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National Cave and Karst Research Institute
Special Paper №1
2007
Published and distributed by
National Cave and Karst Research Institute
Dr. George Veni, Executive Director
1400 Commerce Drive
Carlsbad, NM 88220
www.nckri.org
Peer-review: Dr. Derek Ford (McMaster University, Canada), Dr. Calvin Alexander (University of Minnesota, USA), Dr.
John Sharp (University of Texas, USA), Dr. Philippe Audra (University of Nice, France),
Dr. Armstrong Osborne (University of Sydney).
Citation information:
Klimchouk, A. B. 2007. Hypogene Speleogenesis: Hydrogeological and Morphogenetic Perspective. Special Paper no. 1,
National Cave and Karst Research Institute, Carlsbad, NM, 106 pp.
ISBN-10 0-9795422-0-0
ISBN-13 978-0-9795422-0-6
© 2007 Alexander B. Klimchouk
Second Edition, 2011
This work was prepared in 2006-2007 when the author was staying with the National Cave and Karst Research Institute
(USA) as a Distinguished Visiting Scholar. Minor edits and revisions were made in 2011.
The author's principal affiliation: Ukrainian Institute of Speleology and Karstology, Ministry of Science and Education of
Ukraine and the National Academy of Science of Ukraine.
Tavrichesky National University
4 Prospect Vernadskogo,
Simferopol 95007, Ukraine
Email: institute@speleoukraine.net
Dedication
To Kimberly (Kim) Cunningham, an outstanding person, a genuine friend and a bright cave scientist,
who left an indelible impression on people who where lucky to know him.
Cover photo:
Front: A rising chain of cupolas in Caverns of Sonora, TX, USA (Photo by A. Klimchouk)
Back: A dome possibly leading to a higher story of passages (an exploring caver climbing a rope provides a scale). See
Plate 11 for a broader view. Echo Chamber in Lechuguilla Cave, NM, USA (Photo by S. Allison).
ii
Contents
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iii
List of Figures, Plates, and Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. iv-vi
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
1. Basic concepts and terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
1.1 Karst and speleogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Hypogenic, confined and deep-seated speleogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Karst in the context of the systematized and hierarchical nature
of regional groundwater flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
3. Ascending hypogenic speleogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
3.1 Cross-formational communication and basinal hydraulic continuity . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2 Hydrostratigraphic conversion of soluble formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.3 The concept of transverse speleogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.4 Vertical heterogeneity in porosity and permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.5 Recharge, cave-forming flow and discharge in hypogene settings . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.6 Dissolution processes in hypogenic speleogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.7 Mechanisms of hypogenic transverse speleogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.8 The role of free convection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4. Hypogenic cave features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
4.1 Criteria for distinguishing the hypogenic transverse origin for caves . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.2 Cave patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.3 The maze caves controversy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.4 Cave morphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.5 Selected examples of caves formed by hypogenic transverse speleogenesis . . . . . . . . . . . . . . . . . . 57
4.6 Comparison of confined versus unconfined conduit porosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5. Some implications of the hypogenic transverse speleogenesis concept . . . . . .
87
5.1 Variability in aquifer characteristics and behavior resulting from unconfined and confined
speleogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
87
5.2 The role of hypogenic speleogenesis in the formation of mineral deposits . . . . . . . . . . . . . . . . . . . . 88
5.3. Implications to petroleum geology and hydrogeology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
5.4. Implications for sinkhole hazard and site assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Epilogue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
97
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
98
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
99
iii
Foreword
In 1998, the National Cave and Karst Research Institute (NCKRI) was established by a U.S. Congressional
mandate to facilitate and support cave and karst research, stewardship, and education. I am delighted to
introduce this new publication series, NCKRI Special Papers, as an essential part of NCKRI’s efforts to meet
that mandate. I’m equally pleased that this first book in the series is the highly important work of NCKRI’s
first visiting scholar, Dr. Alexander B. Klimchouk.
