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This paper presents a quantitative study of the relationship between the cave system and the tectonic and karst evolution of the Dong Van Karst Plateau based on analysis and statistics of geometric parameters and orientation of cave passages. The region is located in northern Vietnam and belongs to the extended part of the South China karst belt (Yunnan karst plateau), which is composed mainly of carbonate rocks. Cave classification based on cave conduits geometric parameters shows that caves developed mainly in the vadose zone (27 vadose branchwork caves, 10 mixed caves developed under the control of fault systems, and 12 water-table caves). The degree of correlation between cave levels and planation surfaces suggests that the development of horizontal cave passages is related to two levels of planation surfaces, including one at 1250–1450 masl (equivalent to cave level at 1350–1450 masl), and at 1000–1250 masl (corresponding to cave level at 1200–1250 masl). Additionally, cave passage orientation shows that the cave system formed and developed under the influence of tectonic activities in the Cenozoic. The dominant orientation trend is roughly in the East–West direction and occurred in the early phase (Eocene–Miocene). Next is a trend roughly North–South that occurred in the late phase (Pliocene–Quaternary). The last orientation trend follows the NW–SE direction due to the reactivation of paleo-fault systems in the same direction. Although there are limitations due to accessibility and the level of cave exploration, this research suggests that analysis and statistics of the geometric parameters and orientation of cave passages based on cave survey data can be one of the effective approaches used to identify the development and structure of karstification in the karst region.

The year 2021 is the 60th Anniversary of the first publication of Caves of Indiana by Richard L. (Dick) Powell. To commemorate that anniversary, the Indiana Geological and Water Survey (IGWS) is releasing a digital version of this book. This release also coincides with the UNESCO-sponsored International Year of Caves and Karst. This paper includes a link to the digital book, a memoir from Dick, and a preface from Art Palmer (a mentor of mine and mentee of Dick’s). Another version of Dick’s memoir was recently printed in Volume 23, no. 2 of the Bloomington Indiana Grotto Newsletter. Caves of Indiana has an interesting legacy in the IGWS and a lore among cavers in Indiana. This paper tells that legacy from Dick Powell’s point of view. For many, Caves of Indiana represents a masterpiece of information during the birth of American Speleology. For others, it is an archetype of publications that have damaged caves and relationships between cavers and landowners. Regardless, it is highly recognized for its data gathering and presentation. Many libraries refuse to carry a copy lest it be stolen.[1] Copies oft appear in personal libraries, sometimes with folded pages and broken spines. This version has been carefully revised and redacted to assure that the locations of, directions to, and maps of caves on private land are not available. In this, we attempt to balance the important, and often at odds, need to disseminate accurate information on caves while protecting this important, and frequently overlooked, fragile natural resource. For more information about caves and karst, and guides to responsible caving, please consult with the National Speleological Society (http://www.caves.org), the National Cave and Karst Research Institute (http://www.nckri.org), or caving clubs local to your area.

Deposits of calcite coating the lower passages of Wind Cave in the southern Black Hills of South Dakota were precipitated under phreatic conditions. Data from samples associated with a new cave survey and hydrologic studies indicate that past water tables within Wind Cave reached a maximum height of 45 m above modern levels but were mostly confined to 25 m or less. Uranium-series ages for basal layers deposited on weathered wall rock indicate subaerial conditions in this part of the cave persisted between 1000 and 300 ka. Ages and elevations of wall coatings and cave rafts establish a 300,000 yr paleohydrograph indicating that water-table highstands occurred during interglacial or interstadial-to-early glacial periods and lowstands occurred during full-glacial and stadial episodes. Isotopes of Sr, U, C, and O from dated calcite samples were obtained to evaluate potential shifts in paleo-groundwater composition. For comparison, Sr and U isotopic compositions were determined for modern groundwater from 18 sites previously classified into five hydrogeologic domains. Isotope data for different domains tend to cluster in separate fields, although several fields overlap. Compositions of Calcite Lake (informal name) water reflect modern recharge to shallow aquifers. In contrast, speleothem data indicate that paleo-groundwater highstands were not supported by increased infiltration associated with local recharge, or by upwelling from deeper Proterozoic sources. Instead, cave water was similar to deeper, warmer groundwater from the Madison Aquifer discharging at modern artesian springs flanking the southern Black Hills. Highstands were likely influenced by large-scale hydraulic processes associated with recharge to the Madison Aquifer under the Laurentide ice sheet on the northeast side of the Williston Basin, causing increased hydrostatic pressures in confined aquifers on the south side of the basin.

