Sinkhole distribution in Winona County, Minnesota
JANET DALGLEISH & E.CALVIN ALEXANDER, Jr. University of Minnesota, Minneapolis, USA
ABSTRACT Winona County, located in southeastern Minnesota, is part of a karst region in the upper Mississippi Valley. The karst is developing in flat lying dolomitic Ordovician rocks . As part of a Minnesota Geological Sur vey county atlas program, we have systematically field located sinkholes, and prepared a 1 to 100,000 scale map showing sinkhole locations and sinkhole ~robability . We located 535 sinkholes in Winona County C "- 1600 km ) • Most of these relatively small, geomorphically young sinkholes are not included in the USGS 7. 5 minute topographic maps and c annot be readily detected on air photos. The sinkhole density, while low compared to many karst regions was much greater than local, regional, and state land use plai:iners anticipated.
New bedrock, surficial and hydrogeology maps of Winona County were used for correlation with the geographic distribution of the sinkholes. The primary control on the distribution of sinkholes appears to be the bedrock stratigraphy. The secondary controls, not necessarily in order of importance include slope of the land surface, and composition of sur ficial materials. The . depth to the water table does not appear to have an important affect on sinkhole development. Age data indicate that the rate of sinkhole formation has significatnly increased in recent years. ,- Introduction Karst is an important geomorphic process influencing the landscape and hydrology of southeastern Minnesota. In Winona County, as in most of the region, the density and distri
bution of sinkhole0s varies enormously over small areas. The purpose of this work was to document the density and distribution of sinkholes in Winona County, and to relate that distribution to variations in bedrock geology, surficial materials, and/or hydrogeology. A second goal of this study was to produce a sinkhQ_le proba.bili ty map of Winona County that would aid state, county and local residents in dealing with the environmental problems asso ciated with the karst region.
The topography of Winona County is characterized by a gently rolling upland plateau inci~ed by deep valleys. The rolling upland, making up about 75 percent of the county, is underlain by dolomite and limestone. Numerous karst features, such as enlarged joints, sinkholes, springs, dry valleys, and caves have formed in the upland as illustrated in Figure 1.
Few perennial streams flow across the upland plateau although there are many small dry valleys. Most of the surface water rapidly percolates into the fractured carbonate bedrock. This water eventually discharges from springs flowing from the Cambrian sandstones exposed in deeply incised valleys or directly into the Mississippi River. Water also emerges from the carbonate bedrock and sandstone escarpments on the upland. Water quality of the Prairie du Chien-Jordan aquifer, underlying the karst plateau shows high levels of surface con taminants as is typical of karst.
Southeastern Minnesota's karst is a fluviokarst in the classification system of Sweeting (1973). The fluviokarst is mantled with residuum and/or glacial tills to an average depth of 6 ~o 15 m. At the present time, most of the fluviokarst is actively being exhumed.
Stratigraphy: Winona County's; karst is forming in gently dipping Lower and Middle Ordo vician dolomites and limestones. · Carbonate formations cap three bedrock plateaus separated by sandstone and/or shale escarpments. The stratigraphically lowest, and largest plateau is capped by the Prairie du Chien Group, consisting of the Oneota Dolomite, and Shakopee For mation (Hobbs, 1984) ,, and contains the majority of the sinkholes in· Winona · County. Two smaller plateaus, capped by the Platteville and Galena Formatr ons, h e found in southwestern Winona County.
Geomorphology: Since the Cretaceous, the Paleozoic bedrock of Winona County has been exposed to tropical, glacial and ~emperate climates.. Although the age of the karst is
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Proceedings of the First Multidisciplinary Conference on Sinkholes / Orlando / Florida / 15-17 October 1984 79 unclear, it appears that karsti fication began while south eastern Minnesota was exposed to intensive weathering during the warm humid climate of the Late Cretaceous through Tertiary Periods (Sldan, 19641.
The bedrock is mantled with an iron rich residuum which probably formed during the Ter tiary as the St. Peter escarp ment was eroded to the south west, and the Prairie du Chien was exposed to weathering (Hobbs, 19841. The residuum appears to be pre-Pleistocene in age since it is stratigraphi cally lower than the glacial tills found in the western two thirds of the county. According to Hobbs (19841, the residuum is generally less than 2 m thick, but it reaches 100 m in deep Figure 1. Typical karst and topography relationships depressions believed to be in Winona County. paleokarst sinkholes.