Caves are resources hidden from the view of the general public and most scientists. Their value often goes
unrecognized because they are either not seen or misunderstood. Historically, caves were ignored by many
geoscientists, in part because they did not “follow the rules” of groundwater behavior and thus “had” to be
anomalous features of little significance. While this view has mostly changed, many scientists who realized the
significance of caves had and still have the mistaken notion that areas of carbonate and evaporite rocks that
contain few or no caves are not karst. This book shatters those myths and makes great strides in explaining
what had been some of the most puzzling aspects of karst hydrogeology.
Dr. Klimchouk carefully explains the origin of hypogenic caves and karst, and demonstrates it with a rich,
international array of examples and data. While most karst literature focuses on epigenic karst, formed by
descending groundwater, hypogenic karst stems from ascending groundwater. Understanding the characteristic
set of hypogenic morphological and hydrological features, and the processes that create them, is crucial for
developing accurate models, and effective management plans for these karst systems. This is vital because
hypogenic karst is especially poorly expressed at the surface, and so its vulnerability as a public water supply,
risk of sinkhole collapse, and value as a mineral resource can be severely underestimated.
While this book focuses on karst hydrogeology and speleogenesis, it also has important implications for
many other disciplines, such as understanding the ranges and speciation of cavernicolous organisms, landscape
evolution, and the distribution of paleontological and archeological deposits, to name a few. At a
fundamentally crucial level, the great geographic breadth of hypogenic karst will soon be realized directly as a
result of this work. Certainly, some concepts presented here will be refined with continued research, but this
book firmly establishes a new paradigm that will guide much karst research for decades to come.
Dr. George Veni
Executive Director, NCKRI
April 2007
iv
List of Figures
Figure 1. Epigenic and hypogenic karst in the context of basinal groundwater flow. 10
Figure 2. Evolutionary types of karst and speleogenetic environments. 11
Figure 3. Flow pattern in a multi-story artesian aquifer system. 13
Figure 4. Hydraulic head distribution in cross sections, the Western Canada Sedimentary Basin showing the
influence of topography, particularly river valleys. 14
Figure 5. Hydraulic head distribution in the Upper Devonian Wabamun Group of central and southern Alberta. 15
Figure 6. Conversion of the hydrogeological function of a soluble bed in a multiple-aquifer system in the course of
speleogenesis. 16
Figure 7. A diagram illustrating general concepts of lateral versus ascending transverse flow through a single
fracture and a fissure network encased in a soluble bed. 17
Figure 8. Transverse flow through a fracture network in single level and multiple levels. 17
Figure 9. A cupola at the ceiling of the uppermost story of Caverns of Sonora, Texas, USA. 20
Figure 10. Modes of recharge to a cave formation from a feeding formation, depending on juxtaposed permeability
structures. 21
Figure 11. Variants of hydrostratigraphic position and recharge/discharge relationships for a cave formation in a
layered aquifer system. 22
Figure 12. Regionalization of Optymistychna Cave, western Ukraine, a 214+ km long maze, according to its multi-
story structure, and the reconstruction of recharge-discharge arrangements during the time of its formation. 23
Figure 13. Plan of Wind Cave, Black Hills, South Dakota, USA, and a diagram illustrating the concept of the lifting
origin of the Black Hills maze caves and the stair-case effect of recharge-discharge offset. 23
Figure 14. Schematic representation of the relative importance of hypogenic and epigenic components in the
shallow subsurface environment in different climatic settings. 29
Figure 15. Variations in joint patterns and inherited maze patterns between different horizons of the Miocene
gypsum beds in the western Ukraine, example from Optymistychna Cave. 31
Figure 16. Examples of polygonal and systematic network patterns in the same region, Guadalupe Mountains,
USA. 32
Figure 17. Profile of Lechuguilla Cave, New Mexico, USA. 33