Of all cave types, solution caves have the most complex developmental histories. They are formed by the dissolving action of underground water as it flows through fractures, partings, and pores in bedrock. Such caves must grow rapidly enough to reach traversable size before the rock material that contains them is destroyed by surface erosion. Because of their sensitivity to local landscapes and patterns of water flow, solution caves contain clues to the entire geomorphic, hydrologic, and climatic history of the region in which they are located. At the land surface most of this evidence is rapidly lost to weathering and erosion; but in caves these clues can remain intact for millions of years.

Most caves owe their origin to carbonic acid generated in the soil. In contrast, sulfuric acid caves are produced by the oxidation of sulfides beneath the surface. Although sulfuric acid caves are relatively few, they include some large and well-known examples, such as Carlsbad Cavern, New Mexico. They also provide evidence for a variety of deep-seated processes that are important to petroleum geology, ore geology, tectonic history, and the nascent field of karst geomicrobiology.

Caves in regions of moderate relief are widely regarded as the standard to which all others are compared. Tectonic stability is their most significant characteristic. The presence of moderate relief implies that uplift of the land is slow and erosional processes are able to keep pace. As a result, rivers easily erode to their local base levels, and base-level control is reflected in cave passages. The relation between caves and regional geomorphic history is stronger than in any other setting. Examples are given from the Illinois Basin (Kentucky and Indiana), the Ozark Plateau (Missouri), and the Appalachians.

Ice caves of the USA are limited in number and size for several reasons. The lower 48 states are located at relatively low latitudes compared to most other well-known karst areas, such as Europe; and known karst areas of Alaska are most abundant at low altitudes near sea level. Also, the highest peaks in mountainous regions are composed mainly of intrusive igneous rocks, which contain few significant caves. Many of the highest mountain systems occupy semiarid climates. Volcanic rocks of the Hawaiian Islands contain only a few known ice caves scattered at high altitudes. Most ice caves in the USA are located in the Northern and Central Rocky Mountains at moderate altitudes of 2000–3000 m. A few are also scattered in lava caves in the western states, as far south as New Mexico, where ice accumulates in caves with limited air circulation. In the far northeastern states a few talus caves contain small ice bodies. Because of the small number and scattered distribution of American ice caves, studies of the topic are few. Most records show a declining volume of ice in caves in the USA.

The northern border of the Appalachian Plateaus in New York State is a limestone–dolomite escarpment with sulfate rocks at depth and hypogene karst springs at its base. All springs contain dissolved carbonates, but many are also exceptionally rich in sulfate, sulfide, or CO2. None connect to traversable caves, but their chemistry provides clues to their internal character, flow depth, and underground processes. Many show evidence for dedolomitization driven by sulfate dissolution, which forces calcite travertine to precipitate at the surface. Isotopic variation and radium content reveal groundwater flow patterns. Chemical contrasts with nearby epigenic caves highlight the nature of the hypogene springs. A nearby but separate spring area, fed by deep flow along faults, illustrates the effects of high-pressure CO2 on carbonate groundwater. Despite the lack of underground access, these karst areas give much insight into hypogene processes.

