hypogeniccaves

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HE ROLE O CONDENSAION-CORROSIONIN HERMAL SPELEOGENESIS: SUDy O A HyPOGENIC

SULIDIC CAVE IN AIx-LES-BAINS, RANCE

VLOGA KONDENZNE KOROZIJE V ERMALNI SPELEOGENEZI:UDIJA HIPOGENE SULIDNE JAME V AIx-LES-BAINS,

RANCIJA

Philippe AUDRA1, abien HOBLEA2, Jeanyves BIGO3 & JeanClaude NOBECOUR4

1 quipe Gestion et valorisation de lenvironnement (GVE), UMR 6012 ESPACE du CNRS, Universit o Nice SophiaAntipolis,98 boulevard douard Herriot, BP 3209, 06204 NICE Cde 3, rance; email: [email protected]

2 Universit o Savo, EDyEM, Campus, 73376 LE BOURGE Cde, rance; email: [email protected] rench Association o Karstolog; email: [email protected] rench Association o Karstolog; email: [email protected]

Received/Prejeto: 24.01.2007

COBISS: 1.01

ACA CARSOLOGICA 36/2, 185194, POSOJNA 2007

Abstract UDC 551.435.8:551.3.053(44)Philippe Audra, Fabien Hoblea, Jean-Yves Bigot & Jean-Claude Nobecourt: Te role o condensation corrosion in ther-mal speleogenesis. Study o a hypogenic sulfdic cave in Aix-les-Bains, FranceCondensationcorrosion is an active speleogenetical process inthermal caves where high thermal gradient drives air convection.Wall retreat rates are greater than in meteoric caves. Conversel,evaporation produces depositional processes b replacement olimestone b gpsum and b aerosol decantation leading to theormation o popcorns. Te Chevalle Aven belongs to AilesBains thermalsulfdic cave sstem. Condensation occurs at thecontact o cool walls o large spheres; conversel, evaporationoccurs at the output o the narrow passages where the air sinksdown rom the upper sphere. A weathered laer and bioflms arepresent where slow condensation occurs. Corrosion distribution

varies according to thermal rock conductivit and causes thesphere to develop upwards, laterall, and divergent. Tis morphodnamic pattern avors the development o stacked spheres,isolated b narrow necks, and arranged in a bushlike pattern.Tis development is clearl active in the vadose zone above thethermal water table. We propose that some avens above water table hpogenic caves, like Villa Luz (Meico), ma be ocondensationcorrosion origin instead o phreatic. uture de

velopment will collect phsical and chemical data to calculatethe condensationcorrosion budget and assess its role in cavedevelopment.

Key words: condensationcorrosion, thermal caves, spheregenesis, air convection, AilesBains thermalsulfdic cave sstem, Chevalle Aven, rance.

Izvleek UDK 551.435.8:551.3.053(44)Philippe Audra, Fabien Hoblea, Jean-Yves Bigot & Jean-ClaudeNobecourt: Vloga kondenzne korozije v termalni speleogenezi:tudija hipogene sulfdne jame v Aix-les-Bains, FrancijaKondenzacijska korozija predstavlja aktivni speleogenetski proces v termalnih jamah, kjer kroenje zraka povzroa visok termalni gradient. Raztapljanje jamskih sten in stropa je v taknih

jamah veje, kot v vodnih jamah. Izhlapevanje povzroa tudiodlaganje, ki se vri v obliki nadomeanja apnenca s sadro inz usedanjem aerosola, kar vodi v tvorbo znailnih morolokihoblik (popcorn). Brezno Chevalle sodi k termalnosulfdnemu

jamskemu sistemu AilesBains. Kondenzacija deluje na stikutoplega zraka s hladnimi jamskimi stenami, do izhlapevanja paprihaja na izhodu ozkih jamskih prehodov. Prepereli sloji kamnine in prevleke biolokega izvora se pojavljajo na mestih, kjer