Figure 18. Conceptual models of development of a maze cave. 35
Figure 19. The morphologic suite of rising flow, diagnostic of a confined transverse origin of caves. 36
Figure 20. Distribution of point feeders through the network of master passages in maze caves. 37
Figure 21. Theoretical development of simple and complex spheres by condensation corrosion. 39
Figure 22. Patterns of hydrothermal caves of the Buda Mountains, Hungary. 57
Figure 23. Plan view and profile of Frasassi caves, Italy. 58
Figure 24. Schematic cross-section through Monte Cucco karst system, central Italy. 59
Figure 25. Speleological map and schematic cross-section of Rio Garrafo Gorge, showing occurrence of
Acquasanta caves. 59
Figure 26. Speleological map of Parrano Gorge, central Italy. 60
Figure 27. Phreatic shaft Pozzo del Merro in Italy. 60
Figure 28. Hypogenic maze caves in Cretaceous and Triassic limestones in Western Europe. 61
Figure 29. Hypogenic confined mazes in gypsum in Western Europe. 62
Figure 30. Development of hypogenic caves at the base of a sulfate formation due to buoyancy-driven dissolution,
example from South Harz, Germany. 62
Figure 31. Two-dimensional caves formed by transverse flow across a single bed of Miocene limestone,
Prichernomorsky artesian basin, south Ukraine. 62
Figure 32. Patterns of hypogenic maze caves in Miocene gypsum in the western Ukraine. 63
Pages
v
Figure 33. Maze caves in Siberia: Botovskaya Cave and Bol'shaya Oreshnaya. 64
Figure 34. Geological section across the Judean arch, Israel, and schematic east-west hydrogeological cross-
section, showing the conceptual model for groundwater flow and hypogenic transverse speleogenesis, the Yarkon-
Taninim aquifer and the ASA zone.
66
Figure 35. Stratigraphic section of Cretaceous formations in Samaria Mountain, Israel, and a section of a quarry in
the confined zone showing distribution of caves. 66
Figure 36. Maps of typical caves in the Turonian limestone. 67
Figure 37. Plan view and cross-sections of Jabal Al Qarah caves in the calcareous sandstone of the Upper
Miocene Hofuf Formation, northeastern Saudi Arabia. 67
Figure 38. Simplified map of Sterkfontein Cave and Lincoln-Fault System and de-roofing of breccia body and
breaching of the cave by denudation. 68
Figure 39. Fissure-like caves and ascending pits in eastern Missouri. 69
Figure 40. Map fragment of Jewel Cave, South Dakota, USA, showing superposition of different passage stories. 70
Figure 41. Mystery Cave, Minnesota, USA, presumed to form as a subterranean meander cut-off of the West Fork
of the Root River. 70
Figure 42. Robber Baron Cave, Texas, USA, a maze cave in Cretaceous limestone, above the confined zone of
the Edwards Aquifer. 71
Figure 43. Amazing Maze, Texas, USA, a multi-story maze cave in stratified Cretaceous limestone, an example of
confined transverse speleogenesis in which dissolution by sulfuric acid took part. 72
Figure 44. Map of Caverns of Sonora, Texas, USA. 73
Figure 45. Regional structural setting of the Guadalupe Mountains, USA, and stratigraphic nomenclature of
Permian strata exposed in the Guadalupe Mountains 74
Figure 46. Plans and profiles of some Guadalupe caves: Carlsbad Cavern, Dry Cave, Spider Cave, Endless Cave. 74
Figure 47. Projected vertical profiles through part of Lechuguilla Cave, showing the nearly independent flow
systems through the entrance series and through the Sulfur Shores - Underground Atlanta systems. 76
Figure 48. Line drawing of section through the Capitan Platform on the eastern face of Slaughter Canyon and an
exposure at Indian Shelter in Walnut Canyon, Guadalupe Mountains, New Mexico. 77
Figure 49. A proposed regional speleogenetic model for the Guadalupe Mountains. 78
Figure 50. Longitudinal profile of the Guadalupe ridge from southwest to northeast, with locations, elevations and
vertical ranges of major caves, and age dates from alunite for four caves. 80
Figure 51. Map of Cueva de Villa Luz, Tabasco, Mexico. 81
Figure 52. Profile view of southern most sinkholes of Sistema Zacaton, Tamaulipas, Mexico, showing zones of
varying water types and travertine morphology. 81
Figure 53. Aerial photograph of Sistema Zacaton showing the major features of the area. 81
Figure 54. Geologic map of northeastern Mexico showing locations of deep karst shafts in the region. 82
Figure 55. Toca da Boa Vista and Toca da Barriguda caves in Brazil. 83
