Airborne electromagnetic (AEM) methods proved their accuracy in environmental studies during last decades. Volcanic islands are characterized by heterogeneous geology controlled by various complex factors. La Réunion Island, localized in the south-west part of the Indian Ocean, is composed by two shield volcanoes. Their structures are controlled by large erosive processes driven by steep topography, and weathering in inter-tropical climate and the cyclonic regime. In these conditions, in order to help interpreting a large regional AEM dataset resulting in millions of 3D resistivity values, we propose a strategy to delimit areas where the resistivity structure of the first 100 m of the underground have comparable behaviors - and accordingly comparable geological and/or hydrogeological characteristics.

Agglomerative Hierarchical Clustering (AHC) analyzes variation between the vertical resistivity distributions of all inverted soundings. AHC results are hierarchized in clusters, each one being associated to an average depth-resistivity signature. The AHC method was applied on the AEM dataset acquired on La Réunion Island. Clusters are consistent with the geological background and inform on different geological and hydrogeological phenomena such as weathering. These subdomains will be used with the aim of evaluating various conceptual hydrogeological models throughout the island.


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