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Freshwater lens level and temperature in the corallian karstified island of Lifou (New Caledonia, Soutwest Pacific)

Author(s): Comparison with the Baget karsic system (Ariege, France) as an example of a continental karst
Congress: 2008
Author(s): Pierre Genthon, Wirrman, Hoibian, Mangeas
Wirrmann, Denis, IRD / Paléotropique BP A5 98848 Noumea cedex, mail with noumea.ird.nc Hoibian, Thierry, Univ. Nouvelle Calédonie, BPR4 - 98851 Nouméa Cedex, mail with unv-nc.nc Mangeas, Morgan, IRD / Espace BPA5 98848 Noumea cedex, mail with noumea.ird

Keyword(s): corallian island, Loyalty Islands, freshwater lens, karstic system, monitoring, temperature
AbstractLifou is a a flat topped corallian island generated by coral growth during subsidence of the underlying volcanoe. It has been uplifted up to a near 100m altitude since nearly 1 Ma on the forearc elastic bulge developping on the Australian lithosphere before its subduction at the Vanuatu (formerly New Hebrides) trench. It is the largest (1150 km2) of the three islands that constitute the Province des Iles of New Caledonia. As part of the ADAGE and SAGE projects, funded by the Province des Iles, Lifou has been extensively surveyed for geology and water ressources by teams of the IRD the University of New Caledonia, and the Brgm. We discuss the data gathered at two station located in caves near the main village of the island (Wé) located at the sea shore, where the freshwater level and temperature have been monitored during the year 2003 at a half hour time step. The freshwater temperature presents only smooth changes, which are poorly correlated with rain. This is also the case for the water level, when daily and half daily components associated to the propagation of tides inside the island mass are filtered. These data are compared with those recorded in a cave belonging to the well organized Baget karstic system, where rainy events are generally associated with a several meters water rise and a several tens of a degree temperature change. Consequenses for the kastic system of the Loyalty islands are drawn, as well for water ressources monitoring strategies in this area.
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