Figure 56. Typical hypogenic caves of eastern Australia: Queenslander-Cathedral Cave System and Ashford
Cave. 84
Figure 57. Conceptual model of speleogenetic origin of sulfur deposits in western Ukraine. 90
Figure 58. Conceptual genetic model for sulfur deposits of northern Iraq. 91
Figure 59. Diagrammatic representation of hypogenic karst features in the Delaware Basin and adjacent reef
structures, New Mexico and west Texas, USA. 92
Figure 60. Geologic section in southeast Missouri, and lithostratigraphy of the Ozark Dome region, USA. 93
Figure 61. Distribution of oil and gas fields of west Texas and southeast New Mexico in relation to major features
of regional geology and hypogenic karst. 94
Figure 62. Distribution of breakdown structures in Zoloushka Cave. 96
vi
List of Plates
Plate 1. Feeders: side feeders with rising wall channels. 41
Plate 2. Feeders: side feeders with ear-like or domed orifices. 42
Plate 3. Feeders: point features in passage floors. 43
Plate 4. Feeders: point features in passage floors and lower walls. 44
Plate 5. Feeders: fissure- and rift-like feeders in passage floors. 45
Plate 6. Rising chains of ceiling cupolas and upward-convex arches, ceiling channels and serial cupolas in the
ceiling apex. 46
Plate 7. Ceiling channels and cupolas in linear series. 47
Plate 8. Outlets with connecting ceiling channels or formed within a ceiling channel. 48
Plate 9. Outlets in cupolas and domepits. 49
Plate 10. Outlets breaching to the upper discharge boundary. 50
Plate 11. Mega-outlets in Lechuguilla Cave, Guadalupe Mountains, New Mexico, USA. 50
Plate 12. Bedrock partitions between closely-spaced passages in maze caves. 51
Plate 13. Partitions by carbonate fill of fractures in Zoloushka Cave, western Ukraine. 51
Plate 14. Hypogenic morphology in Mystery Cave, Minnesota, USA. 52
Plate 16. Morphological and geological characteristics of Yellow Jacket Cave, Dark Canyon, Guadalupe
Mountains, New Mexico, USA. 53
Plate 17. Hypogenic morphology in Coffee Cave, New Mexico, USA. 54
Plate 18. Hypogenic morphology in Coffee Cave, New Mexico, USA. 55
Plate 19. Megasinkholes (shafts) associated with hydrothermal systems, with travertine deposition near water
table. 56
List of Tables
TABLE 1
Characterization of cave patterns and porosity in unconfined versus confined aquifers 85
TABLE 2
Average characteristics of conduit patterns for unconfined and confined settings 86
vii
ABSTRACT
1
Abstract
This book provides an overview of the principal
environments, main processes and manifestations of
hypogenic speleogenesis, and refines the relevant
conceptual framework. It consolidates the notion of
hypogenic karst as one of the two major types of karst
systems (the other being epigenetic karst). Karst is viewed
in the context of regional groundwater flow systems,
which provide the systematic transport and distribution
mechanisms needed to produce and maintain the
disequilibrium conditions necessary for speleogenesis.
Hypogenic and epigenic karst systems are regularly
associated with different types, patterns and segments of
flow systems, characterized by distinct hydrokinetic,
chemical and thermal conditions. Epigenic karst systems
are predominantly local systems, and/or parts of recharge
segments of intermediate and regional systems.
Hypogenic karst is associated with discharge regimes of
regional or intermediate flow systems.
Various styles of hypogenic caves that were
previously considered unrelated, specific either to certain
lithologies or chemical mechanisms are shown to share
common hydrogeologic genetic backgrounds. In contrast
to the currently predominant view of hypogenic
speleogenesis as a specific geochemical phenomenon, the
broad hydrogeological approach is adopted in this book.
Hypogenic speleogenesis is defined with reference to the
source of fluid recharge to the cave-forming zone, and
type of flow system. It is shown that confined settings are
the principal hydrogeologic environment for hypogenic
speleogenesis. However, there is a general evolutionary
trend for hypogenic karst systems to lose their
confinement due to uplift and denudation and due to their
own expansion. Confined hypogenic caves may
experience substantial modification or be partially or
largely overprinted under subsequent unconfined (vadose)
stages, either by epigenic processes or continuing
unconfined hypogenic processes, especially when H2S
dissolution mechanisms are involved.