Karst processes were gener- ally inhibited during the Pleistocene. Pre-Wisconsinan glaciation of the western portion of the county eroded some of the residuum, and smoothed the irregular bedrock surface of the upland plateau, covering the karst with glacial till. According to Hobbs (19841, there appear to be two types of tills, a non-calcareous . till in the eastern half of the county, and a calcareous till which is locally leached in the western half of the county. Most of the upland is mantled with loess. There is, however, an area in the west central portion of the county where the loess was either never deposited or has been removed by some process.
During the Pleistocene, the Mississippi River and its tributaries be~ame deeply entre_nched. This lowered the regional base level causing the upland plateaus to return to a more erosional stage.
The karst is actively forming during the present temperate climate as the fluviokarst is exhumed. Both surface and groundwater are dynamic geomorphic agents. Surface streams have aided in lowering the bedrock surface as seen by erosion of the St. Pet~r escarpment which has retreated to the southwest, and by the deeply entrenched streams. M~teoric water, per colating through organic soil and regolith, has dissolved the rock and increased the _rock's secondary permeability. The surface topography is returning to its ' previous irregular form as ' sinkholes reopen and expand their drainage basins, and surface streams dissect the landscape. (
Hydrogeology: The bedrock aquifers underlying Winona County are among the highest yielding aquifers in the United States (Hogberg, 19721. The water quality is generally good, except in the Prairie du Chien~Jordan aquifer where well water frequently exceeds the 10 ppm nitrate-nitrogen drinking water standard. This dolomite-sandstone aquifer is the most wid~ly utilized and shallowest bedrock aquifer over most of the karst plateau , It has I l characteristics of both fractured - flow, and flow through porous media. ,i The Prairie du Chien Group is mostly dewatered in the northea~tern half of the county i where the water level is lowered by water discharging into the deeply entrenched Mississippi i River drainage system. The Jordan Sandstone contains water throughout most of the county.
Methods of Approach , , / The initial step in studying the sinkhole distribution in Winona County was to locate sinkholes. Since many of the sinkholes have been filled, and most of the open ones are less than 10 m in diameter (Figure 21,. only 20% of the depressions can be clearly identified on USGS topographic maps and air photos. Other sources of information on s~nkhole locations included the Minnesota Speleological Survey, and the American Soil Conserv!:ltion Service, which is currently preparing a Soil Survey of Winona County.
80 ,1
Cf) The majority of the sinkholes were identified by systemati~ W 100------~ cally canvassing local residents living on the upland plateaus c3 for information on sinkhole locations on their property or in ~ 80 319 z the area. When a sinkhole was located in the field, physical iii ' 60 characteristics and historical information was recorded. u. 168 O 40 1-- A sinkhole map was prepared in conjunction with the Min ~ 20 nesota Geological Survey , county atlas program. New bedrock, u surficial and hydrogeology maps of Winona County were also pre ~ o~~~~-~-~ ~ <4 4-10 >10 0 pared at a 1 to 100,000 scale for the county atlai. Information METERS z "'U) ~ g was taken from each of these maps to describe the geology of 0 u each sinkhole. A data sorting computer program was used to ana SIZE TYPE lyze the physical, historical, and geological parameters collected on each sinkhole. Figure 2. Sinkhole si.ze General Sinkhole Characteristics and type. Detection of Sinkholes: One conclusion of this paper is that only a small fraction of the sinkholes in Winona County are identifiable on 7.5 minute USGS tbpographic maps or air photos 100 -- the traditional tools of karst geomorphology. Of the 535 0 ...J sinkholes identified in Winona County, 85% were initially 500 "' u: Cf) located through field checking (Figure 3). Prior to this study, Cf) 80 W w ...J Utica Township in western Winona County was widely recognized as ...J400 0 0 I having a high density of sinkholes. Even here, only 37% of the I sinkholes were located by techniques other than field "" 60 ""~ I· ~ 300 Cf) checking. In contrast, few people working with land use u. problems in the county realized that Pleasant Hill Township, in u. 0 0 40 1-- eastern Winona County, has sinkhole densities comparable to ~ 200 w z those found in Utica. All of these sink holes were located al w ::;; 0 through field work. :::, 100 20 ~ z a.. Age and Rate of Sinkhole Formation: Age information was 0 0 obtained for 68% of the sinkholes. Sinkhole ages were divided into three age classes: young, < 6 years; intermediate, 6 to 25 years; and old, > 25 years. The number of young sinkholes is the most accurate of the age classes because the sudden Figure 3. Methods of appearance of a new sinkhole is noted and remembered by local sinkhole landowners. The number of sinkholes