Part 3 Contributions
Published in C.R.Acad. Sci. Paris, t. 324, serie II a, p. 17 a 23, 1997.
1. The Problem of Karstic Denudation
At the beginning of the century, karstologists thought higher karstic denudation rates took place under the most humid climates, i. e. tropical climates. Then Corbel (1957) proved that cold climates also have a certain influence and he proposed a formula for specific dissolution calculation X (mm/millenary): X= 0.4× E× T/N where E is annual rainfall (m), T the carbonate concentration of karstic water (mg/1) and N die proportion of limestone in the catchment basin.
Nevertheless, rainfall was always considered as the major karstic denudation agent and several relationships between karstic denudation and rainfall have been proposed (Pulina, 1974; Lang, 1977). More recently, karstic hydrogeochemistry showed the importance of water inflow enriched with dissolved CO 2 (Nicod, 1975; Bakalowicz, 1979 a; Ford, 1985; Maire, 1990). However up to now Corbel's formula remains the most usual method for calculating the karstic denudation rate.
2. KARSTIC DENUDATION CALCULATION AND MODEL MEASUREMENT
Corbel's formula was later used by Williams (1963) who integrated spring flow, catchment basin area and limestone density. But all these parameters need a sound knowledge of the karstic aquifer system and regular hydrochemical analysis and spring flow measurements over several hydrogeological cycles (Bakalowicz, 1979 b). This is generally not the case in karstic countries developed under extreme climate, for example in tropic monsoon or polar regions.
During an international congress in 1978, limestone tablets were distributed to karstologists from the world over for them to measure the loss of weight after exposure to climatic or pedologic agents. These measures, however gave only 26% of the calculated specific dissolution (Gams, 1985). With a multili-near regression analysis, Gerome-Kupper (1984) noted that rainfall and temperature effectively explained together most of the variance: but only 32% of the total variance of the statistical sample could be so explained. This method cannot be used for comparison of karstogenesis in different climates.
Geochemical balance is certainly the most precise method for karstic denudation measurement. However it needs a perfect knowledge of karstic aquifer and requires daily or weekly water analysis and flow measurements for each hydrogeological cycle (Marjolet and Salado, 1975; Bakalowicz, 1979b; Blavoux and Mudry,1988).
3. MAXIMAL POTENTIAL DISSOLUTION
A mathematical approach called "Maximum Potential Dissolution" (DMP in French) is presented here. Taking into account infiltration, CO2 soil productivity and water concentration in CaCO3 resulting from calcocarbonic equilibrium, the calculation is performed at an annual scale and based upon the following assumptions: (1) rainfall water enters the calcareous karstic system with an inflow corresponding to the infiltration, (2) water immediately dissolves CO2 from the soil according to its average temperature, (3) water immediately dissolves CaCO3 up to saturation (according to Dubreucq et al., 1988). This model leads to the DMP formula: DMP = 400× Ie× C where Ie is infiltration (mm) given by Coutagne's formula (in Remenieras, 1986) and C is water concentration of calcite at saturation (mg/1) give by calcocarbonic reactions (Trombe, 1952) all of whose equilibrium constants Ki. can be approximated by an equation involving absolute temperature (T, ° K) and a set of tabulated parameters ai, bi and ci. (tableI):
log Ki = ai + bi / T + ci× T
CO2 partial pressure of the phase associated with water solution is given by Brook's (1983) formula as a function of Annual Evapo-Transpiration (AET, mm):
log(pCO2) =-3.47 + 2.09×( 1-e-0.00172× AET )
4. DMP MATHEMATICAL FORMULATION
DMP final expression is:
This results are in good agreement with the values of specific dissolution and geochemical balance known all over the world (table II). This expression is not easy to handle because of the complexity of development parameters, but all of them depend only on average rainfall and temperature values. Consequently, we tried to simplify DMP by definiing it in relation to a climatic index. Statistical calculation is performed for 266 meteorological stations all around the world (Miller, 1966; Maire, 1990) and the best adjustment is obtained for the index i20 = R / (T+ 20) where R is the annual rainfall (mm) and T the mean annual temperature (° C). The DMP equation corresponds to the following 3rd degree polynomial:
DMP = - 4.14´ 10-5 i203 +1.93´ 10-2 i202 + 8.02´ 10-1 i20 - 10.5
5. WORLD CLIMATE AND KARSTOGENETIC ACTION
We can now suggest an average karstic denudation rate value for each climate (table 11) and calculate that higher DMP values correspond well to warm humid climates as observed all around the world.