Mammoth Cave owes its origin to the rock called limestone, which readily dissolves in water. Underground water passing through thick limestone layers toward the deep valley of the Green River has formed and enlarged the cave over the past several million years. The rocks are 330–340 million years old, but the cave is much younger. A cap of resistant sandstone overlying the limestone has protected the main parts of the cave from surface erosion, thus preserving many clues to past events. Passage types reflect the nature of the water that formed them. Below, at, and slightly above the local Green River level, all openings in the ground are filled with water. Above this zone, underground water drains downward by gravity along the steepest available cracks in the rock. Where water follows the narrow fissures between rock layers, it forms tall canyon-like passages. Well-shaped vertical shafts form where water is able to descend straight downward along fractures that cut across the layers. Below the water table, underground water follows the most efficient paths of flow, along the widest openings, to form tube-shaped passages. Former positions of the water table can be determined from the change in passage shape, which provides a history of groundwater flow in the region.

Mammoth Cave is an underground part of the vast Mississippi River drainage system. Although the cave occupies a relatively small area, it has preserved about 10 million years of the drainage history of the eastern USA. It is still actively growing today. As surface rivers vary in the shape and pattern of their valleys, the cave records these events as different levels and types of underground passages. The nature and timing of those changes are well preserved in the cave. Their ages can be determined by analyzing the sand and gravel carried into the cave while it was forming. The various cave levels record the long history of the Ohio River and the influence of continental-scale glaciers on surface drainage patterns. The many changes in the erosion level of the Green River help to account for the great complexity of the cave.

The Bighorn Basin of Wyoming is a region of thermal springs and caves, some with lethal levels of H2S and CO2. It also contains many productive oil wells. In one of these caves, “sulfuric acid speleogenesis” was first recognized and documented in North America by Egemeier in 1973. He proposed that most of the cave dissolution was subaerial and the result of H2S oxidation to H2SO4. Later studies by microbiologists have refined his measurements and show that much of the H2SO4 is generated in the stream by sulfur-oxidizing bacteria, by the process of “microbial sulfuric acid speleogenesis.” Other caves with similar chemistry are known in the region, but they have only been partly explored because of the locally high sulfide concentrations in their atmospheres.

The Black Hills contain several extensive maze caves in the early Carboniferous Madison Limestone. They include Wind Cave and Jewel Cave, which are among the world’s longest and most complex. Their origin is debated, with diverse hypotheses ranging from artesian conditions to rising thermal water. Recent evidence indicates a polygenetic origin including early Carboniferous diagenesis and paleokarst; deep burial by Carboniferous–Cretaceous strata; re-exposure of the limestone by the Laramide Orogeny (early Paleogene); and major cave enlargement in the late Paleogene along old paleokarst zones. Cave enlargement depended mainly on diffuse recharge through overlying sandstone, mixing with lateral inflow through carbonate outcrops. Only a few of these processes were hypogenic, but recognizing them all helps to clarify the limits of that process.

The Guadalupe Mountains consist of an uplift of Permian carbonate shelf deposits in a semiarid landscape. A variety of speleogenetic processes, mostly hypogene, have made them one of the world’s best-known cave regions. The most notable caves are Carlsbad Cavern, which contains the largest known cave room in the USA, and Lechuguilla Cave, now the world’s 7th longest. Because the caves are no longer active, there was early confusion about their origin. This was resolved when long-dormant sulfuric acid processes were recognized, with H2S supplied by nearby oil fields. Potassium-argon dating of the by-product mineral alunite in the Guadalupes indicates speleogenetic ages from 12 to 4 million years, decreasing with lower elevation. Caves show abundant evidence for subaerial corrosion, both by sulfuric acid and carbonic acid in water films. Many seemingly phreatic features have resulted from this subaerial process. Microbial alteration of bedrock has contributed to weathering. There is evidence that isolated caves of greater age, lined by large scalenohedral calcite, were formed by supercritical CO2 in deep thermal water.

