Este Boletín es de carácter informal -no arbitrado- preparado con el objetivo de divulgar rápidamente las actividades geoespeleológicas en la región de la FEALC. Sólo se difunde por vía de correo electrónico. Es de libre copia y difusión y explícitamente se solicita a quienes lo reciban que a su vez lo reenvíen a otros posibles interesados, o lo incluyan es páginas web. Todos los números anteriores están disponibles. Igualmente se pide que obtengan copias en papel para las bibliotecas de sus instituciones. Se solicitan contribuciones de cualquier tipo y extensión para su divulgación.

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Copied from: http://www.karst.edu.cn/igcp/igcp299/1992/92.4.htm
RECENT RESEARCH BY IGCP 299 PARTICIPANTS

HYDROGEOCHEMICAL PATTERNS AND MATHEMATICAL CORRELATIONS IN KARST AT THE EXAMPLES OF CUBA

J.R.Fagundo Castillo and J.E.Rodriguez Rubio (Cuba)

Introduction

In this paper, the hydrogeochemical patterns of some karst and non karstic waters from  Cuba ,  as well as the mathematical  correlations  between  ionic contents   and electric  conductivity  of  the   waters,   are   presented. Anthropogenic  on  karst  are also  discussed  in  terms of variations  in mineralization , hydrogeochemical patterns and mathematical relationship in the long run.

Materials and Methods

As  criterion  of  good mathematical agreement we use in this  paper the similarity index SI defined by:

where:
R₁:  relation between the ionic concentration obtained by  chemical  analysis and modeling;
R₂: relation between each ion and the total sum of ions.
Further control of chemical composition of waters can be made by means of the  corresponding  mathematical equations and the measurement  "in  situ"  of electric  conductivity. The theory which support the use of referred  computer programs has been recently reported ( Fagundo , 1990).
The  hydrogeochemical patterns are represented in this paper by  means  of the diagrams proposed by Stiff(1951) and the stecheometric relations Na⁺+K⁺:Ca²⁺: Mg²⁺:Cl^-:HCO₃^-:SO₄^2- , where the sum of anions and cations are both equal to 10 meq/1.

Results and Discussion

In order to study the physical chemical behaviour of the karst waters , its hydro-geochemical  patterns and changes developed by the effect of natural  and anthro-pogenic factors , two typical Cuban karst areas were chosen : San  Marcos river basin in Sierra del Rosario and the developed karst in southern  plain , both in Pinar del Rio province , representatives of mountain and coastal  plain tropical karst , respectively.

San Marcos River Basin

The  lithology  and the water flow conditions are the major  factors  that determine  the  chemical composition of the waters  and the hydrogeochemical patterns. We can  distinguish  the following  water  types:  sodium  calcium hydrocarbonate  for waters  from the  sedimentary-effusive  rocks ,  magnesium hydrocarbonate  for the waters which originate in the ultrabasic  massif , and calcium hydrocarbonate for that waters which flow in the karst areas (at  the source , caves ,  exsurgences and springs from the  saturation  zone ).  Finally , there  are waters of calcium sulphate type from the karst deep drainage  (deep phreatic zone).
These waters change the absolute chemical composition as a consequence of the  rain  regime ,  but practically do not undergo  changes  in  its  relative chemical  composition. The ion stecheometric relations are the same  for  each sample. Similar bahaviour in other systematic sampling points in other regions was observed.
The hydrogeochemical patterns of the waters from San Marcos basin in terms of the corresponding stecheometric relations, appear in Tab.1.
Linear equations were obtained when concentration in each ion and electric conductivity data  were  fitted. The slopes of the corresponding  regression equations are also listed in Tab.1. The magnitude of the slopes are functions of  the  ionic concentrations of the waters and the local  lithology.Three hydrogeochemical patterns characterize all karst waters of the basin and there are other two for the non karstic waters.
The  mean  similarity  index between real and theoretical  values  of  the chemical composition is also expressed for each type of water in Tab.1.

Pinar del Rio Southern Coastal Karstic Plains

In  the  southern part of Pinar del Rio province , there are a  great  karst massif constituted  by Miocene limestones ,  partially dolomitized  and occasionally covered by Quaternary sediments. In this area , a  rich  aquifer occurs whose recharge zone is in the premountains region at the North , and  it is  freely discharged to the sea at the South. The waters in the aquifers  are of  calcium  hydrocarbonate  type in the zone non affected by the  seawater mixing. Toward the coast , some hydrochemical facies occur as the result of the mixing between fresh and marine waters. They are stratified along the vertical profile  of each well and a horizontal profile across the  aquifers (Arellano and Fagundo , 1985).
There are also different modes of water chemical evolution in this region , which depend  on the dolomitization degree of the sampling  site  inside  the aquifer.  In such  conditions different contents of magnesium  for  the  same seawater  mixing level  exist.  We have  observed  at  least ,  four  chemical evolution  paths for the waters of these regions as well as for other  coastal karst aquifers in Cuba.
We have occasionally observed changes in the original hydrogeochemical patterns  in some sampling points (well) in the long run. Generally ,  it  is due  to  a  decrease  in the rain regime and/or an  increase  in  the  aquifer overexploitation. In this case , the mineralization and NaCl salinity showed   a progressive increase during the observational period. The additional  quantity of foreign ions as Na⁺ , K⁺ and Cl^- in hydrocarbonate water increase  calcite  and  dolomite  solubility and considerable quantity of carbonate rock  can  be dissolved from the aquifer.
In  this type of water the corresponding fitting of the ion  contents  and electric conductivity  data is more significant for the  second  degree  than linear equations if all the data are processed. Better results can be obtained processing the data corresponding to each hydrogeochemical pattern(see table 2).
In  this case ,  mathematical equations  are of  linear  type.  Using  these expresions and the electric conductivity measurement in field by means  of  a conductometer connected to a 100m probe it is possible to control the chemical composition  and salinity of the waters , but we need to take into account  the range  in  which each sampling point reflects the  different  hydrogeochemical pattern(see table 3).