Hypogenic confined systems evolve to facilitate
cross-formational hydraulic communication between
common aquifers, or between laterally transmissive beds
in heterogeneous soluble formations, across cave-forming
zones. The latter originally represented low-permeability,
separating units supporting vertical rather than lateral
flow. Layered heterogeneity in permeability and breaches
in connectivity between different fracture porosity
structures across soluble formations are important
controls over the spatial organization of evolving
ascending hypogenic cave systems. Transverse hydraulic
communication across lithological and porosity system
boundaries, which commonly coincide with major
contrasts in water chemistry, gas composition and
temperature, is potent enough to drive various
disequilibrium and reaction dissolution mechanisms.
Hypogenic speleogenesis may operate in both carbonates
and evaporites, but also in some clastic rocks with soluble
cement. Its main characteristic is the lack of genetic
relationship with groundwater recharge from the
overlying or immediately adjacent surface. It may not be
manifest at the surface at all, receiving some expression
only during later stages of uplift and denudation. In many
instances, hypogenic speleogenesis is largely climate-
independent.
There is a specific hydrogeologic mechanism inherent
in hypogenic transverse speleogenesis (restricted
input/output) that suppresses the positive flow-dissolution
feedback and speleogenetic competition in an initial
flowpath network. This accounts for the development of
more pervasive channeling and maze patterns in confined
settings where appropriate structural prerequisites exist.
As forced-flow regimes in confined settings are
commonly sluggish, buoyancy dissolution driven by
NCKRI Special Paper Series No.1
2
either solute or thermal density differences is important in
hypogenic speleogenesis.
In identifying hypogenic caves, the primary criteria
are morphological (patterns and meso-morphology) and
hydrogeological (hydrostratigraphic position and
recharge/flow pattern viewed from the perspective of the
evolution of a regional groundwater flow system).
Elementary patterns typical for hypogenic caves are
network mazes, spongework mazes, irregular chambers
and isolated passages or crude passage clusters. They
often combine to form composite patterns and complex 3-
D structures. Hypogenic caves are identified in various
geological and tectonic settings, and in various
lithologies. Despite these variations, resultant caves
demonstrate a remarkable similarity in cave patterns and
meso-morphology, which strongly suggests that the
hydrogeologic settings were broadly identical in their
formation. Presence of the characteristic morphologic
suites of rising flow with buoyancy components is one of
the most decisive criteria for identifying hypogenic
speleogenesis, which is much more widespread than was
previously presumed. Hypogenic caves include many of
the largest, by integrated length and by volume,
documented caves in the world.
The refined conceptual framework of hypogenic
speleogenesis has broad implications in applied fields and
promises to create a greater demand for karst and cave
expertise by practicing hydrogeology, geological
engineering, economic geology, and mineral resource
industries. Any generalization of the hydrogeology of
karst aquifers, as well as approaches to practical issues
and resource prospecting in karst regions, should take into
account the different nature and characteristics of
hypogenic and epigenic karst systems. Hydraulic
properties of karst aquifers, evolved in response to
hypogenic speleogenesis, are characteristically different
from epigenic karst aquifers. In hypogenic systems, cave
porosity is roughly an order of magnitude greater, and
areal coverage of caves is five times greater than in
epigenic karst systems. Hypogenic speleogenesis
commonly results in more isotropic conduit permeability
pervasively distributed within highly karstified areas
measuring up to several square kilometers. Although
being vertically and laterally integrated throughout
conduit clusters, hypogenic systems, however, do not
transmit flow laterally for considerable distances.
Hypogenic speleogenesis can affect regional subsurface
fluid flow by greatly enhancing initially available cross-
formational permeability structures, providing higher
local vertical hydraulic connections between lateral
stratiform pathways for groundwater flow, and creating
discharge segments of flow systems, the areas of low-
fluid potential recognizable at the regional scale.