in the intermediate range detection. was the most difficult age to - determine and is underestimated. When sinkholes appeared intermediate in age, the information was omitted unless landowners could verify the age. 100------~ The age distribution CFigure 4) implies that the rate of 80 n=362 1-- sinkhole formation in Winon~ County has significantly increased 251 ~ 60 in the last 50 years. Forty-seven of the 535 sinkholes l,ocated 0 have formed in the last 5 years. At the present rate, 'v 9 per ~ 40 a.. year, all of the sinkholes in Winona County could have formed in 20 the last 58 years. Several of the sinkholes are documented as being over 100 years old and the .last known geologic event s5 6-24 :?:25 capable of covering all of the pa)eosinkholes was the loess YEARS deposition 10,000 to 12,000 years ago. Unless geomorphic pro cesses fill sinkholes on a 50 to 100 year time seal•, the rate of sinkhole formation was much lower in the past. Figure 4. Sinkhole age distributions. Aley et al. ( 1972), Foose and Humphreville ( 1979), Newton (1976), and Williams and Vineyard (1976) have documented many cases where human activities have locally increased the rate of sinkhole formation through a variety of mechanisms. The only ~egionally significant human activity on the upland of Winona County is agriculture. Although,we are unable to specify the mechanisms, we conclude that on a regional scale human activities associated with agric~,lture have significantly increased the rate of sinkhole formation. Sinkhole and Sinkhole Probability Map Sinkhole locations and five catego•ries of continued sinkhole activity were identified on a Sinkhole and Sinkhole Probability Map (Dalgleish and Alexander, 1984). The regions of varying sinkhole probability were defined primarily by the observed sinkhole density. Bedrock, topographic, surficial, and hydrogeologic conditions were used when geologic controls of sinkhole distribution were c!early defined.
81 The five regions of sinkhole probability were defined as follows:
No Probability - The surface area exposed in the deep valleys incised below the Prairie du Chien Group is not susceptible to sinkhole formation.
Low - No sinkholes were detected and few if any sinkholes are expected to develop on the steep slopes of the Oneota Dolomite at the top of · the deeply incised valleys.
Low to Medium - Areas where sinkholes are widely scattered with only small isolated clusters of 2 to 3 sinkholes.
Medium to High - Sinkholes are generally moderately distributed with several clusters of 4 to 10 sinkholes.
High - Overall the sinkhole density is relatively high with large clusters of more than 8 sinkholes. This region includes some smaller areas where sinkhole den sities appear more similar to the medium to ·high region1 these areas ·were included because there was no indication of geologic or topographic differ ences from the highly concentrated area to inhibit sinkhole formation. The differences in density are probably random variations in landscape"' develop ment. Geological Controls on Sinkhole Formation Water Table: It appear- that sinkhole formation is generally independent of the depth to the water table. Sinkholes are almost evenly distributed above water table depths from 12 to 104 m (Figure 5). Only two small peaks, which do not appear to be significant, are seen at 30. 5 to 36. 6 m and 79. 2 to 85. 3 m with 9% and 12% of all the sinkholes studied, respectively. It is possible that the water table depth is an additional factor aiding sinkhole formation where other controlling characteristics are already present.
Stratigraphy: The sinkhole density within each bedrock unit (Figure 6), shows that the Shakopee Formation has an overall sinkhole density of .68 ± .07 sinkholes/km2. This PERCENT 0 2 4 6 8 10 12 14 is about twice the sinkhole density found in the Oneota, and t;, 400 120 three times the densities found in the other formations. The Shakopee and Oneota are the most· susceptible bedrock ~ 360 formations to sinkhole development. w3ro = ...J al 280 Figure 7 shows the distribution of sinkholes as a func ;:! 80 v, ~MO ~ tion of elevation above or below the New Richmond Sandstone, w w ~200 60t;; the lower member of the Shakopee. (The upper member is the • 1w ~ Willow River Dolomite.) Most of the sinkholes have deve loped in the stratigraphic range of the Shakopee and Oneota ~ 120 40 with a strong peak in the lower strata of the Willow River ~ 80 a. 20 Dolomite, New Richmond Sandstone, and the upper Oneota Dolo ~ 40 n=535 mite. Al though the bedrock was visible in only six of the 0 ~~~~--'---'--'--'-~ 0 sinkholes seen in the field, the New Richmond Sandstone was 0 2040 60 80 the exposed bedrock unit in four of the cases. The distri NUMBER OF SINKHOLES bution of sinkholes between bedrock formations within each sinkhole probability area displays similar patterns with the Figure 5. Sinkhole distri majority of the sinkholes in the Shakopee for each area. bution~ depth to Bedrock lithology is evidently the primary control on, sink water table. hole formation, while other factors control the relative density of sinkholes, within the Shakopee and Oneota.
