Caves and karst: Research in speleology

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Caves and karst: Research in speleology
Series Title:
Caves and Karst: Research in Speleology
Cave Research Associates
Cave Research Associates
Tumbling Creek Cave Foundation
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Subjects / Keywords:
Inner Space Cavern (Texas, United States) ( 30.607778, -97.687778 )
Geology ( local )
serial ( sobekcm )
30.607778 x -97.687778


General Note:
Contents: The chemical evolution of cave waters, Inner Space Cavern, Texas / Russell S. Harmon. Cave Notes(vols. 1-8) and Caves and Karst: Research in Speleology(vols. 9-15) were published by Cave Research Associates from 1959-1973. In 1975, the Tumbling Creek Cave Foundation compiled complete sets of the journals in three volumes. The Foundation sells hardbound copies of the material to support its activities.
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Tumbling Creek Cave Foundation Collection
Original Version:
Vol. 12, no. 1 (1970)
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See Extended description for more information.

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K26-01006 ( USFLDC DOI )
k26.1006 ( USFLDC Handle )
12497 ( karstportal - original NodeID )
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CA YES AND KARST Research in Speleology Volume 12. No. 1 January/February 1970 Frontispiece The Flowing Stone of Time Inner Space Cavern, Texas. THE CHEMICAL EVOLUTION OF CAVE WATERS, INNER SPACE CAVERN, TEXAS by RUSSELL S H ARMON'" Introduction To date, analytica l data on the solution chemistry and evolution of cave waters are sparce. The major American works in this field h ave been the comprehensive stud y o f cave waters a t Indian Echo Cave : Carpenrer Cave and Luray Caverns b y H olla nd a nd others (1964); and the work on water chemistry and carbonate speleothems in C arlsbad Caverns by Thrailkill (1968a,b). These works have anempted to give a n a l ytica l pr ecis i o n to the stages of cave-water evolution, to verify the carbonate solurion chemistry o f Trombe (1952) and Garrels (1960), and to supply accurate a n a lyrical data to the probl e m o f cave-water evolution. A number of Europeans h ave investi gate d porrions of this probl em m ainly the solution of limestOne Among the papers that h ave conrributed most are those of Trombe (1952), Gams ( 1962), Ford ( 1964), Douglas (1965), a nd Piny (1966). Prior to the work presenred here, no comprehensive study of cave w aters h ad been made in Texas. The objectives of the investig a tion were to: 1) Deter min e the b erors influ e n cing the d eposit i o n of calcium carbo n ate o n a nd around the Flowin g StOne of Time" at Inner Space Cavern (Fronrispiece ) 2 ) Determine the state of saturatio n o f the waters asso'NASA Manned Spacecraft Center, Houston, Texas 77058.


