Geosciences

Ground­wa­ter is the main source of water in limes­tone envi­ron­ments. These resources are often of good qua­li­ty and in suf­fi­cient quan­ti­ty, but the dif­fi­cul­ty lies in their acces­si­bi­li­ty. Loca­ting and sizing water pro­duc­tion faci­li­ties to match needs with avai­lable resources requires prior know­ledge of the envi­ron­ment and tar­ge­ted inves­ti­ga­tions. SISKA pro­vides solu­tions for resear­ching, exploi­ting, mana­ging and pro­tec­ting ground­wa­ter in limes­tone envi­ron­ments.

Karst plays a spe­cial role in the pro­blem of natu­ral hazards. SISKA has deve­lo­ped inves­ti­ga­tion methods for asses­sing and map­ping the fol­lo­wing natu­ral hazards :

Col­lapses occur regu­lar­ly in kars­tic regions. By stu­dying these phe­no­me­na through concrete cases, we can pre­dict the condi­tions that lead to these events. As a result, col­lapse risk maps can be pro­du­ced.

In karst, run-off is essen­tial­ly under­ground and the­re­fore invi­sible. Howe­ver, the under­ground water table can some­times reach the sur­face, floo­ding areas that are nor­mal­ly dry, and pro­du­cing sud­den and signi­fi­cant increases in river flow. Thanks to the models deve­lo­ped by the SISKA (KARSYS, Karst­MOD), it is pos­sible to fore­cast floods and river flows and pro­duce flood hazard maps tai­lo­red to the spe­ci­fic cha­rac­te­ris­tics of karst.

The SISKA sup­ports civil engi­nee­ring pro­jects in kars­tic regions and pro­poses solu­tions to prevent pro­blems of sta­bi­li­ty, water ingress and grey water infil­tra­tion.

The SISKA is fre­quent­ly com­mis­sio­ned to sup­port sur­face deve­lop­ment pro­jects (motor­ways, wind farms) or the construc­tion of under­ground struc­tures (tun­nels, gal­le­ries, etc.). Through its research and deve­lop­ment acti­vi­ties, the SISKA has deve­lo­ped methods for iden­ti­fying and reme­dying the pro­blems posed by construc­tion in kars­tic envi­ron­ments. The Kars­tA­LEA method, the result of col­la­bo­ra­tion with the Fede­ral Roads Office (FEDRO), is an illus­tra­tion of the prac­ti­cal methods deve­lo­ped by the ins­ti­tute.

The SISKA spe­cia­lises in under­ground mea­su­re­ments and docu­men­ta­tion.

The SISKA is fre­quent­ly invol­ved in the pro­duc­tion of under­ground models to help unders­tand, deve­lop and exploit under­ground geo­lo­gi­cal and hydro­geo­lo­gi­cal aspects. Various tools can be pro­po­sed for the loca­tion, topo­gra­phy or 3D acqui­si­tion of under­ground voids. There are many examples of appli­ca­tions :

• Desi­gning under­ground deve­lop­ments : tou­rist infra­struc­tures, laying pipes, etc. or sur­face deve­lop­ments inter­ac­ting with the sub­soil ;
• Plan­ning for the exploi­ta­tion stra­te­gy of under­ground depo­sits (e.g. salt mines) or for the assess­ment of back­fill capa­ci­ties ;
• Docu­men­ta­tion of his­to­ric under­ground struc­tures, etc.

The SISKA also has a great deal of expe­rience in the ins­tru­men­ta­tion of phe­no­me­na in under­ground envi­ron­ments, par­ti­cu­lar­ly in the context of moni­to­ring ground­wa­ter qua­li­ty, the qua­li­ty of the under­ground atmos­phere or tre­mors during deve­lop­ment work.

Karst regions are increa­sin­gly concer­ned with the deve­lop­ment of infra­struc­ture for the pro­duc­tion of rene­wable ener­gy, main­ly hydroe­lec­tric, geo­ther­mal and wind power. The SISKA assists deve­lo­pers with rene­wable ener­gy pro­jects in these regions.

