Sinkhole Activity Research Articles

Current perspectives on the environmental impacts and hazards in karst

Karst geo-ecosystems are highly fragile environments that are suffering a progressive degradation caused by human activities in many regions of our planet. The interactions between Man and karst environments have been relevant since Greek and Roman times (Nicod et al. 1997), but the resulting detrimental effects became particularly significant from the industrial revolution. Despite the long history of human-induced impacts on the karst environments and damage caused by hazardous karst processes, these problems were largely overlooked by the scientific community till the beginning of the 90s. Fortunately, both the perception of the importance of the karst systems and the scientific efforts devoted to their understanding have increased considerably in recent times (Ford and Williams 2007). The results of some investigations have been published in several special issues (Catena supplement, Environmental Geology, Oklahoma Geological Survey Circular, Geological Society of London Special Publication, Engineering Geology) (Williams et al. 1993; Burri et al. 1999; Johnson and Neal 2003; Parise and Gunn 2007; Gutierrez et al. 2008c; Parise et al. 2008) and conference proceedings (Sauro et al. 1991; Beck 2003). Subsidence related to sinkhole activity is the most important hazard in karst landscapes (Beck 2003; Waltham et al. 2005). In many regions, financial losses caused by sinkholes are raising considerably due to the humaninduced increase in the probability of occurrence of sinkholes and the development of hazardous areas (Gutierrez et al. 2008a). Some approaches including, mechanical, hydrogeological and predictive modelling (Salvati and Sasowsky 2002; He et al. 2004), geophysical surveys (Ardau et al. 2007), speleological studies (Klimchouk et al. 2002) and palaeokarst investigations (Gutierrez et al. 2008b) have provided enlightening insights on the processes involved in the subsidence phenomena. Other typical environmental problems in karst terrains are related to water quality and quantity (Drew and Hotzl 1999; Goldscheider and Drew 2007; Ravbar 2007), construction of infrastructures (dams, highways, tunnels) (Milanovic 2002), mining and quarrying (Gunn 2004) and other human activities such as, agriculture, waste disposal or urbanisation. This special issue of Environmental Geology contains a selection of peer-reviewed articles presented at the symposium on ‘‘Natural and Anthropogenic Hazards in Karst Areas’’, held in Vienna, Austria, on 16 April 2007, within the framework of the Natural Hazards Programme of the European Geosciences Union General Assembly. The symposium was co-sponsored by the International Union of Speleology (UIS) and by the International Geographical Union (IGU) Commission of Karst Hydrogeology and Speleogenesis. Out of the 35 contributors to the session, 22 accepted the invitation to submit a full paper and finally, 15 peerreviewed articles have been accepted and included in this special issue. They cover many different geographical areas where the interaction between karst systems and human activities results in significant environmental impacts and hazards: Europe (Austria, Bosnia M. Parise (&) National Research Council, IRPI, Bari, Italy e-mail: m.parise@ba.irpi.cnr.it

Identification, prediction, and mitigation of sinkhole hazards in evaporite karst areas

Sinkholes usually have a higher probability of occurrence and a greater genetic diversity in evaporite terrains than in carbonate karst areas. This is because evaporites have a higher solubility and, commonly, a lower mechanical strength. Subsidence damage resulting from evaporite dissolution generates substantial losses throughout the world, but the causes are only well understood in a few areas. To deal with these hazards, a phased approach is needed for sinkhole identification, investigation, prediction, and mitigation. Identification techniques include field surveys and geomorphological mapping combined with accounts from local people and historical sources. Detailed sinkhole maps can be constructed from sequential historical maps, recent topographical maps, and digital elevation models (DEMs) complemented with building-damage surveying, remote sensing, and high-resolution geodetic surveys. On a more detailed level, information from exposed paleosubsidence features (paleokarst), speleological explorations, geophysical investigations, trenching, dating techniques, and boreholes may help in investigating dissolution and subsidence features. Information on the hydrogeological pathways including caves, springs, and swallow holes are particularly important especially when corroborated by tracer tests. These diverse data sources make a valuable database—the karst inventory. From this dataset, sinkhole susceptibility zonations (relative probability) may be produced based on the spatial distribution of the features and good knowledge of the local geology. Sinkhole distribution can be investigated by spatial distribution analysis techniques including studies of preferential elongation, alignment, and nearest neighbor analysis. More objective susceptibility models may be obtained by analyzing the statistical relationships between the known sinkholes and the conditioning factors. Chronological information on sinkhole formation is required to estimate the probability of occurrence of sinkholes (number of sinkholes/km2 year). Such spatial and temporal predictions, frequently derived from limited records and based on the assumption that past sinkhole activity may be extrapolated to the future, are non-corroborated hypotheses. Validation methods allow us to assess the predictive capability of the susceptibility maps and to transform them into probability maps. Avoiding the most hazardous areas by preventive planning is the safest strategy for development in sinkhole-prone areas. Corrective measures could be applied to reduce the dissolution activity and subsidence processes. A more practical solution for safe development is to reduce the vulnerability of the structures by using subsidence-proof designs.