CAVES AND KARST CA YES AND KARST CAVES AND KARST is a publication of Cave Research Associates. Subscriptions are available for $2.50 per year (six issues) or $6.00 for Volumes 12 through 14. Mid-year subscriptions receive the earlier numbers of the volume. Correspondence, contributions, and subscriptions should be addressed to: CAVE RESEARCH ASSOCIATES, 3842 Brookdale Blvd., Castro Valley, Calif. 94546 Editor: Arthur l. Lange Associate Editor: Alan D Howard Editors: R. deSaussure, J. F Quinlan, Sylvia F. Graham, Mary l. Hege, Lee Christianson Copyright 1970 Cave Research Associates ciated with the "Flow ing Stone of Time" with respect to calcite and dolomite, and 3) Supply and interpret a n a lytic a l dat a concerning the c ar bon a te solution and deposition of ground water in the dolomite o f the lower Edwards form a tion. Geologic setting Inner Space Cav e rn is devel o ped in the Cretaceous Edwards formation about 2.4km southwest of Georgetown, T exas ( Figure 1). This section of the Edwards is characterized by a dol omite a nd dolomitic lim esto ne containing abundant chert nodules and a few cherr b e ds ( Figure 2). The cave has been form e d along j oi nt s and faults of the Balcones f a ult zone, a promina nt n o rtheast trending tect o nic fea ture of central Texas. The major fault movement has s hift e d the lower p o rti ons of the Edwards f o rmation on the west, up against rocks o f the upper Edwards o r Geo rgetown formations o n the east. The chemical evolution of cave waters The evolution o f cave w a t ers has been divided into three phases: 1) A phase of ex posure to a nd a bsorpti o n o f carb o n dioxide in the soil a nd atmosphere, 2) A phase of solution of carbonate b edrock, a nd 3) A phase o f adju s tment of ground water ro the cave a tmosphere (HOLLAND & Others, 1964 ; MOORE & NICHOLAS, 1964). Phase I: Abso rp tion of carbon dioxide in the soil zone: Normal a tmospheric air h as a carbon dioxide pressure o f 3.0xlO--'atm a nd r a in water in equilibrium with atmos pheric c a rbon dioxid e s h o uld contain about 1.37xlO -5 moles per liter of c arbon dioxide FRANKE, 1965). As thi s rain water passes through the soil zone it dissolves a dditional c arbon dioxide, since th e soil zone may contain m any more times as much carbon dioxide as the atmosphere. P hase II : S oilition of C(/rbo nate bedmck: The prese n ce or a bsence of a vapor phase durin g the r eact i o n o f the downward percol a tin g unders a turated subsurface water with the carbonate b e dro c k determines th e exte nt to w hich soluti o n occurs (HOLLAND & others, 1964). The g r ea ter soluti o n of c ar b o nates occ ur s in a n o p e n system, wherein l ost CO" can b e reg a ined fr o m the a ir. Thra ilkill (1968a) has s u gges ted that this downward movement of subsurface water o ccurs almost entirely a l o n g j oi nt s a nd fractures, and because saturation with respect to calcite u s u ally occ urs before a ground-water reservoir i s r eac h ed, it seems unlikely that the saturation of w a t e r with calcium carbonate can occ ur under n or m a l circumstances without th e presence of a vapor phase during solution ; h oweve r enhancement of solubility due ro the pres ence of a vapor ph ase occurs only if the v a p or i s exc h a nged with the a tmosphere or soil. The extent o f such exch a nge i s unkn own. The car bon a te solution c h e mistry o f this seco nd phase of c a ve water evo luti on has b ee n adeq uately described by Garrels ( 1 960 ) Onl y t he ba sic c a rb o nate equilibrium equ at i o n s for d o l o mite a nd d o l om itic limeston e are presented in this paper. The ch a rge-b a l a n ce equation f o r the water contained in these strata is: nH+ + 2mCa++ + 2mMg+ + + mCaHC03 -+ = ,nHCO; + 2mCO; + mOH-. ( 1 ) At the pH co ndi t i o n s present in th e cave, h ow ever certain t e rms become insignific ant a nd t h e c h arg e-b a l a n ce equation can be redu ce d ro 2 m C a ++ + 2mMg++ = mHCO; J (2) 2


VOLUME 12, NO.1 and the complexing of Ca++ and Mg+ + with HCO;-a nd a lso b e disregarded if all th e +2 i ons are c onsi der ed uncombined This yie ld s a maximum a bsol ute er ror of n o m o r e than a fe w percent in the calc u latio n of activity coeffi cients in the p H r a n ge from 6 to 9 (HOLLAND & others, 1964). Following t hese assumptio ns, the i o n ic s trength o f the soluti o n can be stated b y Figure 1 I<.e d Inner Space Cretaceous P e riod 1 ++ ++ I S = 2 ( 4mCa + 4mMg GEORGETOWN o 2 mi rl---+---+I---+I bn o 2 3 --A' Eagle Ford. Buda and Del Ria Fms. Georgetown Fm. Edwa rd s Fm. A_ Miocene Epoch "'--Foul t + mHCO;). Figure 2 I ... > to U u to "" Ul ... ] '\ '\ \ 1\ \ \ \ \ '\. \ \ em -Ii -\ .... \ \ em\ \CZI '\ I;ID \ ft 55 m 16 50 1 4 45 40 1 2 35 1 0 30 8 25 20 6 15 4 1 0 2 0 o Ked KEd Figure 1 Geological Sketch map of the vici nit y of Inner Space Cavern, Georgetown, Texas. Figure 2 Measured sec tion of the Edward s form a ti o n No 2 core h ole, Inner Space Cavern: A) 0 -2.4m: d o lomite: massive, l ight brown, chert nodules common; B) 2 4 -3.0m: dolomite : powdery, grey-white; C) 3.0-3 4m: chert : nodul a r bed, dark grey; 0) 3.44 6m: dolomite: bedded, light brown, uppe r O .6 m contains cheri nodules, fossiliferous; E) 4 .6-5.5m: dolomite, resistant, light brown ; F) 5 5-5 8m: dolomitic limestone, very resis t ant, light grey; G) 5 .8-7.3m: dolomite, semiresistant, wnite ; H) 7 .37 .6m: limonite, highly oxidized zone; I) 7 6 -16 .5 : dolomite, ma ss ive, semi resistant, I ight brow n ; J) 16 .5-16. 8 : soil zone. (3) 3