Uranium-series analyses of water-table-type speleothems from Glenwood Cavern and “cavelets” near the town of Glenwood Springs, Colorado, USA, yield incision rates of the Colorado River in Glenwood Canyon for the last ~1.4 My. The incision rates, calculated from dating cave mammillary and cave folia calcite situated 65 and 90 m above the Colorado River, are 174 ± 30 m/My for the last 0.46 My and 144 ± 30 m/My for the last 0.62 My, respectively. These are consistent with incision rates determined from nearby volcanic deposits. In contrast, δ234U model ages (1.39 ± 0.25 My; 1.36 ± 0.25 My; and 1.72 ± 0.25 My) from three different samples of mammillary-like subaqueous crust collected from Glenwood Cavern, 375 m above the Colorado River, yield incision rates of 271 +58/-41 m/My, 277 +61/-42 m/ My, and 218 +36/-27 m/My. These data suggest a relatively fast incision rate between roughly 3 and 1 Ma. The onset of Pleistocene glaciation may have influenced this rate by increasing precipitation on the Colorado Plateau starting at 2.5 Ma. Slowing of incision just before 0.6 Ma could be related to the change in frequency of glacial cycles from 40 to 100 kyr in the middle Pleistocene. This interpretation would suggest that the cutting power of the Colorado River prior to 3 Ma was smaller. An alternative interpretation involving tectonic activity would invoke an episode of fast uplift in the Glenwood Canyon region from 3 to 1 Ma.

Caves of the Guadalupe Mountains have experienced many modifications since their final phase of sulfuric acid speleogenesis several million years ago. Petrographic and geochemical data reveal details of the change from H2SO4 to CO2-dominated reactions. The H2SO4 dissolution front acquired a coating of replacement gypsum with local pockets of anhydrite and by-products of altered clay, including Fe-Mn oxides. Alteration of bedrock beneath the gypsum produced a white micritized rind with small negative shifts in δ13C and δ18O. Solution basins contain records of the earliest post-speleogenetic processes: corroded bedrock, residual anhydrite, Fe-Mn oxides from fluctuating pH and Eh, mammillary calcite, and dolomitization. Later meteoric water removed or recrystallized much of the gypsum and early micrite, and replaced some gypsum with calcite. Mammillary crusts demonstrate fluctuating groundwater, with calcite layers interrupted by films of Fe-Mn oxides precipitated during periodic inflow of anoxic water. Condensation moisture (from local evaporation) absorbs CO2 from cave air, corroding earlier features and lowering their δ13C and δ18O. Drips of condensation water deposit minerals mainly by evaporation, which increases δ18O in the speleothems while δ13C remains nearly constant. By forcing calcite precipitation, evaporation raises the Mg content of remaining water and subsequent precipitates. Dolomite (both primary and replacive) is abundant. In areas of low air circulation, water on and within carbonate speleothems equilibrates with cave-air CO2, causing minerals to recrystallize with glassy textures. Fluorite on young evaporative speleothems suggests a recent release of deep-source HF gas and absorption by droplets of condensation water.

