Identification, prediction, and mitigation of sinkhole hazards in evaporite karst areas |
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Authors: | F Gutiérrez A H Cooper K S Johnson |
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Institution: | (1) Edificio Geológicas, University of Zaragoza, C/. Pedro Cerbuna, 12, 50009 Zaragoza, Spain;(2) British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK;(3) Oklahoma Geological Survey, Energy Center, 100 E. Boyd, Norman, OK 73019-0628, USA |
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Abstract: | 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. |
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Keywords: | Sinkholes Evaporite karst Hazard assessment Mitigation |
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