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

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 to recognize 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 and temporal 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, such as weather conditions. 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, derived from limited records and based on the assumption that past sinkhole activity may be extrapolated to the future, are noncorroborated 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 to reduce the dissolution activity and subsidence processes, but these are difficult. A more practical solution for safe development is to reduce the vulnerability of the structures by using subsidence-proof designs.

Sinkhole susceptibility, Lazio Region, central Italy

“…This second group includes brittle gravitational deformation of the cover material (collapse) caused by an upward migration of the collapse through dissolution conduits (piping sinkholes) (Beck, 2005;Galve et al, 2009;Gutiérrez, Cooper, & Johnson, 2008;Waltham, Bell, & Culshaw, 2005).…”

“…Sinkholes cause severe damage to man-made structures, and in some cases catastrophic collapse sinkholes have also caused the loss of human life. Therefore, an important task for sinkhole risk mitigation is the development of maps providing information on the distribution of pre-existing sinkholes and the probability of occurrence of new sinkholes (Gutiérrez et al, 2008;Waltham et al, 2005). This paper presents a sinkhole inventory of the Latium region formed by 393 active or extinct sinkholes.…”

Voids

“…In order of increasing solubility (and dissolution rates), the common soluble rocks are: dolomite (MgCa(CO3)2) and limestone (CaCO3), plus the evaporites including gypsum/anhydrite (CaSO4.2H2O/CaSO4), halite or rocksalt (NaCl) (Gutiérrez et al, 2008;Warren, 2016). Natural karstic voids range in size from those widened by dissolution generating fissures a few millimetres wide to enormous cave systems with volumes of millions of cubic metres (Ford and Williams, 2007).…”

6.35 Dealing with Gypsum Karst Problems: Hazards, Environmental Issues, and Planning

“…The sinkholes form across the wide spectrum of styles described by Gutiérrez et al (2008a) and summarized by Gutiérrez and Cooper (this volume). The subsidence processes range from gentle sagging to sudden collapse that can cause severe damage to buildings and infrastructure (Gutiérrez et al, 2008b).…”