INVENTORY AND GEOMETRIC ANALYSIS OF FLANK MARGIN
CAVES OF THE BAHAMAS
By
Monica J. Roth
A Thesis Submitted to the Faculty of Mississippi State University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Geosciences in the Department of Geosciences
Mississippi State, Mississippi
August 2004
Copyright by
Monica J. Roth
2004
INVENTORY AND GEOMETRIC ANALYSIS OF FLANK MARGIN
CAVES OF THE BAHAMAS
By
Monica J. Roth
Approved:
______John E. Mylroie Brenda L. Kirkland Professor of Geosciences Adjunct Professor of Geosciences Graduate Coordinator of the (Committee Member) Department of Geosciences (Director of Thesis)
______Darrel W. Schmitz Philip B. Oldham Professor of Geosciences Dean of the College of Arts (Committee Member) and Sciences
Name: Monica J. Roth
Date of Degree: August 7, 2004
Institution: Mississippi State University
Major Field: Geosciences
Major Professor: Dr. John E. Mylroie
Title of Study: INVENTORY AND GEOMETRIC ANALYSIS OF FLANK MARGIN CAVES OF THE BAHAMAS
Pages in Study: 117
Candidate for Degree of Master of Science
Flank margin caves are karst features that develop in the freshwater/saline mixing zone within the carbonate islands of the Bahamas. The flank margin caves that are currently exposed developed during the last interglacial sea level highstand (+6 m; ~125 ka). Initially small ovid chambers, the caves increase in size to about 100 m2, then interconnect with adjacent chambers to form medium-sized caves. At about 1000 m2, these medium-size caves interlink forming large caves that are laterally extensive, vertically restricted, do not penetrate the fresh-water lens a significant amount, and run parallel to the axis of the ridge in which they formed. Small caves have a much smaller area to perimeter ratio than do large caves. As cave chambers grow and interconnect, perimeters become much more complex, and the number of bedrock columns in the cave increases. These results have implications for water resource management, and porosity modeling.
DEDICATION
To my Mother, Father, Brother and Dan, for all of your support through good times and in hard times. To my Uncle Herbie, Aunt Mildred and Aunt Nora who have passed on to
bigger and better places while I was away at school, I will forever carry your
encouragement in every aspect of my life.
I love you all.
ii
AKNOWLEDGEMENTS
I would like to thank John Mylroie, the most supportive and enthusiastic advisor
any student could ask for. Thanks to Dr. Darrel Schmitz and Dr. Brenda Kirkland for their insightful suggestions and genuine interest in my research. I appreciate all fieldwork assistance from colleague and friend Lica Ersek from Mississippi State University and his wife Carmen Ersek, as well as Dr. Jim Carew from the College of Charleston has been invaluable to the creation of this thesis. I must also thank Joan Mylroie for her fieldwork assistance and for her incredible ability to make any situation easier to handle. Finally, I would like to thank all of the people who before me, bravely entered the flank margin caves of the Bahamas and created many of the maps used in this research.
Funding for my research was provided by Total S.A., the Department of
Geosciences at MSU, and the Gerace Research Center on San Salvador Island, Bahamas.
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TABLE OF CONTENTS
Page
DEDICATION……………………………………………………………………….. ii
ACKNOWLEDGEMENTS………………………………………………………….. iii
LIST OF TABLES…………………………………………………………………… vi
LIST OF FIGURES………………………………………………………………….. vii
CHAPTER
I. INTRODUCTION……………………………………………………………. 1
II. THE BAHAMAS……………………………………………………………... 3 Geographic Setting……………………………………………………….. 3 Geology and Tectonics…………………………………………………… 5 Stratigraphy………………………………………………………………. 6 Hydrology………………………………………………………………… 12
III. ISLAND KARST…………………………………………………………….. 15 Carbonate Island Karst Model ...... 15 Karren ...... 18 Depressions...... 19 Blue Holes...... 19 Pit Caves ...... 20 Banana Holes ...... 21 Lake Drains...... 21 Fracture Caves ...... 21 Porosity Development...... 22 Flank Margin Caves...... 23
IV. FIELD INVESTIGATION AND METHODOLOGY ...... 25 Field Investigation ...... 25 Creating Maps...... 26
iv
CHAPTER Page
Digitizing Maps…………………………………………………………… 26 Data Analysis………………………………………………….………….. 28
V. RESULTS ...... 29
VI. DISCUSSION………………………………………………………………… 51
VII. SUMMARY………………………………………………………………….. 62
REFERENCES……………………………………………………………………….. 64
APPENDIX
A. MAPS OF THE ISLANDS………………………………………………….. 69
B. FLANK MARGIN CAVE MAPS...... 74
C. GRAPHS ...... 102
D. TABLES...... 108
v
LIST OF TABLES
TABLE Page
1. Flank margin cave geometric data ...... 32
2. Flank margin caves of the Bahamas ranked by increase in area..………….. 37
3. Initial geometric conditions found for each flank margin cave ...... 109
4. Bedrock column geometric conditions for each cave……………………… 111
5. Smallest quadrangle fit around each cave...... 113
6. Cave size ranked for each island...... 115
7. Breakdown of cave size by island...... 117
vi
LIST OF FIGURES
FIGURE Page
1. Map of the Bahamas showing each platform, as well as a tectonic boundary (Carew and Mylroie, 1995)...... 4
2. Map of the Bahamian archipelago showing the regional variation of rainfall. (Whitaker and Smart, 1997)…………………………………………..……. 5
3. A physical stratigraphy of the Bahamas (Panuska et al, 1999).……………. 8
4. A physical stratigraphy of San Salvador and other Bahamian Islands as developed by Hearty and Kindler (1994).………………………………….. 11
5. Representation of a fresh-water lens on a carbonate island showing the hydrologic environments from the land surface to the saline groundwater (Mylroie and Carew, 1995)………………………………..……………...... 12
6. The four major carbonate island types, each with distinctive karst features (Mylroie et al., in press)...... 16
7. Model of a carbonate island showing the relative locations of various karst features (Mylroie and Carew, 1995).…………………………………….… 20
8. Diagram showing void development at a small and large scale……………. 23
9. Map of Benzie Hill North Cave showing layers created in AutoCAD…….. 27
10. The AutoCAD figure of Benzie Hill North Cave used in determining the dimensions of the cave. ……………………………………………………. 27
11. Cave area plotted against cave perimeter for all flank margin caves………. 34
12. Cave area plotted against cave perimeter for each island…………………... 34
13. Square root of the cave area plotted against the perimeter of the cave.……. 35
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FIGURE Page
14. Log of the cave area plotted against the log of the perimeter ……………… 39
15. Plot of cave area versus rank number for all caves………………………… 39
16. Plot of cave area versus rank number for small caves ……………………... 40
17. Plot of cave area versus rank number for medium caves…………………… 40
18. Plot of cave area versus rank number for large caves……………………… 41
19. Plot of area versus perimeter for simple geometric shapes………………… 43
20. Plot of area versus perimeter for simple shapes, and caves...... 43
21. Plot of area versus perimeter for simple shapes and small caves ...... 44
22. Plot of area versus perimeter for simple shapes and medium sized……….... 44
23. Plot of area versus perimeter for simple shapes and large caves...... 45
24. Plot of quadrangle length versus quadrangle perimeter for the smallest theoretical quadrangle that each cave can fit in…………………………... 46
25. Plot of cave area versus quadrangle area…………………………………… 46
26. Plot of quadrangle length to width ratio versus cave area …………………. 47
27. Plot of cave area versus cave area divided by quadrangle area ...... 47
28. Map of Maroon Hill Caves found on Great Inagua Island, Bahamas...... 49
29. Map of Salt Pond Hill Cave found on Great Inagua Island, Bahamas ...... 49
30. Map of Hatchet Bay Cave found on Eleuthera Island, Bahamas…………… 50
31. Map of Lighthouse Cave found on San Salvador Island, Bahamas...... 50
32. Flank margin cave passages end abruptly in bedrock walls ...... 52
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FIGURE Page
33. Hatchet Bay Cave on Eleuthera Island, Bahamas, has significant development of cave formations...... 52
34. Hatchet Bay Cave on Eleuthera Island has large passages that interconnect...... 53
35. View of one flank margin caves found at The Cliffs, Eleuthera, Bahamas... 54
36. View looking out from a cave at The Cliffs, Eleuthera, Bahamas ...... 55
37. Entrance to Henry Morgan’s Cave, North Andros, Bahamas...... 56
38. Map of Closet Cave, a small flank margin cave on San Salvador Island ...... 58
39. Map of Dance Hall Cave, a medium size cave, San Salvador Island ...... 58
40. Map of Cartwright Cave, a medium size cave, Long Island...... 60
41. Map of Bat Cave, a medium size cave, New Providence Island ...... 60
42. Map of The Cliffs, Eleuthera ...... 61
43. Map of Hatchet Bay Cave, a large cave, Eleuthera ...... 61
44. Map of Cat Island...... 70
45. Map of Eleuthera Island...... 70
46. Map of Great Inagua Island ...... 71
47. Map of Long Island...... 71
48. Map of New Providence Island...... 72
49. Map of Andros Island, including North and South Andros...... 72
50. Map of San Salvador Island...... 73
51. AMCS standard cave symbology ...... 75
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FIGURE Page
52. Map of Altar Cave, San Salvador Island ...... 76
53. Map of Archways Cave, South Andros Island...... 76
54. Map of Bahamas West Cave, New Providence Island ...... 77
55. Map of Beach Cave, San Salvador Island...... 77
56. Map of Benzie Hill North Cave, Long Island...... 78
57. Map of Benzie Hill South Cave, Long Island...... 78
58. Map of Blowhole Cave, San Salvador Island ...... 79
59. Map of Bluff Cave, Cat Island...... 79
60. Map of Brackish Well Cave, Cat Island ...... 80
61. Map of Bug City Cave, San Salvador Island...... 80
62. Map of Captain Morgan’s Cave, North Andros Island...... 81
63. Map of Cave Point East Cave, New Providence Island...... 81
64. Map of Cave Point West Cave, New Providence Island ...... 82
65. Map of Chinese Firedrill Cave, San Salvador Island...... 82
66. Map of Clifton East Cave, New Providence Island ...... 83
67. Map of Cluster Caves, South Andros Island...... 83
68. Map of Crab Cay Cave, San Salvador Island ...... 84
69. Map of Crescent Top Cave, San Salvador Island ...... 84
70. Map of Crown Cave, Cat Island ...... 85
71. Map of Deep Creek Cave, South Andros...... 85
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FIGURE Page
72. Map of Deep Hole Cave, San Salvador Island ...... 86
73. Map of Dripping Rock Cave, San Salvador Island...... 86
74. Map of Emerald Cave, San Salvador Island ...... 87
75. Map of Garden Cave, San Salvador Island...... 87
76. Map of George Storr’s Cave, San Salvador Island...... 88
77. Map of Granny T’s Cave, San Salvador Island ...... 88
78. Map of Harry Oakes Annex, New Providence Island...... 89
79. Map of Harry Oakes Cave, New Providence Island...... 89
80. Map of Hunts Cave, New Providence...... 90
81. Map of Industrious Hill Cave, Cat Island ...... 90
82. Map of Little Little Creek Cave, South Andros Island...... 91
83. Map of Long Low Cave, North Andros Island...... 91
84. Map of Lucky Day Cave, Great Inagua...... 92
85. Map of Majors Cave, San Salvador Island ...... 92
86. Map of Midget Horror Hole, San Salvador Island...... 93
87. Map of Nugget Cave, Cat Island...... 93
88. Map of Old Bottle Cave, San Salvador Island...... 94
89. Map of Peek-A-Boo Cave, North Andros Island...... 94
90. Map of Pipe Cave, San Salvador Island...... 95
91. Map of Port Howe Sea Cave, Cat Island ...... 95
xi
FIGURE Page
92. Map of Preachers Cave, Eleuthera Island...... 96
93. Map of Rat Bat Cave, Eleuthera Island ...... 96
94. Map of Reckley Hill Pond Maze Cave, San Salvador Island ...... 97
95. Map of Reckley Hill Pond Water Cave, San Salvador Island ...... 97
96. Map of Salt Pond Cave, Long Island...... 98
97. Map of Sliver Cave, San Salvador Island ...... 98
98. Map of South Deep Creek Cave, South Andros Island ...... 99
99. Map of Stella Maris Cave, Long Island...... 99
100. Map of Stepwell Cave, Cat Island ...... 100
101. Map of Strawline Cave, Cat Island...... 100
102. Map of Ten Bay Cave, Eleuthera Island...... 101
103. Map of Whale Creek Cave, Cat Island ...... 101
104. Plot of cave area versus quadrangle area for the caves on Cat Island ...... 103
105. Plot of log area versus log perimeter for caves found on Cat Island ...... 103
106. Plot of cave area versus quadrangle area caves found on Long Island...... 104
107. Plot of log area versus log perimeter caves on Long Island ...... 104
108. Plot of cave area versus quadrangle area caves found on New Providence Island ...... 105
109. Plot of log area versus log perimeter for caves on New Providence Island .. 105
110. Plot of cave area versus quadrangle area for caves found on San Salvador Island...... 106
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FIGURE Page
111. Plot of log area versus log perimeter for the flank margin caves found on San Salvador Island...... 106
112. Plot of cave area versus quadrangle area for the flank margin caves found on South Andros Island ...... 107
113. Plot of log area versus log perimeter for the flank margin caves found on South Andros Island...... 107
xiii
CHAPTER I
INTRODUCTION
The purpose of this thesis is to inventory flank margin caves of the Bahamas, and to examine their development through geometric analysis. Caves in the Bahamas were not initially well recognized by the majority of the scientific community.
