Karst: multiple concepts for a unique geological object Dr Michel Bakalowicz

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1 Karst: multiple concepts for a unique geological object Dr Michel Bakalowicz Michel.Bakalowicz@gmail.com

2 By way of an introduction The project of exploiting a lignite deposit in a limestone environment of Eastern Turkey 1/5/2009 SCRF Stanford 2

3 Boring a well in a Miocene lignite basin, in Eastern Turkey Question: will some problems occur during the exploitation because of karst? Limestone outcrops 1/5/2009 SCRF Stanford 3

4 The first field studies concluded to the absence of any karst feature either at the surface or at depth But we can claim yes, karst developed at depth without visiting the field Why? 1/5/2009 SCRF Stanford 4

5 Formation of coal deposits in a Miocene basin Dejection cones along the slope Basin with a river valley limestone Alluviums limestone Lignite (Coal) and paleosoils 1/5/2009 SCRF Stanford 5

6 Development of karst in a Miocene basin Dejection cones along the slope Basin with a river valley Water and vegetation (Soil CO 2 ) limestone Alluviums limestone Difference in elevation Lignite (Coal) and paleosoils 1/5/2009 SCRF Stanford 6

7 The potential for karst development The two conditions external to the carbonate aquifer: A difference in elevation Water and CO2 are necessary for developing karst They form the potential for karst development (PKD) or potential for karstification 1/5/2009 SCRF Stanford 7

8 In the example from Turkey Karst must occur at depth It does not necessarily present a hydrological functioning, because it is abandoned and flooded A classical hydrological study will show that the aquifer is homogeneous, with a typical porous or fissured behavior. It could be modeled classically. 1/5/2009 SCRF Stanford 8

9 Demonstration of karst occurrence 13 boreholes were located at places considered as potential paleoepikarst or paleodrainage In each borehole, the first 100 m in the limestone were cored 90% showed karst features, much more than expected! 1/5/2009 SCRF Stanford 9

10 Cores showing karst caves and their sediment filling 1/5/2009 SCRF Stanford 10

11 Cores showing karst caves and their sediment filling 1/5/2009 SCRF Stanford 11

12 Cores showing karst caves and their sediment filling 1/5/2009 SCRF Stanford 12

13 Predictable consequences of the exploitation of lignite Lowering of the water table by pumping Dewatering of the karst conduits of the paleo karst system Because of its wide extension, huge volumes will be pumped (pumping rate estimated to be at least 5 CM per sec) Deplugging of sediment infilling and risks of sudden flooding of the mine, as it occurred elsewhere (Poland, China) 1/5/2009 SCRF Stanford 13

14 Two sets of conditions for developing a karst system: 1. External conditions which determine the PKD: the regional hydraulic gradient (direction, intensity), linking the recharge zone to the base level the quantity of water and its dissolving power (CO 2 or other) 2. Internal conditions which control: the geometry of the carbonated formation, the original permeability of the carbonated rock, the rate of impurities within the rock 1/5/2009 SCRF Stanford 14

15 Karst development, a matter of competition The dissolution of rock at depth, responsible for the formation of conduits, is a matter of competition between flow velocity and solution kinetics: A part of water flows slowly and dissolves the rock close to the surface, producing the surface landscape. Another part infiltrates rapidly and dissolves at depth,, creating the conduit system. 1/5/2009 SCRF Stanford 15

16 Main consequences All carbonate formations are more or less karstified Many of them were karstified several times (polyphased karst) Ancient karst features may be abandoned and plugged. But once they are exposed in conditions close to those of their formation, they are re-juvenated and can work again, at least locally. 1/5/2009 SCRF Stanford 16

17 One of the issues is To put each observation, data, etc. in the space where the whole karst structure developed. To set it with respect to the prevailing PKD The reference must be the karst system,, i.e. the hydrological functioning unit, including the conduit system and the possible surface area drained by swallow holes. 1/5/2009 SCRF Stanford 17

18 Linear cave system in the French Pyrenees: Niaux-Lombrives Lombrives-Sabart Two cave levels, associated with two stages of the main river. Allogenic point recharge The lower system Ariège river The upper system 1/5/2009 SCRF Stanford 18

19 Mammoth Cave system, Kentucky Four superimposed cave levels associated with the Green River valley, corresponding to four stages of the river. 1/5/2009 SCRF Stanford 19

20 A multilevel cave system in the French Pyrenees: the Arbas karst Cross section The oldest conduit levels, non functioning Old conduit level, with a seasonal functioning Present conduit level, functioning 1/5/2009 SCRF Stanford 20

21 Karst aquifers are not only made of a conduit system Beside the conduits, it exists karst voids more or less hydraulically connected to the conduits. Many voids are also present, which were not modified by karst processes: initial porosity, cracks and joints, with a hydraulical connectivity more or less developed. 1/5/2009 SCRF Stanford 21

22 Finally, different models are proposed for the processes of dissolving carbonate rocks at depth for the development of karst conduit system for the functioning of karst aquifers 1/5/2009 SCRF Stanford 22

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32 How does karst aquifer work? In order to know how karst aquifer works, we can refer to one of the two following approaches: We can go inside to have a look: this is the direct approach. We also can study the aquifer behaviour, i.e. its functioning: this is the indirect approach. 1/5/2009 SCRF Stanford 32

33 The direct approach that of the explorer, the caver or the geographer, who describes natural underground galleries, belonging generally to parts abandoned by groundwater. Approach compared to that of medecine professor, who dissect a body, opens it to look at inside. It does not allows to understand how it works! The explorer only maps the galleries where water does not flow anymore! 1/5/2009 SCRF Stanford 33

34 The indirect approach allows to know how it works. This approach is comparable to doctor s s approach : one ausculates, measures, samples, analyses and diagnoses for characterising the aquifer behaviour, the functioning. 1/5/2009 SCRF Stanford 34

The indirect approach Doline Champ de lapiaz

Epikarst Zone d infiltration Grotte Perte Réseau

actif Calliscope - 1999 Source karstique 2 2 0 2 0

Stanford 8 0 35 1 2 0 6 0 4 0 2 0 0 08:00 09:00

35 The indirect approach Doline Champ de lapiaz Relief ruiniforme Sol Canyon Lac éphémère Aven Epikarst Zone d infiltration Grotte Perte Réseau Fossile Zone noyée Source de trop-plein Réseau actif Calliscope Source karstique C µ g / l /5/ SCRF Stanford :00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00

36 The indirect approach of karst The indirect approach gives a schematic view of: The extension, limits and boundary conditions of the karst system The groundwater flow organisation, The comprehensive functioning, The exploitable resource, The exploitable storage capacity. 1/5/2009 SCRF Stanford 36

37 ! 1/5/2009 SCRF Stanford 37

38 The end! 1/5/2009 SCRF Stanford 38

Surface Processes Focus on Mass Wasting (Chapter 10)

Surface Processes Focus on Mass Wasting (Chapter 10) 1. What is the distinction between weathering, mass wasting, and erosion? 2. What is the controlling force in mass wasting? What force provides resistance?