karst: multiple concepts for a unique geological objecta unique geological object dr michel...

Karst: multiple concepts for Karst: multiple concepts for a unique geological objecta unique geological object

Dr Michel BakalowiczDr Michel BakalowiczMichel.Bakalowicz@gmail.comMichel.Bakalowicz@gmail.com

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By way of an introductionBy way of an introduction

The project of exploiting a lignite deposit in The project of exploiting a lignite deposit in

a limestone environment of Eastern a limestone environment of Eastern

TurkeyTurkey

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Boring a well in a Miocene lignite basin, in Eastern Turkey

Limestone outcropsQuestion: will some problems Question: will some problems occur during the exploitation occur during the exploitation because of karst?because of karst?

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The first field studies concluded to the The first field studies concluded to the absence of any karst feature either at the absence of any karst feature either at the surface or at depthsurface or at depthBut we can claim But we can claim ““yes, karst developed at yes, karst developed at depthdepth”” without visiting the fieldwithout visiting the fieldWhy?Why?

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Formation of coal deposits in a Formation of coal deposits in a Miocene basinMiocene basin

Basin with a river valleyDejection cones along the slope

Alluviums

limestone

Lignite (Coal) and paleosoils

limestone

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Development of karst in a Miocene Development of karst in a Miocene basinbasin

Basin with a river valleyDejection cones along the slope

Alluviums

limestone

Lignite (Coal) and paleosoils

limestoneDifference in Difference in elevationelevation

Water and Water and vegetation vegetation (Soil CO(Soil CO22))

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The potential for karst developmentThe potential for karst development

The two conditions external to the carbonate The two conditions external to the carbonate aquifer:aquifer:

A difference in elevationA difference in elevationWater and CO2Water and CO2

are necessary for developing karstare necessary for developing karstThey form the potential for karst They form the potential for karst development (PKD) or development (PKD) or potential for potential for karstificationkarstification

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In the example from TurkeyIn the example from Turkey

Karst must occur at depthKarst must occur at depthIt does not necessarily present a It does not necessarily present a hydrological functioning, because it is hydrological functioning, because it is abandoned and floodedabandoned and floodedA classical hydrological study will show A classical hydrological study will show that the aquifer is homogeneous, with a that the aquifer is homogeneous, with a typical porous or fissured behavior. It typical porous or fissured behavior. It could be modeled classically.could be modeled classically.

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Demonstration of karst occurrenceDemonstration of karst occurrence

13 boreholes were located at places 13 boreholes were located at places considered as potential paleoepikarst or considered as potential paleoepikarst or paleodrainagepaleodrainageIn each borehole, the first 100 m in the In each borehole, the first 100 m in the limestone were coredlimestone were cored90% showed karst features, much more 90% showed karst features, much more than expected!than expected!

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Cores showing karst caves and Cores showing karst caves and their sediment fillingtheir sediment filling

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Cores showing karst caves and Cores showing karst caves and their sediment fillingtheir sediment filling

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Cores showing karst caves and Cores showing karst caves and their sediment fillingtheir sediment filling

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Predictable consequences of the Predictable consequences of the exploitation of ligniteexploitation of lignite

Lowering of the water table by pumpingLowering of the water table by pumpingDewatering of the karst conduits of the Dewatering of the karst conduits of the paleo karst systempaleo karst systemBecause of its wide extension, huge Because of its wide extension, huge volumes will be pumped (pumping rate volumes will be pumped (pumping rate estimated to be at least 5 CM per sec)estimated to be at least 5 CM per sec)Deplugging of sediment infilling and risks Deplugging of sediment infilling and risks of sudden flooding of the mine, as it of sudden flooding of the mine, as it occurred elsewhere (Poland, China)occurred elsewhere (Poland, China)

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Two sets of conditions for Two sets of conditions for developing a karst system:developing a karst system:

1.1. External conditions which determine the External conditions which determine the PKD:PKD:

•• the regional hydraulic gradient (direction, intensity), the regional hydraulic gradient (direction, intensity), linking the recharge zone to the base levellinking the recharge zone to the base level

•• the quantity of water and its dissolving power (COthe quantity of water and its dissolving power (CO22 or or other)other)

2.2. Internal conditions which control:Internal conditions which control:•• the geometry of the carbonated formation,the geometry of the carbonated formation,•• the original permeability of the carbonated rock,the original permeability of the carbonated rock,•• the rate of impurities within the rockthe rate of impurities within the rock

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Karst development, a matter of Karst development, a matter of competitioncompetition

The dissolution of rock at depth, responsible The dissolution of rock at depth, responsible for the formation of conduits, is a matter of for the formation of conduits, is a matter of competition between flow velocity and competition between flow velocity and solution kinetics: solution kinetics:

A part of water flows slowly and dissolves the A part of water flows slowly and dissolves the rock close to the surface, producing the surface rock close to the surface, producing the surface landscape.landscape.Another part infiltrates rapidly and dissolves at Another part infiltrates rapidly and dissolves at depthdepth, creating the conduit system., creating the conduit system.