Conclusions

The lithology and the water flow conditions determine the hydrogeochemical patterns ,  characterized  by a given stecheometric relation. In  the  case  of tropical karst  and  non  karstic  waters   there  is ,   generally ,  one hydrogeochemical pattern in the same sampling point , where many of the factors remain constants. In case of underground waters there are less changes of  the relative  chemical  composition than in the first surface  waters.  A  discret number of hydrogeochemical patterns can characterize all the  waters  running through the limestones.
More  variability can be distinguish in coastal karst aquifers  encroached by seawaters , where waters in the aquifer are stratified along  vertical  and horizontal profiles. In such cases, different chemical facies in the same well occur.
The human activity can change the natural hydrogeochemical patterns in the karst as a consequence of the waste water input , the chemical treatment in the agriculture and  the  aquifer overexploitation. In coastal  karst  areas , the latter increases signifi-cantly the water salinity and the karstic processes.
In all the cases , empirical mathematical relationships were found  between ionic chemical composition and the electric conductivity of the waters. In one of the controlling factors of the chemical composition acquisition is dominant , as for instance , the lithology , the most accurate equations are of the  linear Type , but if more than one of these factors play the major role in the mode of chemical compo-sition acquisition we can found that non linear equation are the better when all the data are processed, and linear equation are the best  when the  corresponding  data  of each  hydrogeochemical  pattern  are  separately processed.  By  means of these equations and field  measurements  of  electric conductivity it is possible to control the water quality in terms of  chemical composition, mineralization and salinity.

Tab.1 Hydrogeochemical patterns (as a function of the stecheometric relations); slopes of the linear relationship between ionic concentration and electric conductivity of the water from the San Marccs river basin, and the similarity index (SI) between real and modelling values of the chemical composition
________________________________________________________________________________
Geological environment   N   stecheometric   relation slope of the regression equation                                    SI          
Na+K Ca Mg Cl HCO₃ SO₄   HCO₃       Cl       SO₄        Ca        Mg       Na+K _________________________________________________________________________________________
Sedimentary-effusive      34        3       5   2     1     9        0     10.013   1.276   0.393   5.947   1.933     3.802    0.894
Ultrabasic                          13        1       0   9     0     9        1     10.537   1.253   0.332   0.338   10.296  1.478     0.898
Limestones from Guajaibon
and Chiquita formations  140     2        7   1   1      8         1     8.994     1.003   1.148     7.148   7.832   1.242    0.883
Limestones from Mil
Cumbres region                 27       2        7   1    1     8         1     9.57       0.912    1.405     8.751   1.005   2.131   0.893
Water from karst deep
drainage                             12        2        7     1   0    1          9    0.781     0.276     7.866   6.256     1.157   1.510   0.978
_________________________________________________________________________________________

Tab.2 Hydrogeochemical patterns (as a function of the stecheometric relations) slopes of the linear relationship between ionic concentration and electric conductivity of the water from some wells of Pinar del Rio s outhern coastal karst aquifer and similarity index (SI) between real and modelling value of the chemical composition
________________________________________________________________________________
Hydrogeochemical     N          Stecheometric relation slope of the regression equation                                      SI
pattern                                    Na+K   Ca  Mg  Cl  HCO₃  SO₄   HCO₃       Cl       SO₄        Ca         Mg     Na+K _________________________________________________________________________________________
HP1                                4          2         8   0      2      8           0       6.558   1.923   0.251   6.890    0.438   1.404   0.932
HP2                                5          2         7   1      4      6           0       5.609   3.541   0.227   5.884    1.000   2.493   0.923
HP3                                3          4         5   1      5      5           0       4.583   4.570   0.449   4.924    1.149   3.529   0.958
HP4                                4          5         4   1      6      4           0       3.685    5.421  0.419   4.008    1.229   4.218   0.945
HP5                               10        5         3    2     6     4             0       3.134    6.019  0.367   3.340    1.311   4.869   0.898
HP6                                4         6          3   1       7     3            0        2.436   7.487   0.406  3.121    1.618   5.590   0.936
HP7                               11       6          3    1      8     2            0       1.710    7.778   0.633  2.510    1.492   6.119   0.919
HP8                               21       7          2    1      8     1            1       0.986    8.055   0.574  1.604    1.400   6.611   0.931
HP9                               6         7           1    2      9     1            0       0.628    8.477   0.558    1.265   1.700   6.698   0.941
HP10                            7          8           1    1      9                   1       0.282    8.913   0.665    0.844   1.419   7.567   0.944 __________________________________________________________________________________________

Tab.3 Electric conductivity ranges in which each well from part of the Pinar del
Rio coastal karst aquifer reflects the different hydrogeochemical patterns   ___________________________________________________________________________________
Well    Deep     HP1      HP2      HP3     HP4         HP5         HP6          HP7         HP8           HP9         HP10 __________________________________________________________________________________
P2              60-100      300-399    400-585    590-689     690-969      970-1219      1200-1879     1820-3779      3780-4691     4700-6000         >6000
P4             60-90                                                            600-794       800-1279     1200-1799      1800-2449     2450-5159      5160-7000        >7000
P5             20-50                                                                               500-999        1000-1699      1700-1839     1840-4249     4250-7709          >7710
P1             70-100     400-529     530-649    650-779     780-950
P6            60-90                                                                                200-359         360-449           450-1699       1700-4000
P3            30-40                                                            600-999        1000-1699    1700-2288       2300-2899    2900-4399      4400-8299        >8300
P7            40-70                                                                                                                             500-849         950-4129        4130-7399         >7400 ________________________________________________________________________________

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HYDROLOGY AND DYNAMICS OF THE TROPICAL KARSTIC PROCESSES IN CUBA

J.E.Redriguez and J.R.Fagundo (Cuba)

Abstract

     Since 1975 , Cuban karst hydrological and hydrochemical characteristics and the dynamics and intensity of the karstic processes,have being investigated by a group of Cuban specialists. A  research  program  in order to asses  intensity  of  the  contemporary karstic processes in some karstic regions of the world started in 1984.  This research program  is  a  part of  the Cuban- Polish  collaboration on  the International Commi ssion for Physico-Chemical and Hydrological Karst Research of International Union of Speleology. The  Pan de Guajaibon massif in western Cuba was chosen for this  research as  an experimental representative area of the tropical lower mountain  karst. Other karstic localities in plains , hills and lower mountains were also chosen for developing similar investigations , as validaion areas. Some  results of the hydrodynamic and hydrogeochemical characteristics  of the karstic massifs were obtained and different karst circulation regimes were found , as well as the quantitative determination of these massifs response for rainfalls by using a typical water debit response curves  and  hydrochemical composition.  Moreover , the influence of intensive tropical rains action  and their spetial and temporary distribution on the karst denudation process  were studied. The  karst denudation was calculated by a hydrochemical method. Values  of 40-50 and 115-130 m³/km² year respectively were reported in Pan de  Guajaibon massif. Same values in another validation karstic areas of the  country  have been determined.

Introduction

     About  the  65% of Cuban territory (71,500km²) is covered  by  limestones from Jurassic to Quaternary age , in greater or lesser degree affected  by  the karstic processes , where 85% of the underground water reserves in the country are concentrated  and the large number of rivers are  circulating  in  direct interaction with this geological environment. The  rainfall amount and its spatial and temporary  distribution  together with other non-climatic factors , e.g. , lithology , relief ,geological structure , hydrology  and vegetation , have greatly  influenced  the karst development intensity and its typology as well. Thus , the joined occurrence and development of many karst types with different hydrodynamical  and geomorphological characteristics  and   under identical  climatic  conditions , give place to find in Cuban  territory  vasts karst plains--the most extended karst type in the country--as well as  hills , plateau and lower mountains karst types, stand out among the latter, the cone and  tower karst , which , although appear like a typical in  tropical  regions , are not the most frequent in the Cuban territory.

