COBISS: 1.01 LAKES IN GyPSUM KARST: SOME ExAMPLES IN ALPINE AND MEDITERRANEAN COUNTRIES JEZERA V KRASU V SADRI: NEKAJ PRIMEROV IZ ALPSKIH IN SREDOZEMSKIH DEŽEL Jean NICOD1 Abstract: UDC 556.55(467.1) 551.444(467.1) Jean NICOD: Lakes in Gypsum Karst: some examples in Al-pine and Mediterranean countries. Numerous lakes of varying types have been studied in these ar-eas. Teir origin proceeds from the geomorphological process-es in the gypsum karst: land subsidence or collapses in relation with the active dissolution of the gypsum and other evaporites, particularly in depth, at the groundwater level. Most are small lakes, ofen ephemeral ponds in the alpine gyp-sum karsts, or fooded sinkholes in alluvial plains, in keeping with the fuctuations of the water-table. However, in the Mediterranean lands and Central Europa, some lacustrine basins are more important expanse; they arise from a complex evolution, and put various environmental problems. So are particularly studied the case of the lake of Besse in Provence, and in com-parison the problems of the lakes of Pergusa (Sicily) and Ban-yoles (Catalonia). key words: Evaporite karst, gypsum, lake, Alps, Mediterranean. Izvlecek UDK 556.55(467.1) 551.444(467.1) Jean Nicod: Jezera v krasu v sadri: nekaj primerov iz alpskih in sredozemskih dežel V teh predelih so bila preucevana številna jezera razlicnih tipov. Nastala so zaradi geomorfoloških procesov v krasu v sadri, kot so: ugrezi ali udori v zvezi z raztapljanjem sadre in ostalih evaporitov, predvsem v globinah, v višini talne vode. Vecina teh jezer je majhnih, cesto so to obcasna jezerca v krasu v sadri v Alpah, ali pa zalite vrtace v aluvialnih ravninah, ki odražajo nihanje gladine talne vode. V sredozemskih deželah in v Srednji Evropi pa so nekatera povodja teh jezer precej vecja; njihovemu nastanku so botrovali razlicni dejavniki in v zvezi z njimi se pojavljajo razlicne ekološke težave. Kot primer je posebej predstavljeno jezero Besse v Provansi, za primerjavo pa še jezeri Pergusa (Sicilija) in Banyoles (Katalonija). kljucne besede: evaporitni kras, sadra, jezero, Alpe, Sredozemlje. INTRODUCTION Although the lakes in gypsum or evaporites karst are not generally studied, but only by local or punctual works, their processes of formation and evolution are very inter-esting. Tey present specifc characteristics comparatively to karstic lakes in limestones and dolomites: - the quick genesis of their basin, frequently by breakdown, collapse or sufosion processes consecutive to the accelerated solution of the gypsum or andhydrite (and more in the halite lens!) (NICOD 1993, KLIM-CHOUK 1996, 2002); - the possible extension by solution and land subsidence, recess of the borders by solution and collapse, or coalescence of contiguous sinkholes; - their variable water level, depended not only on the hydrologic conditions (change of the groundwater level, input-output balance), but also on the subsidence or collapse of their basin bottom; - the silting by the clay derived from the weathering of the argilaceous beds joined up the gypsum or other evaporites: 1 Emeritus professor, florida 1, 35 Av. 24 Avril 1915, f 13012 MARSEILLE. Received / Prejeto: 13.03.2006 ACTA CARSOLOGICA 35/1, 69–78, LJUBLJANA 2006 JEAN NICOD - the high mineralization, poor ichtyologic fauna, locally anoxic water and possible sulfydric gas irrup-tion in relation with the bacterial action on dissolved sulphates. As do all the phenomenons in gypsum karsts when they occur in the urban and suburban areas, the gypsum THE LAKES IN SMALL KARSTIC DEPRESSIONS Most small lakes are located in karstic forms, funnel or sinkholes, produced by breakdown or collapse processes in relationship with active solution (fg. 1). In the alpine gypsum karst, as that of Col du Joly Beaufortin (Savoie, france), a feld of many funnels extend upon the outcrop of gypsum layers, in the mountain pasture, near 1900-2000 m (NICOD 1988). When the bottom of these de-pressions are blocked by residual clay or issued from mo-rainic deposits, the lakes can be formed, but fast changed into marshs and bogs. (Photo 1) Photo 1: Small transient