1.0 Surficial Geology: Hobbs (1984) has identified five N "'..J surficial units in Winona County: ~ 0.8 ..J Q'. > 0>° <[ 'Cf> 0.6 ! "'>- "'>- z Q-RL - Thick loess over residuum. w "'z >- ...J 0 "' a."' <[ "'..J QRTL - Thick loess over older non-calcareous till and "'a. ..J <[ ~0.4 0 ,-: a. ! V) "' residuum. Residuum and till thins to the east. "<[ :':,"' 0.2 I QSCL - Thick loess over calcareous till, locally V) ! ! Cf) ! leached. Loess and till and patchy on slopes. 0 BEDROCK QSCS - Thin sand and till over bedrock . wfth lit~le or no loess cover. QSCP - Moderately thick, . 5 to 3 m, loess over . patchy Figure 6. Sinkhole density over patchy till on the plateau · the St. Pe'ter - bedrock units. escarpment.
82 r ;
IC Sinkhole density within each sur PERCENT ficial unit (Figure 81 shows that I- 0 10 20 30 the greatest density is found in I.LJ tj 320 r------,------,,------,----,---, thin sand and till with little or i= "-_ 280 !1_J 80 no loess cover, unit QSCS. The '-"-~Oo 24 0 "' lowest densities are in the thick t ~ 200 n=535 I 60 loess covered calcareous till, J-- ~ 160 QSCL, and moderately thick loess 0: ::.
2.0 ·area is located on the upland plain within the regional recharge zone which may aid additional sinkhole development. This com "'E 1.6 -"' bination falls entirely within the high sinkhole probability area. The second combination is the Oneota covered with calcareous till 1/)' 1. 2 I.LJ ..J . and loess, QSCL. The density is 2.38 ±. .67 sinkholes/km2. This combination - is considered less significant since it includes only ~ ~ 8 ! i 5.9 km2 and 14 sinkholes. Most of this combination is on gentle Z0.4"" ui • slopes near the edge of the Prairie du Chien plateau. The calcium o~------~I _J _J _J c;_arbonate in this area may be more leached than in central areas 0: t- u u"' uQ_ i 0: of the plateau, due to more surface water flowing toward the pla 0 0 "'0 0 0 "' "' teau's edge. The Shakopee Formation mantled with residuum and loess has a Figure 8. Sinkhole density of 1.33 ±. .21 sinkholes/km2. Where the Shakopee is cover density - ed with loess, non~calcareous till, and residuum, QRTL, the den surficial sity is .86 ±. .11 sinkholes/km2 . These combinations have medium units. sinkhole densities.