Pan De Guajaibon Experimental Area

     The Pan de Guajaibon massif is found belonging to the Northwestern extreme part  of  Sierra del  Rosario , Pinar del Rio province. It is a 10km² are a composed  of  two  parallel carbonate massifs --Pan de  Guajaibon  and  Sierra Chiquita-separated by an upper karstic valley. The highest point is  Guajaibon peak 692m.a.s.l. The  experimental area is drained by the San Marcos river basin and has  a pluvio-metric  network  with one pluviometer each 2km² , two  gauging  stations installed  in the massif springs and a standard climatic station for the air temperature and relative moisture records. The annual and seasonal climatic mean values  parametres and rainfall distribution  for the observational period in the experimental area ,  can  be seen in the Tab.1. From a geological point of view , this is a very complex region , typical of the overthrust  and  nappes  tectonical  style  and composed  by  a   really lithological mosaic. By using standard field methods and equipments, the hydrochemical analysis and  water  PH ,  temperature  and electric conductivity ,  were  measured  and recorded. From   an hydrochemical point of view , all the massif  circulation ,  waters are calcium-hydrocarbonate , except the waters from the allogenic feeding  zone in the northeast of the massif, which have circulated on  effusive-sedimentary rocks and are sodium-calcium-hydrocarbonate waters. Taking into account  the results of Pan de Guajaibon hydrological characteristics , it is possible to affirm that from a hydrodynamical point of view ,  it is a merokarst massif without deep circulation below base level. Due to the karst processes intensity and forms development , the massif runoff  is fundamentally  underground  and  it is integrated by  two  continuous karstic drainage systems-Ancon and Canilla. The  Canilla system feed is a mixture of autogenic and  allogenic  runoff , with circulation at the same level of the surface rivers Laslevel. Whereas the Ancon system feed is totally autogenic , with suspended circulation 60 meters above the base level. By the means annual and seasonal discharge analysis registered during  the observational period ( see Tab.2) , the major and more regular runoff regime  was proved in Ancon system as compared with Canilla system.  This is in correspondence with the physico-geographical conditions  and  rainfall distribution   in both basins and consequently , the infiltration rate  for  the Ancon system was higher ( 70-85%) than for the Canilla system(35-40%). The higher and more stable waters mineralization of the Ancon system  than the ones of the Canilla  is in function of the combined effect  of  some hydrodynamical, lithological and microbiological factors. According to all above mentioned , the mean annual and seasonal karstic denudation  values  for  the observational period (see  Tab.3)  are  remarkably higher in the Ancon system than in the Canilla system (115-130 and 40-50m³/km³ year respectively). It  must  be  emphasized that the denudation  process  in  Cuban  tropical climatic conditions , is a continuous and seasonal uninterrupted process during all  the  year and keeps up practically the same intensity during the rainy season(60%) than during the less rainy seasons , in function of the homogeneous spatial and temporary rainfall distribution. It does not happen in temperate and  polar  latitudes where during the greatest part of the year the karstic processes have a lower dynamics or it is practically stopped. The  karst  denudation values reported in Pan de Guajaibon massif  for a complete  five years hydrological cycle , give a reliable measurement  of  this process intensity in the tropical Cuban lower mountain karst.

Guaso Plateau

New Program: Zapata Basin

     Unlike the researching program in hills and lower mountains karst areas , a new investigation   program  concerning  to  the process,   dynamics   and environmental changes  in the tropical karst of Cuba , has been started  on  a plain  karst region: Zapata basin, in the southern karstic plain  of  Matanzas province. Zapata basin comprises all the south slope of Matanzas province. It is  a complex open sea karstic aquifer system, developed fundamentally in  carbonate and carbonate-terrigenous Miocene transgressive sequencies , which compose  the major part of the emerged area of the Cuban archipelago. The distinctive water circulation particularities of the  Zapata  aquifer system  in relation  to  these  kind of aquifers  and  its relatively  easy hydrodynamical behavior , depend on the presence of the structural  depression in  the southern  part of  the basin ,  filled  up  by  carbonate  Pliocene-Pleistocene deposits , over which , the big marsh area of Zapata Swamp has been developed. From  a  hydrodynamical point of view , it obviously is a holokarst  basin with 150-200 meters of estimated karstification thickness ,  in  which ,  some aquifer levels and not less than three superposed drainage systems are  found , defined   by textural  differences  into  the   limestones   and   frequently interconnected by really hydrogeological windows. Interesting karstic processes of accelerated corrosion by  mixed  waters , saline effect and biochemical factors, occurred there , as well as the  aquifer water overexploitation,  uncontrolled  waste waters   inputs, agricultural intensive exploitation and other anthropogenic impacts,increase the sea waters intrusion and the aquifer contamination processes. The development of an international investigation program in  the  Cuban plain karst areas, are very interesting from the scientifical  and practical points  of  view , not  only within Cuban boundaries,  but  also  in  all the Caribbean  basin  and Gulf of Mexico coastal region, which have had  the same geological history and evolution from the Neogene and Quaternary and wherever , these  kinds  of karst plains , with similar  hydrological  and  hydrodynamical characteristics can be found.

Tab. 1 Annual climatic mean parameters values for the obersavational period in Pan de Guajaibon Experimental Basin and it’s comparison with the hyperannual standards

Tab. 2 Water balance for the observational period in both karstic systems of Pan de Guajaibon experimental basin ( Mean annual and seasonal parameters )

Q —debit ; I—infiltration ; P—precipitation ; IC—infiltration coefficient ; E—evapotranspiration .

Tab. 3 Mean annual and seasonal karst denudation values for a complete hydrological cycle in Pan de guajaibon experimental basin .

W—Total runoff ; Y—Yield ; EC—Electric Conductivity ; AT , T –Mineralization .

Tab. 4 Hydrological information analysis and water balance of Guaso Plateau

i I , rI , tI—Intermediate regional and total infiltration ; R—surface runoff .

