How 3d volcanic stratigraphy constrains headscarp collapse scenarios: the Samperre Cliff case study (Martinique Island, Lesser Antilles)

Abstract

Abstract. Gravitational instabilities can be significant threats to populations and infrastructures. For hazard assessment, it is of prior importance to estimate the geometry and volume of potential unstable masses. This characterization can be particularly difficult in volcanic context due to the succession of deposition and erosion phases. Indeed, it results in complex layering geometries where the interfaces between geological layers may be neither parallel nor planar. Geometry characterization is all the more complex when unstable masses are located in steep and hardly accessible landscapes, which limits data acquisition. In this work, we show how remote observations can be used to estimate the surface envelope of an unstable mass on a volcanic cliff. We use ortho-photographs, aerial views and topographic surveys to (i) describe the different geological units of the cliff, (ii) identify stable and unstable units, (iii) infer the paleo-morphology of the site and (iv) estimate potential unstable volumes. We use the Samperre cliff in Martinique (Lesser Antilles, French West Indies) as a study site, where recurrent destabilizations since at least 1988 have produced debris flows that threaten populations and infrastructures. Our analysis suggests that the destabilizations occurring on the cliff may be associated to the re opening of a paleo-valley filled by pyroclastic materials. We estimate that between 3.5 × 106 m3 and 8.3 × 106 m3 could still be mobilized by future destabilizations in the coming decades.