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Main consequencesMain consequences

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

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One of the issues is One of the issues is ……

To put each observation, data, etc. in the space To put each observation, data, etc. in the space where the whole karst structure developed.where the whole karst structure developed.To set it with respect to the prevailing PKDTo set it with respect to the prevailing PKD

The reference must be the The reference must be the karst systemkarst system, i.e. , i.e. the hydrological functioning unit, including the the hydrological functioning unit, including the conduit system and the possible surface area conduit system and the possible surface area drained by swallow holes.drained by swallow holes.

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Linear cave system in the French Linear cave system in the French Pyrenees: NiauxPyrenees: Niaux--LombrivesLombrives--SabartSabart

The upper system

The upper systemThe lower system

The lower system

Ariège river

Allogenic pointAllogenic pointrechargerecharge

Two cave Two cave levels, levels, associated associated with two with two stages of stages of the main the main river.river.

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Mammoth Mammoth Cave system, Cave system,

KentuckyKentucky

Four superimposed cave Four superimposed cave levels associated with levels associated with the Green River valley, the Green River valley, corresponding to four corresponding to four stages of the river.stages of the river.

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Present conduit Present conduit level, functioninglevel, functioning

Old conduit level, with a seasonal

functioning

The oldest conduit levels, non functioning

A multilevel cave system in the A multilevel cave system in the French Pyrenees: the Arbas karstFrench Pyrenees: the Arbas karst

Cross section

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Karst aquifers are not only made of Karst aquifers are not only made of a conduit systema conduit system

Beside the conduits, it exists karst voids Beside the conduits, it exists karst voids more or less hydraulically connected to the more or less hydraulically connected to the conduits.conduits.Many voids are also present, which were Many voids are also present, which were not modified by karst processes: initial not modified by karst processes: initial porosity, cracks and joints, with a porosity, cracks and joints, with a hydraulical connectivity more or less hydraulical connectivity more or less developed.developed.

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Finally, different models are Finally, different models are proposed proposed ……

…… for the processes of dissolving for the processes of dissolving

carbonate rocks at depthcarbonate rocks at depth

…… for the development of karst conduit for the development of karst conduit

systemsystem

…… for the functioning of karst aquifersfor the functioning of karst aquifers

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How does karst aquifer workHow does karst aquifer work ? ?

In order to know how karst aquifer works, In order to know how karst aquifer works, we can refer to one of the two following we can refer to one of the two following approaches:approaches:

We can go inside to have a look: this is the We can go inside to have a look: this is the direct approach.direct approach.

We also can study the aquifer behaviour, i.e. We also can study the aquifer behaviour, i.e. its functioning: this is the indirect approach.its functioning: this is the indirect approach.

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

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The indirect approachThe indirect approach ……

…… allows to know how it works.allows to know how it works.

This approach is comparable to This approach is comparable to doctordoctor’’s approachs approach : one ausculates, : one ausculates, measures, samples, analyses and measures, samples, analyses and ……diagnoses for characterising the diagnoses for characterising the aquifer behaviour, the functioning. aquifer behaviour, the functioning.

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The indirect approachThe indirect approach ……

RRééseau actifseau actif

Réseau Fossile

PertePerte

Lac éphémèreAven

Relief ruiniformeChamp de lapiazDoline

Source detrop-plein

Source karstique

Grotte

CanyonEpikarst

Epikarst

Sol

Zon

e d

’infil

trat

ion

Zon

e no

yée

Calliscope

Calliscope ®®-- 1999

0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 6 0

1 8 0

2 0 0

2 2 0

0 8 : 0 0 0 9 : 0 0 1 0 : 0 0 1 1 : 0 0 1 2 : 0 0 1 3 : 0 0 1 4 : 0 0 1 5 : 0 0 1 6 : 0 0 1 7 : 0 0 1 8 : 0 0 1 9 : 0 0 2 0 : 0 0 2 1 : 0 0

C µ g / l

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The indirect approach of karstThe indirect approach of karst

The indirect approach gives a schematic The indirect approach gives a schematic view of:view of:The extension, limits and boundary The extension, limits and boundary conditions of the karst systemconditions of the karst systemThe groundwater flow organisation,The groundwater flow organisation,The comprehensive functioning,The comprehensive functioning,The exploitable resource,The exploitable resource,The exploitable storage capacity.The exploitable storage capacity.

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!!

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The end!The end!