CAVES AND KARST Air Pool Water Inflowing W ate r D a t e Temperature (oC) Temperature (0C) Temperature (oC) 8 F ebruary 18.1 19.0 20. 5 16 February 18. I 19. 0 2 1.0 18 Februar y 18. I 1 9 0 20. 5 21 February 18. 3 19. 5 20. 5 23 February 18. 3 19. 5 20. 5 27 February 18. 3 19.5 20. 5 2 March 18.1 19.5 20.5 6 March 18. I 19. 5 20.5 9 March 18.3 19.5 20.5 13 March 18. I 19.5 20.5 16 March 18.1 19.5 20. 5 12 April 18.1 19.5 20. 5 Table Water a n d air temperatures. Usi n g the calculated value for the i onic strength the activity coefficients of t he ion i c species w i thin the system can be cal culated by the DebyeH iicke l method. The conce n trations of the dissolved ionic species are given by the equations ++ (Ca )(CO;) cac03 (H+) (HCO;) H2C03 un(CO;)=K (HCO;) HC03 (4) 1 0 8 28 (5) 1 0 -6 30 (6) (7) (8) (9) The state of saturation of the water with respect to calcite can then be determined by either comparing the product of the m eas ured calcium concentration and carbon dioxide p a rticle pressure with the sanlration product of calcite a t the desired temperature or by comparing the measured pH a nd c a lcium concentration with the equilibrium curves of Trombe (1952). For this investigation the l a tter method was used Phase Ill: Adjustment to the ca've atmosphere: Once grou n d water enters a cave, evaporation a nd equi l ibr atio n of carbon dioxide between the c a ve water and cave atmos phere are the two primary processes that a ffect this water. If the water gains additional c a rb o n dioxide upon entering a cave, the solution o f carbonate rock can continue; but if carb o n dioxide is lost to the cave atmosphere, the n precipitation o f a carbon a te miner a l is likely. B eca u se th e relative humidit y in most caves is g reater than 90% and the presence o f a vapor phase l ow in CO o is the more common situation, the loss of carbon dioxide from the water to the cave atmosphere is the m ore common of the two events. The calcium to ma g n esium co ncentr a tion ratio of percolating water or cave water i s a n imp orta nt factor, since it can often b e a useful indicator in determining the origin o f the calcium and m agnes ium in so luti on, and in determ i nin g the mechanism causing t he pre c ipit at i o n o f calcium from solution. Congruent sol uti o n o f c a lcium a nd m ag nesium from dol o mite results in a calcium to m ag nesium r a ti o approac hin g 1. A constant magnesium content in the water before 4