Tab. 5 Chemical denudation of Guaso Plateau

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Cockpit Country in Jamaica is the type location for cockpit karst. Cockpit Country was the name given to the area by the British in the 17th century because it reminded them of the then-popular cock-fighting arenas which were hot, humid and dangerous places where men gathered to watch and bet on the "sport". Note that cockfighting is illegal now (but is still practised -Easter 2001- in some areas of Jamaica): the concept was still familiar enough to aviators in the early 20th century for them to use "cockpit" as the name for their station on an aircraft. The word "karst" derives from 'Kras' in Slovenia:- "a dry, waterless place". Although the Cockpit Country receives high rainfall annually (1500mm to 2500mm), it is still considered "waterless" because limestone acts as a sponge: surface water is drained vertically and rapidly and each cockpit bottom ("sink") is drained by a sinkhole. Don't hike without a guide! (See one group's experience)

The formation of Cockpit Country started about 12 million years ago with a faulted limestone plateau when Jamaica emerged from the sea. The plateau rose to about 600m (2000ft) above sea level, with a tilt of between 5 and 15deg to the NW. Erosion of this plateau formed the regular array of round-topped, conical hills and sinks that we know today.  There are at least two theories as to how cockpit karst forms. The "solution" theory holds that heavy tropical rainfall washing through a fissured limestone plateau over millions of years dissolved and eroded the fissures and washed the debris through the sinkholes eventually out to sea.A recent researcher measured the orientation of the faults in the area and found them to be largely aligned along three primary axes mutually at 120 degrees.
He surmises that a sinkhole forms when three faults intersect.This theory provides an explanation of the typical, regularly-spaced, round-topped, conical hills.At the top of the hill, the water moves slowly so that little erosion takes place; as the water runs down the hill, it gathers momentum and also gathers debris so that its scouring action becomes more and more pronounced. This accounts for the slope being so steep at the base. Of course, each cockpit has one or several sinkholes but there is a tendency for these to become blocked by debris.

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KARST LANDFORMS AND LAKES

Robert W. Blair, Jr.*

INTRODUCTION

This chapter is concerned with the recognition and origin of karst topography and certain types of lake basins and is not intended to be a comprehensive text-style dissertation on either karst or lakes. For more specific information, see Jennings (1971), Sweeting (1972), or Hutchinson (1957). The category of lakes, although a separate topic from karst, has been included because we believe that it does not warrant a special chapter and because the number of good images displaying karst is limited. The approach is by necessity a regional one, with little discussion related to landforms that are not observable from space.

KARST

Introduction

The term "karst" stems from the region Krs in Slovenia, now in northwestern Yugoslavia, which is typified by stony barren rock (Figure 7.l). The Indo- European word "kar" for rock and the Italian word "carso" evolved to the Germanized term"karst," which is now the accepted term for solution-derived landscapes like those just north and east of the Adriatic Sea.Karstification is the geologic process of differential chemical and mechanical erosion by water on soluble bodies of rock, such as limestone, dolomite, gypsum, or salt, at or near the Earth´s surface. Karstification is exhibited best on thick, fractured, and pure limestones in a humid environment in which the subsurface and surface are being modified simultaneously. The resulting karst morphology is usually characterized by dolines (sinkholes), hums (towers), caves, and a complex subsurface drainage system.

Factors in Karst Development

The development of karst terrain depends on the interplay of at least seven important factors in varying degrees. These are: lithology, structure, relief, hydrology, climate, vegetation, and time.

Lithology. Several lithologies are susceptible to karstification, but limestones and dolomites, owing to their solubility and nature of resistance and widespread distribution, are overwhelmingly dominant. According to Pettijohn (1975), 75 percent of the Earth´s surface is covered with sedimentary rocks, and of that, 10 to 20 percent consists of limestones or dolomite. Karst morphology can occur on carbonates with less purity than 80 percent, but generally the purer the limestone, the better the development of karst morphology (Jennings, 1971). For example, the Cretaceous and Early Tertiary Dinaric karst limestones of Yugoslavia are 95 to 100 percent pure (Herak, 1972), and white limestone in Jamaica seldom exhibits less than 98 percent purity. Numerous compositional variations can exist in carbonates, and many of these are discussed in Sweeting (1972) and Jennings (1971).

	Figure 7.1
	Map 7-1

Figure 7.1. Part of Landsat image 3009-09094-7, June 8, 1978, showing the type locality region of karst topography in the Slovenian Dinaric Mountains of Yugoslivia. The map, taken from an article by Demek et al. in Geomorphology of Europe (C. Embleton, Ed.) (1984) shows karstic features in approximately the same region. Numbers on the map refer to poljes: (1) Grosupeljsko, (3) Globodol, (13) Losko, (14) Babno, (15) Postojnsko, (17) Crnovrsko, (18) Zadlog. Key to symbols: (1) blind valley, (2) pocket valley, (3) dry valley, (4) dry valley system, (5) border polje, (6) overflow polje, (8) dammed polje, (9) karst doline, (10) uvala, (11) karst plain (Demek et al., 1984).

In addition to the composition of limestone, the thickness of individual beds, the nature of interbeds, especially shaly beds, and lateral facies variations affect the style and degree of karstification. In the Dinaric Mountains, the depth of surface karstification is sometimes limited by impermeable beds which have aided the development of broad flat-floored valleys called poljes (Herak, 1972).

Structure. Structure is used here in the structural geologic sense and is concerned with the attitude and deformational effects of bedrock. Limestones and dolomites at or near the surface tend to deform by brittle fracture. This tendency to form complex joint sets is directly responsible for the secondary permeability required for the development of subsurface solution drainage and subsequent three-dimensional cave development. Vertical fractures usually manifest themselves at the surface and focus the solution processes along them. The influence of fracturing is paramount in southeast China, where thousands of square kilometers are affected by several consistent sets of joints (see Plate KL-1, karst of south China). Folding, in addition, may have the effect of isolating watersheds and directing ground-water flow. This has occurred in the Dinaric karst of Yugoslavia.

Large-scale structures or tectonics not only have led to the development of specific landforms like poljes but have also influenced the rates and degree of karstification. Most poljes, for example, are associated with boundary faults (Roglic, 1972). Uplift and deformation of a carbonate plateau accelerates the dissolution of the limestone because: (1) fracture density increases, (2) any elevation rise is usually accompanied by an increase in precipitation, and (3) increased relief increases piezometric surface gradients. These conditions can: (1) lead to solution-enlarged conduits along fracture planes, (2) impart to the limestone a high hydraulic conductivity, and (3) cause rapid fluctuations in the water table with accompanying accelerated solution (Fetter, 1980)

Relief. Topographic relief is the elevation difference between the highest and lowest points on the surface for a given area. The Julian Alps in the inner region of Yugoslavia have a topographic relief near 2000 m. This mountainous area is associated with an abundance of potholes and few caves. Both characteristics are thought to be a consequence of this high relief (Herak, 1972). Related to relief is the depth of the vadose zone, which is the vertical distance between the surface and the water table. In Florida, the vadose depth is small, as is the topographic relief. However, throughout low sea level stands during the Pleistocene, the increased depth of the vadose zone probably led to the development of a more extensive and efficient subsurface drainage system with an increase in dissolution along fractures and fissures. With the absence of the buoyancy effect of a high water table surface, the formation of collapse dolines may have been accelerated (see Plate KL-4, Florida karst). Even today the effects of water table drawdown due to excessive pumping have rendered some urban areas susceptible to the sudden and unexpected collapse of buried solution cavities. Such a collapse occurred in Winter Park, Florida, in May 1981.

