| アブストラクト |
Thermal and electrical investigations on a quiescent volcanic conein Piton de La Fournaise (La Reunion Island, France) have revealedcorrelations between thermal and eletric data (Antoine et al., 2009).The thermal pattern and the correlations with electric data have beensuccessfully explained by air convection within the volcanic soilcomposing the structure of the cone. At the scale of volcano,electrical map show a specific pattern previously interpreted as theeffect of meteoritic water circulation. Thermal images of fractureslocated near the caldera show the same behavior than the volcaniccone. Extrapolating our result at Formica Leo to the entire volcanoled us to propose the existence of convection cells at the volcanoscale (Antoine et al, submitted). The occurrence of this phenomenon atother terrestrial volcanoes is currently under investigation in theframe of a collaboration between OMP, IPGP and ERI in Japan. These findings for terrestrial volcanic and permeable soils may alsoapply to other planets. Thermal data are available on Mars, and thesecond part of the presentation will focus on thermal observations ofthe red planet. The terrestrial studies show that the occurrence ofaerothermal systems is mostly controlled by the permeability of thesoil. Permeable regions of Mars were searched with the double criteriaof coarse grains (e.g., debris apron) and extensive stresses. Resultsare presented at Central Elysium Planitia and Arsia Mons. Thermal,geologic and geometric characteristics of Cerberus Fossae and ArsiaMons’ skyholes and collapsed sinuous rills were documented in detail.We will report on the finding of thermal anomalies, which can not beexplained by the geometry and/or geology. In addition, the pitsdistribution across Arsia Mons south flank revealed a link with areasin extension, consistent with the conditions required for airconvection. This convection system would consist of cold air enteringat the base of the volcano flanks, flowing up the slope while beingwarmed by the geothermal flow. The atmospheric air will exit warmer,at places where permeability is high. In addition, the occurrence ofsuch aerothermal systems on Mars is shown to be plausible using a 2Dnumerical model. If true, temperature differences observed at the exitare dependant on the quantity of heat transported by air convection.This might give us an indirect estimation of the martian geothermalflow. The existence of such convection system may participate to thealteration of martian volcanic rocks through the transport of volatilespecies. |