je poasna kondenzacija. Porazdelitev korozijskega delovanjaje odvisna od termalne prevodnosti kamnine in povzroa nastanek stropnih, stenskih in divergentnih kronih oblik. aknimorodinamini vzorci omogoajo oblikovanje raznih kupol,loenih z oinami in vejasto razvrenimi. akne morolokeoblike so znailne za vadozno cono. Nekatere zoitve nad vodno gladino v hipogenih jamah (npr. Villa Luz v Mehiki) so kondenzacijskokorozijskega in ne reatinega nastanka. Prihodnjeraziskave fzikalnokeminih lastnosti bodo pokazale pomen

vpliva kondenzacijskokorozijskih procesov za razvoj jam.Kljune besede: kondenzacijska korozija, termalne jame,sphere genesis, zrana cirkulacija, AilesBains thermalno

sulfdni jamski sistem, brezno Chevalle, rancija.


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INRODUCION

Convection and condensationcorrosion are generallconsidered as minor processes or cave development,producing onl etching or smoothing o owinduced

eatures and conduits. However, some authors have putorward the importance o condensationcorrosion inspecic conditions. Mller (1974) was among the rstto relate spherical cupolas (called spheres in this paper)to air convection above thermal lakes, whereas Rudnicki(1978) had attributed them mainl to phreatic convection. Sphere development b condensation has beensimulated numericall, ocusing on the role o pressurechanges connected to ooding in the epiphreatic zone(Mucke & al., 1983; Lismonde, 2000) or cooling o risingair above thermal lakes (Cigna & orti, 1986; Szunogh,1990; Lismonde, 2003). Dublansk & Dublansk (2000)updated a review o worldwide contributions about condensation. inall, Drebrodt & al. (2005) recentl perormed a comprehensive modeling o this process within

various boundar conditions. As a rule, most o theseauthors stated the ecienc o convectioncondensationon speleogenesis onl in specic conditions that are notwidespread in meteoric caves, but more requent in hpogenic caves such as thermal caves or caves with highcarbonic or suldic atmospheres.

Te stud o Chevalle and Serpents Caves in AixlesBains, rance, clearl shows the importance o this process which is enhanced b suldic corrosion. AixlesBains

Caves, located in the Northern rench Prealpes in Savo,are still active and provide an outstanding picture o convection processes and related corrosion and depositionphenomena, particularl with gpsum replacement.

Tis paper presents the rst results o a stud o themorpholog o the cave, the distribution o the deposits, and the distribution o condensation and evaporationzones, in order to make an assessment o the role o condensationcorrosion role in cave development. A secondstud is being undertaken to calculate the condensationcorrosion budget through the collection o phsical andchemical data. Te rst part o this paper summarizescurrent knowledge about condensationcorrosion andthe development o spheres. Te second part examinescondensationcorrosion and the resulting morphologiesand deposits in Chevalle and Serpents Caves. inall, wewill discuss the respective role o the diferent speleogenetical processes.

ACA CARSOLOGICA 36/2 2007186

CONDENSAION-CORROSION AND HE DEVELOPMEN O SPHERES

SPELEOGENESIS By SULUR RELEASEAND SULIDIC CAVES

Hpogenic caves ormed rom sulur release producingsuluric acid and limestone corrosion with replacementb gpsum were onl recentl identied (Morehouse,1968; Egemeier, 1981). Te have been particularl studied in the Guadalupe Mountains, USA (Hill, 1987), in therasassi Caves, Ital (Galdenzi & Menichetti, 1990; orti,1996), and in rance (Audra & al., 2002; Audra & Ho

mann, 2004; Audra & Huselmann, 2004; Audra, 2005).Te active participation o microbial processes was identied in Movile Cave, Romania (Sarbu & al., 1996), andin Villa Luz Cave, Mexico (Hose & Pisarowicz, 1999).

CONVECION ABOVE A HERMAL LAKEAir convection occurs when a thermal gradient exists between a lake heated b thermal ow and the upper parto the cave which is cooler. Evaporation rom the thermallake produces warmmoist air that rises, while cooler airsinks. Since the thermal gradient is maintained b heat

transer through the cooler rock mass toward the surace(Lismonde, 2003), permanent convection cells exchangeheat and water between the diferent parts o the cave.Te thermal ux is independent o the distance to thesurace (Drebrodt & al., 2005), but high gradients mabe present close to topographic suraces where meteoricseepage can cool the cave roo.