Hydrogeology. Hydrogeology is concerned with the interrelation ships of geologic materials and processes with water (Fetter, 1980). The karstification process involves not only the solution of limestone but also the sometimes overlooked mechanical erosion of limestone. Because the solution chemistry of carbonates is well known (Jennings, 1971; Sweeting, 1972; Bogli, 1980), only a brief summary will be presented here.The dissolution of limestone involves three principal components: carbon dioxide, water, and calcium carbonate. Initially, atmospheric carbon dioxide diffuses into the moisture within the air or soil and simultaneously becomes hydrated to form carbonic acid:

In the presence of limestone, carbonic acid dissolves the calcite. The reaction is often presented as:

The only water that is capable of dissolving limestone is aggressive water, which is water undersaturated with respect to dissolved carbonate. The time required for aggressive water in karst regions to be neutralized or to reach saturation equilibrium varies considerably, depending on a number of factors such as temperature, turbulence, variations in the partial pressure of carbon dioxide, dilution, presence of other acids, and surface area of limestone. To achieve equilibrium may require several days; however, laboratory studies suggest that most of the limestone dissolution resulting from an influx of fresh aggressive water may occur within minutes to a few hours (Sweeting, 1972; Jakucs, 1977; Ritter, 1978). Additional acids, such as organic acids from soils and most recently sulfuric and nitric acids from acid rain, will contribute to the dissolution of carbonate rocks.

Once saturation equilibrium is achieved, any change to warmer water temperatures or decreases in the partial pressure of carbon dioxide can drive equation 7-2 to the left, resulting in the deposition of calcium carbonate (see Figure 7.2).

Erosion rates have been calculated for many karst regions around the world and vary widely even within the same climatic zone (Smith and Atkinson, 1976).

	Figure 7.2. Saturation equilibrium curves for solution of calcium carbonate at selected temperatures as a function of carbon dioxide equilibrium in solution (modified after Jennings, 1971, p. 26).

Table 7-1 lists some of the calculated erosion rates for karst regions discussed in this chapter. Although these erosion rates are useful for comparative purposes, they are not indicative of the duration intensity of the erosion process. The dissolution of the limestone does not take place at a constant rate, but fluctuates with storm events that flood the karst surface and subsurface with undersaturated water. In other words, the actual dissolution occurs episodically with maximum peaks corresponding to surges in the karst water flow. In Jamaica, intense storm events result in subsurface flooding, and because the existing conduit system is not of sufficient size to handle excessive infiltration rates, backfilling of caves and solution channels occurs with fresh undersaturated water (Versey, 1972). These flood events can be of the single-storm variety or may be seasonal, as with the winter flooding of poljes in Yugoslavia.

Because of the unusually high permeabilities and the periodic flooding associated with most karst regions, the water table correspondingly exhibits drastic fluctuations. This has been observed by many spelunkers. The water table in karst rock is frequently difficult to define, especially in free- flow carbonate aquifers that display a complex multitude of enlarged open conduits. The water table can occur at considerable depths below the land surface, especially in mountainous regions like the Dinaric Mountains, Yugoslavia. Water can also be perched under solution depressions above the water table or it may be discontinuous if the permeability is principally fracture-controlled (Fetter, 1980). Zones with few or no fractures yield little or no water, in contrast to dense fracture zones that can potentially supply abundant water.

Table 7-1
Erosion Rates for Image Areas Discussed

Climate. The best-developed karst regions of the world are found in tropical (e.g., Jamaica) and temperate (e.g., Yugoslavia) environments. Considerable discussion has evolved as to whether tropical or temperate environments are more conducive to karstification (Smith and Atkinson, 1976). Lehmann (1970), a strong advocate of climatic geomorphology, asserts that solutional erosion rates are more intense in the tropics because of greater rainfall and carbon dioxide production in soils at higher temperatures. In contrast, Corbel (1959) contends that the intensity is greater in cold humid climates where larger quantities of carbon dioxide can be absorbed by water. The higher the carbon dioxide absorption in water, the stronger is the resultant carbonic acid. However, because Corbel overlooked the rates of reaction, which slow down at lower temperatures, the levels of CO²content may be irrelevant (Embleton, 1985, personal communication).

The absorption of carbon dioxide is temperature-dependent so that cooler water for a given volume can absorb larger quantities of carbon dioxide. If the water temperature rises from 0 to 35°C, the carbon dioxide saturation level will decrease between one-third to two-thirds (Jennings, 1971). Therefore, waters in cold climates can hold greater quantities of carbon dioxide in the ionic state, thus being more effective in dissolving limestone. However, more important than temperature is the partial pressure of carbon dioxide, which at sea level is relatively constant at 0.035 percent. The partial pressure of carbon dioxide in soil air can exceed that of the atmosphere from ten to several hundred times (Bogli, 1980). As a consequence, the presence and nature of soil cover can be far more important in karstification intensity than atmospheric air.

A study by Smith and Atkinson (1976) of comparative karst data from around the world indicates that mean annual runoff, rather than precipitation, is the principal parameter directly related to erosion rate. Temperature is believed to be important only with regard to its influence on supporting a continuous cover of soil and vegetation.

Vegetation. Arid karst regions, such as the Nullarbor Plain in Australia, are associated with sparse vegetation, thin soils, and therefore, a slowed rate of surface karstification. In contrast, if the existing soil and climate can support a dense vegetation cover, an intensified surface and subsurface karstification occurs, as observed in Jamaica and south China. Biogenic carbon dioxide, introduced to the soil by plant root systems and bacterial decay, is regarded as the most important control of solution erosion of limestones (Jennings, 1971).

Generally, where vegetation is most lush, the highest concentration of moisture, the highest biogenic activity, and the highest production rates of carbon dioxide occur. Under these conditions and free water circulation, the highest solution erosion rates can be achieved. Such conditions are found in both Jamaica and south China (Table 7-1). In Jamaica, the forest canopy has been cited as one of the prime factors responsible for the overdeepening of cockpits (Versey, 1972).

Time. The early karst studies of Cvijic and Grund at the turn of the 20th century were strongly influenced by the cyclic evolutionary teachings of Davis and Penck (Roglic, 1972). Thus, karst topography has been thought to evolve through stages of development beginning with fluvial action and the initial formation of dolines. As the surface drainage is slowly captured by swallow holes and the developing subsurface drainage, dolines coalesce to form uvalas, which, in turn, expand to poljes. This sequence is now considered to be antiquated, and according to Roglic, poljes are structurally controlled and are not related to uvalas.