VOLUME 12, NO.1 and after precipitation indicates that evaporation of water was unimportant; while the loss of carbon dioxide was important to the process R es ults and discussion The Frontispiece shows the "Flowing StOne of Time in Inner Space Cavern The cave waters from 5 areas associated with this feature were periodically sampled for 3 months. Measurement of pH were taken at the cave with a portable PhOtovolt Omnirange pH meter as the water samples were collected. Results were reproducible to .05 pH unit. Temperarures were determined with a standard laboratOry mercury thermometer (Table 1). The concentration of calcium and magnesium in the water samples was de termined by means of EDTA titration as outlined by Lewis & Melnick (1960). In Figure 3 the calcium concentration of the water samples has been plotted against the magnesium concentration In all cases the calcium concentration greatly exceeds the magnesium concentration, thus giving very high calcium to magnesium ratios (Table 2). This may be explained in rwo ways. First, the cave is located on l y 11.5m below the sur face, and the overlying bedrock is highly fractured due to faulting, resulting in the very rapid passage of water through this bedrock. Secondly this indica tes solution of minor amounts of calcite in the overlying strata r a ther than selective solution of calcium over magnesium from the overlying do l omite strata. Observa tions also show that the calcium to m ag nesium ratios drop markedly between water just entering the cave and the pool waters, and the lower calcium concentr at ion of the pool waters indicates that the precipitation of calcium carbonate has occurred, also shown by the fact that a thermometer placed in the northwest pool in February was covered with a 0.03mm coating of calcite by April. The fact that the commercial portions of the cave a re well ventilated indicates that evaporation might be a significant factor in the precipitation of calcium carbonate from the cave water. The variability of the magnesium content of the pool waters compared with the constant magnesium content of the water entering the cave seems to bear this out, but still indicates that precipitation of calcium carbonate due to loss of carbon dioxide from solution exceeds that resulting from evapora tion by a ratio of 10 to 1. The faa that the water level of all pools fell nOticeably during the winter dry period also could be a n indication of evaporation, but it is difficult to distinguish this effect from that of seepage out into the adjacent bedrock. Due to the absence of complete chemical analyses of the water samples from the cave it was impossible to cleterm ine the exact degree o f saturation of these waters wirh respect to calcite. Nevertheless saturation dererminations of a general n at ure c a n be obtained by plotting rhe measured calcium content a nd pH of rhe cave waters on [he equilibrium curves of Trombe (1952), assuming that [he minor presence o f magnesium does not affect the saturation of calcite. Mg +2 Concentration. mrnple sl liter 2 0_5 3 2 6 o. 1.0 1 2! 2 7 1.5 15 1 3 4 1 9 7 . 19, 12 0 1 4 22 20 2 0 dripping waters pool waters flowing waters (top) flowing waters (bottom) 6 0 9 14 , ,11 8 02 5 2 5 Ca + 2 Concentration, mmoles/liter I F igure 3 Ca + + and Mg + + concentrations in water samples from Inner Space Ca vern. 5


6 CAVES AND KARST IQ I>l I'< l I'< '" -IQ I>l I'< -N IQ I>l I'< M N ::E '" ::;;

pH 8.5 8.0 7.5 7 0 1.0 1 2 18 21 27 . 26 2.0 12 9 20 19 25 15 10 13 22 4 7 11 + + 8 6 + 5 (17 3.0 VOLUME 12, N O 1 + __ flowing (bottom) E!t -flow i n g waters (top) pool water 5 -dripping waters Supersaturated Saturation line for ./ calcite Undersaturated 4.0 Ca + 2 Concentration, mmoles {liter Figure 4 Ca++ and p H of water samp l es from I nner Space Cavern. In Figure 4 the calcium concenrration and pH of each water sampl e collecred is plorred against the calcium carbonate equil i brium curve f o r 20 C. This plot indica tes tha t t he increase in the pH observed between samples 16 ro 17 a nd 23 ro 24 results from the loss of carbon dioxide a s the water e nrers the c a ve a nd flows d ow n the flowsro ne mound. The w a ter, undersaturated with respect ro calcite when enrering the c ave, becomes super sarurated upon sranding in the pools a nd prec ipita tes calcite Measuremenrs o f pH a lso indic a te that a slight pH stratification existed in the norrh west pool such that a lower pH occurred at the surface of the p oo l th a n a t depth Finally o bservations indic a te that the precipitati o n o f calcite is greater during d ry periods th a n wet periods. Simil a rly the calcium co nrenr of the waters enrering the cave is found ro be l ower duri n g wet periods especially following times of heavy rainfa ll (Figure 5). Summary The basic results of this investigation are stated as follows: 1) Precipitation of CaCO occurs primari l y due ro the loss of CO" from so l utio n but precipitation due ro evaporation does occur fr o m the pools as evi denced from a sl ight variation of the magnesium concenrrations o f the c a ve waters within the l imits 0.05 to O.5mmo l /l. 2) The amount of precipitation o f CaCO due ro loss of CO exceeds that d u e ro ev a poration by about an order of magnitude. 3) The Ca + + /Mg + + r a tios o f the water ju s t enrering the cave is consistenrly greater than those of the waters which h av e greater time to e qui l ibr a te with the cave atmosphere. 4) The high Ca ro Mg ratios o f the cave waters indic ate that calcium a nd magnesium are n o t being congruenr l y dissolved from th e d o lomite a nd limestOne of the Edwards formation ; calcite is bein g selectively dissol ved ove r do l o mite 5) The va lue of the solubility product o f dolomite of H olla nd & others (1964) appears ro b e hig h b y an o rd e r of m ag nirude whi l e rhat o f G arre l s & others (1960) ap-7