Cave development is related to the geomorphic evolution. Their morphology, preserved far longer than correlative surface features allows reconstructing the regional history of the surrounding landscape. Modeling shows that initial cave development occurs along the water table with loops in the phreatic zone along fractures. Consequently, cave profiles and levels reflect the local base level and its changes. Cave profile is controlled by timing, geological structure, and recharge. In first exposed rocks, juvenile pattern displays steep vadose passages. In perched aquifers, vadose erosion produces large passage along aquiclude. In dammed aquifers, the main drain is established at the water table when recharge is fairly regular. But when irregular recharge causes backflooding, looping profiles develop throughout the epiphreatic zone. Interconnected cave levels correspond to some of the largest cave systems in the world. The oldest abandoned highest levels have been dated beyond 3.5 Ma (Mammoth Cave). However, when base level rises, the deepest parts of the karst are flooded; the flow rises along phreatic lifts, and discharges at vauclusian springs. In the epiphreatic zone, floodwater produces looping tubes above the low-flow water table. In such a case of baselevel rise, per ascensum speleogenesis can produce higher-elevation passages that are younger than passages at lower elevations. Base-level rises occur after tectonic subsidence, filling of valleys, or sea-level rise, as for instance around the Mediterranean in response to the Messinian Crisis. Deep-phreatic karst, if not hypogenic, can generally be attributed to flooding by a base-level rise. L’évolution des cavités dépend de l’évolution géomorphologique. Leurs morphologies, beaucoup mieux conservées que les témoins de surface correspondants, permettent de reconstituer l’évolution régionaledes paysages. Les modélisations montrent que le développement initial se produit à proximité de la surface piézométrique, avec des boucles le long des fractures plongeant dans la zone noyée. Par conséquent, le profil des cavités reflète la position du niveau de base et ses changements. Ce profil est contrôlé par le temps, la structure géologique et le mode de recharge. Lors d’une première karstification un réseau juvénile se développe, constitué de conduits vadoses inclinés. Dans les aquifères perchés, l’érosion torrentielle produit de vastes conduits ébouleux au contact du soubassement imperméable. Dans les aquifères barrés, lorsque l’alimentation est régularisée, le collecteur s’établit à proximité de la surface piézométrique. Quand l’alimentation est irrégulière, les mises en charge sont fréquentes et favorisent le développement d’un profil en montagnes russes dans la zone épinoyée. Les niveaux de cavités interconnectés ont produit certains des plus longs réseaux au monde. Dans Mammoth Cave (USA), les niveaux les plus hauts ont plus de 3,5 Ma. Cependant, en cas de remontée du niveau de base, les parties du karst les plus profondes sont ennoyées ; les écoulements remontent le long de puits-cheminées et émergent à des sources vauclusiennes. Dans la zone épinoyée, les mises en charge produisent des conduits en montagnes russes au-dessus de la surface piézométrique d’étiage. Dans ce cas de remontée du niveau de base, la spéléogenèse per ascensum produit des niveaux plus élevés qui sont finalement plus récents que les niveaux inférieurs. De telles remontées du niveau de base proviennent de subsidence tectonique, de remplissage de vallées, ou de remontées du niveau marin, ce qui fut le cas autour de la Méditerranée à la fin de la Crise messinienne. Par conséquent, les karsts noyés profonds, s’ils ne sont pas d’origine hypogène, peuvent être généralement attribués à des remontées du niveau de base.

Certain caves formed by dissolution of bedrock have maze patterns composed of closed loops in which many intersecting fractures or pores have enlarged simultaneously. Their origin can be epigenic (by shallow circulation of meteoric groundwater) or hypogenic (by rising groundwater or production of deep-seated solutional aggressiveness). Epigenic mazes form by diffuse infiltration through a permeable insoluble caprock or by floodwater supplied by sinking streams. Most hypogenic caves involve deep sources of aggressiveness. Transverse hypogenic cave origin is a recently proposed concept in which groundwater of mainly meteoric origin rises across strata in the distal portions of large flow systems, to form mazes in soluble rock sandwiched between permeable but insoluble strata. The distinction between maze types is debated and is usually based on examination of diagnostic cave features and relation of caves to their regional setting. In this paper, the principles of mass transfer are applied to clarify the limits of each model, to show how cave origin is related to groundwater discharge, dissolution rate, and time. The results show that diffuse infiltration and floodwater can each form maze caves at geologically feasible rates (typically within 500 ka). Transverse hypogenic mazes in limestone, to enlarge significantly within 1 Ma, require an unusually high permeability of the non-carbonate beds (generally ≥ 10−4 cm/s), large discharge, and calcite saturation no greater than 90%, which is rare in deep diffuse flow in sedimentary rocks. Deep sources of aggressiveness are usually required. The origin of caves by transverse hypogenic flow is much more favorable in evaporite rocks than in carbonate rocks.

