L’apport du géoradar pour l’étude des impacts géomorphologiques du tsunami du 26 décembre 2004

Résumé 0

This article aims at emphasizing the importance of the Ground Penetrating Radar (GPR) campaign that has been carried out after the December 26th, 2004 tsunami. Out of a large amount of data collected in the field, we are unveiling here the sand dunes’ erosion and the correlated sandy deposits. This study takes place in Lampuuk at two different spots where either erosion or deposition was clearly identified. GPR data were completed with traditional destructive methods in order to calibrate the radargram. Results concern the coastal dunes’ eroded structure chopped by the tsunami. This structure appeared as a succession of 45° inclined layers, horizontally cut on the top, with, a post-tsunami sandy deposit cover – this last deposit certainly brought by wind deflation. The deposit area – in a coconut trees field – is located behind the dunes-field. It revealed a layered structure of sandy deposit that coincides with the water table progressive retreat. The sandy deposits were in average 45 cm deep, and showed some local variations mainly due to topography details. Then, owing to 3D processing we could also calculate the tsunami deposit volume in the coconut trees plantation: 4 415 m3.ha-1. In the end, the GPR allowed us to detect non-autochthonous deposits bellow the 2004 tsunami deposit that certainly result from a paleo-tsunami.