ponds in gypsum funnels, in the alpine pasture near Col du Joly (1989 m), in the northern Beaufortin (Savoie). On the contrary the gypsum lakes in the lower alti-tudes, in plateau or plain, are connected with the aquifer, either in alluvial deposits, example of the lagunas (doline-lakes) in the Ebro terraces (W Zaragoza SORIANO, 1991), or with a multilayered aquifer, as in gypsum karst of the triassic plateaus of the inner Provence (example of the Louciens, La Roquebrussane, Var Department). Te level of those lakes depends to the watertable, as the case they can be perennial or temporary; in the occurence of speed groundwater lowering, the bottom of the basin may be changed by subsidence or collapse processes. In the ex-ample of the Grand Loucien, the excessive level variation cause sometimes rockslides in limestone borders: so this crater-like landform tend to extend. (Photo 2) lakes give main impact problems: the changes of lake lev-el and possible extension, or on the contrary silting and trend to marsh. Photo 2: Te « grand loucien » near la Roquebrussanne (Central var Department). Collapse basin in middle trias limestones, variable level in connection to the groundwater. THE POSSIBLE COMBINATION Of PROCESSES. Some lacustrine basins proceed from a combination of two or several development processes. So in high alti-tude (near 2300 m) and alpine landscape, the lake of the Combe de la Nova in Beaufortin (Savoie), a submerged uvala in triassic gypsum band between shales, fows out in a sink-cave, active rockfall site (fg. 1, II). In the case of the lake of Mont-Cenis pass (1970 m, in Savoie, at the french-italian border) the glacial origin is clear, but a part of this basin is in a triassic gypsum band, where numer-ous funnels and sinkhole are opened; this structural ar-rangement has given a problem of losses, because of the raised level since the ftting out of the basin as reservoir for the hydroelectric power-plant (NICOD 1993). In the case of the Bonne Cougne pond, near flassans in central Var Departement, it is spring-lake located in small polje in dolomites of middle Trias, now drained; its origin is in keeping with the dissolution of the underlying evapor-itic lens, as in the lake of Besse (infra). In the « Causses » of the Middle Atlas (Morocco), several lacustrine ba-sins in liassic limestones and dolomites proceed from the same processes: disssolution of underlying triassic gyp-sum lens, some in diapiric structures, and subsidence of the layers on top. Some are seasonal lakes (daias), as in the Ouiouane polje, and turn into salt crust in summer (MARTIN 1981). (Photo 3) fORMS AND ORIGINS Of THE GyPSUM LAKES. 70 ACTA CARSOLOGICA 35/1 – 2006 LAKES IN GyPSUM KARST: SOME ExAMPLES IN ALPINE AND MEDITERRANEAN COUNTRIES Geologic setting 1-mode of iformation of the basin Type Processus Hydrology 2-Lakes in evolution Type Hydrology Examples References 3-Lakes at the end of evolution modes of formation and evolution of the gypsum lakes I - 3 sequences with respect to lithologic and geomorphologic conditions A- Gypsum & anhydrite band : Alpine Karsts b- Alluvial plain/ gypsum or evaporites C- limestone plateau/ gypsum or evaporites funnel Solution vadose circulation Under-alluvial doline Solution + subsidence at alluvial water-table level n Breakdown in defooded cave (i of n) funnel-lake over « plug », possible drain gypsum lakes Col du Joly Beaufortin NICOD (1988) Lake in doline permanent or temporary at alluvial water-table level n Lagunas in Ebro terraces W Zaragoza SORIANO (1991) « Crater » lake variable level n in keeping with the deep water-table Grand Loucien La Roquebrussanne (Var) NICOD (1967, p.175) A*-Contact karst Gypsum / shales II – Compound cases C* Polje in compound structure Gypsum lens in triassic dolomites Lac de la Nova (Beaufortin , Savoie ) NICOD (1988) Lac de Bonne Cougne (SE flassans, Var) Fig. 1: Some basic types of formation and evolution of the lakes in gypsum karst. ACTA CARSOLOGICA 35/1 – 2006 71 JEAN NICOD Photo 3: Te lake of the Combe de la Nova (2300 m, Beaufortin Savoie), submerged uvala in triassic gypsum band between shales. loss