Cave exploration and mapping can provide considerable insight into the nature of groundwater flow and geologic processes in soluble rocks. The Appalachian Mountains provide an ideal setting for this exchange of information because their geology varies greatly over short distances. Caves reveal the way in which groundwater flow is guided by geologic structure, and they help to clarify aquifer test data, well yield, and contaminant dispersion. Well tests in karst aquifers often reveal confined or unconfined conditions that make little sense stratigraphically, but which can be explained with the aid of cave mapping. With regard to geologic mapping, many caves reveal structures that are not visible at the surface. Caves also show evidence for underground geochemical processes that cannot be detected from well data. Subtle mineralogical clues are generally erased by weathering and erosion at the surface, but persist in many caves. The information that caves have provided about subsurface geology and water flow is now being used by explorers, even those with no geologic background, to help them find new caves. DOI: 10.4311/jcks2008es0042

Cosmogenic 26Al and 10Be in sediments washed into Mammoth Cave, Kentucky, record the history of 3.5 m.y. of water-table position, governed by incision and aggradation of the Green River, a tributary of the Ohio River. Upper levels of the cave formed during a period of slow river incision and were later filled with sediment due to river aggradation at 2.3–2.4 Ma. A brief surge of river incision ca. 2 Ma was followed by river stability and cave-passage formation at a lower level. Rapid incision through 15 m of bedrock ca. 1.5 Ma was prompted by repositioning of the Ohio River to its present course along an ice-sheet margin. Renewed incision ca. 1.2 Ma and aggradation at 0.7–0.8 Ma correlate with major ice advances in the Ohio River basin. Measurements of 26Al and 10Be also indicate that sandstone-capped uplands have maintained slow erosion rates of 2–7 m/m.y. for the past 3.5 m.y., despite accelerated Pleistocene river incision rates of ∼30 m/m.y.

Cueva de Villa Luz, a hypogenic cave in Tabasco, Mexico, offers a remarkable opportunity to observe chemotrophic microbial interactions within a karst environment. The cave water and atmosphere are both rich in hydrogen sulphide. Measured H 2 S levels in the cave atmosphere reach 210 ppm, and SO 2 commonly exceeds 35 ppm. These gases, plus oxygen from the cave air, are absorbed by freshwater that accumulates on cave walls from infiltration and condensation. Oxidation of sulphur and hydrogen sulphide forms concentrated sulphuric acid. Drip waters contain mean pH values of 1.4, with minimum values as low as 0.1. The cave is fed by at least 26 groundwater inlets with a combined flow of 200–300 l/s. Inlet waters fall into two categories: those with high H 2 S content (300–500 mg/l), mean P CO 2 =0.03–0.1 atm, and no measurable O 2 ; and those with less than 0.1 mg/l H 2 S, mean P CO 2 =0.02 atm, and modest O 2 content (up to 4.3 mg/l). Both water types have a similar source, as shown by their dissolved solid content. However, the oxygenated water has been exposed to aerated conditions upstream from the inlets so that original H 2 S has been largely lost due to outgassing and oxidation to sulphate, increasing the sulphate concentration by about 4%. Chemical modelling of the water shows that it can be produced by the dissolution of common sulphate, carbonate, and chloride minerals. Redox reactions in the cave appear to be microbially mediated. Sequence analysis of small subunit (16 S ) ribosomal RNA genes of 19 bacterial clones from microbial colonies associated with water drips revealed that 18 were most similar to three Thiobacilli spp., a genus that often obtains its energy from the oxidation of sulphur compounds. The other clone was most similar to Acidimicrobium ferrooxidans , a moderately thermophilic, mineral-sulphide-oxidizing bacterium. Oxidation of hydrogen sulphide to sulphuric acid, and hence the cave enlargement, is probably enhanced by these bacteria. Two cave-enlarging processes were identified. (1) Sulphuric acid derived from oxidation of the hydrogen sulphide converts subaerial limestone surfaces to gypsum. The gypsum falls into the cave stream and is dissolved. (2) Strongly acidic droplets form on the gypsum and on microbial filaments, dissolving limestone where they drip onto the cave floors. The source of the H 2 S in the spring waters has not been positively identified. The Villahermosa petroleum basin within 50 km to the northwest, or the El Chichon volcano ~50 km to the west, may serve as source areas for the rising water. Depletion of 34 S values (−11.7‰ for sulphur stabilized from H 2 S in the cave atmosphere), along with the hydrochemistry of the spring waters, favour a basinal source.