It is questionable whether any two karst regions anywhere in the world have evolved sequentially in the same manner or even display identical morphological forms. Each karst region evolves within its unique combination of dynamic and static factors. However, this does not preclude the comparison of areas of similar morphology in an attempt to evaluate common factors.

From the examples of Landsat imagery in this chapter, it becomes apparent that each region has developed its own morphologic signature. To understand the evolution of a given karst terrain, it is necessary to comprehend the roles of length of time, style, and intensity of the energy flow through the hydrologic system. Those karst regions with the largest potential energy, related to the thickness of the vadose zone, and kinetic energy, or flooding, will also exhibit a higher energy morphology more rapidly and more fully than regions of lower total energy. High-energy morphology can be manifested in the form of larger caves, increased relief, density, and magnitude of dolines, hums, flood deposits, and a more extensive underground solution network.

KARST FROM SPACE

Within the realm of geomorphology, each geologic process leaves its own imprint on the Earth´s landscape, and each process will develop its own characteristic assemblage of landforms (Thornbury, 1969). For karst landscapes, this imprint is expressed as solution morphology on the regional scale. Because of the relatively large ground resolution distance of 79 m, many karst landforms cannot be discerned from Landsat MSS images; only the larger solution and fracture-controlled dolines and uvalas can be recognized. Thus, the advantage of the space perspective is not the identification or the recognition of individual landforms, but the collective pattern and texture they impart to a region of hundreds or thousands of square kilometers. This can occur only where given geologic processes and materials, such as carbonates, dominate a large region for a sufficient length of time.

The Landsat imagery discussed in this chapter has been chosen from the known karst regions of the world. Some well-researched regions are not included either because good imagery has not been available (e.g., New Guinea) or because man´s overprint (e.g., Indiana, U.S.A.) is so dominant as to obscure natural topographic patterns.

A cursory examination of all the karst images reveals a number of features specifically associated with the solution process:

Most important is the absence of a well-developed integrated surface drainage. Indeed, for the Nullarbor Plain, Australia, and Yucatan, Mexico, it is difficult to identify any recognizable drainage. Major rivers can be seen to incise the south China carbonate plateaus, but there is a distinct lack of well-developed tributaries draining into the river channels.

Most karst areas exhibit a relatively homogeneous pock-marked or dimpled texture. In south China, this pattern is overprinted with solution- incised joint sets. In Florida, the pattern is expressed as numerous large water-filled collapsed basins.

Joint sets are not recognized in all karst areas at Landsat scale. This does not preclude the presence of joints, but merely points out that they may be obscured because: (1) joints are too closely spaced, (2) solution relief of joints is slight, (3) dense vegetation cover is present, or (4) joints may indeed be absent or sparse.

What accounts for the large differences observed in karst regions is not variation in the karst process, but variation in lithology, structure, and the overprint of other processes like fluvial, tectonic, eolian, and glacial, and variations in the energy flow through the karst system through time.

LAKE BASINS

Introduction

According to the American Heritage Dictionary (Dell Publishing Co., Inc., 1983), a lake is defined as "a large inland body of water." The interpretation of the word "large" is conjectural. For our purposes, a lake must be large enough to be recognizable on Landsat imagery, which is limited by the ground resolution distance of 79 m and 30 m for the MSS and TM sensors, respectively. It is because of the presence of water that we easily recognize and focus our attention on these geomorphic forms. To develop a lake requires two things: (1) geomorphic process(es) to form a depression, and (2) the proper hydrologic and climatic conditions to maintain a confined body of water on the Earth´s surface.

Classification

Virtually every geomorphic process is capable of producing a depression either singly or in combination. A classification of lakes is, in essence, a classification of various geomorphic processes. Davis (1882) proposes a classification of lakes based on constructive, destructive, and obstructive processes, and Hutchinson (1957) presents a detailed classification system based on various geologic processes.

The following is a modified Hutchinson classification:

Origin

One objective of this section is to study various lake basins observable from space, and from their geometry, geologic, and geomorphic associations, point out characteristics that could reveal information about their origin. The study of the origin of lakes can be segmented into two lines of inquiry: (1) causes of topographic depression, and (2) explanation for the presence of water. The first line of inquiry listed is more amenable to study through space imagery than the latter. Note that many depressions exist that do not contain water, and as a consequence, their presence may be overlooked.

Physical criteria useful in the analysis of lakes from space are shape, size, density, and nature of the surrounding terrain.

Shape. Lake shape in many instances can narrow the choices of geologic process responsible for an inland depression. Circular topographic basins, for instance, can be produced by collapse (dolines, calderas), by explosions (volcanic craters, meteoric impact), or from wind (deflation hollows). Circular lakes, associated with these processes and visible on Landsat imagery, include the doline lakes in north central Florida, the caldera lakes from Nicaragua, a volcanic crater lake at Crater Butte, California, an impact lake in Chubb Lake, Quebec, and the deflation hollow lakes found on the Llano Estacado, Texas.

The best-developed elliptical basin lakes are the Carolina Bays in North and South Carolina and the oriented lakes of Alaska. Surface wave erosion, aided by wind at right angles to the long axis, is believed to be the major controlling factor in their elongation (Kaczorowski, 1976).

Figure 7.3a.. This Landsat scene (1057-16305-7), September 18, 1972) shows numerous linear lakes produced by glacial scouring along fracture zones in Canadian Shield crystalline rocks in the Lac La Ronge area, central Saskatchewan.

Dammed drainage basins produce dendritic lake patterns. The dams may be natural or, more frequently, manmade. In 1959, Earthquake Lake formed as a result of the Hebgen Lake earthquake, which jolted into motion 20 million m³ of rock and debris that subsequently dammed the Madison River in southwestern Montana (Costa and Baker, 1981). Lake Kioga in East Africa formed after epeirogenic tilting reversed the drainage in a large watershed and caused the eventual flooding of the tributary valleys. Manmade reservoirs are especially abundant in the southeastern United States, but they may be found in virtually every country of the world.

Linear lakes, including many on the Canadian Shield (Figure 7.3a and Figure 7.3b), are commonly imposed on fracture- or fault-controlled zones of weakness that localize streamflow or are gouged out by glacial scour. Triangular lake basins are found in the stabilized dune fields of Senegal. Rectangular lake basins have been noted in northwestern Yukon Territory, Canada; their origin is unknown, but structure and permafrost probably play a role in their development. Lunate or oxbow lake basins are common along meandering river channels such as the Mississippi River. These lakes are formed from abandoned meanders, usually during flood cycles. Irregular or amoebic-shaped lake basins are frequently associated with glacial till and are caused by the differential melting of buried ice or by water filling the low points on a hummocky moraine. These lakes are common in north-central North America and in Scandinavia. Some lake basins are so irregular and abundant that they resemble ink-splatter patterns and can be found in Canada, in Scandinavia, and in Siberia where large areas of bedrock have been laid bare by continental ice sheets. Frozen tundra, bedrock structure, and differential erosion have contributed to their highly irregular pattern.