Middleton and Waltham (1986) state that cave development in the Bahamas is dominantly below the water-table and sea-level. They also note that major known cave systems can be found in the blue holes, and that the unexplored entrances are found at over 100 m depth on the platform edge. Current research for this thesis shows that many caves are exposed sub-aerially throughout the Bahamas. Also, some of the caves found to date are extensive in length and area, while others are quite small.
Caves of the Bahamas can be found in several small databases. However, these databases do not always discern between cave type. Wilson et al., (1995) used 20 flank margin caves from San Salvador Island in their study. They listed the general dimensions of the caves, and gave a very simplified description. Their paper presented one graph on the cumulative size distribution of these 20 caves, but he presented no further work on flank margin caves.
Caves in this study were divided into groups by size, and general morphology was noted. Also included is a detailed analysis of flank margin cave development throughout the Bahamas as well as cave development on each of the islands studied.
1 2
Included in this inventory are several overland surveys of the land surface above flank margin caves. The data presented in this thesis are a subset of a much larger project involving numerical analysis of flank margin cave morphology. That larger project is proprietary.
CHAPTER II
THE BAHAMAS
Geographic Setting
The Bahama Islands are an archipelago of islands (figure 1) extending 1400 km from the tectonically stable Florida peninsula, to the tectonically active Caribbean Plate boundary near Hispaniola (Carew and Mylroie, 1995a). Bordered to the north by the
Blake Plateau, to the west by the Florida Straits, to the south by Cuba, and to the east by the Bahamas-Blake-Antilles escarpment, the Bahamas can be divided into two generalized topographic provinces. Two large platforms make up the northern Bahamas.
The Little Bahama Bank platform contains, but is not limited to Grand Bahama Island,
Great Abaco Island and Moore’s Island. The Grand Bahama Bank platform includes
Bimini, North Andros, South Andros, New Providence Great Exuma, Eleuthera, Cat
Island, and Long Island and more. Smaller, more isolated platforms, including the islands of San Salvador, Rum Cay, Samana Cay, Crooked Island, Acklins Island,
Mayaguana, Great Inagua (Uchupi et al., 1971; Mullins and Hine, 1989), and other small islands make up the southeastern Bahamas.
3 4
Figure 1. Map of the Bahamas showing each platform, as well as a tectonic boundary (Carew and Mylroie, 1995a).
The Bahama Island chain can also be divided into two climatic provinces (figure
2), with the islands in the north having a positive water budget, and the islands in the south having a negative water budget (Whitaker and Smart, 1997). In total, The Bahamas covers an area of 300,000 km2, however, the archipelago has 125,000 km2 of shallow
platform, 11,404km2 of which is currently sub-aerially exposed islands (Meyerhoff and
Hatten, 1974). The platform and trough morphology of The Bahamas exhibits platform
water depths of 10-15 m, and trough depths of up to 4,000 m (Meyerhoff and Hatten,
1974).
5
Figure 2. Map of the Bahamian archipelago showing the regional variation of rainfall. (Whitaker and Smart, 1997)
Geology and Tectonics
The Bahama Islands are composed of Quaternary carbonate deposits. Bahamian geology is dominantly eolian calcarenites, and reef facies, as well as subtidal, shoal, and beach facies. Four main types of karst features are found in the Bahamas, including karren, depressions, blue holes, and caves. Paleokarst is also found in the Bahamas.
The Bahama Islands have been considered to be tectonically quiescent during the
Late Quaternary, as none of the exposed sediments show signs of deformation (Carew and Mylroie, 1995b). The Bahama banks are currently undergoing both depositional progradation and erosional segmentation (Eberli and Ginsberg, 1987; Mullins and Hine,
6
1990). Although the Bahamas are tectonically quiescent today, there is evidence of active tectonics in the area in the past. It has been calculated that the rate of subsidence in the Bahamas was 1-2 meters per 100 thousand years during the Pliocene and
Pleistocene (Mullins and Lynts, 1977), and again 1-2 meters per 100 thousand years during the Late Pleistocene (Carew and Mylroie, 1995b).
Two main theories exist on the development of the Bahamas. A “graben” hypothesis proposed by Mullins and Lynts (1977) gives an explanation for the current configuration of the Bahamas using the plate tectonics that occurred in the Mesozoic (the opening of the Atlantic). They say the bank and trough pattern is a result of the initial horst and graben pattern that occurred from continental rifting.
The second theory, called the “megabank hypothesis” states that the Bahamas are a segmented remnant of a very large Mesozoic carbonate platform (Meyerhoff and
Hatten, 1974; Sheridan et al., 1981; Ladd and Sheridan, 1987). Vertical failure surfaces associated with mass wasting events do exist (Daugherty et al, 1986; Carew and Mylroie,
1989; Carew et al, 1992), and it has been suggested that in the Tertiary, tectonic activity along the North American/Caribbean plate boundary produced bank segmentation and large scale bank-margin retreat, which would have created the small platforms seen in the southern Bahamas (Freeman-Lynde and Lohmann, 1992; Mullins et al., 1992).
Stratigraphy
A general stratigraphy for the Bahamas was developed largely from the study of the rocks on San Salvador Island; however, data from many other islands were
7 incorporated (Carew and Mylroie, 1995a). Exposed rocks in the Bahamas are all Middle to Late Quaternary in age, with subtidal facies at low elevations, and eolianites found above 6 m. The rock can be divided into several depositional packages, each bounded by an unconformity. Panuska et al. (1999) have divided the stratigraphy into four distinct formations (figure 3).
The oldest exposed rocks are dominantly peloidal/bioclastic eolianites, referred to as the Owl’s Hole Formation (Stowers et al., 1989), which is Pleistocene in age. It is
predicted that the islands with no Owl’s Hole outcrops in fact do contain this unit, but
younger deposits bury it. In places where an Owl’s Hole Formation is found, there is a
terra-rosa paleosol cap, or evidence of the existence of one prior to erosion. This
paleosol indicates a long period of exposure of the formation during a sea level low-
stand. Paleomagnetic analysis has been performed on the paleosols of various islands in
the Bahamas. The signatures of paleomagnetism have been proven useful in the
stratigraphic correlation of the islands, and have recently allowed for the division of the
Owl’s Hole into the upper and lower formations. (Panuska et al., 1999)
8
Figure 3. A physical stratigraphy of the Bahamas (Panuska et al, 1999)
Overlying the Upper Owl’s Hole Formation, and its paleosol cap, is the Grotto
Beach Formation, also Pleistocene in age. The Grotto Beach Formation is a depositional package known to have been deposited during oxygen isotope substage 5e, 132,000 to
119,000 years ago (Chen et al., 1991). Two members make up the Grotto Beach
Formation. The first is a transgressive-phase eolian deposit (containing well developed ooids), known as the French Bay Member, which is found throughout the Bahamas
(Carew and Mylroie, 1995a). The Cockburn Town Member of the Grotto Beach formation includes the subtidal and standstill through regressive phase beach and eolian deposits. Subtidal deposits, including reefs, are up to 4 m above current sea level, and are
9 most often covered by stillstand and regressive phase deposits (Carew and Mylroie,
1995b). All subaerialy-exposed marine deposits found in the Bahamas are categorized as
Cockburn Town Member.
Grotto Beach eolianites are composed dominantly of ooids. Eolianite dunes of this formation reach up to, and sometimes exceed 30 m in height. It is known that these ridges develop close to their source (the submerged platform), adjacent to beaches. Many researchers have traditionally thought that ooid development requires a large platform or bank area; however, ooid development found on the smaller platforms in the Bahamas suggests ooid development is in part due to water temperature and other environmental factors, and that a large platform is not necessary. The Grotto Beach Formation is also capped by a terra-rosa paleosol, although it has been eroded away in several localities.
(Carew and Mylroie, 1995a)
The Rice Bay Formation is Holocene in age. These rocks lie above the unconformity that is represented by the terra-rosa paleosol that overlies the Grotto Beach Formation.
The Rice Bay Formation is divided into two members, the North Point Member, and the
Hannah Bay member, according to differences in bedding character, allochem composition, and position according to current sea level (Carew and Mylroie, 1995a).
Transgressive phase eolianites of the Rice Bay formation have steeply dipping foreset beds, and characteristically have their base at least 2 m below current sea level. These eolianites are considered North Point Member. This unit is found to outcrop on many of
The Bahama Islands (Carew and Mylroie, 1995a). The Hannah Bay Member of the Rice
Bay Formation consists of still-stand beach and eolian facies. Hannah Bay deposits were
10 emplaced during the current sea level stand, and are found at the same elevation as modern beaches. It is predicted that these rocks are found on all Bahama Islands (Carew and Mylroie, 1995a).
Other Bahama researchers such as Hearty and Kindler (1994) use different methods to delineate stratigraphy than used by Carew and Mylroie (1995a). A stratigraphy of San Salvador Island (figure 4), created by Hearty and Kindler (1995), concurs with their previous research on eight other Bahamian islands. Work done by
Hearty and Kindler (1995) on Eleuthera Island and on San Salvador (1993) involved amino acid racemization to date the rock layers. An amino acid racemization study done on Cerion shells from San Salvador Island (Mirecki et al, 1993) have shown the results of
Hearty and Kindler’s dating techniques to be in question as it is not possible to correlate amino acid dates with sea level history. More recently, Purcell and Oches (2000) have reported that whole rock amino acid racemization can be used to support stratigraphy determined by physical relationships, but it is not reliable on its own.
Hearty and Kindler agree with Carew and Mylroie about the presence of one
Holocene Formation. However, Hearty and Kindler (1995) have divided the
Pleistocene’s Grotto Beach Formation (into the Almgreen Cay Formation and the underlying Grotto Beach Formation) based solely on the amino acid racemization relationships, as such a distinction cannot be shown in the field (Panuska et al, 2002).