Geological and environmental implications of the evaporite karst in Spain

In Spain, evaporite outcrops cover approximately 7% of the total area of the country. Most of the evaporitic formations are made up of Ca-sulfates (gypsum/anhydrite) or Ca-sulfates and halite. Certain Paleogene marine evaporites also contain K-Mg-chlorides, and some Tertiary continental formations bear substantial amounts of Na-sulfates in the subsurface (glauberite and thenardite). Mesozoic evaporitic formations commonly wedge out towards the ground surface, passing into condensed sequences and dissolution-collapse breccias. Some of these highly porous breccias constitute major regional aquifers. In several areas, interstratal karstification of the evaporites has given rise to gravitational deformations such as basin structures, monoclines, and collapse structures covering several square kilometers that record a cumulative subsidence in excess of 200 m (Teruel and Calatayud Grabens). A widespread consequence of evaporite dissolution processes in Spain is the hydrochemical degradation of surface waters. Some of the largest and most outstanding lake systems, from an environmental perspective, occur in karstic depressions developed in evaporitic formations (Fuente de Piedra, Gallocanta, Bujaraloz, and Banolas lakes). Sinkhole activity is a major geohazard in several evaporite karst areas. The sinkhole risk has a particularly high impact in sectors where Tertiary evaporites are overlain by Quaternary alluvial aquifers (Calatayud, Zaragoza, and Madrid areas). Some of the detrimental effects of subsidence include severe damage to historical monuments (Calatayud), the demolition of a whole village (Puilatos), or the derailment of a freight train (Zaragoza area). The deepest gypsum caves are found in Triassic diapiric structures (El Sumidor Cave, 210 m deep), and the longest ones are developed in horizontally lying Neogene sequences (Sorbas caves, and Estremera maze cave). The Cardona diapir hosts salt caves up to 4,300 m long whose genesis is related to flooding of mine galleries caused by the interception of a phreatic conduit. The main anthropogenic impacts on the endokarstic systems are related to the disposal of wastewaters and the destruction of caves by quarrying. The fluvial valleys that cross Tertiary evaporitic outcrops commonly show peculiar geological characteristics related to dissolution-induced synsedimentary subsidence phenomena: (1) Thickened alluvium filling dissolution basins up to several tens of kilometers long and more than 100 m deep. The largest thickenings are found in areas where the bedrock contains halite and glauberite. (2) Superimposed alluvial units locally bounded by angular unconformities. (3) Abundant deformational structures and paleosinkholes related to the rockhead and/or interstratal karstification of the substratum. These fluvial valleys typically are flanked by a prominent gypsum escarpment. Rock-falls favored by the dissolutional enlargement of joints derived from these scarps are the type of mass movement which has caused the highest number of casualties in Spain.

Use of 2D Multi Electrodes Resistivity Imagining for Sinkholes Hazard Assessment along the Eastern Part of the Dead Sea, Jordan

Sinkholes and subsidence are natural phenomena can be occurred in shallow geology sediments at different regions in the world. Sinkholes assessment is one of the most difficult near subsurface investigations. Geophysical prospecting is appropriate method to determine environmental and geotechnical problems. 2D multi electrodes resistivity imagining with Wenner-Schulmberge array was conducted within active sinkholes area. The objective of the survey is to detect features combined with sinkhole formation like zone of weakness, cavities and fractures. Soil in the study area contains alluvial, conglomerate and silty clay which represent good target for resistivity survey. The interpretation of resistivity data along the profiles show different model of the resistivity variation in active sinkhole zones compared with inactive zones in the study area. The deformation in the layer continuity and the direct contact between high resistive and low resistive layers can appear only in the subsidence area or active sinkhole zones.

Fracture-controlled fluid circulation and dissolutional weathering in sinkhole-prone carbonate rocks from central Italy

Fractures, karstic cavities, and calcite precipitates are analysed on Mesozoic, carbonate strata from the Cornicolani Mountains, central Italy, to quantify the relationships between fractures and related karstic cavities and to infer the fracture-controlled fluid pathways. The study area is characterized by active sinkholes and other karstic caves, which are among the deepest ones in the world. Results show a clear control of fractures on the process of dissolutional weathering and, therefore, on the fluid circulation. A model is proposed, in which two different modes of dissolutional weathering coexist: (i) a mode of diffuse weathering consisting in the dissolutional enlargement of closely spaced joints and bedding surfaces. This process affects the strata situated at depths of up to 5 m; (ii) a mode of more concentrated weathering active along highly permeable fault damage zones at depths of at least 70 m. These processes are mostly connected with the shallow circulation of calcite-dissolving meteoric waters, and are controlled by the disparity of permeability between the fault damage zones and the surrounding jointed strata. Some calcite precipitates along the studied fault damage zones may be connected with a dissolutional process operated by waters that interacted with the adjacent quiescent volcanic district. Such calcite-dissolving waters and the presence of high-permeable fault damage zones, along which the waters may ascent, are probably the cause for the development of some of the deep sinkholes along faults in the study area.