DMP calculation includes current knowledge on main agents of karstic denudation:
infiltration, calcocarbonic equilibrium and CO2 productivity of the soil. It can be calculated everywhere in the world using only annual rainfall and average temperature. Moreover, its application to paleoclimates has been successfully tried by Gombert (1988).
J. Speleol. Soc. Japan, 20: 27-37, March 30, 1996
Kazuhisa YOSHIMURA1) , Mari IWAYA-INOUE2), Takashi
1) Department of Chemistry, Faculty of Science, Kyushu University Ropponmatsu,
Abstract The cascade at the entrance to Akiysohi-do Cave, Yamaguchi, is made of biologically induced carbonate, tufa. The groundwater issuing from the cave was supersaturated for calcite and the degree of supersaturation was the highest at the entrance to the cave. The pH of the tufa suspension increased with the light exposure. Photosynthetic cyanobacteria were predominant among algal flora on the surface of the tufa deposits distributed on sites of lower light intensity, while not on sites of higher light intensity. The CaCO3 local supersaturation on the surface of tufa is caused by the local increase in the CO32- concentration because the bacteria consume the dissolved CO2 and/or HCO3- and the pH of the solution is increased. Tufa deposition at the entrance to the cave is, therefore, related to the activity of cyanobacteria having a sticky mucous sheath and to the resulting CaCO3 precipitation around the bacteria.
Kazuhisa YOSHIMURA1), Kensaku URATA2), Akiniro
1)Department of Chemistry, Faculty of Science, Kyushu University
Abstract Tufa is biologically induced carbonate deposited in freshwater. Tufa deposition is related to the growth of photosynthesizing organisms such as cyanobacteria and also to the rapid CaCO3 precipitation around them: the CaCO3 local supersaturation on the surface of tufa is one of the most important factors. Tufa deposits in some limestone areas in Southwest Japan: Akiyoslii-dai Plateau (Yamaguchi), Hirao-dai Plateau (Fukuoka), Shirokawa (Ehime) and the Gizabanta Coast (Okinawa), are here reported for the first time. The widest tufa deposit occurs in Shirokawa: it is 380 m long, 10 m wide, and over 1 m thick. The depositional rate is so high that even a mislaid cotton glove was encrusted with tufa. Tufa deposits exhibit annual layers due to seasonal variations in biological activities. In Akiyoshi-do Cave, Yamaguchi, the groundwater flows above the groundwater level, because the hydraulic gradient profile from Kotogafuchi (the groundwater located at the farthest place from the entrance) to the entrance to the cave, has been maintained constant by the tufa cascade located at the entrance to the cave. The CaCO3 supersaturation in the stream water, the absence of big storm runoffs, and the lack of human interference, may be critical factors in tufa formation. Further research on tufa is now continuing.
Morphological Processes of
Polygonal Karst in Pan De Guajaibon
(Sierra del Rosario, NW de Cuba)
ABSTRACT : The massif Pan de Guajaibon in Sierra del
Rosario is one of the best investigated karst areas in Cuba. Massif forms a block of
carbonate deposits divided to two systems of karst circulation, separated by a distinct
fault zone. Large part of the massif is a relict of the polygonal karst. The whole area,
strongly elevated above surroundings, is drained through the underground system Ancon.
Based on observations and measurements made in that system during flood conditions in
March 1987 the activity of morphological processes was examined. Among the current karst
processes formation of pits is important. The process is concentrated at the interface of
bedrock and surficial bauxitic deposits. Therefore climatic factors, influencing hydrology
of karst depressions in poygonal karst, control intensity of the discussed processes.
Amount and distribution of precipitations in a year are the must important. Heavy rains in
dry seasons play crucial role in development of the collapse processes in the polygonal