The Kaskaskia paleokarst, part of the Mississippian-Pennsylvanian unconformity in North America, is typified by sink-holes, fissures, and dissolution caves at and near the top of the Kaskaskia Sequence (Madison Limestone and equivalents) and is covered by basal Absaroka siliciclastics (Chesterian to Morrowan). In the Rocky Mountains and Black Hills of the northwestern U.S.A. it post dates earlier features produced by sulfate-carbonate interactions, including breccias, dissolution voids, bedrock alteration, and mineralization. Both the paleokarst and earlier features have been intersected by post-Laramide caves. Ore deposits, aquifers, and petroleum reservoirs in the region are also concentrated along both the paleokarst horizons and earlier sulfate-related features. Each phase of karst modified and preferentially followed the zones of porosity and structural weakness left by earlier phases, producing an interrelated complex of now-relict features. All should be considered together to explain the present aspect of the paleokarst.

Wind Cave, South Dakota, is a three-dimensional, rectilinear maze cave developed in 90 m of Mississippian limestone and dolomite that is overlain by thick clastic cover strata. Beneath an area of 1.8 km 2 , 87 km of small, drained, phreatic passages are known. Exploration terminates at a water table 160 m below the highest parts of the cave. As the cave was draining, calcite precipitated from its waters. Uranium-series measurements (85) were taken on fragments of broken calcite crusts collected in the lower 93 m of the cave. The measurements reveal that it has been draining as a backwater for at least the past 300,000 yr. 234 U/ 238 U ratios in the water were remarkably constant, allowing estimation of ages beyond 400 ky B.P. After deducting glacial-interglacial cyclic oscillations (of 10- to 20-m amplitude), the water table appears to have been lowered at a steady rate of 0.4 m per 10 3 yr since ≥400 ky B.P. Most of this fall is attributed to the increase of hydraulic conductivity in the ~260 m of cover strata that separates the carbonate aquifer from its spring discharge points. A subaqueous calcite deposition zone extended to ~70 m below the contemporary water table at all times, where mean rates of deposition were 0.12 mm per 10 3 yr or less. Modeling of the precipitation kinetics suggests a well-mixed water body, with a Ca 2+ concentration close to the thermodynamic equilibrium value and variations of depositional rate being controlled by hydrostatic pressure.

Limestone caves form along ground-water paths of greatest discharge and solutional aggressiveness. Flow routes that acquire increasing discharge accelerate in growth, while others languish with negligible growth. As discharge increases, a maximum rate of wall retreat is approached, typically about 0.01-0.1 cm/yr, determined by chemical kinetics but nearly unaffected by further increase in discharge. The time required to reach the maximum rate is nearly independent of kinetics and varies directly with flow distance and temperature and inversely with initial fracture width, discharge, gradient, and PCO2. Most caves require 104 - 105 yr to reach traversable size. Their patterns depend on the mode of ground-water recharge. Sinkhole recharge forms branching caves with tributaries that join downstream as higher-order passages. Maze caves form where (1) steep gradients and great undersaturation allow many alternate paths to enlarge at similar rates or (2) discharge or renewal of undersaturation is uniform along many alternate routes. Flood water can form angular networks in fractured rock, anastomotic mazes along low-angle partings, or sponge-work where intergranular pores are dominant. Diffuse recharge also forms networks and spongework, often aided by mixing of chemically different waters. Ramiform caves, with sequential outward branches, are formed mainly by rising thermal or H2S-rich water. Dissolution rates in cooling water increase with discharge, CO2 content, temperature, and thermal gradient, but only at thermal gradients of more than 0.01 °C/m can normal ground-water CO2 form caves without the aid of hypogenic acids or mixing. Artesian flow has no inherent tendency to form maze caves. Geologic structure and stratigraphy influence cave orientation and extent, but alone they do not determine branch-work versus maze character.