	Figure 7.3b. Aerial view of glacial scour lakes along fractures in the eastern Canadian Shield (Canadian Department of Energy, Mines, and Resources, A11607-84).

Size. Of the world´s ten largest lake basins based on water surface area, six have a tectonic origin and four are glacially derived (Smith, 1968). At various times during the Pleistocene, glacial lakes have grown in size and probably out-numbered large tectonic lakes. Lake Bonneville in the Basin and Range of Utah and Minchin Lake in Bolivia are examples. These pluvial lakes were large because the cooler climate during glacial periods favored the storage of surface water. The largest lake basins have developed in response to a regional stimulus in contrast to small isolated lakes that may result from local influences.

Density. The density of lake basins per unit area can again indicate the regionality of a geomorphic process. The tens of thousands of lakes in central Canada and north-central United States reveal the ubiquity of the glacial process. The Carolina Bays of the southeastern United States and the oriented lakes of Alaska exhibit the regional influence of wind and, in the case of Alaska, further influence by permafrost. With isolated small lakes, such as Earthquake Lake, Montana, local geomorphic processes must be examined to determine the lake´s origin.

Associated Terrain. Clues to a lake´s origin, as viewed on Landsat imagery, are frequently revealed by the regional overprint of a particular geomorphic process. The presence of dune fields in Senegal and glacial moraines in Quebec, Canada, and the abundance of volcanoes around Lake Nicaragua, all suggest to the observer a cause-and-effect relationship. Many rift lakes display straight-lined shores with angular bends mirrored on the opposite shore. Inland faults may parallel the lake edge and indicate a tectonic origin. Lake Tanganyika is an example. Lakes associated with the dimpled surface texture indicative of karst topography may well be water-filled dolines. The Dinaric Mountains of Yugoslavia have a few lakes of this variety. However, the most well-developed karst regions of the world as in Yugoslavia, south China, and Jamaica do not display abundant lakes. This is due, in part, to the efficient infiltration of precipitation and a subterranean piezometric surface.

Time

Within our timeframe, lakes may develop catastrophically from volcanic eruptions, landslides, and earthquake activity, or they may form from slower acting processes like wind, glacial, and epeirogenic activity. However, it is important to emphasize that, geologically, lakes are temporary and form rapidly and decay quickly (Smith, 1968). Because most of the Earth´s land surface is dominated by fluvial erosion, lakes that do occur are threatened with either capture and draining by expanding tributaries or infilling of sediment until the lake becomes extinct. The mere presence of a lake, then, demonstrates the dynamic restlessness of the Earth´s surface.

PLATE KL-3
CENTRAL YUCATAN PENINSULA

Plate KL-3	Map

This image includes part of the Yucatan Platform within the Yucatan Peninsula in the states of Campeche, Quintana Roo, and Yucatan. Although no coastline is exposed in the image area, it is surrounded on three sides by the sea. This part of Mexico receives between 1000 mm of rainfall near Merida and 1500 mm toward the south edge of the image. Nearly all of this rain falls between May and September. Of the total precipitation, approximately 85 percent returns to the atmosphere via evapotranspiration, while the remaining 15 percent infiltrates to the ground-water table (Hanshaw and Back, 1980). As can be seen from the image, no drainage network has developed over the region; thus, runoff is insignificant.

The Yucatan Peninsula and adjoining continental shelf (Campeche Bank) consist of relatively flat-lying Tertiary carbonates (Figure KL-3.1) covering some 350 000 km² of area (Weidie et al., 1978). The Campeche Bank extends about 200 km into the Gulf of Mexico both north and west of the peninsula. The narrow Caribbean shelf borders the peninsula to the east and rarely exceeds a few tens of km in width. The exposed Tertiary rocks attain thicknesses up to 1000 m in northwestern Yucatan and consist primarily of dolomites, limestones, and marls. Most of the surface rocks exposed in the image area are Eocene and Paleocene in age. Other ground scenes typical of karst terrain in the Yucatan are shown in Figure KL-3.2 and Figure KL-3.3.

Figure KL-3.1	Figure KL-3.2

The most prominent structure in the region is the Ticul Fault and associated Sierrita de Ticul escarpment, which trends N60W for about 200 km (see index map and image). Movement on the fault has probably been sporadic since the Late Cretaceous (Weidie et al., 1978). Sierrita de Ticul is a series of hills, forming an arcuate ridge with a relief of nearly 50 m (West, 1967). The Sierrita marks the boundary between the flattish Yucatan Plain to the north and the hilly Campeche region to the south. Most of the Yucatan Peninsula is dominated by karst topography (Figure KL-3.3) consisting of cenotes (steep-walled sinks that usually penetrate the water table), bare limestone platforms, aquadas (broad shallow solution basins), and resumideros (funnel-shaped conical depressions). The cenotes and aquadas are the two most important sources of water in the region, and as a consequence, most of the Mayan cultural development and population centers are found to be closely associated with these karst features. Where the limestone is not bare, it is covered with a thin terra rossa soil, usually less than 20 cm thick, developed on weathered limestone (Hanshaw and Back, 1980). Where bare limestone is exposed, it often exhibits deep solution channels or karren that can pose a problem for vehicular travel (West, 1967).

Figure KL-3.3

It is because of the karst that no surface drainage exists in the northern and central parts of the peninsula. The high porosity and permeability of the limestones provide for an efficient internal drainage (Southworth, 1984). The Yucatan Peninsula is similar to Florida because both have thick sequences of relatively flat-lying Tertiary limestones; however, in Yucatan, the lack of Upper Tertiary clays and marls overlying the limestone results in rapid infiltration or rainfall. The presence of an extensive interconnected subsurface drainage network is suggested by: (1) a gentle piezometric surface gradient that has been measured as 1.2 to 1.5 m above sea level in areas 80 km inland from the coast at an elevation of 30 m above sea level, (2) the lack of notable drawdown observed in heavily used wells, and (3) the young age of water dated from its C¹⁴ content (Hanshaw and Back, 1980).

Hanshaw and Back (1980) believe that chemical mass wasting in the zone of dispersion is perhaps the most important geomorphic process in the region. From their measurements on the concentration of dissolved solids, the surface in places could be lowered by as much as 340 mm/1000 yr. This figure is misleading, however, because much of the dissolution occurs along subterranean passageways.

