Comparison between a geophysical survey, soil analyses and excavation data revealing a combined effect of soil compaction and erosion

In the vicinity of the Montbaron farm site (Indre, France), a mediaeval archaeological site was excavated initially in 1977 and again more thoroughly during 1998–2000. The observed stratigraphic sections reveal that strong changes have occurred between these two dates: in some places, 40–50 cm of fine-grained soil has disappeared. Geophysical surveys provide a second source of independent substantiate of this dramatic reduction of soil thickness; a comparison between two resistivity surveys undertaken in 1992 and 1996 confirms a major reduction in the thickness of the fine-grained layers above the hard limestone surface. This example emphasizes the importance of an erosion and compaction assessment for which, in plateau contexts similar to that of Montbaron, resistivity prospection is a valid and relevant tool.