in the gypsum rockfall (1994). THE CASE Of AGUELMANE AZIGZA: RAIN-GAUGE LAKE ! Aguelmane Azigza (the Green Lake in Berber language) is situated in the southern part of the Causses of the Middle Atlas (Morocco). Tis main lake of the Causse of Ajdir, without outlet, gives spectacular inter-annual water-level changes: it is a record of the dry and humid periods at the regional scale. It is extended in the eastern end of an important polje, old landform expanded in the liassic dolomites, near 1490 m high, characterised by cu-pola hums and fat ground covered by residual deposits, dolomitic sands and terra rossa (MARTIN, 1981). Te basin of the lake is a subsidence depression, following the fault system, in relationship with the dissolution of the evaporites in the underlying triassic formation. Active collapses and block-fallings in dominant scarps of liassic dolomitic limestones prove the permanence of this proc-ess. Tis play of dissolution at groundwater level, in the area of Causse of Ajdir is correlated with some sulphated and salt springs, north of this Causse, in the Oum-er-Rbia canyon (EL KHALKI & AKDIM 2001). (Photo 4 and Photo 5) Photo 4: Small lake (daia), doline in diapiric structure (Causse d’Ajdir, middle Atlas). Dry in summer, with salt crust (Photo y. El Khalki). Photo 5: Te lake Azigza, in the Causse dAjdir (middle Atlas). low level showed by the white scree, below the trail and cedar forest. Tis part of the Middle-Atlas Causses is relatively good sprinkled and snow-covered in winter; the cedar forest subsists on the base of the scarps; but the inter-annual change of the rainfall and snow amount is very important. Te rainfall and snow-melting in the polje supply the Aguelmane, however with high evaporation (~ 600 mm/y); but the lake-level is in connection with the aquifer in the dolomitic layers. Also this level can changed between 1490 m (in 1960) and 1471 m (1984), and even 1470 m in 1990. In high level, the lake may overfow in the polje; in lowest level, it covers only 37 ha, with 38 m of maximum deep. Te low level is in relationship with dry sequences, but a phase-lag of one or two years between the weak precipitations and the lowest water-level has be recog-nised (fLOWER & fOSTER, 1992): in my opinion that is caused by the slow response of the aquifer play in the liassic dolomites. SOME MAIN LAKES. In Central-Europe and Mediterranean countries, some largest lakes give variable forms, in relationship with diverse structures and hydrogeological settings, multiple evolution processes and various water supply Te table 1 shows the most important and knownest lakes, as rep-resentative examples of environmental problems. 72 ACTA CARSOLOGICA 35/1 – 2006 LAKES IN GyPSUM KARST: SOME ExAMPLES IN ALPINE AND MEDITERRANEAN COUNTRIES Tab. 1: Main gypsum lakes in Central-Europe and Mediterranean countries, sorted according to their extension. Lake Region, Land References L. Invârtita (Nucsoara) Arges Distr., Transilvania, Rom. BULGAREANU 1997 L de besse (Besse-sur-Issole) Var Dept, E Provence, f. NICOD 1991/99 nixsee (Nixei) Harzvorland (E Göttingen), D. PRIESNITZ, 1969 Laguna Grande (Archidona) Betic range, Andalucia, Spain PULIDO-BOSCH, 1989 Aguelmane Azigza Causse of Ajdir, Middle-Atlas, M. MARTIN 1981 Lago di Pergusa (Enna) Central Sicily, Italy DAMORE 1983 estany de banyoles (Bañolas) Ampurdan, Catalonia, Spain JULIA BRUGUES 1980 Demiryurt gölü (Todürge gölü) Karst of Sivas, Anatolia, Turkey ALAGÖZ, 1967 Surface Altitude Depth. average max 0.02 km² 877 m ~5 m 0.04 km² 245 m 3-4 m 9 m 0.02-0.08 in food ? 250 m 6 m 0.06 km² 0.34 km² 1490 à 1471 m 33 m (en 1989) 1.18 km² 667 m 1,8 m 1.83 km² 173 m 10 m au N 20 m au S 130 m ! 3.3 km² 1295 m ~4 m 28 m (funnel) Type Genesis Lithology Extended sinkhole from a ponor in the end of 19th c. gypsum, aquitanian sandstone Collapse doline Middle-Trias limestones -id.