Although Hearty and Kindler (1995) are comfortable with their amino acid racemization results, they do not have stratigraphic field evidence to back up all of their claims as do
Carew and Mylroie (1995a).
11
In a less controversial manner, Hearty and Kindler (1995), have documented outcrops on Eleuthera Island that have had a significant impact on the interpretations of other Bahamian stratigraphy researchers. They have shown, through field succession, that Eleuthera contains multiple units older than 5e. However, due to the solid field evidence, rather than uncertain lab techniques, the stratigraphy of Carew and Mylroie
(1995a) will be referred to when discussing Bahamian geology.
Figure 4. A physical stratigraphy of San Salvador and other Bahamian Islands as developed by Hearty and Kindler (1994).
12
Hydrology
Carbonate islands have a fresh-water lens, the top of which is the water table.
This lens-shaped body of fresh water floats on the underlying marine groundwater due to density contrast (figure 5). This lens is controlled by the permeability of the rock and the amount of recharge from meteoric sources. The more permeable the rock, the thinner the fresh-water lens becomes. In an ideal island setting, the fresh-water lens is thickest in the center of the island, and pinches out at the edge of the island (Raeisi and Mylroie, 1995).
Figure 5. Representation of a fresh-water lens on a carbonate island showing the hydrologic environments from the land surface to the saline groundwater (Mylroie and Carew, 1995).
On carbonate islands, portions of the fresh-water lens have been at various positions in relation to the rock units over time. These positions include the vadose-
13 phreatic transition zone (at the top of the fresh-water lens), within the fresh-water lens, and at the halocline (mixing zone) at the base of the fresh-water lens where the lens meets the underlying marine water. If the base of the freshwater lens has a very sharp transition to the marine water below, it is called a halocline. A mixing zone is present when there is a substantial boundary of brackish water between the fresh-water and marine water, up to several meters thick. The vadose-phreatic zone and the fresh-water/salt-water mixing zone are both extremely aggressive dissolutional environments for the carbonate material
(Mylroie and Carew, 1995). Dissolutional aggressiveness is due to the mixing water chemistries, as well as decay of organic material trapped at the top and bottom of the lens.
Carbonate island morphology is greatly affected by changes in sea level. Island groups such as the Bahamas express many indications of eustacy. Migration of the fresh- water lens (as well as the dissolutionally-aggressive zones) occurs due to fluctuations in sea level. Deposition of the carbonate material occurs during sea level high-stands, when the platform tops are partially or totally submerged. When sea level is low enough to allow for subaerial exposure of some or all of the carbonate material, karst processes that result from meteoric dissolution occur (Mylroie et al., 1995). Vadose dissolution occurs at the surface as well as in the rock down to the water table. Below the water table, phreatic dissolutional processes occur.
Dissolution characteristics on tectonically active carbonate islands such as the
Mariana Islands in the Pacific are much more complex than tectonically stable islands
14 such as the Bahamas, due to eustatic sea level fluctuation, uplift/subsidence, and the presence of allogenic materials.
At the current sea-level position, the dune and swale topography of the Bahama
Islands often causes a partitioning of the fresh-water lens within the arid islands of the southeastern Bahamas (figure 2). Many dune ridges found on the southern Bahama
Islands are a source of small fresh water lenses, with the majority of the fresh water following the axis of the ridge. In the wetter climate of the northern Bahamas, the freshwater lens exists across the entire island.
Many of the creeks found in the Bahama Islands are tidal channels rather than fresh-water streams, such as Pigeon Creek on San Salvador Island. However, the islands with a positive water budget may have some fresh-water streams such as Deep Creek and
Little Creek on South Andros, which behave like estuaries. The northern islands contain fresh-water lakes, and the southeastern islands contain marine and or hypersaline bodies of water (Carew et al., 1998).
CHAPTER III
ISLAND KARST
Karst geology on modern carbonate islands is unique due to the extensive interaction between fresh and saline groundwater within young, porous rock, which results in a geologic setting different than that of continental karst (Vacher and Mylroie,
2002). Carbonate island karst development has been explained by use of the carbonate island karst model (Mylroie et al., 2001). Karst features found on carbonate islands include karren, depressions, blue holes, and caves. Several types of caves are found on carbonate islands, including caves found in blue holes, pit caves, banana holes, lake drains, fracture caves, and flank margin caves. Blue holes and other cave types are easily divided into several sub-categories, according to their mode of development.
Carbonate Island Karst Model
The carbonate island karst model (CIKM) is a model used to describe the distinctive karst features found on carbonate islands (figure 6). The CIKM model was developed using examples from the Bahama Islands, Bermuda and Caribbean (Mylroie and Carew, 1995). More recently, the CIKM has been applied to fieldwork done on the
Mariana Islands in the Pacific (e.g. Mylroie et al., 2001; Mylroie et al., 2004).
15 16
Figure 6. The four major carbonate island types, each with distinctive karst features (Mylroie et al., 2004).
17
Five basic ideas are the foundation for the CIKM model:
1. The fresh-water/ salt-water boundary allows for mixing dissolution. The fresh-water lens allows for organic-trapping horizons at its upper and lower boundaries.
2. Glacioeustacy has forced the fresh-water lens to migrate vertically through time. (It has moved over 100 m in the Quaternary.)
3. Local tectonics can overprint the glacioeustatic sea-level fluctuations, creating a more complex record.
4. The karst is eogenetic, having developed in young carbonate rock that has never been buried below the range of meteoric diagenesis.
5. The CIKM presents four general situations for geomorphic modeling of individual carbonate islands. The classifications are dependent on geologic basement and sea level relationships.
a. Simple carbonate island b. Carbonate cover island c. Composite island d. Complex island
There are four basic types of carbonate islands as presented by the CIKM, each of which is classified based on geomorphology and structure. Simple carbonate islands consist of only carbonate rocks at the surface, to a depth below the fresh-water lens.
Carbonate cover islands have a carbonate cap, with non-carbonate basement rocks that extend above sea level, partitioning the lens. Composite islands have both carbonate and non-carbonate rocks exposed at the surface, causing the fresh-water to be directed into what could possibly be several fresh-water lenses where the carbonate rocks are present.
Complex carbonate islands have both carbonate and non-carbonate rocks exposed at the
18 surface, but are called complex due to a variety of structural and facies features that may exist and interact with the lens.
Considered to be a classic model for carbonate deposition, the Bahamas provide a modern example of older depositional environments. According to the carbonate island karst model (CIKM), the Bahama Islands represent a “simple carbonate island” model.
Thus, there are no non-carbonate rocks that affect the geology and hydrology of the islands.
Karren
Karren is described as dissolutional sculpture that occurs from dissolution by meteoric waters on limestone in karst areas. They range from millimeter to meter scale, and are commonly separated by sharp ridges (Jackson and Bates, 1997). Karren are small-scale dissolutional etchings on bedrock or soil covered bedrock that grades down into the epikarst (Mylroie and Carew, 1995). Viles (1988) explains that on exposed rock surfaces, the etching is sharp and jagged, but under soil surfaces, it is smooth and curvilinear. She also explains that coastal karren is formed dominantly by sea spray, rather than biological activity. Karren of carbonate islands is distinct from that of other settings (Taborosi et al., in press). They explain that the diagenetic condition of the host rock is the singlemost important factor in karren formation, with lithology, physiochemical and biological processes, and environmental setting taking only minor roles in karren development. The dominantly eogenetic character of the young carbonate island rocks favors the development of highly irregular and composite karren. Also, the
19 diagenetically mature rocks that may be found locally on some islands exhibit karren features that are more typical of continental settings. (Taborosi et al., in press)
Depressions
Large, closed depressions are constructional, and originated as swales between dune ridges and as lagoonal basins. Some of these depressions are below sea level, and in the southeast Bahamas, because of climatic conditions, have saline and hypersaline lakes, and they may be tidally influenced through caves that link them to the sea.
Blue Holes
Blue holes are polygenetic in origin, and are described as “subsurface voids that are developed in carbonate banks and islands; are open to the earth’s surface; contain tidally influenced waters of fresh, marine, or mixed chemistry; extend below sea level for a majority of their depth; and may provide access to submerged cave passages” (Mylroie et al., 1995, p. 225). The name “blue hole” was given to these features because of the blue color of the water they contain. Blue holes form by the drowning of surface and vadose karst features (eg./ sinkholes), phreatic dissolution along the halocline, collapse of deep-seated dissolution voids or conduits, or by fracture associated with bank margin failure (or a combination of these processes). “There are two general types of blue holes.
Ocean holes contain only marine water, are tidally influenced, and are open directly into the ocean, or a lagoon by way of a cave passage or cave passages. Inland blue holes generally have fresh surface water overlying marine waters, separated by a halocline.
20
They are open to the land surface or an isolated body of water such as a pond or lake, and may be tidally influenced.” (Mylroie et al., 1995, p. 225)
Figure 7. Model of a carbonate island showing the relative locations of various karst features (Mylroie and Carew, 1995).
Pit Caves
Pit caves formed as a result of dissolution by meteoric water by collecting in the
epikarst after descending through the vadose zone (Pace et al. 1993; Mylroie and Carew,
1995; Mylroie et al, 1995). They are found in Pleistocene eolianite ridges. With a width
to depth ratio of less than one, these caves rarely penetrate through to the fresh-water lens
(figure 7). Pit caves are often found to descend in a stair-step fashion, and/or have small
lateral chambers. (Mylroie and Carew, 1995)
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Banana Holes
Banana holes (figure 7) are characteristically isolated sinkholes produced by the collapse of shallow phreatic chambers that developed at the top of a past fresh-water lens
(Harris et al., 1995). They are generally found to have a width to depth ratio greater than one, and at concentrations up to 3,000 per square kilometer. Banana holes are found in a variety of Pleistocene rock, generally at elevations of 2 to 7 m in the Bahamas (Mylroie and Carew, 1995), and are known to have developed during the last interglacial, approximately 125,000 years before present. The name “banana hole” originates from the use of these caves for agricultural purposes such as gardening (Jackson and Bates, 1997).
A more accurate term would be “water-table cave”.
Lake Drains
Lake drains are the cave conduits found in depressions and blue holes that allow for a tidal influence, and the maintenance of normal marine salinity in its respective depression or blue hole (Mylroie and Carew, 1995). The only true conduit feature on these small carbonate islands, they are not well understood (Davis and Johnson, 1989).
Fracture Caves
Fracture caves develop along fractures in the rock. These caves are generally described as long and linear, having been dissolutionally enhanced by the water entering the fracture. The fractures in which these caves develop are generally related to bank- margin failure (Carew et al., 1998).
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Porosity Development
Interpreting how porosity within a carbonate islands changes over time is very important in interpreting the development of flank margin caves. A young or “immature” carbonate island has a very high initial intergranular porosity. Over time, this primary porosity decreases and cementation of the carbonate grains both occur. However, when a fresh water lens first develops on a carbonate island, dissolution and cementation occur.
Cementation is a result of dissolution elsewhere, resulting in the development of small voids, on a millimeter scale, that are interconnected. As bulk porosity decreases, permeability increases (Vacher and Mylroie, 2002). On a meter scale, the voids may begin to loose their nearly circular shape. Finger-like protrusions will develop along the walls of the chamber, likely following paths of higher rates of groundwater flow, or possibly inhomogenieties in the rock (figure 8). These large voids continue to grow and develop. Voids will interconnect with neighboring voids, forming large, semi-linear chambers along the margin of the fresh-water lens.
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Figure 8. Diagram showing void development at a small scale on the left, and at a large scale on the right.