CAVES AND KARST r?infct!l t Ca inn,o l/l (;:liciurn content of waters c ntt!ring cave I StlrfilCt> r infall 0.0 2.5 2.0 1 5 1.0 0 5 APHI L F igure 5 Rainfall and Ca++ concentration for waters entering Inner Space Cavern. pears ro be low by the same amounc. A K D of lOl s.on is suggested by the dara from Inner Sp ace C ave rn if saturation of the inpuc flow with respect co bach calcite and dolomite is assumed. 6) The calciwn concencration of waters is lowest in pools havin g a surface film of calcite or covered with "cave ice; i.e., in water that has had the greatest amounc of time co equilibrate with the cave atmosphere. 7 ) A stratification of pH values is n oted in one pool showing the surface pH ro be greater than that at depth. S) Preliminary results indicate that precipiration of CaCO is greater during dry periods than wet periods Acknowledgements This work was supported by an undergraduate research grant from the University of Texas co fulfill the r e quirements o f a n honors' thesis f or the Bachelor of Arts degree. I am ind eb ted co Mr. D. Claws on, and the management of Inner Space Cavern, for p l acing their facilities at my disposal. Al so I want to express fmrher appreciation to Dr. 1. ]. Turk, P. R. Brett, and 1. S. L a nd f or the i r suppOrt and commencs on the manuscript. References DOUGLAS, I. (1965). Calcium a nd mag ne s ium in k a rst waters. [ i elict it e 3 : 23-36. foORD D. C. (1964). The Caves of Derbyshire. Clapham, Dalesma n Pub!. C o. FRANKE, H. W. (1964). The theory behind s tala gmite shapes. Siudies ill Spele%g y 1 : 89-95. GAMS, l. (1962 ) M e rtitue kortozijske intenzitete V Slivcniji in njihov pmen za geomovfologiji. Gcog r afic h c skii V e stuik 3 4: 3 -16. G/\RRELS, R. M. ( 1960 ) .IHill el"fl/ eq 1lilibrirl. Harper and Brothers, New York. 2 531' GARRELS, R.lvf. M. E THOMPSON, & R. SE 1VER (1960). Stab ility of some carbonates at 2 5 C a n d one arm osp h e r e rora l pressure /lme ricrlII j OIIl"l/(f/ 0 / Sci ence 258: 4024 1 8 HOLLAND, 1-1. 1-1., T. U. KIRSIPU,]. S. HUEBNER, & U. OX BURGH ( 1964). On some as peas of the chemical ev o luri o n of cave wa t ers. jUllrtlal 0/ Geo l ogy 72: 36-67. INGLE-SI\'IITH, D. & D. lvLEAD ( 1962). The so luti o n of lim estone with specia l r efe r ence to Mendip. Brislol Unil 'Ns il y S/Je/eologica/ S ociet ) Procee dill g s 9: I 8S 2 1 I. LEWIS, L. L. &. L. M. MELNICH ( 1960) D e l erminat i o n of calcium a n d magnes ium with (eth ylene d initro) tetra acetic acid. A ualylic(I/ Cbe ll/islr y 32: 3t' !l2. 1-.mORE G. W & BROTHER G. NICHOLAS (1964). S/)e /eol ogy -/ 1 slurly o f cares. D. C. Heath Co., Boswn 1 2 01'. P1TTY, 1\. f. ( 1966). An approac h 10 the s tudy of karsr w a ters. i -i,,11 U lli ve rsit ) OCC"s;oll((1 Pape r N n 5 TH R A ILKI LL. .J. V. (I 96il). C h e m ical a n d hl'Jrologi c faclOr s in th e exc a vat io n o f limesr o n e caves. Gcolog ic," Society u f 11l11e ric(( B"lI e l ili 79: 1 9-45. TROl\ffiE, F. ( 195"). Twile rle Sp i /enl agio P aris Payo r, 3 7 6p. YANATEVA. o. r;:. ( 1 95 i ) So luhilill' "f d o l u milc in \\"alc r i n rhe presence o f corbu n d i o xid e / l k ,tdclllia N((IIl: SSS R. Olrle/ a llie r:.billl i rb csk i k!J N d k i zreJ l ii d n o 6: 1119-11 20

Contents: The chemical evolution of cave waters, Inner
Space Cavern, Texas / Russell S. Harmon.
Cave Notes(vols. 1-8) and
Caves and Karst: Research in Speleology(vols. 9-15)
were published by Cave Research Associates from 1959-1973. In
1975, the Tumbling Creek Cave Foundation compiled complete
sets of the journals in three volumes. The Foundation sells
hardbound copies of the material to support its