Preliminary soil-temperature measurements over 16 months indicate an important geothermal flux of at least 0.4 Wm−2 on the summit of a scoria cone in the Chaîne des Puys (France). This anomaly can be explained by a residual hydrothermal flux that has begun when the maar and the overlying cone were formed around 30000 years ago. To cite this article: M. Aubert, C. R. Geoscience 336 (2004).