Spatio-temporal evolution of temperature and fluid flow through a new “thermo-lithological” boundary; the case of a pit crater of Karthala volcano (Comoros archipelago) refilled on January 13th 2007 by a lava flow
Résumé
On January 13 th 2007 the effusive eruption of Karthala volcano, in the Comoros islands, emitted a lava flow which has been perfectly constrained inside the cylindrical shape of the Choungou Chagnoumeni pit crater; 225m in diameter and with a thickness of about 7m. The good knowledge of the geometry of this lava flow allowed modeling its cooling, with the Rheolef code, with a good accuracy. The results of the thermal modeling were compared with other measurements performed on the field: (1) a high resolution electrical resistivity tomography profile crossing the boundary of the crater and (2) the thermal monitoring of temperature with eleven sensors, spaced 1 meter apart, at 30 cm depth, perpendicularly to the boundary of the crater. Thanks to this multidisciplinary approach it has been possible to display that, in the first order, the resistivity distribution in the soil 2 years and 5 months after the eruption is directly influenced by the residual temperature and not by the structural boundary. During the first three years of cooling, an inversion in the shallow lateral temperature gradient was observed in temperature data set collected at 30 cm depth.
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