| abstract: |
Thermal and electrical investigations on a quiescent volcanic cone
in Piton de La Fournaise (La Reunion Island, France) have revealed
correlations between thermal and eletric data (Antoine et al., 2009).
The thermal pattern and the correlations with electric data have been
successfully explained by air convection within the volcanic soil
composing the structure of the cone. At the scale of volcano,
electrical map show a specific pattern previously interpreted as the
effect of meteoritic water circulation. Thermal images of fractures
located near the caldera show the same behavior than the volcanic
cone. Extrapolating our result at Formica Leo to the entire volcano
led us to propose the existence of convection cells at the volcano
scale (Antoine et al, submitted). The occurrence of this phenomenon at
other terrestrial volcanoes is currently under investigation in the
frame of a collaboration between OMP, IPGP and ERI in Japan.
These findings for terrestrial volcanic and permeable soils may also
apply to other planets. Thermal data are available on Mars, and the
second part of the presentation will focus on thermal observations of
the red planet. The terrestrial studies show that the occurrence of
aerothermal systems is mostly controlled by the permeability of the
soil. Permeable regions of Mars were searched with the double criteria
of coarse grains (e.g., debris apron) and extensive stresses. Results
are presented at Central Elysium Planitia and Arsia Mons. Thermal,
geologic and geometric characteristics of Cerberus Fossae and Arsia
Mons’ skyholes and collapsed sinuous rills were documented in detail.
We will report on the finding of thermal anomalies, which can not be
explained by the geometry and/or geology. In addition, the pits
distribution across Arsia Mons south flank revealed a link with areas
in extension, consistent with the conditions required for air
convection. This convection system would consist of cold air entering
at the base of the volcano flanks, flowing up the slope while being
warmed by the geothermal flow. The atmospheric air will exit warmer,
at places where permeability is high. In addition, the occurrence of
such aerothermal systems on Mars is shown to be plausible using a 2D
numerical model. If true, temperature differences observed at the exit
are dependant on the quantity of heat transported by air convection.
This might give us an indirect estimation of the martian geothermal
flow. The existence of such convection system may participate to the
alteration of martian volcanic rocks through the transport of volatile
species.
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