Karst development potential and base level changes in Mediterranean regions:
a unique reference model

Michel BAKALOWICZ¹, Bertrand AUNAY², Paul LE STRAT², Nathalie DÖRFLIGER³, Perrine FLEURY⁴

¹ Hydrosciences, Université Montpellier II, cc MSE, 34095 MONTPELLIER CEDEX 5 (France)
Tel 00 34 467 143 933
Fax 00 34 467 144 774
E-mail: baka@msem.univ-montp2.fr
² Service Géologique Régional, BRGM, 1039 rue de Pinville, 34000 MONTPELLIER (France)
³ Unité RMD, BRGM Eau, 1039 rue de Pinville, 34000 MONTPELLIER (France)
⁴ Nymphea Water, Les Dauphins, 520 av. de Jouques, 13685 AUBAGNE CEDEX (France)

Karst develops only when necessary conditions occur, named the karstification potential, KP. KP includes a "solvent", generally water and dissolved CO₂, and an "engine" driving the ground water flow. The main "engine" is the difference in altitude between the recharge area and the discharge point, the base level, BL. BL fixes up the position of the karst network. When BL drops down, the karst network is abandoned and a new one is created. In a reverse way, after a rising up of BL, the karst structure becomes flooded and non-functional.

The Mediterranean karst regions have been subjected to a major event at the end of Miocene, the Messinian crisis, 5.5 My ago. The sea level dropped down to 1000-1200 m below the present day level. In their lower part, the main rivers deeply embanked, very often in carbonate rock formations. The new KP organised karst structures related to a very deep BL. Pliocene began with a very rapid rising up sea level and the flooding of the Messinian karst structure. Since Upper Pliocene, BL changed several times, related to glacial periods. These changes were only in the range 100-150 m, i.e. without significant consequences on karst development and functioning. The main consequence on present day karst aquifers is a very complex functioning, with the existence of huge karst reservoirs, the presence of vaucluse-type springs, i.e. vertical phreatic conduit discharging at the main springs, natural sea water intrusion deeply in the aquifers and submarine springs along the coast.