Flank Margin Caves
Flank margin caves develop at the distal margin of the fresh water lens (figure 7)
(around the perimeter of the island). Here, a vadose/ phreatic mixing zone occurs at the top of the fresh water lens, and a marine/ fresh-water mixing zone at the bottom of the fresh-water lens. Carbon dioxide production from the floating organics occurs at both horizons and with severe organic loading, anoxic conditions may develop, further enhancing dissolution (Bottrell et al., 1993). Due to the thinning of the fresh-water lens, these two zones become superimposed, allowing for increased dissolution. Because these caves form at the distal margin of the lens, under the flank of the enclosing landmass, they are called flank margin caves (Mylroie and Carew, 1990). Flank margin caves are
24 hypogenic in origin (Palmer, 1991). Void development is due to mixing, in areas where dissolutionally aggressive waters exist, they develop with no openings to the surface.
Flank margin cave development commonly ignores bedding and structure as it develops parallel to the fresh-water lens. The area of dissolution occurs in a zone that is relative to sea level. These caves, being hypogenic in nature, are not linear conduits, but are chamber-like voids, extended in the horizontal dimension but restricted in the vertical dimension, reflecting the lens geometry at those locations. Flank margin caves that are currently exposed subaerially in The Bahamas are known to have developed during oxygen isotope substage 5e, during the most recent sea level highstand above modern levels (~ +6 m). Cave development is linked to glacioeustatic changes in that the caves develop at the margin of the fresh-water lens, and as glacioeustacy occurs, the fresh- water lens migrates vertically with sea level.
CHAPTER IV
FIELD INVESTIGATION AND METHODOLOGY
This study was performed to develop an inventory, survey, and classify the flank margin caves of the Bahamas. In addition to the inventory, the study involved evaluating cave morphology and development.
Field Investigation
Early winter 2003, an initial site investigation was conducted on the island of
San Salvador. This investigation provided a basic working knowledge of the carbonate island karst environment, including cave location and exploration. Fieldwork was conducted during the summer of 2003, which involved locating and mapping caves on the islands of Eleuthera, Great Inagua, New Providence, North Andros, and San
Salvador. Several land surveys were conducted on the ridges above the caves as to determine the orientation of the flank margin caves in reference to the ridge axis.
All pre-existing maps as well as the newly drafted maps of flank margin caves in the
Bahamas were gathered. These maps were created from caves on eight islands, Cat
Island, Eleuthera, Great Inagua, Long Island, New Providence, North Andros, San
Salvador, and South Andros Island. The number of flank margin caves that have been mapped on each island is as follows: Cat Island has 9 mapped caves, Eleuthera has 3 mapped caves, Long Island has 6 mapped caves, and New Providence has 8. San
25 26
Salvador has 28 known flank margin caves, 23 of which have been mapped and used in this thesis. Great Inagua has 3 flank margin caves, while South Andros has 6 flank margin caves documented and mapped.
The Gerace Research Station is found on San Salvador, thus the large number of flank margin caves known on San Salvador island is likely due to an exploration bias.
Other islands studied for this thesis have not been thoroughly explored, and are likely to contain many more flank margin caves.
Creating Maps
Data from caves surveyed during the summer 2003 field season were reduced using the software package WALLS (McKenzie, 2002). This software effectively plots data collected with a compass, inclinometer, and tape, with corrections for minor loop errors and regional magnetic declination. The resulting line plots were used as a base for drafting spatially accurate maps, either by use of Corel Xara 2.0 (Xara, 1997), or by hand.
Digitizing Maps
Each cave map was digitized and imported into the computer program AutoCAD.
The outline of the cave was traced, giving the initial area and perimeter of the void.
Bedrock columns were traced, giving the area and perimeter of each bedrock column, when several columns were present, their values were added. The total perimeter of each flank margin cave was found by adding the initial cave perimeter with the column perimeter, and the total area was found by subtracting the column area from the initial cave area. Also using AutoCAD, the length and width of the smallest possible
27 quadrangle to fit each cave was calculated. Figure 9 and figure 10 show an example of the resulting AutoCAD images from which all of the data is based.
Figure 9. Map of Benzie Hill North Cave found on Long Island, Bahamas, shows the layers created in AutoCAD that were used to determine the dimensions of the cave.
Figure 10. The AutoCAD figure of Benzie Hill North Cave used in determining the dimensions of the cave. The red line is the outline of the cave, the column is outlined in blue, and the green lines determine the smallest possible quadrangle length and width.
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Data Analysis
The data gathered from digitizing each flank margin cave map was entered into a
Microsoft Excel spreadsheet. In order to more thoroughly investigate the geometric properties of these caves, the log of the total area and total perimeter were calculated.
Also, the square root of the total area, the area to perimeter ratios for both the initial and total data as well as the bedrock columns were also determined. Each cave was ranked by size in relation to the island on which it is found, as well as in relation to all other
Bahamian flank margin caves. Graphs were then created from several dimensional combinations, yielding data on cave development and character.
CHAPTER V
RESULTS
Flank Margin Cave Database
In order to better understand the nature of flank margin cave development and morphology, cave maps must be created and studied. Maps were gathered and analyzed for each of the eight islands studied. Different people and computer programs draft maps in different ways, some are more precise than others. Due to the lack of in-depth studies performed on individual caves, two-dimensional maps are the standard data used in this study for geometric analysis.
All data used were gathered from a digitized version of each map, thus any descrepencies in the data are due either to survey error or drafting error. The assumption was made that all maps were drafted correctly, and that the caves have not been significantly modified by anthropogenic activities.
Flank margin caves in the Bahamas range in size from 14.1 m2 to 8931.3 m2, and the perimeters range from 17.9 m to 2533.9 m. Of the 61 mapped flank margin caves in the
Bahamas, 22 caves have been found to have an area less than 100 m2, 32 caves have an area between 100 m2 and 1000 m2, and 7 caves have an area greater than 1000 m2. The eight islands in the study have only been partially explored for flank margin caves with many more caves likely to exist. Other Bahamian islands are likely to contain flank margin caves as well.
29 30
Cat Island has been found to have 1 small, 6 medium and 2 large documented flank margin caves. Eleuthera Island has 1 known medium sized flank margin cave, and also has 2 of the largest known flank margin caves in the Bahamas. Great Inagua has 3 known medium sized caves, and Long Island has been found to have 2 small, 2 medium, and 2 large flank margin caves. New providence Island, the most populous island in the
Bahamas, has documented 2 small, and 6 medium sized flank margin caves. San
Salvador, an island well studied by students from many universities through the Gerace
Research Center, has a known 11 small, 11 medium, and 1 large flank margin caves.
South Andros has 6 small flank margin caves mapped, and north Andros has 3 medium sized caves mapped. There appears to be no correlation between cave size and island size or island location.
It is known that flank margin caves are hypogenic in origin, and develop by the mixing of freshwater and saltwater at the margin of the freshwater lens on carbonate islands and carbonate coasts. Flank margin caves are theorized to grow as single chambers (with no surface entrance), and at a threshold point, likely dependent on the localized geology and hydrology, adjacent chambers will begin to interconnect. The process of adjacent chambers growing into one another allows for the development of bedrock columns in the caves. If dissolution of the chambers were completely efficient, there would be no columns, just one large open chamber in the subsurface. Because bedrock columns affect the area and perimeter of the cave chamber, they must be taken into account when studying the geometry of the cave. Each column that exists in a cave adds to the perimeter of the cave, but subtracts from the potential area of the cave. As a generalization, the larger caves contain a greater number of bedrock columns. Further
31 area and perimeter is added by the “finger like” protrusions extending in the direction of the fresh-water lens that are characteristic of many flank margin caves. Table 1 expresses the total area and perimeter for each cave in the study.
Figure 11 expresses cave area vs. perimeter for all 61 flank margin caves in the study. As can be seen, the R2 is at 0.67 showing a moderately tight growth trend,
however, when the flank margin caves are divided into their respective islands (figure
12), R2 ranges from 0.71 for San Salvador Island to 0.99 for Long Island. The R2 value is important in the analysis as it gives the fraction of the total variance of x and y as explained by their linear relationship. All trend lines found in this study are a linear autoregressive fit using all of the data in the set unless otherwise stated. They are used to study the first-order trend of the data. Therefore, all y-intercepts are chosen mathematically by the data rather than being generically set at zero, so they are slightly skewed due to an exploration bias.
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Table 1. Flank margin cave geometric data.
Island Name Cave Name Total Total AP Perimeter (m) Area (m^2) Ratio
Cat Island Nugget Cave 69.1 80.3 1.2 Whale Creek Cave 144.1 257.9 1.8 Industrious Cave 195.9 332.3 1.7 Port Howe Sea Cave 153.4 411.6 2.7 Brackish Well Cave 205.6 723.0 3.5 Bluff Cave 222.1 787.1 3.5 Strawline Cave 302.7 923.5 3.1 Stepwell Cave 858.8 2362.5 2.8 Crown Cave 1348.6 3778.5 2.8
Eleuthera Preacher's Cave 86.0 345.5 4.0 Ten Bay 2249.0 5147.0 2.3 Hatchet Bay Cave 1382.8 5934.2 4.3
Great Inagua Maroon Hill Caves 178.9 159.9 0.9 Salt Pond Hill 208.7 209.0 1.0 Lucky Day Cave 113.4 340.4 3.0
Long Island Benzie Hill North 59.6 60.4 1.0 Benzie Hill South 85.2 100.0 1.2 Cartwright Cave 150.3 260.1 1.7 Stella Maris cave 117.7 277.8 2.4 Salt Pond Cave 1083.0 3900.8 3.6 Hamilton's Cave 2082.9 8931.3 4.3
New Providence Clifton East Cave 36.8 32.3 0.9 Harry Oakes Annex Cave 89.3 85.7 1.0 Cave Point East Cave 79.4 289.3 3.6 Cave Point West 145.2 359.0 2.5 Bahamas West Cave 328.3 477.5 1.5 Bat Cave 344.6 482.4 1.4 Hunts Cave 462.5 547.5 1.2 Harry Oakes Cave 266.7 573.6 2.2
North Andros Peek-a-boo Cave 23.6 21.5 0.9 Long Low Cave 74.0 343.7 4.6 Henry Morgan's Cave 161.4 563.1 3.5
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Table 1 continued.
Island Name Cave Name Total Total AP Perimeter (m) Area (m^2) Ratio
San Salvador Granny T's 17.9 14.1 0.8 Closet Cave 24.7 17.5 0.7 Pipe Cave 46.1 29.5 0.6 Reckley Hill Pond Maze Cave 93.5 31.3 0.3 Old Bottle Cave 57.9 37.0 0.6 Midget Horror Hole 66.7 39.6 0.6 Chinese Firedrill Cave 91.0 43.4 0.5 Emerald Cave 55.6 56.5 1.0 Bug City Cave 98.3 63.9 0.7 Blowhole Cave 74.2 92.1 1.2 Deep Hole Cave 74.5 96.4 1.3 Crescent Top Cave 171.9 116.4 0.7 Reckley Hill Pond Water Cave 61.6 136.6 2.2 Dance Hall 179.5 146.4 0.8 Crab Cay Cave 97.1 156.9 1.6 Major's Cave 82.5 216.8 2.6 Sliver Cave 77.1 289.2 3.8 George Storr's Cave 121.5 324.2 2.7 Garden Cave 520.3 530.9 1.0 Dripping Rock 105.0 549.0 5.2 Beach Cave 350.1 620.0 1.8 Altar Cave 165.5 638.5 3.9 Lighthouse Cave 2533.9 1377.6 0.5
South Andros Archways Cave 32.0 22.0 0.7 Little Little Creek 47.0 30.5 0.6 Deep Creek 77.0 57.1 0.7 South Deep Creek 76.7 95.6 1.2 Cluster Caves 108.8 94.4 0.9 Rat Bat Cave 218.7 902.0 4.1
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Figure 11. Cave area plotted against cave perimeter for all flank margin caves in the Bahamas. There appears to be many more small and medium sized caves than large caves in the Bahamas.