The karst nature of the image area can be recognized by the lack of any developed drainage network and by the presence of residual karst knobs found south of Sierrita de Ticul. Lago de Chichancanal (see index map) may be fracture-controlled like some of the lakes east of the image area that are influenced by the Holbox fracture system. Alignment of cenotes due to fracture control has also been documented in the eastern part of the peninsula (Southworth, 1984). Landsat 21089-15115, January 15, 1978.

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BOOK REVIEWS

Caribbean Journal of Science, Vol. 34, No. 3-4, 340-341,1998
College of Arts and Sciences, University of Puerto Rico, Mayagüez

Jamaica Underground. The Caves, Sinkholes and Underground Rivers of the Island. Por Alan G. Fincham. The Press University of the West Indies (Barbados, Jamaica, Trinidad and Tobago), 447 páginas y 16 láminas a color. Disponible con cubierta de cartulina o de cartón.

La segunda edición del libro Jamaica Underground viene a cubrir con creces el vacío dejado por la primera edición de la obra, que desde hace varios años está agotada. Esta edición incluye contribuciones prepara-das por varios científicos dedicados a distintas ramas relacionadas con el estudio de las cavernas, los cuales son bien conocidos por su larga experiencia en trabajos de campo en las Antillas Mayores 5• especialmente en Jamaica. Gracias a esto, el libro es una fuente única de información, no sólo sobre el karst y las cuevas, sino también sobre bioespeleología, paleontología, hidrogeología y otras especialidades, así como sobre la historia de las investigaciones espeleológicas en Jamaica. Sobre esta base se puede afirmar que Jamaica Underground es el único volumen existente con un trata-miento abarcador de los problemas más importantes de la espeleología y karstología jamaicanas.

El libro está dividido en once capítulos y nueve apéndices. Hay tres capítulos dedicados a la historia de la exploración de cuevas y la espeleología en Jamaica (A. Fincham, R. Read, y T. Shaw), la geología de las cavernas jamaicanas (G. Draper, y G. Wadge), la geomorfología de las regiones calizas (G. Draper, y A. Fincham), la hidrología de las cavernas jamaicanas (A. Fincham), la paleontología (R. D. E. MacPhee), y los invertebrados (S. Peck) y vertebrados (D. McFarlane) de las cuevas jamaicanas. Un pequeño capítulo trata el problema de la histoplasmosis, una enfermedad provocada por hongos (A. Fincham). La mayor parte del libro está dedicada al catálogo de las cuevas Jamaicanas, que con más de 1,200 registradas, incluye descripción, mapas y anotaciones históricas. La bibliografía incluye unos 500 títulos, algunos de ellos anotados. Los apéndices abarcan un listado de la ubicación de las cavernas, las cuevas más largas y más profundas de Jamaica, la distribución de las cuevas por tipos y edad de las rocas, una clasificación morfológica de las cuevas, un glosario de términos especializados y otros datos importantes.

La isla de Jamaica presenta una superficie de 11,420 kilómetros cuadrados, de los cuales 2/3 están ocupa-dos por rocas calizas del Terciario. Jamaica se conoce bien entre los karstólogos, por ser la localidad tipo del karst cockpit. Este tiene una morfología muy peculiar determinada por la combinación de colinas y valles de geometría cónica, que vista desde el aire tiene el aspecto de la pared de un panal de abejas. También se describen el karst de torres, las poljas, y muchas otras formas del relieve, incluidas las acanaladuras y micro acanaladuras. Dos mediciones de la actividad del karst en Jamaica arrojan valores de 72 y 86 mm/1,000 años.
Los espeleólogos jamaicanos han descubierto y cartografiado más de 1,200 cuevas en la isla, tanto secas como sumergidas bajo las aguas subterráneas. De acuerdo a su morfología, estas cavernas se clasifican como pasadizos, laberintos, salones, caídas verticales, solapas y sus combinaciones. Su origen se relaciona al flujo vertical de las aguas de lluvia, al flujo horizontal de las aguas fluviales y la combinación de ambos. Sin embargo, los movimientos del agua subterránea también dependen de la estructura interna de los macizos calizos (planos de estratos, grietas y fallas, así como la porosidad primaria y secundaría). Las cuevas más profundas son Dunn's Hole (230 m), Morgans Pond Hole (186 m) y Volcano Hole (177 m), mientras que las más largas son Gourie Cave (3,505 m), Tackson Bay Cave (3,360 m) y Still Waters Cave (3,355 m). La altura a que están localizadas las cuevas varía entre 0 y 1,200 metros, pero predominan aquellas entre 0 y 800 metros; reflejo del relieve montañoso moderado de Jamaica y de la altitud de los macizos calizos.
Jamaica Underground está también dedicada a cuestiones de bioespeleología. Leyendo el libro uno aprende que, en sólo 60 cuevas estudiadas hasta el momento, se han encontrado 250 especies de macro invertebrados, 42 de ellas estrictamente troglobias. Estas cifras indican el gran potencial de estudio que aún tienen las cuevas jamaicanas. Veintiocho especies de vertebrados se han encontrado en los ambientes cavernarios, incluyendo peces, anfibios, reptiles, pájaros y mamíferos (jutías y murciélagos). Pero las cuevas de Jamaica también guardan el tesoro de los restos fósiles de 14 especies de animales ya extinguidos, incluidos primates, roedores, aves y reptiles.

Un elemento relevante de este libro es el catálogo bien documentado de las cuevas jamaicanas, que incluye muchos mapas, secciones transversales y longitudinales, descripciones y algunas anotaciones históricas. Esta base de datos tiene un gran valor por si misma, pero sobre todo, servirá de fuente para nuevas investigaciones sobre la espeleología y el karst de la isla.
Cada persona tiene su opinión sobre como se debería escribir un libro; por eso no es totalmente justo afirmar que a esta obra le falte tal o cual aspecto. A mí me hubiera gustado ver un capítulo sobre las formaciones cristalinas de las cuevas, otro dedicado al estudio de los procesos que operan en la formación y transformación kárstica de los macizos de calizas, y un trata-miento más extenso de los problemas referidos a la karstología ambiental.
En conclusión, considero que el libro Jamaica Underground puede recomendarse como una obra que no debe faltar en la biblioteca de los interesados en la espeleología y el karst, así como en los departamentos de Ciencias de la Tierra de las universidades e instituciones científicas. El público en general no sólo disfrutará las muchas y bellas fotografías a color que contiene el libro, sino que verá en él una obra de referencia muy útil para conocer mejor los misterios y las bellezas de la naturaleza.

DR. MANUEL A. ITURRALDE-VINENT, Miembro de la Sociedad Espeleológica de Cuba, Museo Nacional de Historia Natural, La Habana Vieja, Cuba.

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