Designing foundations around sinkholes

There is an increasing awareness among developers and owners, of the need to conduct subsurface exploration studies before planning a project. The use of geophysical methods in subsurface exploration has been established to be valuable in locating sinkhole activity and suggesting pro-active measures. However, the value of geophysical exploration to supplement geotechnical investigation has not yet been stressed, primarily out of cost concerns. Ground penetrating radar and electrical resistivity tests, which were used to determine void spaces below proposed buildings are gaining wider acceptance. As a result of information obtained from geophysical tests, foundation designs were modified, to use post-tensioned mats or to include grouting. An improved grouting technique that controls the volume of grout being pumped is also discussed. This paper is an attempt to document some case studies which resulted in making design improvements to mitigate the effects of known sub-surface solution activity. These case studies illustrate the use of geophysical exploration methods in adding value to the engineered design.

Cover‐Subsidence Sinkhole Evaluation of State Road 434, Longwood, Florida

This paper presents the results of a cover‐subsidence sinkhole evaluation. In this case, the sinkhole activity caused a slow, gradual settlement of the State Road 434/Harbour Isle Way intersection, in Longwood, Florida. The subsoil conditions were explored with numerous cone penetrometer tests and permanent piezometers. The study indicated that the settlement was caused by internal soil erosion and raveling. Piezometric elevation contour maps revealed a well‐defined depression that coincided with the observed surface settlement. The piezometer monitoring results suggest this may be an effective technique for economically identifying potential sinkhole locations.

Groundwater withdrawal impacts in a karst area

During a 3000-gpm pump test on a groundwater supply well in Augusta County, Virginia, residential properties were impacted. The impacts included lowered farm pond water levels, development of a sinkhole, and water level decrease in residential wells. A study was performed to assess whether a lower design yield was possible with minimal impacts on adjacent property. This study included a 48-h 1500-gpm pump test that evaluated impacts due to: (1) sinkhole development and potential damage to homes, (2) loss of water in residential wells, and (3) water-quality degradation. Spring flows, residential well levels, survey monuments, and water quality were monitored. Groundwater and surface water testing included inorganic water-quality parameters and microbiological parameters. The latter included particulate analyses,Giardia cysts, and coliforms, which were used to evaluate the connection between groundwater and local surface waterbodies. Although results of the study indicated a low potential for structural damage due to future sinkhole activity, it showed that the water quality of some residential wells might be degraded. Because particulate analyses confirmed that groundwater into the supply well is under the direct influence of surface water, it was recommended that certain residents be placed on an alternate water supply prior to production pumping and that filtration be provided for the well in accordance with the Surface Water Treatment Rule. A mitigation plan was implemented. This plan included crack surveys, a long-term settlement station monitoring program, and limitation of the groundwater withdrawal rate to 1.0 million gallons per day (mgd) and maximum production rate to 1500 gpm.

The applicability of the florida mandatory endorsement for sinkhole collapse coverage. Part II. Case history: Foundation settlement of a residential structure—was it a sinkhole?

The Winter Park sinkhole created publicity for sinkhole activity in the state of Florida. In fact, Florida requires insurance companies to provide sinkhole coverage to residential homeowners However, to receive payment on a sinkhole claim, the homeowner must have sustained “sinkhole loss” according to the definition presented in Florida statue §627 706

RETENTION BASIN FAILURES IN CARBONATE TERRANES1

ABSTRACT Sinkholes and subsidence in areas subject to dewatering of carbonate formations have been documented in several geologic and hydrologic investigations. Excessive ground‐water pumpage has been cited as a causative factor in areas of increased sinkhole activity. Subsurface erosion of unconsolidated materials underlain by carbonate rocks is one cause of the collapses. Infiltrating water from retention basins may cause subsurface erosion and eventual failure by collapse of the structure. The resulting ground‐water contamination would be great as the pollutants spread throughout the solution‐cavity system.

Sinkhole Prediction: ABSTRACT

Important sinkhole activity accompanied the spring drought of 1967 in central Florida. Several sinkholes developed in a large subdivision near Bartow, Florida. Mobil Chemical Company, and other phosphate companies in the area cooperated with local officials to make test corings near unaffected houses in an attempt to predict any further sinkhole activity. The writer conducted Mobil's drilling program and found a relation between surface subsidence and large basin-shaped structures on the bedrock surface. Evidence was used to advise homeowners of possible future sinkhole development under their homes. End_of_Article - Last_Page 1834------------