CONDENSAION ON COOL WALLS

Warmmoist rising air cools at the contact o the colderwalls and ceilings producing condensation. Condensation, in turn, releases heat at the wall surace that lowers the thermal gradient itsel (Drebrodt & al., 2005).or vaporsaturated air, the condensation rate dependson the thermal gradient. Tus, maximal condensationrates appear when hot thermal water is present withina cave close to the surace, at the ceiling o the upperpassages, and more generall in chambers which arerelativel isolated b narrow passages rom lowermostwarmer places.

PHILIPPE AUDRA, ABIEN HOBLEA, JEAN-yVES BIGO & JEAN-CLAUDE NOBECOUR


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ACA CARSOLOGICA 36/2 2007 187

CORROSION O HE ROCK WALLSWhen condensation water quickl reaches equilibriumwith carbon dioxiderich cave atmosphere and residencetime o contact between aggressive condensation water and limestone wall is sucient, corrosion can occur

(Drebrodt & al., 2005). Such weathering o walls hasbeen demonstrated in Movile Cave, Romania, where sofresidue displas Clight isotopic ratios. Tis depleted carbon results rom the solution o biogenic carbon dioxide(Sarbu & Lascu, 1997). Modeling o wall retreat withinthermal conditions shows rates about one order o magnitude above those o meteoric karst, ranging rom 2 to20 cm / ka (Mucke & al., 1983; Cigna & orti, 1986; Drebrodt & al., 2005), thus allowing the possibilit o cavedevelopment in a reasonable timespan. Modeling hasalso shown that in normal meteoric caves condensationcorrosion does not reach sucient rates to be con

sidered as a main speleogenetic process.Consequentl, condensationcorrosion represents amain process onl in the ollowing cases: 1/ when warmmoist air condenses in the entrance o a cold cave in summer; 2/ above thermal lakes where the thermal gradientis high; 3/ where CO

2or H

2Srich atmosphere gives a

high aggressivit to the condensed water, even i this parameter is considerabl less important than the condensation itsel (Szunogh, 1990). Condition 2 ma combinewith 3.

DEPOSIIONAL PROCESSES

Several tpes o depositional processes ma occur separatel or in combination: 1/ b evaporation o the condensed water at the base o walls where air is warmer;2/ b replacement o limestone b gpsum when H

2S is

released rom thermal lakes; 3/ b decantation o aerosolsbuilding popcorns in the lowest part o passages (Dublansk & Pashenko, 1997). ig. 1 resumes the steps in

volved in condensationcorrosion.

SPHERE GENESIS By CONVECION ANDCONDENSAION

Te term sphere roughl corresponds to hemispheric or

semispherical holes located in the ceiling. Spheres madevelop b dierent processes, involving convection andsometimes additionall condensation: 1/ b pressure riseand condensation afer ooding in the epiphreatic zone(Mucke & al., 1983; Lismonde, 1999); 2/ b mixingcorrosion in the phreatic zone (Bgli, 1964, 1978); 3/ b con

vection o water in the phreatic zone (Rudnicki, 1978);4/ b air convection above thermal lakes (Mller, 1974;Szunogh, 1990). Except or (1), these processes correspond to slow moving uid (water or gas) and convectionmore or less directl connected to uprising water, conditions encountered more requentl in hpogenic cave

sstems (Osborne, 2004). We will initiall consider step(4) alone, that is air convection above thermal lakes making almost perect spheres.

Te thermal conductivit o rock produces higherthermal gradients at the top o ceiling holes (Cigna &orti, 1986; Szunogh, 1990), thereb creating the great

Fig. 1: Scheatic prole view o movile Cave (Sarbu & Lascu,1997).

A. Lower passage; B. Upper dry passage

1. Evaporation o water at the surace o the lake

2. Teral fux through the bedrock

3. Condensation o water vapor onto the colder cave walls andceiling in the upper cave passage

4. Dissolution o CO2

into the condensate and oration ocarbonic acid.