Karst ground­wa­ter offers some poten­tial for gene­ra­ting elec­tri­ci­ty. Howe­ver, such exploi­ta­tion is not without risk to the envi­ron­ment, and the risks must be asses­sed by spe­cia­lists.
The SISKA is active in this field, pro­vi­ding sup­port for pro­jects and car­rying out impact stu­dies. We are in a posi­tion to make a diag­no­sis at the pre-pro­ject stage to see whe­ther the pro­ject has a chance of suc­cess and what adap­ta­tions would be neces­sa­ry to com­ply with the various laws and prac­ti­cal ins­truc­tions rela­ting to pro­jects in karst.

The ins­tal­la­tion of wind tur­bines in kars­tic envi­ron­ments must be sub­ject to spe­ci­fic sup­port in terms of envi­ron­men­tal impact and, conver­se­ly, the risks of sta­bi­li­ty for the struc­ture.

The heat pro­pa­ga­tion mecha­nisms in karst sub­soils are very dif­ferent from those in other geo­lo­gi­cal envi­ron­ments. Exploi­ta­tion pro­jects often require adap­ta­tion and spe­cia­li­sed sup­port. The SISKA has tools and expe­rience in this field, and works in col­la­bo­ra­tion with the Centre for Hydro­geo­lo­gy and Geo­ther­mal Ener­gy at the Uni­ver­si­ty of Neu­châ­tel, which is a reco­gni­sed centre of exper­tise.

Caves and kars­tic land­scapes are the result of the dis­so­lu­tion of limes­tone in rain­wa­ter. In some cases, dis­so­lu­tion can result from other causes (e.g. deep gas upwel­ling). Unders­tan­ding how caves are for­med is of obvious inter­est to the caver explo­ring them. Howe­ver, pre­dic­ting the pre­sence of an under­ground void is also impor­tant infor­ma­tion for an engi­neer buil­ding a tun­nel or a hydro­geo­lo­gist col­lec­ting water.

Seve­ral nume­ri­cal models of spe­leo­ge­ne­sis have been deve­lo­ped over the last 35 years. They have taught us a great deal about the prin­ciples, rates of for­ma­tion and broad out­lines of the geo­me­try of under­ground gal­le­ry net­works. Howe­ver, the cha­rac­te­ri­sa­tion of the ground para­me­ters that feed these models is com­pa­ra­ti­ve­ly late. The SIS­KA’s research is the­re­fore hel­ping to pro­vide field data, represent it and com­pare it with the results of simu­la­tion models.

Karst struc­tures clear­ly do not deve­lop ran­dom­ly. We have iden­ti­fied the gene­ral cha­rac­te­ris­tics and can sketch out the areas that are poten­tial­ly the most kars­ti­fied. Howe­ver, if we are to gene­rate rea­lis­tic net­works, there is still work to be done for future gene­ra­tions…

Our work main­ly concerns :

• The spa­tial dis­tri­bu­tion of kars­tic conduits (concept of incep­tion hori­zons)
• The gene­sis of kars­tic net­works in the epi­phrea­tic zone (loops)
• The laye­ring of kars­tic net­works (spe­leo­ge­ne­tic phases)

At present, they are concen­tra­ting main­ly on pre­dic­ting the (pro­ba­bi­lis­tic) posi­tion of ducts and on cha­rac­te­ri­sing them (size, shape, filling, water, etc.).

Although at first sight a high­ly aca­de­mic sub­ject, a detai­led unders­tan­ding of the under­ground cli­mate is impor­tant for the mana­ge­ment of archaeo­lo­gi­cal, ornate and tou­rist caves, and even for cer­tain spe­leo­lo­gi­cal pro­jects. It is also impor­tant for unders­tan­ding the ther­mal cha­rac­te­ris­tics of kars­tic mas­sifs, and hence the ins­tal­la­tion of geo­ther­mal probes, or for explai­ning the pre­sence of a natu­ral gla­cier. Final­ly, it is neces­sa­ry to inter­pret the varia­tions obser­ved in the growth of sta­lag­mites and to pro­duce palaeo­cli­ma­tic recons­truc­tions.