Figure 12. Cave area plotted against cave perimeter for flank margin caves, divided into individual islands.
35
When examining the square root of the area plotted against perimeter (to allow
expressing the data as a dimensionless ratio) for all caves (figure 13), there appears to be
only one significant outlier cave, Lighthouse Cave on San Salvador Island. The remainder of the caves appears to group together and form a semi-straight line correlation. The log of the cave area was plotted against the log of cave perimeter to display the data in a concise manner (figure 14). A tight R2 of 0.80 correlates all
Bahamian flank margin caves, and shows that there are no outlier caves in regards to the
overall trend of area and perimeter growth.
Figure 13. The square root of the cave area plotted against the perimeter of the cave.
36
When all of the Bahama flank margin caves are ranked in order by size (table 2),
and plotted on a graph of cave area vs. rank number (figure 15), a line with several slopes
appears. Three best-fit lines were placed on the data, expressing three very distinct
slopes. The first line placed closest to the origin, represents small flank margin caves.
These are all caves of less than 100 m2. The R2 of the line is 0.96, a very tight fit, and the
slope of the line is 4.47 (figure 16). Medium sized flank margin caves were concluded to be between 100 m2 and 1000 m2. The medium sized caves have an R2 of 0.93, and a slope
of 22.73, greater than the square of the slope of the small caves (figure 17). Large flank
margin caves (figure 18) express an R2 of 0.93, and a slope of 1113.3, more than two
times the square of the slope expressed by medium sized caves. Large caves were
concluded to all have areas greater than 1000 m2.
These data reflect how dissolution in the distal margin of the fresh-water lens is
distributed. Large caves developed where lens characteristics allowed for rapid
dissolution of the chambers, and consequently, interconnection of neighboring chambers.
Smaller caves were allowed the same time frame for development as larger caves, thus
smaller caves were not loctaed in areas where the lens and saline waters were interacting
so aggressively. Rapid growth may reflect the nature of the touching-vug porosity
system within the portion of the lens where large caves exist.
37
Table 2. Flank margin caves of the Bahamas ranked by increase in area.
Cave Name Island Name Size Rank Area (m2)
Small Granny T's San Salvador 1 14.1 Caves Closet Cave San Salvador 2 17.5 Peek-a-boo Cave North Andros 3 21.5 Archways Cave South Andros 4 22.0 Pipe Cave San Salvador 5 29.5 Little Little Creek Cave South Andros 6 30.5 Reckley Hill Pond Maze Cave San Salvador 7 31.3 Clifton East Cave San Salvador 8 32.3 Old Bottle Cave San Salvador 9 37.0 Midget Horror Hole San Salvador 10 39.6 Chinese Firedrill Cave San Salvador 11 43.4 Emerald Cave San Salvador 12 56.5 Deep Creek Cave South Andros 13 57.1 Benzie Hill North Long Island 14 60.4 Bug City Cave San Salvador 15 63.9 Nugget Cave Cat Island 16 80.3 Harry Oakes Annex Cave New Providence 17 85.7 Blowhole Cave San Salvador 18 92.1 Cluster Caves South Andros 19 94.4 South Deep Creek Cave South Andros 20 95.6 Deep Hole Cave San Salvador 21 96.4 Benzie Hill South Long Island 22 100.0
38
Table 2 continued.
Medium Caves Crescent Top Cave San Salvador 23 116.4 Reckley Hill Pond Water Cave San Salvador 24 136.6 Dance Hall Cave San Salvador 25 146.4 Crab Cay Cave San Salvador 26 156.9 Maroon Hill Caves` Great Inagua 27 159.9 Salt Pond Hill Great Inagua 28 209.0 Majors Cave San Salvador 29 216.8 Whale Creek Cave Cat Island 30 257.9 Cartwright Cave Long Island 31 260.1 Stella Maris Cave Long Island 32 277.8 Sliver Cave San Salvador 33 289.2 Cave Point East Cave New Providence 34 289.3 George Storrs Cave San Salvador 35 324.2 Industrious Cave Cat Island 36 332.3 Lucky Day Cave Great Inagua 37 340.4 Long Low Cave North Andros 38 343.7 Preacher's Cave Eleuthera 39 345.5 Cave Point West New Providence 40 359.0 Port Howe Sea Cave Cat Island 41 411.6 Bahamas West Cave New Providence 42 477.5 Bat Cave New Providence 43 482.4 Garden Cave San Salvador 44 530.9 Hunts Cave New Providence 45 547.5 Dripping Rock Cave San Salvador 46 549.0 Henry Morgan's Cave North Andros 47 563.1 Harry Oakes Cave New Providence 48 573.6 Beach Cave San Salvador 49 620.0 Altar Cave San Salvador 50 638.5 Brackish Well Cave Cat Island 51 723.0 Bluff Cave Cat Island 52 787.1 Rat Bat Cave South Andros 53 902.0 Strawline Cave Cat Island 54 923.5
Large Caves Lighthouse Cave San Salvador 55 1377.6 Stepwell Cave Cat Island 56 2362.5 Crown Cave Cat Island 57 3778.5 Salt Pond Cave Long Island 58 3900.8 Ten bay Cave Eleuthera 59 5147.0 Hatchet Bay Cave Eleuthera 60 5934.2 Hamiltons Cave Long Island 61 8931.3
39
Figure 14. Plot of the log of the cave area plotted against the log of the perimeter. It can be seen that there are no true “outlier” caves in regards to area and perimeter growth trends.
Figure 15. All 61 flank margin caves in the database have been ranked in order by size and placed on this plot of cave area versus rank number. Three distinct slopes can be distinguished from this graph.
40
Figure 16. Plot of cave area versus rank number for small flank margin caves. The linear trendline has a very tight fit to all of the data points, and the small slope of 4.47.
Figure 17. Plot of cave area versus rank number for medium sized flank margin caves. The linear trendline has a very tight fit to all of the data points, and has a slope of 22.73.
41
Figure 18. Plot of cave area versus rank number for large flank margin caves. The linear trendline has a very tight fit to all of the data points, and has a slope of 1113.30.
Flank margin caves act similar to simple shapes such as a circle, square, or rectangle in the sense that they increase in area with an increase in perimeter (figure 19).
Circles, squares, and simple rectangles are most efficient, respectively in gaining area with increases in perimeter. Figure 20 shows the area and perimeter of flank margin caves plotted on the same axes as several rectangles with various length to width ratios.
No flank margin caves of large size (> 1000 m2) have perimeters less than 600 m.
As can be seen in figure 21, the majority of small flank margin caves have a growth characteristic between that of a rectangle with a ratio of 1 to 10, and a rectangle with a ratio of 1 to 100. Figure 22 shows that most medium sized flank margin caves also have a growth characteristic between that of a rectangle with a ratio of 1 to 10, and a rectangle with a ratio of 1 to 100. Large flank margin caves, as seen by figure 23, have
42 growth characteristics similar to a rectangle with a ratio of 1 to 100, and greater. The caves thus appear to increase in perimeter much more rapidly than they do in regards to size area.
A circle, being the most efficient simple shape in increasing area with perimeter, increases much more rapidly in area than does the shape of flank margin caves. All caves studied show a remarkable similarity in growth trend to extended rectangles with large ratios. Due to the complex wall morphology of flank margin caves, perimeter increases at a much higher rate than does the area within the cave. In general, large caves have a larger area to perimeter ratio than do small caves. The joining of adjacent chambers as caves grow in size creates the increase in complexity. The caves, however, do not appear to develop with a ratio of 1 to 100 or any similar ratio for cave length versus cave width.
Measurements of length versus width for the caves in the study have ratios of 1 to 1.1 through 1 to 5.4, with an average ratio of 1 to 2.3.
The reason for the flank margin caves to plot where they do on figures 20, 21, 22, and 23 is that they have a complex wall structure. Even though the perimeter is measured by linear distance and area by distance squared, increasing cave area requires including the perimeter of adjacent voids. Thus, the perimeter complexity makes up for the linear versus square difference.
43
Figure 19. Plot of area versus perimeter for simple geometric shapes.
Figure 20. Plot of area versus perimeter for simple shapes, as well as all flank margin caves of the Bahamas.
44
Figure 21. Plot of area versus perimeter for simple shapes as well as all flank margin caves with an area of less than 100 m2. All of the caves shown on this graph appear to have an area to perimeter relationship between a rectangle with a width to length ratio of 1/2, and a width to length ratio of 1/100.
Figure 22. Plot of area versus perimeter for simple shapes as well as all flank margin caves with an area between 100 m2, and 1000 m2. It is clear that the majority of caves this size have an area to perimeter relationship between that of a rectangle with a width to length ratio of 1/10 and 1/100
45
Figure 23. Plot of area versus perimeter for simple shapes as well as flank margin caves with an area greater than 1000 m2. The caves presented on this graph have an area to perimeter relationship similar to that of a rectangle with a width to length ratio of 1/100 or a rectangle of an even higher ratio.
Quadrangle length was plotted against quadrangle width (figure 24). Length was shown to increase at a much greater rate than width. This proves that adjacent chambers interconnect along the distal margin of the lens. Larger flank margin caves are known to be linear rather than globular in shape. When cave area is plotted along with quadrangle area (figure 25), there is a strong trend (R2= 0.93) in the growth pattern. A graph of
quadrangle length to width ratio plotted against cave area was created (figure 26), which
shows no clear pattern. However, despite the similarity of the flank margin cave plots in
figures 20, 21, 22 and 23, to that of a rectangle with a width to length ratio similar to a
rectangle with a ratio of 1 to 100, the caves do not look anything like an extended
rectangle. As shown in figure 102, the length to width ratios of flank margin caves rarely
exceeds 5, thus perimeter complexity is not gained by extension, but by convolution of
the perimeter as the cave grows larger.
46
Figure 24. Plot of quadrangle length versus quadrangle width for the smallest theoretical quadrangle that each cave can fit in.
Figure 25. Plot of quadrangle area versus cave area.
47
Figure 26. Plot of quadrangle length to width ratio versus cave area.
Figure 27. Plot of cave area versus cave area divided by quadrangle area.
48
Cave area divided by the quadrangle area creates a decimal expressing how efficiently the cave fills the smallest fitting quadrangle. When cave area divided by quadrangle area is plotted against cave area on a graph (figure 27), it is seen that the majority of small and medium sized caves (< 1000 m2) fill 30 to 75% of the best-fit
quadrangle. Large caves however, are generally less efficient, filling 20 to 42% of the
best-fit quadrangle. Thus, as a cave becomes large in size (> 1000 m2), the bedrock
columns, and deviation from a standard shape (such as a quadrangle) to a more complex
shape becomes more severe, the cave will fill its quadrangle less efficiently.
Land surveys done on top of two of the largest flank margin caves in the Bahamas,
and two medium-sized cave were performed. The cave map was placed on a topographic
map (or a map expressing the ridge orientation) created by the land survey. Orientation
of each cave in relation to the ridges in which they developed was examined.
Development of the void in relation to the ridge axis can be seen on medium sized caves
such as Maroon Hill (figure 28), and Salt Pond Hill (figure 29), both found on Great
Inagua. Large caves express continuity of the cave development along the ridge as can
be seen at Hatchet Bay, Eleuthera (figure 30) where the cave trends between the edge of the dune, and the dune axis. The map of Lighthouse Cave on San Salvador (figure 31)
shows that the majority of the cave is found beneath the contours representing 5 and 10
meters above mean sea level. Lighthouse cave apprears to mirror the curves in the
contour lines as well.
49
Figure 28. Map of Maroon Hill Caves found on Great Inagua Island, Bahamas. A land survey was conducted above this cave to distinguish where the cave developed in relation to the ridge axis. As can be seen here, the cave has an orientation parallel to the ridge axis.