Discharge of artesian karst springs, which are modern
outlets of hypogenic karst systems, is often very large and
steady, being moderated by the high karstic storage
developed in the karstified zones and by the hydraulic
capacity of an entire artesian system. Hypogenic
speleogenesis plays an important role in conditioning
related processes such as hydrothermal mineralization,
diagenesis, and hydrocarbon transport and entrapment.
An appreciation of the wide occurrence of hypogenic
karst systems, marked specifics in their origin,
development and characteristics, and their scientific and
practical importance, calls for revisiting and expanding
the current predominantly epigenic paradigm of karst and
cave science.
INTRODUCTION
3
Introduction
Most studies of karst systems are concerned with
shallow, unconfined geologic settings, supposing that the
karstification is ultimately related to the Earth's surface
and that dissolution is driven by downward meteoric
water recharge. Such systems are epigenic (hypergenic).
Concepts and theories developed for unconfined karst
systems overwhelmingly predominate in karst and cave
science, particularly in karst hydrology and
geomorphology, forming a core of the current karst
paradigm. Hypogenic karst, originating from depth and
not related to recharge from the overlying surface,
although becoming more recognized during the last two
decades, remains poorly understood and integrated into
the bulk of karst science.
There are specific reasons for this bias, arising from
the historic paths through which the knowledge of the
karst domain evolved. Epigenic karst systems evolve
when soluble rocks occur in the shallow subsurface or
become exposed, so they inherently express surface
components, readily available for observations and
affecting many aspects of human activity. Epigenic karst
systems form by water infiltrating or in-flowing from
overlying or immediately adjacent recharge surfaces and
develop in genetic relation to landscape. Caves commonly
have a hydrologic connection with the surface and
“genetically inherent” entrances. Karst knowledge in
Western Europe and North America had originally
commenced mainly from exploration and study of such
caves. These factors in combination led to a deeply rooted
belief that epigenic unconfined karst systems
overwhelmingly predominate1. Karst features, routinely
1 In contrast, in some regions where karstology as a scientific
discipline preceded cave exploration, and where “covered”
(deep-seated) karst settings are widespread, such as in the
former Soviet Union, deep-seated, hypogene, confined karst and
encountered by wells and mines in soluble rocks at
substantial depths, were (and still are) commonly
regarded as paleokarst features, originally formed in
epigenic settings and subsequently buried under younger
sediments.
Some explored caves, however, display patterns,
morphologies, sediments, and minerals that do not readily
conform to established concepts of epigenic karst
development and speleogenesis. Until recently, they were
(and in many cases still are) explained in terms of
epigenic/unconfined speleogenesis, which led to
numerous more or less obvious misconceptions and
controversies. Over the last 20 years there has been a
rapid increase in the development of speleogenetic ideas
implying a hypogenic and/or confined origin of caves,
with reference to a deep source of acidity or to a confined
flow system. However, in the general context of the
predominant karst paradigm, such caves are still largely
regarded as special, aberrant cases. In his classic work on
cave origin, Palmer (1991) estimated that hypogene cave
systems account for only about 10% of the studied cave
systems, although they include some of the largest ones.
Since then, ongoing re-interpretation of some known
caves has probably increased this percentage. Enhanced
understanding of hypogenic speleogenesis and the
refinement of criteria for their recognition are going to
further increase this figure. More important is the fact that
hypogene/confined karst systems are globally much more
widespread than it is now believed, and the relatively
small fraction of known caves of this type is merely an
exploration bias resulting from their genetic irrelevance to
the surface and inherent lack of accessibility.
some relevant processes have been long recognized, at least in
general terms.
NCKRI Special Paper Series No.1
4
Significant advances in understanding of
speleogenesis in hypogene (deep-seated) and confined
(artesian) settings made during recent years remain
somewhat fragmented and uncoordinated. This is partly
because discussions of the particular cases of “atypical”
speleogenesis (sulfuric acid, hydrothermal, in some sense
– speleogenesis in evaporites) focus attention on
geochemical processes of solutional porosity creation
with the hydrogeologic framework of cave formation
often remaining poorly understood. There is a misleading
trend to label particular types of speleogenesis, or even
types of karst, by the dissolutional mechanism assumed to
have created the caves. This obscures the fact that most
hypogenic/confined karst systems share many major
common features in their geo/hydrogeological settings,
patterns and morphologies. Although geochemical
attributes and dissolution mechanisms are indispensable
components of the speleogenetic environment, the
principal component is groundwater flow. Other attributes
largely depend on the position of a given karst system in
the basinal groundwater flow system and evolution of
boundary conditions. By way of analogy, in creating
dissolutional porosity the groundwater flow system is a
“master,” the type of recharge is a “tool” and
dissolutional mechanisms are the “fuels” to power the
tools. The shape, pattern and size of holes produced by a
tool (dentist drill, hand drill, borehole drill bit, bulldozer
or excavator) depend more on the intentions of a master
and the type of tool rather than on the fuel that drives it.