\ Discussion J BEDROCK UN IT The lower Shakopee, and in par ONEOTA SHAKOPEE ST. PETER PLATTEVILLE GALENA ticular the New Richmond Sandstone, !:: appears to be the bedrock strata most z Q-RL 0.18 ± 0.05 1.33 ± 0 .21 conducive to sinkhole formation. Con ~ QRTL 0.36± 0.06 0.86 ± 0 .1 1 sidering that the majority of the ..J 83 The density of sinkholes is not constant over the areas where the New Richmond Sandstone is the uppermost bedrock~ therefore, other geologic controls must be affecting sinkhole for mation. Surficial geology appears to have an impact on sinkhole development. Another fac tor to consider with the type of surficial materials is the age of the bedrock surface. In Winona County, the age of the bedrock surface generally decreases to the west, as the car bonate content of the surficial material increases. The sinkhole density is greater in areas where carbonate concentrations are low or absent in the surficial material. Water percolating through non-calcareous sediments wi+l be more aggressive, when it contacts the Oneota Dolomite than water percolating through calcareous sediments. In .contrast, a few sinkholes have developed in calcareous tills, which Hobbs (1984) reports to be locally leached. It remains to be proven if the sinkholes preferentially form in areas that are leached in the calcareous tills. It seems probable that more water has percolated into places where sediments are locally leached than into the surrounding calcareous sediments. If this is true, it is reasonable to suspect that the additional aggressive water will preferentially dissolve the bedrock allowing sinkholes to form. Since the Prairie du Chien bedrock surface appears to decrease in age to the southwest, the northeast has been exposed to weathering for a longer period of time. This implies that the paleokarst surface is progressively younger to the southwest. The irregular paleokarst' surface probably directs water percolating through the sediments into previously enlarged joints and sinkholes. Paleokarst sinkholes would not only provide additional water for further dissolution of the rock, but the increased volume of water would be capable of transporting sediment deeper into the bedrock. As sediment is transported deeper into the bedrock, cavities will form due to piping, eventually resulting in surface collapse or subsidence. Initially sinkholes may open in sites of paleosinkholes. Once the renewed sinkhole opens surface water may be channelled toward that area causing additional collapses. This process is more evident in eastern Winona County where there are wide shallow depressions with small almost vertical holes in the center. It appears that the bedrock, paleokarst surface, and surficial material are inter' twinned controls on sinkhole formation in Winona County. The relative importance of these factors probably varies throughout the study area. Conclusions 1. Traditional tools for sinkhole detection, topographic maps and air photos, are not adequate in areas with low to moderate densities of small sinkholes. Detection of sinkholes in such areas must be done from field studies. 2. Age data indicate that the rate of sinkhole formation has significantly increased in recent years. 3. Depth to the water table does not appear to control sinkhole formation in Winona County. 4. Stratigraphic position is a primary control on sinkhole development. 5. Surficial deposits are a secondary control, and significant carbonate contents inhibit sinkhole formation. Acknowledgements This study was funded by Winona County, the Minnesota Geological Survey, and a grant from the Legislative Commission on Minnesota Resources. References Aley, T.J., Williams, J.H., and Massello, J.W., 1972, Groundwater contamination and sinkhole collapse induced by leaky impoundments in soluble terrain: Missouri Geological Survey and Water Resources Engineering Geology, Series 5, 32 p. Dalgleish, J.D. and Alexander, E.C., Jr., 1984, Sinkholes and sinkhole probability, Plate 5, Balaban, N.H., and Olsen, B.M., eds., Geological Atlas of Winona County: Minnesota Geological Survey. Foose, R.M. and Humphreville, J.A., 1979, Engineering geological approaches to foundations in the karst terrain of the Hershey Valley: Bulletin of the Association of Engineering Geologists, v. 16, p. 355-381. 