Figure 29. Map of Salt Pond Hill Cave found on Great Inagua Island, Bahamas. A land survey was conducted above this cave to distinguish where the cave developed in relation to the ridge axis. As can be seen here, the long axis of the cave is parallel to the long axis of the ridge.
50
Figure 30. Map of Hatchet Bay Cave found on Eleuthera Island, Bahamas.
Figure 31. Map of Lighthouse Cave found on San Salvador Island, Bahamas. A land survey was conducted over the cave to determine the cave development in relation to the ridge axis. Where the topographic contours curve, the cave curves as well. (Modified from Daugherty et al., 1986).
CHAPTER VI
DISCUSSION
Flank Margin Cave Geometric Analysis
Flank margin cave development was first studied in depth in the Bahamas. In recent years however, caves on Isla de Mona, Puerto Rico, and in the Commonwealth of the
Northern Marianas have become important to the study of carbonate island geology by increasing the understanding of void development.
Understanding growth characteristics of flank margin caves is an important aspect of geologic research in regard to carbonate islands and coasts. Void development deals directly with the hydrology and geology of the island, and may potentially be hazardous to life on the island (Wilson et al., 1995) if a collapse were to occur. It is known that flank margin caves develop by hypogenic (mixing chamber) processes rather than epigenic (flow-through) processes due to the morphology of the caves. Each cave chamber develops with no entrances, as they develop by mixing dissolution in the subsurface. All passages end abruptly in bedrock walls (figure 32) and are generally unrelated to the bedding and structure of the rock. Epigenic caves, otherwise known as stream caves, found most commonly on continental settings, develop through recharge from surface waters, and dissolve by stream flow in the subsurface. Stream caves are often dendritic in pattern, or follow structure in the rock such as many surface streams.
They discharge back to the surface as point sources, or springs.
51 52
Figure 32. Flank margin cave passages end abruptly in bedrock walls.
Similar to stream caves, flank margin caves often contain large volumes of formations such as stalactites, stalagmites and flowstone (figure 33). Because formations are unrelated to the development of the void, they were not included in this study.
Bedrock columns are very important to the geometric analysis of flank margin caves, in that they are original rock material that was not removed in the development of the voids.
Often larger flank margin caves contain more bedrock columns than smaller caves due to the joining of adjacent chambers during cave development (figure 34).
Figure 33. Hatchet Bay Cave on Eleuthera Island, Bahamas, has significant development of stalagmites and other cave formations.
53
Figure 34. Hatchet Bay Cave on Eleuthera Island has large passages that interconnect with one another.
Flank margin cave development occurs at the distal margin of the freshwater lens where mixing with saline waters can occur. Thus, many subaerially exposed flank margin caves in the Bahamas can be found partially eroded along coastal cliff facies
(figures 35 & 36). Caves that are currently exposed at the surface developed during a previous sea level high-stand (oxygen isotope substage 5e), and are also found inland under the eolianite ridges on the islands (figure 37).
54
Figure 35. This is a view of one of the flank margin caves found along The Cliffs, on Eleuthera Island, Bahamas.
Attempting to develop an initial understanding of cave development includes making assumptions that the geology, geochemistry and hydrology of each island in the study were similar at the time of cave development. One cave in this study, Lighthouse
Cave on San Salvador Island (figure 31) is known to still have tidal fluctuations within the void. The majority of the caves in the study are currently dry, with no interactions with current sea level.
55
Figure 36. This view is looking out from a flank margin cave at The Cliffs on Eleuthera Island, Bahamas.
Exploration bias is also important to note when interpreting the results of the geometric analysis. Some islands, such as San Salvador and Eleuthera have been studied significantly more than others, such as Cat Island and Great Inagua in regards to flank margin caves. Also important is that the caves in the database are the known caves in the
Bahamas. There are significantly more medium and small caves than large caves in the database. Because these voids develop with no surface entrance, the study is dependant on erosional processes to open the caves and allow for human entrance and study. In all probability, many more small and medium sized caves occur in the Bahamas, because larger caves require much more dissolution and joining of smaller caves. Thus, it is more likely that small and medium caves will be found due to the larger numbers that are likely to exist.
56
Figure 37. Flank margin caves are not only found along island coastlines, but in thick jungle as well as can be seen at the entrance to Henry Morgan’s Cave on North Andros Island, Bahamas.
When a flank margin cave develops, it begins as a small void, developed as secondary porosity at the margin of the fresh-water lens. Initially, on the small scale, void development is predicted to be nearly circular, with an increasingly complex perimeter as growth continues. The vadose/phreatic mixing zone at the top of the fresh water lens and the fresh-water mixing zone at the bottom of the fresh water lens, where the lens thins near carbonate island coasts, there are zones of enhanced dissolution, causing the void to grow at a greater rate than karst features found in areas where no mixing occurring
(Bottrell et al., 1993). As the void continues to grow, chambers will enlarge and develop a more complex perimeter than a simple circle. Closet Cave, San Salvador is an example of a small flank margin cave (figure 38). As the void continues to enlarge, protrusions will develop on the inland side of the original chamber, following discontinuities in the rock. Dance Hall Cave on San Salvador Island is an example of a medium size cave
(figure 39). A further increase in cave size allows for adjacent chambers in the rock
57 begin to interconnect, as can be seen by the medium sized caves, Cartwright Cave (figure
40) found on Long Island, and Bat Cave (figure 41) on New Providence Island, eventually creating one large cave from several small or medium size cave chambers.
As adjacent chambers interconnect, a flank margin cave is likely to have increased numbers of bedrock columns within due to the incomplete efficiency in the chamber connection process. To determine the efficiency in which flank margin caves develop, a method of placing the smallest quadrangle that could be placed around each cave was developed. In each case, the caves were significantly smaller in area than the quadrangle in which they fit. In other words, initial flank margin growth is by enlargement of cave chambers by absorbing adjacent touching-vug porosity, as area vs. perimeter plot (figure
11) indicates. This creates a cave with a high cave/quadrangle ratio. But as the chambers get larger, they intersect adjacent caves. If the intersecting caves are not of equal size, the quadrangle to enclose the joined pair needs to be bigger in area than the sum of the separate quadrangle areas that could enclose each cave. Therefore, the cave divided by quadrangle ratio decreases as overall cave area increases.
58
Figure 38. Map of Closet Cave, a small flank margin cave found on San Salvador Island, Bahamas (Vogel, 1992)
Figure 39. Map of Dance Hall Cave found on San Salvador Island, Bahamas (Vogel, 1992)
59
Examination of flank margin cave development in relation to the ridge in which they develop yields data showing that the caves develop parallel to the ridge axis, on the flank of the ridge. This location of development is due to the position of the fresh-water lens during the sea level high stand (oxygen isotope substage 5e) in which cave development was actively occurring. Because these caves are mixing chambers, where fresh water and salt water interact, they develop with no entrances, and the caves are now known only because of later erosion and collapse of portions of the ridges. As can be seen by The
Cliffs (figure 42), found on Eleuthera Island, when flank margin caves develop near a coastline, they are breached, and appear to create a series of coves. Flank margin caves are not linear conduits, but are large chambers developed due to the joining of adjacent voids. Thus, the flank margin caves included in the land survey portion of the study show that flank margin caves extend horizontally, but are restricted in the vertical dimension, which reflects the freshwater lens geometry during the time of development within the ridge. Large flank margin caves, such as Hatchet Bay Cave on Eleuthera
(figure 43), express the horizontal continuity predicted from the joining of adjacent chambers of smaller caves.
60
Figure 40. Map of Cartwright Cave found on Long Island, Bahamas (Mylroie et al., 1991)
Figure 41. Map of Bat Cave found on New Providence Island, Bahamas (Mylroie et al., 1991)
61
Figure 42. Map of The Cliffs on Eleuthera shows a series of breached flank margin caves along the coastline
Figure 43. Map of Hatchet Bay Cave found on Eleuthera Island, Bahamas
CHAPTER VII
SUMMARY
Flank margin cave maps were created and gathered for the 61 known and mapped flank margin caves in the Bahamas. Their initial areas and perimeters were analyzed as well as the areas and perimeters of the bedrock columns within. The total areas and perimeters were the data utilized most as they represent the true nature of the caves.
Previous studies have gathered some data regarding flank margin cave morphologies, but none to the scale of this thesis.
The data gathered regarding flank margin cave geometry has established that flank margin caves form a unique type of porosity on carbonate platforms. These caves have a unique size and shape relationship that may allow them to be differentiated from voids formed by epigenic or structural processes. Geometric data gathered from the quantitative analysis indicates that large flank margin caves develop by coalescing smaller voids, and that this joining of adjacent chambers occurs preferentially along strike. Bahamian flank margin caves have been found to develop through three distinct size ranges (< 100 m2, 100-1000 m2, and > 1000 m2) by joining of adjacent cave
chambers. When small cave development reaches areas of about 100 m2 neighboring caves are predicted to interconnect to form medium sized caves. When adjacent medium sized caves reach about 1,000 m2, they are predicted to join, forming large caves. The
62 63 small, medium and large size distinctions were chosen at their given designations (< 100 m2, 100-1000 m2, and > 1000 m2) because those numbers are what the data divided itslef.
The strong similarities between the area and perimeter of flank margin caves to
extended rectangles shows that as a flank margin cave enlarges and joins with adjacent
chambers, the perimeter increases at a much faster rate than does the area of the cave.
Rapidly increasing perimeter is accounted for by the joining of adjacent chambers, and
the residual bedrock columns found in the void, as well as the cave development
following discontinuities in the rock due to fresh water/ salt water mixing. Smaller caves
tend to be ovid in shape, however the larger caves extend horizontally, are vertically
restricted and do not penetrate a significant distance into the island lens. Thus, the caves
appear to mimmic the coastline near which they developed.
Small and medium size flank margin caves do not have perimeters as complex as
those of large caves. If a small or medium size cave was placed in a best fit quadrangle,
the cave would fill the majority of the space. Large caves, due to their complex
perimeters (a result of the joining of many smaller caves of irregular shape) fill less than
half of the quadrangle placed around it.
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Hearty, P.J., and Kindler, P., 1993, New perspectives on Bahamian geology; San Salvador Island, Bahamas. Journal of Coastal Research, v.9, iss.2, pp. 577-594.
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Ladd, J.W., and Sheridan, R.E., 1987, Seismic stratigraphy of the Bahamas. American Association of Petroleum Geologists Bulletin, v. 71, p. 719-736.
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Meyerhoff, A.A., and Hatten, C.W., 1974, Bahamas salient of North America; Tectonic framework, stratigraphy, and petroleum potential. American Association of Petroleum Geologists Bulletin, v. 58, p. 1201-1239.
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Middleton, J., and Waltham, T., 1986, The underground atlas: A gazetteer of the world’s cave regions. Robert Hale Limited, London. p. 239.
Mirecki, J.E., Carew, J.L., and Mylroie, J.E., 1993, Precision of amino acid enantiomeric data from fossiliferous late Quaternary units, San Salvador, The Bahamas. In White, B., (ed).,Proceedings of the sixth symposium on the geology of the Bahamas, Bahamian Field Station, San Salvador, Bahamas, p. 95-101.
Mullins, H.T., Breen, N., Dolan, j., Wellner, R.W., Petruccione, J.L., Gaylord, M., Anderson, B., Melillo, A.J., Jurgens, A.D., and Orange, D., 1992, Carbonate platforms along the southeast Bahamas-Hispaniola collision zone. Marine Geology, v. 105, pp. 169-209.
Mullins, H.T., and Hine, A.C., 1989, Scalloped bank margins: Beginning of the end for carbonate platforms?, Geology, v. 17, p. 30-39.