- gypsum Little polje dolomites gypsum of Zechstein Subsidence depression gypsum & halite of Trias Collapse fault trough near polje in dolomites of Lias Trias clay + evaporites Large doline Pliocène marls Messinian gypsum + halite Coalescence of sinkholes + travertine dam Eocene marls/gypsum Submerged uvala Miocene gypsum Working Hydrosystem Peculiarities Supplied by groundwater anoxic basin emit HS 2 In connection with aquifer + made-man supply by Issole partial drain-of in 1989 flooded by spring (Springwiese) outfow ? ponor In relation with aquifer ? fuente Camacho Saline, dry in summer Supplied by polje & aquifer very variable water-level Rain-gauge lake! Rain supply + groundwater without outlet trend to silting Supply by aquifer Anoxic bottom emit HS 2 Supply by aquifer +afuent Outfow ? Kizyl-yrmak summer reduction ?salt crusts ENVIRONMENTAL PROBLEMS Te leak of the Lac de besse (Central Provence), a «bot-tomless lake»! Tis widest lake (4 ha) in the triassic plateaus of the Var Department is located near the old little town of Besse-sur-Issole. Its basin is a karstic depression in an-ticlinal structure of the middle Trias limestones (Mus-chelkalk); below the factured limestones (that make up the spur and clif at the NW), the «Anhydritgruppe» for-mation is constituted by dolomites, dolomitic marls and gypsum (fg. 2). Mainly, the confned aquifer in these triassic formations and the outfow to the Issole river main- tains the level of the lake, normanly nine metres deep; but in the dry years, the level can progressively subside, as in 1878; on account of this lowering, a small canal di-verted from the Issole contributes to the supply of the basin. (Photo 6) In december 1989, the level falls quickly, and the regional press print in enormous headlines: «Après le goufre glouton, le lac qui fuit!», afer the greedy pit, the leaky lake! A small cave opened on foot of the lime-stone clif has absorbed in part the lake water (fg. 3), as previously in similar event in 1987 for one river near ACTA CARSOLOGICA 35/1 - 2006 73 JEAN NICOD Fig. 2: Sketch of the lake of Besse, in its geological site. Fig. 3: Partly draining of the lake of Besse in December 1989, by cleared pipe in the muschelkalk spur. lakes 1) Tourrettes in eastern Var Department. Tis phenom-enon in lake of Besse is in relation with the drastic subsidence of the water-table, near 20 m. Two factors are added: - the efect of several consecutive dry years; - the efect of the over-working of the alluvial groundwater in the Issole valley by numerous well-bor-ings, because the two aquifers are partly in connection. Some improvment are worked in 1990, fnanced by Var Department: - tightness of the critic area, by a cover of clay com-pacting; - reftting of the canal from Issole river. for this improvment, the lake level is restored; un-fortunately a new falling occurs for some years, in relation with new dry climatic period. 74 ACTA CARSOLOGICA 35/1 - 2006 Photo 6: Te lake of Besse-sur-Issole (Central var Department) in 2005. view towards the muschelkalk spur. Arrow marks the place of the 1989 sink. furthermore, in the decreased lake, the water be-come sligtly anoxic. Tese conditions cause some envi-ronmental problemes in the town of Besse, because the circumference of the water plan is shady recreation area, very important at the time of summer days for the citi-zens and tourists of next camping. Te decay of the Lago di Pergusa (near enna, in Central Sicily). Tat larger lake (1.83 km²), without outlet, is locat-ed in a wide oval karstic basin, from subsidence origin, in pliocene marls, upper gypsums of the gessoso-solffera formation of Messinian (upper Miocene) (fg. 4). Numerous karstic phenomenons are recognized in this formation (fORTI & SAURO, 1996). Te fowing on the sur-roundly sides (catchment area of 6 km²), and the ground- LAKES IN GyPSUM KARST: SOME ExAMPLES IN ALPINE AND MEDITERRANEAN COUNTRIES water of multilayered aquifer maintain the level. But its surface is reduced by the sedimentation, with silts from the weathering in Pliocene marls, and aquatic vegetation growth; moreover its level tend to subside (Tabl. 2). tab. 2: Decay of the Lago di Pergusa, from D’AMORE, 1983. Dimensions 1896 1977 Perimeter 5.5 km 4.3 km Surface 1.83 km² 1.35 km² Maximum depth 4.6 m 2.4 m Middle depth 2 m 1.8 m Volume 5.8 x 106 m3 2.6 x 106 m3 Unfortunately, the site