84 Hobbs, H.C., 1984, Surficial geology, Plate 3, of Balaban, N.H. and Olsen, B.M., eds., l Geologic Atlas of Winona County, Minnesota: Minnesota Geological Survey. Hogberg, R.K., 1972, Ground-water resources in Minnesota, in Sims, P.K. and Morey, G.B., eds., Geology of Minnesota: A Centennial Volume: -Minnesota Geological Survey, p. 595-602. Newton, J.G., 1976, Induced and natural sinkholes in Alabama - A continuing problem along highway corridors: Subsidence Over Mines and Caverns, Moisture and Frost Actions, and , Clas~i(i1cation, Transportation Research Record 612, National Academy of Sciences, Wash1ngtcn, D.C., p. 9-46. Sloan, R.E., 1964, The Cretaceous system in Minnesota: Minnesota Geological Survey Report of Investigations, no. 5, 64 p. Sweeting, M.M., 1973, Karst landforms: New York, Columbia Press, 362 p. Williams, J. H. and Vineyard, J. D., 1976, Geologic indicators of catastrophic collapse in karst terrain in Missouri: Subsidence Over Mines and Caverns, Moisture and Frost Actions, and Classification, Transportation Research Record 612, National Academy of Sciences, Washington, D.C., p. 31-37. (, 85 / I PROCEEDINGS OF THE FIRST MULTIDISCIPLINARY CONFERENCE ON SINKHOLES ORLANDO/FLORIDA/ 15-17OCTOBER 1984 SINKHOLES: THEIR GEOLOGY, ENGINEERING AND ENVIRONMENTAL IMPACT Edited by BARRY F.BECK Florida Sinkhole Research Institute, University of Central Florida, Orlando Sponsored by the Florida Sinkhole Research Institute, College ofEngineering, University of Central Florida A.A.BALKEMA I RO'l'IERDAM I BOSTON I 1984 , ; Table of contents Sinkhole terminology IX Barry F.Beck 1. The geologic framework and mechanisms ofsinkhole development Review of induced sinkhole development 3 J.G.Newtbn Florida karst - Its relationship to geologic structure and stratigraphy 11 Walter Schmidt & Thomas M.Scott Karst progression 17 Dennis J.Price _,; Impact of ground-water chemistry on sinkhole development along a retreating scarp 23 Sam B. Upchurch & Fred W.Lawrence Sinkhole collapse induced by groundwater pumpage for freeze protection irrigation near Dover, Florida, January 1977 29 Susan ! .Metcalfe &. Larry E.Hall Influence,of a karstified limestone surface on an open-marine, marsh-dominated coastline: West Central Florida 35 Joan 'G.Hutton, Albert C.Hine, Mark W.Evans, Eric B.Osking & Daniel F.Belknap Seismic-reflection studies of sinkholes and limestone dissolution features on the northeastern Florida shelf 43 Peter Popenoe,F,A.Kohout & F.T.Manheim Structural and hydrogeologic applications of remote sensing data, eastern Yucatan Peninsula, Mexico 59 C.Scott Southworth A comparison of sinkhole depth frequency distributions in temperate and tropic karst regions 65 J. W. Troester, Elizabeth L. White & William B. White - / Sinkhole distribution in the central and northern Valley and Ridge province, Virginia 75 David A.Hubbard, Jr. Sinkhole disttibution in Winona County, Minnesota 79 / Janel Dalgleiih & E.Calvin Alexander ~ Tectonics and geology in karst development of Northern Lower Michigan 87 Tyrone J.Black Pattern and,antiquity of sinkholes along an alluviated karstified valley: Friars Hole, West Virginia 93 S.R.H. Worthington & D.C.Ford Karst and subsidence in China 97 Zhang Shouyue A contour map, v,;;ilume estimate, and description of Teague's Sinkhole J05 James !.Hollingshead ,; Development, occurrence, and triggering mechanisms of sinkholes in the carbonate rocks of lhe Lehigh Valley, eastern Pennsylvania- 111 Paul B.Myers, Jr. & Michael Perlow, Jr. Submarine 'sinkholes' : A review 11 7 Marco Taviani A brief review of the South.African sinkhole problem 123 Anthony B.A.Brink 2. Site studies an~ evaluation ofsinkhole-susceptibility Catastrophic subsidence: Shelby County, Alabama ' 131 Philip E.LaMoreaux Sinkhole development in North-Central Puerto Rico 137 Mikolaj Wegrzyn, AlejandroE.Soto & Juan A.Perez Proceedings .of the First Multidisciplinary Conference on Sinkholes/Orlando /Florida /15-17 October 1984 V Collapse sinkholes ih the blanket sands of the Puerto Rico karst, {)~JC 143 Alejandro E.Soto & Wanda Morales Predicting the location of surface collapse within karst depressions: A Jamaican example 147 Michael Day Investigation techniques on dolomites in South Africa 153 Peter W.Day & Fritz van M. Wagener / New Jersey sinkholes: Distribution, formation, effects, geotechnical engineering 159 Joseph A .Fischer & Richard W. Greene Sinkhole risk analysis for. aselected area in Warren County, Ne_w Jersey 167 D.Raghu & Charles Tiedeman Use of percussion probes for the design and construction of foundations