Mullins, H.T., and Lynts, G.W., 1977, Origin of the northwestern Bahama Platform: Review and reinterpretation. Geological Society of America Bulletin, v. 88, p. 1447-1461.
Mylroie, J.E., Jenson. J.W., Taborosi, D., Jocson, J.M.U., Vann, D.T., and Wexel, C., 2001, Karst features of Guam in terms of a general model of carbonate island karst. Journal of Cave and Karst Studies, v. 63, iss.1, pp. 9-22.
Mylroie, J.E., Mylroie, J.R., Jenson, J.W., 2004, Modeling carbonate island karst. In Martin, R., and Panuska, B., (eds.), Proceedings of the Eleventh Symposium on the geology of the Bahamas and other carbonate regions, Gerace Research Center, San Salvador Island, Bahamas. p. 135-144.
Mylroie, J.E., Carew, J.L., Sealey, N.E., and Mylroie, J.R., 1991, Cave development on New Providence Island and Long Island, Bahamas. Cave Science, v. 18, iss. 3, pp. 139-151.
Mylroie, J.E., and Carew, J.L., 1995, Chapter 3, Karst development on carbonate islands, in Budd, D.A., Saller, A., and Harris, P.M., (eds.), Proceedings of the Fifth Symposium on the Geology of the Bahamas. Bahamian Field Station, San Salvador Island, Bahamas, pp. 185-191.
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Mylroie, J.E., Carew, J.L., and Moore, A.I., 1995, Blue Holes: Definition and genesis, Carbonates and Evaporites, v. 10, n. 2, pp. 225-233.
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APPENDIX A
MAPS OF THE ISLANDS
69 70
Figure 44. Map of Cat Island (Modified from Bahamas, Cayman Islands, Cuba, Haiti, Jamaica, Naussa Island Operational Navigation Chart, 1974).
Figure 45. Map of Eleuthera Island (Modified from Bahamas, Cayman Islands, Cuba, Haiti, Jamaica, Naussa Island Operational Navigation Chart, 1974).
71
Figure 46. Map of Great Inagua Island (Modified from Cuba Map, 1992)
Figure 47. Map of Long Island (Modified from Bahamas, Cayman Islands, Cuba, Haiti, Jamaica, Naussa Island Operational Navigation Chart, 1974).
72
Figure 48. Map of New Providence Island (Modified from Bahamas, Cayman Islands, Cuba, Haiti, Jamaica, Naussa Island Operational Navigation Chart, 1974).
Figure 49. Map of Andros Island, showing the difference between North Andros and South Andros (Modified from Bahamas, Cayman Islands, Cuba, Haiti, Jamaica, Naussa Island Operational Navigation Chart, 1974).
73
Figure 50. Map of San Salvador Island (Modified from Bahamas, Cayman Islands, Cuba, Haiti, Jamaica, Naussa Island Operational Navigation Chart, 1974).
APPENDIX B
FLANK MARGIN CAVE MAPS
74 102
Figure 51. AMCS standard cave symbology (Sprouse, 1991)
76
Figure 52. Map of Altar Cave found on San Salvador Island, Bahamas (Daugherty et al., 1986)
Figure 53. Map of Archways Cave found on South Andros Island, Bahamas (Carew et al, 1998)
77
Figure 54. Map of Bahamas West Cave found on New Providence Island, Bahamas (Mylroie et al., 1991)
Figure 55. Map of Beach Cave found on San Salvador Island, Bahamas
78
Figure 56. Map of Benzie Hill North Cave found on Long Island, Bahamas (Mylroie et al., 1991)
Figure 57. Map of Benzie Hill South Cave found on Long Island, Bahamas (Mylroie et al., 1991)
79
Figure 58. Map of Blowhole Cave found on San Salvador Island, Bahamas
Figure 59. Map of Bluff Cave found on Cat Island, Bahamas (Palmer, R.J., 1982)
80
Figure 60. Map of Brackish Well Cave found on Cat Island, Bahamas (Palmer, R.J., 1982)
Figure 61. Map of Bug City Cave found on San Salvador Island, Bahamas (Vogel, 1992)
81
Figure 62. Map of Captain Morgan’s Cave found on North Andros Island, Bahamas
Figure 63. Map of Caves Point East Cave found on New Providence Island, Bahamas (Mylroie et al., 1991)
82
Figure 64. Map of Caves Point West Cave found on New Providence Island, Bahamas (Mylroie et al., 1991)
Figure 65. Map of Chinese Firedrill Cave found on San Salvador Island, Bahamas (Daugherty et al., 1986)
83
Figure 66. Map of Clifton East Cave found on New Providence Island, Bahamas (Mylroie et al., 1991)
Figure 67. Map of Cluster Caves found on South Andros Island, Bahamas (Carew et al, 1998)
84
Figure 68. Map of Crab Cay Cave found on San Salvador Island, Bahamas (Daugherty et al., 1986)
Figure 69. Map of Crescent Top Cave found on San Salvador Island, Bahamas
85
Figure 70. Map of Crown Cave found on Cat Island, Bahamas (Palmer, R.J., 1982)
Figure 71. Map Deep Creek Cave found on South Andros Island, Bahamas (Carew et al, 1998)
86
Figure 72. Map of Deep Hole Cave found on San Salvador Island, Bahamas (Daugherty et al., 1986)
Figure 73. Map of Dripping Rock Cave found on San Salvador Island, Bahamas (Daugherty et al., 1986)
87
Figure 74. Map of Emerald Cave found on San Salvador Island, Bahamas
Figure 75. Map of Garden Cave found on San Salvador Island, Bahamas
88
Figure 76. Map of George Storr’s Cave found on San Salvador Island, Bahamas
Figure 77. Map of Granny T’s Cave found on San Salvador Island, Bahamas
89
Figure 78. Map of Harry Oakes Annex Cave found on New Providence Island, Bahamas (Mylroie et al., 1991)
Figure 79. Map of Harry Oakes Cave found on New Providence Island, Bahamas (Mylroie et al., 1991)
90
Figure 80. Map of Hunts Cave found on New Providence Island, Bahamas (Mylroie et al., 1991)
Figure 81. Map of Industrious Hill Cave found on Cat Island, Bahamas (Palmer, R.J., 1982)
91
Figure 82. Map of Little Little Creek Cave found on South Andros Island, Bahamas (Carew et al, 1998)
Figure 83. Map of Long Low Cave found on North Andros Island, Bahamas
92
Figure 84. Map of Lucky Day Cave found on Great Inagua Island, Bahamas
Figure 85. Map of Major’s Cave found on San Salvador Island, Bahamas
93
Figure 86. Map of Midget Horror Hole found on San Salvador Island, Bahamas
Figure 87. Map of Nugget Cave found on Cat Island, Bahamas (Palmer, R.J., 1982)
94
Figure 88. Map of Old Bottle Cave found on San Salvador Island, Bahamas (Daugherty et al., 1986).
Figure 89. Map of Peek-a-boo Cave found on North Andros Island, Bahamas
95
Figure 90. Map of Pipe Cave found on San Salvador Island, Bahamas
Figure 91. Map of Port Howe Sea Cave found on Cat Island, Bahamas (Palmer, R.J., 1982)
96
Figure 92. Map of Preacher’s Cave found on Eleuthera Island, Bahamas
Figure 93. Map of Rat Bat Cave found on South Andros Island, Bahamas (Carew et al, 1998)
97
Figure 94. Map of Reckley Hill Pond Maze Cave found on San Salvador Island, Bahamas (Vogel, 1992)
Figure 95. This map is of Reckley Hill Pond Water Cave found on San Salvador Island, Bahamas. (Vogel, 1992)
98
Figure 96. Map of Salt Pond Cave found on Long Island, Bahamas (Mylroie et al., 1991)
Figure 97. Map of Sliver Cave found on San Salvador Island, Bahamas
99
Figure 98. Map of South Deep Creek Cave found on South Andros Island, Bahamas (Carew et al, 1998)
Figure 99. Map of Stella Maris Cave found on Long Island, Bahamas (Mylroie et al., 1991)
100
Figure 100. Map of Stepwell Cave found on Cat Island, Bahamas (Palmer, R.J., 1982)
Figure 101. Map of Strawline Cave found on Cat Island, Bahamas (Palmer, R.J., 1982)
101
Figure 102. Map of Ten Bay Cave found on Eleuthera Island, Bahamas
Figure 103. Map of Whale Creek Cave found on Cat Island, Bahamas (Palmer, R.J., 1982)
102
APPENDIX C
GRAPHS
103
Figure 104. Plot of cave area versus quadrangle area for the flank margin caves found on Cat Island, Bahamas.
Figure 105. Plot of log area versus log perimeter for the flank margin caves found on Cat Island, Bahamas.
104
Figure 106. Plot of cave area versus quadrangle area for the flank margin caves found on Long Island, Bahamas.
Figure 107. Plot of log area versus log perimeter for the flank margin caves found on Long Island, Bahamas.
105
Figure 108. Plot of cave area versus quadrangle area for the flank margin caves found on New Providence Island, Bahamas.
Figure 109. Plot of log area versus log perimeter for the flank margin caves found on New Providence Island, Bahamas.
106
Figure 110. Plot of cave area versus quadrangle area for the flank margin caves found on San Salvador Island, Bahamas.
Figure 111. Plot of log area versus log perimeter for the flank margin caves found on San Salvador Island, Bahamas.
107
Figure 112. Plot of cave area versus quadrangle area for the flank margin caves found on South Andros Island, Bahamas.
Figure 113. Plot of log area versus log perimeter for the flank margin caves found on South Andros Island, Bahamas.
APPENDIX D
TABLES
108 109
Table. 3. Initial geometric conditions found for each flank margin cave.
Island Name Cave Name Area (m^2) Perimeter (m) AP Ratio
Cat Island Nugget Cave 80.3 69.1 1.2 Whale Creek Cave 264.5 115.1 2.3 Industrious Cave 348.0 144.5 2.4 Port Howe Sea Cave 411.6 153.4 2.7 Brackish Well Cave 731.7 192.9 3.8 Bluff Cave 795.3 182.0 4.4 Strawline Cave 1001.8 217.1 4.6 Stepwell Cave 2750.3 591.7 4.6 Crown Cave 4017.8 1142.8 3.5
Eleuthera Preacher's Cave 345.5 86.0 4.0 Ten Bay 6553.4 1492.2 4.4 Hatchet Bay Cave 6037.7 1320.0 4.6
Great Inagua Maroon Hill Caves 164.4 164.9 1.0 Salt Pond Hill 214.4 184.6 1.2 Lucky Day Cave 340.4 113.4 3.0
Long Island Benzie Hill North 61.4 55.7 1.1 Benzie Hill South 100.0 85.2 1.2 Cartwright Cave 260.1 150.3 1.7 Stella Maris cave 277.8 117.7 2.4 Salt Pond Cave 4032.2 906.7 4.4 Hamilton's Cave 9213.7 1817.9 5.1
New Providence Clifton East Cave 32.6 34.4 0.9 Harry Oakes Annex Cave 90.7 77.8 1.2 Cave Point East Cave 289.3 79.4 3.6 Cave Point West 359.0 145.2 2.5 Bahamas West Cave 460.6 276.8 1.7 Bat Cave 504.4 254.3 2.0 Hunts Cave 591.9 402.4 1.5 Harry Oakes Cave 618.0 178.2 3.5
North Andros Peek-a-boo Cave 21.5 23.6 0.9 Long Low Cave 343.7 74.0 4.6 Henry Morgan's Cave 579.4 155.6 3.7
110
Table 3 continued.