has been altered in the sixties at the time of the development programme of mezzogior-no: an autodrom has encircled the lake! Te growth of the Pergusa village, with hotels and campings, has increased the water polllution in summer, and the eutrophication Fig. 4: Te lago di Pergusa, in its environment. g eology from the Carta geologica d’Italia, 1/100 000, CAltANISSEttA , II Ediz., 1955 with the proliferation of the green algae (Charophyceae). for to cure to the site deterioration, the Consorzio di Bonifca di Borgo Cascino di Enna supply the lake from the regional hydrosystem and the site has been classifed as «green Zone». Te estany de banyoles (bañolas), the large lake of Catalonia in urban area. Te large lake (~2 km²) of Banyoles is situated in the NE of Barcelona, at the active tectonic boundary be-tween the hills of Garrotxa and the subsiding basin of the Ampurdan (fg. 5). Te lacustrine complex depression is located in the blue marls over gypsum and limestone formations of the Eocene. Te confned artesian aquifer of these limestones, supplied by a large catchment in the north-western hills, concurs to gypsum dissolution. Te lake has a double origin: - the coalescence of some funnels and subsidence depressions; ACTA CARSOLOGICA 35/1 – 2006 75 JEAN NICOD - the water-level control by a travertine dam, build-ed on the Riu Terri outlet. Round the lake, eight ponds (estanyols), of which one from a recent collapse in 1978 near Porqueres, show the enlargement by the solution and subsidence process-es. In the lake bottom, several deep funnels (Cap de Bou - 130 m) play as artesian springs (fg. 6). In funnels, sul-phate muds are in suspension (SANZ, 1985). Te travertine dam has been builded on the water-falls at the outlet of the lake to Riu Terri, with waters of high carbonate-sulphate mineralization and by the ac-tion of the incrusting algae (Cyanophyceae) (JULIA BRU- 76 ACTA CARSOLOGICA 35/1 - 2006 Fig. 5: Te geomorphological situation of the lake of Banyoles. GUES, 1980). A part of the town of Banyoles is builded on the travertines and several levels of travertine forma-tions are extended in the Terri valley, with paleontologi-cal and archeological sites; but the oldest and highest ac-cumulation is the Pla d’Usall in the north. In this plateau, the Platja spring, more 40 m above the lake-level, proves again the power of the artesian hydrosystem. Te Estany of Banyoles constitutes an noteworthy ecological site with its ichtyologic fauna (abundance of carps), but also important recreation area for all water sports. Clearly that activity, and the urbanization of the area round the lake are pollutant sources. LAKES IN GyPSUM KARST: SOME ExAMPLES IN ALPINE AND MEDITERRANEAN COUNTRIES Fig. 6: Te bottom of the lake of Banyoles (from SANZ,1985). CONCLUSION Te three lakes of Besse, Pergusa, and Banyoles show the specifc hydrogeological conditions. On account that most representative examples of environmental hazards produces high sensivity to anthropogenic changes, par- and problems. As all phenomenons in gypsum karsts, ticularly with. the extent of urbanization atreas. their evolution depends on the active dissolution, and ACTA CARSOLOGICA 35/1 – 2006 77 JEAN NICOD REfERENCES Abella, C. i Amettler 1986: L’Estany de Banyoles con a unitat ecologica; «1 Jornades sobre l’Estany de Ban-yoles (1984)», Diputació de Girona, p. 27-32. Alagöz, C.A., 1967: Jips karst Olaylari ... - Les phénomènes karstiques du gypse aux environs et à lest de Sivas; Ankara Universitesi Pasimevi, 126 p. + cartes h.t. Andreichuk, V. & Klimchouk, A., 2002: Karst breakdown mechanisms from observations in the gypsum caves of the western Ukraine: implications for subsidence hazard assessement; Int. J. Speleol. 31 (1/4) p. 55-88. Bulgäreanu, V.A.C., 1997: Solution lakes in gypsum evaporites: Lake Invârtita (Nucsoara) Romania; Internat. 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Soriano, M.A., 1991: Characteristics of the alluvial dolines developed because of gypsum dissolution materials in the Central Ebro Basin (Spain); Z. Geomorph. N.f., Suppl. Bd. 85, p. 59-72. 78 ACTA CARSOLOGICA 35/1 – 2006