HR: 1340h
AN: H23G-1695    [Abstracts]
TI: Thermal convection and vertical permeability in karstic networks
AU: * GENTHON, P
EM: genthon@msem.univ-montp2.fr
AF: Hydrosciences / IRD, MSE Univ. Montpellier II cedex 05, Montpellier, 34095, France
AU: FONTAINE, F
EM: fontaine@ipgp.jussieu.fr
AF: Geosciences Marines / IPGP, 4 Place Jussieu cedex 05, Paris, 75255, France
AU: MANGIN, A
EM: alain.mangin@lsm.cnrs.fr
AF: FRET, Laboratoire souterrain, Moulis, 09200, France
AB: Karstic networks constitute highly heterogeneous aquifers. Modelling such aquifers at the 1000 yr time-scale is a fully coupled problem involving flow and reaction of meteoric waters with the carbonated matrix. A better knowledge distribution of groundwater in karstic area is required for water policy in these regions. Yet, the localization of caves in a karstic network cannot be presently predicted. Dissolution by meteoric waters in carbonated formations has been recently explored by accurate models. The drainage networks produced by these models are mainly controlled by the initial heterogeneity distribution (fault or joint, for example), by the regional state of stress and by boundary conditions. The main extension of these networks is mainly along the horizontal, from the top of the formation toward an outlet near a river. However, vertical voids such as shafts or vertically organized series of caves are present in several karstic networks. Shaft are believed to form by roof collapse and to connect superposed networks induced by base level changes, for example during the Messinian crisis in the Mediterranean areas. Roof collapse is however not the only mechanism able to form vertically organized structures and any mechanism involving gravity may be involved. Cooling of upwelling waters has been known for long to form so-called hydrothermal karst, due to the reverse solubility behaviour of carbonated minerals (i.e. their solubility increases with decreasing temperature). Moreover convection inside a fracture zone produced thin vertical upwelling currents which are able to produce vertically organized dissolution zones , at the opposite of round shaped zone expected from convection inside an homogeneous medium. Here we explore how thermal convection inside a fracture can induce chimney-like dissolution zones, by mean of coupled flow and reaction models designed for a series of theoretical cases. Then the conditions required to induce significant dissolution in vertically organized zones inside a limestone formation are discussed.
DE: 1828 Groundwater hydraulics
DE: 1847 Modeling
DE: 5104 Fracture and flow
DE: 5144 Wave attenuation
SC: Hydrology [H]
MN: 2007 Fall Meeting