Island Name Cave Name Area (m^2) Perimeter (m) AP Ratio
San Salvador Granny T's 14.1 17.9 0.8 Closet Cave 17.5 23.7 0.7 Pipe Cave 30.3 41.2 0.7 Reckley Hill Pond Maze Cave 41.2 44.8 Old Bottle Cave 37.2 55.4 0.7 Midget Horror Hole 39.8 64.7 0.6 Chinese Firedrill Cave 45.5 84.4 0.5 Emerald Cave 57.3 48.2 1.2 Bug City Cave 64.7 87.6 0.7 Blowhole Cave 92.1 74.2 1.2 Deep Hole Cave 96.6 72.8 1.3 Crescent Top Cave 126.1 129.7 1.0 Reckley Hill Pond Water Cave 136.6 61.6 2.2 Dance Hall 142.5 195.5 0.7 Crab Cay Cave 160.1 76.8 2.1 Major's Cave 216.8 82.5 2.6 Sliver Cave 289.2 77.1 3.8 George Storr's Cave 172.5 71.0 2.4 Garden Cave 591.4 295.7 2.0 Dripping Rock 549.0 105.0 Beach Cave 633.4 291.7 2.2 Altar Cave 165.5 638.5 0.3 Lighthouse Cave 1645.6 631.9 2.6
South Andros Archways Cave 22.0 32.0 0.7 Little Little Creek 30.5 47.0 0.6 Deep Creek 57.1 77.0 0.7 South Deep Creek 101.3 59.8 1.7 Cluster Caves 95.3 102.8 0.9 Rat Bat Cave 902.0 218.7 4.1
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Table 4. Bedrock column geometric conditions for each cave.
Island Name Cave Name Column Column Column # of Area (m^2) Perimeter (m) AP Ratio Columns
Cat Island Nugget Cave 0.0 0.0 0.0 0 Whale Creek Cave 6.6 29.0 0.2 1 Industrious Cave 15.7 51.4 0.3 8 Port Howe Sea Cave 0.0 0.0 0.0 0 Brackish Well Cave 8.7 12.7 0.7 1 Bluff Cave 8.2 40.1 0.2 6 Strawline Cave 78.3 85.6 0.9 2 Stepwell Cave 387.8 267.1 1.5 11 Crown Cave 239.3 205.8 1.2 12
Eleuthera Preacher's Cave 0.0 0.0 0.0 0 Ten Bay 1406.0 756.8 1.9 36 Hatchet Bay Cave 103.5 62.8 1.6 2
Great Inagua Maroon Hill Caves 0.0 0.0 0.0 0 Salt Pond Hill 4.5 14.0 0.3 3 Lucky Day Cave 5.4 24.1 0.2 2
Long Island Benzie Hill North 1.0 3.9 0.3 1 Benzie Hill South 0.0 0.0 0.0 0 Cartwright Cave 0.0 0.0 0.0 0 Stella Maris cave 0.0 0.0 0.0 0 Salt Pond Cave 131.3 176.6 0.7 16 Hamilton's Cave 282.5 265.0 1.1 17
New Providence Clifton East Cave 0.4 2.4 0.2 1 Harry Oakes Annex Cave 5.0 11.6 0.4 2 Cave Point East Cave 0.0 0.0 0.0 0 Cave Point West 0.0 0.0 0.0 0 Bahamas West Cave 13.1 51.5 0.3 2 Bat Cave 22.1 90.2 0.2 28 Hunts Cave 44.4 60.1 0.7 2 Harry Oakes Cave 44.4 88.5 0.5 16
North Andros Peek-a-boo Cave 0.0 0.0 0.0 0 Long Low Cave 0.0 0.0 0.0 0 Henry Morgan's Cave 16.3 5.8 2.8 3
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Table 4 continued.
Island Name Cave Name Column Column Column # of Area (m^2) Perimeter (m) AP Ratio Columns
San Salvador Granny T's 0.0 0.0 0.0 0 Closet Cave 1.0 0.1 16.2 1 Pipe Cave 0.8 4.8 0.2 2 Reckley Hill Pond Maze Cave 9.9 48.7 0.2 15 Old Bottle Cave 0.2 2.5 0.1 2 Midget Horror Hole 0.2 2.0 0.1 1 Chinese Firedrill Cave 2.1 6.7 0.3 1 Emerald Cave 0.8 7.4 0.1 2 Bug City Cave 0.7 10.7 0.1 8 Blowhole Cave 0.0 0.0 0.0 0 Deep Hole Cave 0.2 1.7 0.1 1 Crescent Top Cave 9.7 42.2 0.2 15 Reckley Hill Pond Water Cave 0.0 0.0 0.0 0 Dance Hall 4.0 16.0 0.2 4 Crab Cay Cave 3.2 20.3 0.2 9 Major's Cave 0.0 0.0 0.0 0 Sliver Cave 0.0 0.0 0.0 0 George Storr's Cave 6.1 25.2 0.2 7 Garden Cave 60.4 224.6 0.3 10 Dripping Rock 0.0 0.0 0.0 0 Beach Cave 12.8 58.4 0.2 23 Altar Cave 0.0 0.0 0.0 0 Lighthouse Cave 267.9 1902.0 0.1 30
South Andros Archways Cave 0.0 0.0 0.0 0 Little Little Creek 0.0 0.0 0.0 0 Deep Creek 0.0 0.0 0.0 0 South Deep Creek 5.7 16.9 0.3 2 Cluster Caves 0.9 6.0 0.2 2 Rat Bat Cave 0.0 0.0 0.0 0
113
Table 5. Smallest quadrangle fit for each cave.
Island Name Cave Name Quadrangle Quad. Quad. L/W Quad.Area Length (m) Width (m) Ratio (m^2)
Cat Island Nugget Cave 24.3 8.9 2.7 216.3 Whale Creek Cave 32.3 14.0 2.3 452.2 Industrious Cave 35.6 17.8 2.0 633.7 Port Howe Sea Cave 36.0 27.2 1.3 979.2 Brackish Well Cave 74.5 19.6 3.8 1460.2 Bluff Cave 74.5 15.9 4.7 1184.6 Strawline Cave 73.0 28.5 2.6 2080.5 Stepwell Cave 80.2 72.0 1.1 5774.4 Crown Cave 156.2 88.9 1.8 13886.2
Eleuthera Preacher's Cave 29.7 15.7 1.9 466.3 Ten Bay 181.0 147.0 1.2 26607.0 Hatchet Bay Cave 285.0 53.0 5.4 15105.0
Great Inagua Maroon Hill Caves 34.5 14.5 2.4 500.3 Salt Pond Hill 51.7 12.2 4.2 630.7 Lucky Day Cave 40.8 17.5 2.3 714.0
Long Island Benzie Hill North 17.5 9.0 1.9 157.5 Benzie Hill South 30.0 6.0 5.0 180.0 Cartwright Cave 41.5 11.0 3.8 456.5 Stella Maris cave 25.0 20.0 1.3 500.0 Salt Pond Cave 138.0 69.0 2.0 9522.0 Hamilton's Cave 300.0 125.0 2.4 37500.0
New Clifton East Cave 8.5 6.0 1.4 51.0 Providence Harry Oakes Annex Cave 20.3 8.9 2.3 180.7 Cave Point East Cave 25.5 16.8 1.5 428.4 Cave Point West 26.7 23.2 1.2 619.4 Bahamas West Cave 36.0 22.5 1.6 810.0 Bat Cave 55.0 12.0 4.6 660.0 Hunts Cave 47.0 18.5 2.5 869.5 Harry Oakes Cave 46.0 23.9 1.9 1099.4
North Andros Peek-a-boo Cave 7.2 5.2 1.4 37.4 Long Low Cave 27.6 17.2 1.6 474.7 Henry Morgan's Cave 41.7 27.9 1.5 1163.4
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Table 5 continued.
Island Name Cave Name Quadrangle Quad. Quad. L/W Quad.Area Length (m) Width (m) Ratio (m^2)
San Salvador Granny T's 5.7 4.8 1.2 27.4 Closet Cave 7.0 4.5 1.6 31.5 Pipe Cave 13.1 4.5 2.9 59.0 Reckley Hill Pond Maze Cave 9.0 7.2 1.3 64.8 Old Bottle Cave 19.2 5.5 3.5 105.6 Midget Horror Hole 11.7 7.5 1.6 87.8 Chinese Firedrill Cave 17.3 13.7 1.3 237.0 Emerald Cave 12.0 7.0 1.7 84.0 Bug City Cave 13.5 5.0 2.7 67.5 Blowhole Cave 21.0 5.0 4.2 105.0 Deep Hole Cave 23.4 8.6 2.7 201.2 Crescent Top Cave 18.0 10.0 1.8 180.0 Reckley Hill Pond Water Cave 15.9 14.7 1.1 233.7 Dance Hall 32.1 11.7 2.7 375.6 Crab Cay Cave 20.5 10.0 2.1 205.0 Major's Cave 22.0 11.3 1.9 248.6 Sliver Cave 21.6 19.0 1.1 410.4 George Storr's Cave 28.0 17.5 1.6 490.0 Garden Cave 58.0 30.3 1.9 1757.4 Dripping Rock 27.9 27.0 1.0 753.3 Beach Cave 55.0 15.5 3.5 852.5 Altar Cave 51.0 15.0 3.4 765.0 Lighthouse Cave 100.0 49.0 2.0 4900.0
South Andros Archways Cave 9.2 5.7 1.6 52.4 Little Little Creek 10.7 6.9 1.6 73.8 Deep Creek 24.7 6.1 4.0 150.7 South Deep Creek 28.0 15.8 1.8 442.4 Cluster Caves 19.8 15.3 1.3 302.9 Rat Bat Cave 79.5 21.7 3.7 1725.2
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Table 6. Cave size ranked for each island.
Island Name Cave Name Size Rank
Cat Island Nugget Cave 1 Whale Creek Cave 2 Industrious Cave 3 Port Howe Sea Cave 4 Brackish Well Cave 5 Bluff Cave 6 Strawline Cave 7 Stepwell Cave 8 Crown Cave 9
Eleuthera Preacher's Cave 1 Ten Bay 2 Hatchet Bay Cave 3
Great Inagua Maroon Hill Caves 1 Salt Pond Hill 2 Lucky Day Cave 3
Long Island Benzie Hill North 1 Benzie Hill South 2 Cartwright Cave 3 Stella Maris cave 4 Salt Pond Cave 5 Hamilton's Cave 6
New Providence Clifton East Cave 1 Harry Oakes Annex Cave 2 Cave Point East Cave 3 Cave Point West 4 Bahamas West Cave 5 Bat Cave 6 Hunts Cave 7 Harry Oakes Cave 8
North Andros Peek-a-boo Cave 1 Long Low Cave 2 Henry Morgan's Cave 3
116
Table 6 continued.
Island Name Cave Name Size Rank
San Salvador Granny T's 1 Closet Cave 2 Pipe Cave 3 Reckley Hill Pond Maze Cave 4 Old Bottle Cave 5 Midget Horror Hole 6 Chinese Firedrill Cave 7 Emerald Cave 8 Bug City Cave 9 Blowhole Cave 10 Deep Hole Cave 11 Crescent Top Cave 12 Reckley Hill Pond Water Cave 13 Dance Hall 14 Crab Cay Cave 15 Major's Cave 16 Sliver Cave 17 George Storr's Cave 18 Garden Cave 19 Dripping Rock 20 Beach Cave 21 Altar Cave 22 Lighthouse Cave 23
South Andros Archways Cave 1 Little Little Creek 2 Deep Creek 3 South Deep Creek 4 Cluster Caves 5
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Table 7. Breakdown of cave size by island.
Cat Eleuthera Great Long New North San Salvador South Island Island InaguaIsland Providence Andros Island Andros # small 1 0 0 2 2 0 11 6 # medium 6 1 3 2 6 3 11 0 # large 2 2 0 2 0 0 1 0