly appear in the southern area only. In this paper, we have integrated 15 years of field observations related to sinkholes and subsidence with interpretation of space borne radar interferometric outputs, aerial photographs and satellite images. This has helped to place hazardous areas in their geological context and to clarify them within the framework of the general tectonic setting of the area. 相似文献