5. Reaction between carbonic acid and the carbonate bedrockwith oration o bicarbonate

6. ransport o bicarbonate along the walls

7. Precipitation o aragonite crusts and dissociation obicarbonate

HE ROLE O CONDENSAION-CORROSION IN HERMAL SPELEOGENESIS ...

Fig. 2: Developent o a sphere in the ceiling, where theral gradient is the highest, by condensation-corrosion (Szunyogh,1982).


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est condensationand thus strongest corrosion:the sphere continues developingupward, where

condensation isat the maimum,and laterall,where seepageoccurs, since it isconnected to thelower conduit ba narrow neck

Fig. 4: Teoretical developent o siple and coplex spheres.Siple sphere develops upwards and laterally (le); an irregularityin the ceiling produces a new sphere developent that ts withinthe previous one (right); two neighboring spheres diverge towardthe greatest zone o heat transer (right) (aer Szunyogh, 1990,odied).

Fig. 5: 3D view o Stork-puszta Cave, the bush-like pattern cavetype, ade o stacked up spheres (mller & Sarvary, 1977).


Fig. 3: Condensation occurs at the ceiling. Wall benets ro bothcondensation plus seepage. Evaporation plus saturated runofoccur at the botto, thus preventing the expansion o the neck(ro Szunyogh, 1990, redrawn).

ig. 2, 3. Modeling shows that irregularit o the ceilingproduces a new sphere development that ts within theprevious one Szunogh, 1990. Te development o twoneighboring spheres will be divergent, toward the greatest potential heat transer, because the rock in betweenthe two spheres has less transer potential and remains

warm ig. 4. Such a process eplains the developmento stacked up spheres arranged in a bushlike structure,as ound in the Storkpuszta Cave, Hungar ig. 5.Te smooth ceiling results rom the regular corrosion ba thin lm o condensed water rather than discrete dripsMucke & al., 1983; slow runo o condensed water atthe base o the sphere makes corrosion urrows, and calcite deposits as popcorn at the outlet o the sphere aferevaporation Cigna & orti, 1986.

AIx-LES-BAINS HERMAL-SULIDIC CAVES (CHEVALLEy AVENAND SERPENS CAVE)

BUSH-LIKE SPHERES AND WAER ABLEPAERN

AilesBains is a thermal resort in Savo, locatedbetween the Bourget Lake shore and the oot o theBauges massi in Northern rench Prealps. ChevalleAven and Serpents Cave belong to the same sstemig. 6 Hobla, 1999; Gallino 2006. Chevalle Avenis made o stacked spheres arranged in a bushlikepattern Storkpuszta Cave tpe. Chevalle Avenrises rom the thermal water table and does not break

through the surace, and the present entrance is artiicial. Serpents Cave is a water table cave, with spheresand avens at the ceiling. he active Alum thermalspring lows into the cave at the upstream end. hegaller is gentl sloping downstream and is plugged atthe end with till.

A SULIDIC AND HERMAL UPWELLING LOWTe discharge o the Alum spring ranges rom 8 to 42 Ls 1;the temperature oscillates seasonall between 33.5 and


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46.6 C on account o some mixing with meteoric component (Muralt, 2003). Water has a high concentration ocalcium, sulate, and secondar sodium, magnesium, andsilica (ab. 1). It degasses some H

2S and CO

2and brings

up microbial sof akes. Te temperature, high silica andsalt content, and the presence o trace elements suggest a

deep artesian owpath (about 2000 m), conned underthe Bourget Lake sncline, where riassic evaporites areleached (Carantan & al., 1998).

H2S degassing seems less strong in Chevalle Aven,

probabl due to the standing water. On the contrar, thewater owing turbulentl out rom the Alum spring produces a stronger degassing, as is evidenced b the characteristic rotten egg smell, together with a thick coatingo replacement gpsum and native sulur covering wallsaround the spring pool (Audra et. al., 2007). Martel(1935) was the rst to identi the suldic origin o Serpents Cave.