in and on carbo11ate formations 'L 171 D.Raghu, J.JLifrieri & F.C.Rhyner · Methods for describing and predicting the occurrence of sinkholes 177 Albert E.Ogden Factors affecting the collapse of cavities 183 Thomas F.Beggs & Byron E.Ruth ,,, Relationship of modern sinkhole development to large scale-photolinear features 189 J.R.Littlefield, M.A.Culbreth, S.B. Upchurch&: M.T.Stewart _Application of double Fourier series analysis to ground subsidence susceptibility mapping in covered karst terrain 197 Marcus J. W. Thorp & George A.Brook . . . Evaluation of subsidence or collapse potential due. to subsurf~ce cavities · 201 Richard C.Benson & Lester J.La Fountain Examination of sinkholes by seismif rd1ecti.on 217 Don W.Steeples, Ralph W.Knapp & Rii:ha;dD~Miller Geophysical characteristics of fracture traces in the carbonate Floridan Aquifer 225 Mark Stewart & John Wood Sinkhole prediction ~ Review of electrical resistivity methods 231 'Eberhard Werner 3. Sinkhole-likefeatures (subsidence pits) ,Hydrocompaction sinkholes in the San Joaquin Valley, California Nikola P.Prokopovich Sinkholes in southeastern North Carolina - A geologic phenomenon and .related engineering problems 243 Henning F.Koch .;S.oil cavities formed by piping_ 249 Ralph I.Hodek, Allan M.Johnson & Dean B.Sandri Sinkholes at Tarbela Dam project .255 lzharul Haq & Altaf-ur-Rehman Self-healing sinkholes in an earth dam foundation 261 Neil H. Wade & Lloyd R.Courage Sinkhole problem rel:;i:te\i W dam .eng~eering 267 Robert C.Lo · 4. ·environmental I societal impact ofsinkholes The influence of urbanization on sinkhole development in central Pennsylvania 275 Elizabeth L. White, Gert Aron & William B. White Sinkhole flooding associated with urban development upon karst terrain: Bowling Green, Kentucky 283 Nicholas C. Crawford Litigious problems as~ociated with sinkholes, emphasizing recent Kentucky cases alleging liaµjlity when sinkholes were flooded 293 James F. Quinlan · " · ·· · · •Toxic and explosive fumes rising from carbonate aquifers: A hazard for residents of sinkhole plain~ . . 297 Nicholas C.Crawford VI '1 · Characterization of the shallow groundwater system in an area with thin soils and sinkholes (Door Co., WI) James H. Wiersma, Ronald D.Stieglitz, De Wayne L. Cecil & Glenn M.Metzler Altura Minnesota lagoon collapses 311 KCalvin Alexander & Paul R.Book Part I: The applicability of the Florida Mandatory Endorsement for Sinkhole Collapse Coverage - Legal aspects 319 William G.Salomone Part 2: The applicability of the Florida Mandatory Endorsement for Sinkhole Collapse Coverage - Case history, foundation settlement of a residential structure - Was it a sinkhole? 329 William G.Salomone v 5. Case histories: Remedial engineering ofsinkholes Remedial measures,associated with sinkhole-related foundation distress 335 John E. Garlanger A geological survey's cooperative approach to analyzing and remedying a sinkhole related disaster in an urban environment 343 1. Robert Canace & Richard Dalton Sinkhole activity in the vicinity of the Sunny Point, N.C., Military Ocean Terminal 349 Earl F. Titcomb, Jr. & Jack M.Keeton Evaluation, repair and stabilization of the Boling Sinkhole FM 442, Wharton County, Texas 353 Boyd V.Dreyer & Clyde £ .Schulz Engineering problems associated with.sinkholes in the Valley of Virginia 359 HG.Larew & E.o :Gooch Ma,turation of the Winter Park sinkhole 363 S.E.Jammal 6. Engineering in sinkhole-prone areas Correction and protection in limestone terrane 373 George F.Sowers Sinkhole and subsidence damage and protective measures 379 Nath S.Parate Geotechnical considerations in the location, design, and construction of highways in karst terrain - 'The Pellissippi Parkway extension', Knox-Blount Counties, Tennessee 385 Harry L.Jl1oore A model study of a proposed concrete road pavement over a potential sinkhole area 391 I .Marius Louw, Paul H. Goedhart & Frederick J. van Zyl Foundation problems on karstic limestone formations in Western Thailand - A case of Khao'Laem Dam 397 Dennes T.Bergado, Chanin Areepitak & Friedrich Prinzi ' Construction on dolomite in South Africa 403 Fritz von M. Wagener & Peter W.Day High-volume grouting to control' sinkhole subsidence 413 Christopher R .Ryan Collapse and compaction of sinkholes by dynamic compaction 419 Christian A. Guyot Late paper to Part 3 Sinkhole development inAeclaimed smectitic spoil./ 425 Maurice B.Dusseault, J.Doii. Scott & Steve Moran VII