This paper intends to give an overview of the
principal environments, main processes and
manifestations of hypogenic speleogenesis, in order to
show the place of hypogenic karst systems in the basinal
groundwater flow systems, thus demonstrating the
common genetic background of various styles of
hypogenic karst and caves that were previously
considered unrelated, specific either to lithologies and/or
chemical mechanisms. I intend to demonstrate the
fundamental importance of the type of flow system in the
formation of hypogenic (confined) karst and caves, and
establish hypogenic karst as one of two major types of
karst systems.
The appreciation of the widespread occurrence of
hypogenic karst systems, marked specifics in their origin
and development, and their scientific and practical
importance, calls for revisiting and expanding the current
paradigm of karst and cave science.
BASIC CONCEPTS AND TERMINOLOGY
5
1. Basic concepts and terminology
1.1 Karst and speleogenesis
As this book focuses on phenomena and processes
poorly integrated into the established conceptual framework
of karst, it is necessary to clarify some basic concepts and
terminology.
Most modern texts, encyclopedias, and reviews define
karst from a largely geomorphological perspective: “Karst is
terrain with distinctive hydrology and landforms arising
from the combination of high rock solubility and well-
developed solutional channel (secondary) porosity
underground” (Ford and Williams, 1989; Ford, 2004)..
Distinctive landforms and surface hydrology, however, are
not necessarily characteristic for hypogenic karst.
Although it is often claimed that approaches, concepts
and methodologies to study karst differ between
geomorphology and hydrology, the modern conceptual
framework in karst hydrology seems to remain constrained
by the historically prevailing largely geomorphological
paradigm of karst as an epigenic unconfined system, closely
related to surface drainage (White, 2002; Bakalowicz, 2005).
Moreover, earlier firmly rooted, historically biased views
that only karst features in carbonates are considered a true
karst are still reiterated in modern publications:
“Karst features mainly occur in carbonate rocks,
limestone and dolomite, in which formations it is considered
as true karst” (Bakalowicz, 2005);
“Karst: Landforms that have been modified by
dissolution of soluble rocks (limestone and dolostone)”
(Poucher and Copeland, 2006);
“Karst is defined as a limestone landscape with
underground drainage” (Waltham, in Luhr, 2003).
Another illustration of the poor integration of hypogenic
karst into modern karst knowledge is that the recent two
fundamental encyclopedias on caves and karst (Gunn, 2004;
Culver and White, 2004) do not contain distinct entries on
hypogenic karst, although they do consider many aspects of
hypogenic karst and certainly hypogenic caves (as they
include some of the largest and most important caves in the
world).
Although such focusing was certainly productive in
consolidating the conceptual framework and methodology in
studying the epigenic type of karst systems, the situation
with the predominantly epigenetic approach to karst,
reflected in general reviews on the subject, hinders progress
in recognition and study of hypogenic karst.
An emerging approach to karst hydrogeology is more
integrative and universal by encompassing the whole range
of karst processes and phenomena. Following proposals of
Huntoon (1995) and Klimchouk and Ford (2000), karst is
defined here as “an integrated mass-transfer system in
soluble rocks with a permeability structure dominated by
conduits dissolved from the rock and organized to facilitate
the circulation of fluids.” Whether karst is expressed at the
surface or not is irrelevant. A karst system can operate in the
subsurface without any apparent relationship to the surface,
being represented exclusively by underground forms that
draw their input water from and discharge their output water
to other non-karstic rocks.