HE CONVECION CELLS IN CHEVALLEyAVEN (ig. 7)

Te aerial thermal gradient, between the pool at about 32to 34 C and the top o Chevalle Aven at 26 C rangesrom 0.2 to 0.3 C/m, so, air convection cells occur. Tedistribution o air loops is controlled b the presence inthe main passage o a cool dripping originating rom bothcondensation and seepage. Te cool airow sinks into themain passage whereas the warm airow rises rom thethermal pool through lateral passages. Te highest airow velocit is about 15 cm/s in the narrow passages.

Beore 1996, water seepage originated rom natural rainwater percolation through the soil. Since the building othe thermal Spa, seepage originates rom leakage romthe thermal pool. We present here the observations madein the small vent connecting the Lower Galler and theAixinoise galler (ig. 7). Preliminar measures weredone the 10/26/2006 using a heated wire anemometer(esto V1) which includes a digital thermometer. Deviceaccurac is 1 cm/s or air velocit and 0.1 C or air temperature.

SUDy O CONDENSAION-CORROSIONAND EVAPORAION-DEPOSIION PROCESSES

OCCURRING INO HE VEN (ig. 8)Tis vent is a narrow inaccessible passage about 3 m

long. emperature is 32.7 C at the base, and 28.4 C atthe upper mouth. Te air ow velocit is ver low, about1 cm/s or less. Warm air rises up through the vent andsome sinking secondar loops appear at the contact othe cooler lateral walls o the central sphere. Te accumulation o condensation produces runo as a lmalong the sphere walls and dripping at the tip o downacing pendants. Airow is considered close to saturation regarding moisture. Consequentl, cooling rom rising air produces condensation in the narrow ssures, at

Fig. 6: Outline o Chevalle Aven and Serpents Cave, cross-section view (surve SC Savo, EDyEm). Serpents Cave is a water tablecave, with spheres and avens at the ceiling. Te active Alu theral spring ows into the cave at the upstrea end. Chevalle Aven isade o stacked up spheres arranged in a bush-like pattern and reaches the theral water table. Te paleowater table corresponds tothe water level beore the digging o the adit in 1859.

ab. 1: main phsical and cheical data ro the Alu spring,Serpents Cave, Aix-les-Bains (ain data afer muralt, 2003).

Physico-chemistry

Values Reference, if other than Muralt (2003)

Temperature 33,5 46,6 C

Discharge 8 - 42 L.s-1

Conductivity 576 691 S.cm-1 Hobla, 1999

pH 6,5 Hobla, 1999

TDS 496 mg.L -1

HCO3- 262 mg.L-1

SO4-- 60 - 230 mg.L-1

Cl- 15 - 30 mg.L-1

Na+ 20 - 40 mg.L-1

Ca++ 100 - 150 mg.L-1

K+ 3 - 6 mg.L-1

Mg++ 10 - 25 mg.L-1

SiO2

22 - 26 mg.L-1

H2S 5 mg.L-1 Iundt & al., 1987

Trace

elements

Al, Fe, Mn, Pb, B,

Sr, Sn, Sb, Ba, Li

Iundt & al., 1987



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the ceiling, and on the walls o the central sphere whichis covered with condensation drips; conversel, cool airthat sinks rom an uppermost chimne warms up andproduces evaporation at the upper mouth o the vent,which is dr. At the upper part o the lowermost neckevaporation also occurs rom secondar convection cellsin the central sphere.

he corrosion rate depends on condensation;thus corrosion occurs mainl on the ceiling and wallso the sphere that is graduall enlarged. he sphereceiling and the upper part o the walls displa a regularand smooth cupola shape made o a weathered limestone laer, 23 cm in thickness, where boxwork veins

protrude. Te condensation lm dissolves the limestonemicrite cement, dissociates the sparite grains, and progresses deepwards into the host rock as an incompleteweathering ront (ZupanHajna, 2003). Along the wallso the sphere, the runo rom the accumulation o condensation dissolves the walls; consequentl, no weathered material subsists over the lower rockwalls. At thebase o the sphere, the condensation ow becomes saturated, and calcite deposits as small transparent crstalsin a sof and wet paste.