Cur­rent pro­jects :

• Cave­Seds
• Ana­ly­sis of the inter­ac­tions bet­ween ven­ti­la­tion, CO2 levels and water che­mis­try in the Milandre cave
• Long-term moni­to­ring of seve­ral natu­ral gla­ciers in the Jura

Past pro­jects :

• Ther­mo­karst
• Stu­dy of natu­ral gla­ciers in the Jura
• Ana­ly­sis of the cli­mate in the Las­caux cave
• Stu­dy of the ther­mal pro­per­ties of kars­tic mas­sifs
• Assess­ment of the ther­mal poten­tial of kars­tic mas­sifs
• Arti­fi­cial ven­ti­la­tion test in a kars­tic cavi­ty (Milandre)

Iso­la­ted from exter­nal ero­sion pro­cesses, caves pre­serve sedi­men­ta­ry sequences span­ning hun­dreds of thou­sands or even mil­lions of years. The stu­dy of these depo­sits, whe­ther detri­tal sedi­ments (i.e. lami­nites, pebbles) or spe­leo­thems (i.e. sta­lag­mites), pro­vides valuable infor­ma­tion on cli­ma­tic and envi­ron­men­tal changes over time. From gla­cial cycles to sea­so­nal fluc­tua­tions, cave sedi­ments pro­vide valuable infor­ma­tion about our past envi­ron­ment.
In addi­tion to dating these sedi­ments, the SISKA is stu­dying their mine­ra­lo­gi­cal (cal­cite, ara­go­nite, quartz, etc.), geo­che­mi­cal (Mg, Sr, Ba, S, etc.) and iso­to­pic (d18O, d13C, etc.) signa­tures, as well as their fau­nal (microin­ver­te­brates, bones) and bota­ni­cal (pol­lens) content.

See also our exper­tise in archaeo­zoo­lo­gy.

Cli­ma­tic condi­tions have many influences on karst. Among these, the SISKA is main­ly asses­sing the effect of cli­mate change on the fol­lo­wing ele­ments.

• Infil­tra­tion of water into the sub­soil or recharge of aqui­fers. This has a direct influence on the quan­ti­ty of ground­wa­ter avai­lable. It is the result of a deli­cate balance bet­ween cli­ma­tic fac­tors (rain­fall, tem­pe­ra­ture, etc.) and bio­pe­do­lo­gi­cal fac­tors (vege­ta­tion and soil).
• The pre­ci­pi­ta­tion of cal­cite in sta­lag­mites is par­ti­cu­lar­ly rele­vant to palaeo­cli­ma­tic recons­truc­tion. The layers of cal­cite depo­si­ted in sta­lag­mites record the cli­ma­tic condi­tions pre­vai­ling at the time of their depo­si­tion, in a simi­lar way to the rings on the trunk of a tree.
• The dis­so­lu­tion of limes­tone plays a role in slo­wing down glo­bal war­ming. Indeed, it has been shown that glo­bal war­ming increases bio­lo­gi­cal acti­vi­ty in soils, lea­ding to an increase in the soil’s CO2 content. Water infil­tra­ting the soil the­re­fore dis­solves more CO2, which in turn allows it to dis­solve more limes­tone. The result is that for each addi­tio­nal mole­cule of limes­tone dis­sol­ved, one mole­cule has been remo­ved from the soil, and the­re­fore from the ear­th’s atmos­phere. This remo­val of CO2 could explain a large part of what spe­cia­lists call the « car­bon sink », i.e. the fact that atmos­phe­ric CO2 is increa­sing less qui­ck­ly than model esti­mates.