Speleogenesis is viewed as “the creation and evolution
of organized permeability structures in a rock that have
evolved as the result of dissolutional enlargement of an
earlier porosity” (Klimchouk and Ford, 2000, p.47), making
it the most essential part of the karst concept. One can assert
that karst is a function of speleogenesis, a statement for
which the validity is particularly evident in cases where the
surface landscape component is absent or subdued as in
hypogenic karst. The notion of “karst,” however, is broader
than that of “speleogenesis,” as it includes features and
phenomena induced by speleogenesis but not encompassed
by it.
NCKRI Special Paper Series n.1
6
Though some uncertainties still remain in the scope of
the related and overlapping concepts/terms (discussed in the
next section), three basic genetic settings are broadly
recognized now for caves (Ford and Williams, 1989; 2007;
Klimchouk et al., 2000; Ford, 2006): 1) coastal and oceanic,
in rocks of high matrix porosity and permeability; 2)
hypogenic, predominantly confined, where water enters the
soluble formation from below, and 3) hypergenic (epigenic),
unconfined, where water is recharged from the overlying
surface. Although coastal and oceanic settings are commonly
characterized by unconfined circulation, they are treated
separately because of the specific conditions for
speleogenesis determined by the dissolution of porous,
poorly indurated carbonates by mixing of waters of
contrasting chemistry at the halocline.
1.2 Hypogenic, confined and deep-seated
speleogenesis
Hypogenic (or hypogene) caves are usually considered
the opposite to the common epigenic caves formed by water
recharged from the overlying or immediately adjacent
surface due to carbonic acid dissolution. A more appropriate
antonym to “hypogenic” is hypergenic (or hypergene); the
term widely used in Eastern Europe to denote processes
operating near the surface through the action of descending
solutions.
The term and concept of hypogenic speleogenesis has
seen increasing use during the recent two decades, although
still with some uncertainty in its meaning. Two approaches
appear in recent works. Ford and Williams (1989) and
Worthington and Ford (1995) defined hypogenic caves as
those formed by hydrothermal waters or by waters
containing hydrogen sulfide. Hill (2000a) tends to narrow
the notion of hypogenic karst and speleogenesis to H2S-
related processes and forms. Palmer (1991) defined
hypogenic caves more broadly, as those formed by acids of
deep-seated origin, or epigenic acids rejuvenated by deep-
seated processes. Later on, Palmer (2000a), presented the
definition in a slightly modified, even broader form:
hypogenic caves are formed by water in which the
aggressiveness has been produced at depth beneath the
surface, independent of surface or soil CO2 or other near-
surface acid sources. This modification is important, as it
formally allows us to include in the class of features formed
by still surface-independent but non-acidic sources of
aggressiveness (such as aggressiveness of water with respect
to evaporites). Reference to acid sources seems to be
confusing however, as it again tacitly implies that features
formed by non-acid dissolution are not pertinent.
Palmer's definition relies on the source of
aggressiveness. The aggressiveness is a transient attribute of
water, which can be delivered from depth or acquired within
a given soluble formation (due to mixing or redox processes,
for instance). It is suggested here that the definition of
hypogenic speleogenesis should rather refer to the source of
groundwater, as it is a medium of transport of aqueous and
nonaqueous matter and energy, a reactive agent and a major
component of the speleogenetic environment. Hypogenic
speleogenesis is defined here, following the recent
suggestion of Ford (2006), as “the formation of caves by
water that recharges the soluble formation from below,
driven by hydrostatic pressure or other sources of energy,
independent of recharge from the overlying or immediately
adjacent surface.”
Hypogenic speleogenesis does not rely exclusively on
certain dissolutional mechanisms; a number of dissolutional
processes and sources of aggressiveness can be involved (see
Section 3.6 below). Its main characteristic is the lack of
genetic relationship with groundwater recharge from the
overlying surface. In many instances, hypogenic
speleogenesis is climate-independent. It may not be
manifested at the surface at all (deep-seated karst).
Hypogenic caves commonly come into interaction with the
surface as relict features, largely decoupled from their
formational environment, when ongoing uplift and
denudation shift them into the shallow subsurface.
The concept of hypogenic speleogenesis is closely