Sulate produced b replacement corrosion on thelimestone wall is also washed down b condensationruno. Tis process has also been noticed in rasassi(Cigna & orti, 1986). Runo arriving at the base o thesphere becomes saturated with gpsum. Evaporationonto the calcite grains wet paste causes microcrstal

line gpsum to deposit in a thin crust. Dripping romthe top o the sphere ma redissolve the gpsum thatredeposits downward into the narrow passage as gpsum owstones, stalactites and columns made o massivegpsum crstals.

Biolms coat most o walls, except: where intensecondensation or runo washes the walls; or where evaporation prevents the microbial development that needspermanent moisture.

Evaporation dries up the upper lip o the vent.Water is attracted b capillarit toward this dr zonethat maintains a continuous recharge o dissolved

species o carbonate. he evaporation allows calciteprecipitation as a rim, similar to a small draper,shaped b both airlow and evaporation (ig. 9). Suchcave eatures are characteristic o caves having a highthermal gradient and develop at the upper mouth ochimnes connecting cave levels where convectionairlow cells occur. he ma develop in the ollowingsituations:

1 in avens above a thermal water table located atdepth, such as JszeHeg barlang, Budapest (auth.obs.);

2 where impervious laers covering karst preventmeteoric seepage that ma homogenize temperaturesthroughout the cave prole (Wind Cave, Black Hills);

Fig. 9: Twin upper vents at the bottom o the Aixinoise gallery(photo. Ph. Audra).

Fig. 7: Chevalley Aven cross-section. Air convection is shown,together with present water seepage originating rom leakage othe thermal swimming pool located above. Beore the building othe new thermal center in 1996, this water seepage was providedby natural rainwater infltration through the soil.



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Fig. 8: Overview of the condensation-corrosion and evaporation-deposition processes. See text for details.

3 in arid areas or the same reason (Endless Cave,Guadalupe Mountains; see photography in Hill & orti,1997, p. 91);

4 in tropical caves where strong humidity and temperature gradients may exist between active galleries edby surace seepage and galleries where strong airfowbetween entrances dries walls (N2 Cave System, Kammouan, Laos; auth. obs.)

HE VEN, A CAVE EAURE COMBINING

CONDENSAION / EVAPORAION PLUSCORROSION / DEPOSIION PROCESSESigure 8 shows that the morphological setting stronglyinfuences the distribution o processes.

Te upper mouth o the vent opens above the bottom o the uppermost sphere: the condensation water othe uppermost sphere fows away in another direction.Consequently, the vent collects its own condensationonly that becomes visible in the lowest part o the narrowwhere clear suraces covered with a weathered layer are

visible.


Fig. 10: Te vent viewed from below, in the Lower Gallery; widthof the vent is about 20 cm (photo. Ph. Audra).


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Te lowermost vent located below the centralsphere acts as a unnel that collects condensation romthe upper narrow, rom the central sphere that is the mainruno provider, and rom its own condensation occurring in the lowermost part. Consequentl, condensationruno is important. Tus, b an overtopping eect, con

densation runo transers the processes normall occurring at the base o the central sphere downwards. Insteado evaporating slowl, condensation water with high sulate content ows downward into the narrow where it

DISCUSSION

A POSIIVE EEDBACK DEVELOPS SPHERES INBUSH PAERN

Te distribution o corrosion and deposition processesproduces a morphodnamic evolution according to thesize o the conduits:

spheres, where condensationcorrosion is high,evolve aster and tend to enlarge;

narrow passages evolve slowl due to the smallamount o condensed water collected, b neutralizationo the condensation runo afer some distance, or evaporation.

Tus, a positive eedback tends to enlarge the wider places that evolve to orm a spherical shape, whereasnarrows remain small. Such a morphodnamic tends

towards the development o stacked up spheres arranged in a bushlike pattern that are isolated b narrow necks.

HE ORIGIN O SPHERES IN BUSH PAERNREMAINS ENIGMAIC

Te accurate observation o condensationcorrosion andevaporationdeposition processes clearl demonstratesthat aerologic convections tend to exaggerate the dierence in size o the voids located in the vadose zone justabove thermal water table, and nall ma develop asspheres in bush pattern and avens.

However, the origin o the Chevalle Aven is stillobscure:

did it develop exclusivel rom this aerologic convection process b hollowing into massive rock?

did an older phreatic lif exist, that was drained bbase level lowering and which evolved aferwards underaerologic conditions? And in this case, could a phreaticorigin have initiated the development o the spheres?looding rom meteoric invasions is also evoked as acontribution to the aven genesis, which would have enhanced mixingcorrosion processes tpical o transitional karst Hobla, 1999; Dublansk, 1997.

I the origin o the protocave is still under debate,we propose that a major part o the cave volume, i not

the entire cave, could develop under aerologic conditionsinvolving condensationcorrosion b a progressive upward propagation o voids into the rock mass which nall produces spheres in bush pattern. Similarl, in Mo

vile Cave, condensationcorrosion is considered to be themain process o current wall retreat or airlled passagesabove the water table Sarbu & Lascu, 1997.

IMPLICAION OR HE UNDERSANDING OHyPOGENIC WAER ABLE CAVES (VILLA LUZ,

SERPENS CAVE)Te Villa Luz Cave abasco, Mexico is similar to Ser

pents Cave, since it has an active water table cave withsuldic springs upstream. Numerous avens are present,some being blind, some having broken through the surace as sklights. Tese avens are considered as phreaticlifs due to their spectacular scallops showing rising owolder than the drainage o the cave and the developmento the main galler Hose & Pisarowicz, 1999. However,Villa Luz is a tpical water table cave, clearl connectedto the bottom o a small local valle and displaing a lowgradient ree surace ow. Te avens starting rom thiswater table galler and developing upward cannot be older than the galler itsel. Consequentl, the must havedeveloped simultaneousl to the main water table galleror later, thus not in phreatic conditions. Te phreaticscallops that have been taken as indicators o upowing, in act would result rom corrosive convection in thewarm suldic atmosphere. Such airow would produceeatures ver similar to the scallops. Some o the avensstill contain huge masses o replacement gpsum made othe accumulation o gpsum crust detached rom walls.Other avens have breached through the surace, allowing the meteoric inltration to wash awa the gpsumdeposits Palmer, 2003.


nall evaporates and where it deposits secondar gpsumas speleothems made o massive crstals. Tese gpsumdeposits develop downward till the arrive at the ceilingo the lowermost sphere, where condensation and corrosion are predominant ig. 10.

Tus, a calcite rim ma line the upper mouth o a

vent i it is located above the drainage point o the uppersphere; on the contrar, condensation runo washes andtransports dissolved minerals downwards, to the lowernarrow.


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In Serpents Cave, the Hells Aven, which is the natural entrance, probabl has a similar origin, that is to sa abreakthrough surace o an aven made b corrosive airconvections. However, and contrar to Villa Luz, the

Hells Aven is located just above the Alum spring (g. 6);in this case, there remains the possibilit that the avencould be an older phreatic lif drained afer a base levellowering (Hobla, 1999).

CONCLUSION

Observation o condensation and evaporation areas, corrosional morphologies, and o the distribution o thedeposits have shown the strong relationship betweencondensation and corrosion, and conversel betweenevaporation and deposition. Moreover, the distributiono the condensation and evaporation processes strongldepends on the morpholog o the cave. Condensationcorrosion tends to enlarge the largest voids, leading nal

l to a pattern o stacked spheres. Tese rst conclusions,based on the stud o cave eatures, indicate the possibilit o speleogenesis mainl through condensationcorrosion. Tis hpothesis is currentl under investigation. Weare collecting data (temperature, airow speed, pCO

2and

pH2S, chemistr o condensate water), in order to calcu

late a budget o condensation rates and corrosion volumes which will be compared to the cave dimensions.

ACKNOWLEDGEMEN

We are grateul to the Head o Chevalle thermal resortor the permission to access the caves, particularl Mr.

J.. Michel, S. Bienvenue, . Canella, J.P. Morin, and Mrs.A. Labrosse.


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