Major natural hazards in a tropical volcanic island: A review for Mayotte Island, Comoros archipelago, Indian Ocean

Mayotte is a French Overseas Territory of the Comoros archipelago. Since the 1980. Mayotte has developed quickly: its population has multiplied by four in less than 30 years, infrastructure expanded rapidly in lowlands and slums developed in steep areas (through deforestation) or close to riverbeds. This development urgently required steps to ensure the safety of urban areas. From 2002 to 2006, a major programme of natural hazards evaluation and zonation was conducted by the French Geological Survey in the 17 districts of Mayotte. The programme resulted in the publication of the first single-hazard zonation maps for Mayotte, at 1:25 000-scale in rural areas and at 1:10 000-scale in urban areas. Hazard maps regarding landslides and rock falls, stream floods, seismic lithological and topographical amplification potential, liquefaction potential and cyclonic marine submersion were produced for mayors and land planners. These atlases also included prevention guidelines to minimize risks associated with land-use or urbanization within hazard-prone areas. This article presents the main achievements of the programme whose main problems were the absence of archives, of previous studies and the original volcanic geology of the island of Mayotte. The atlases highlight areas with numerous landslides, zones susceptible to flash floods, sectors likely to be submerged by storm surges and areas subject to seismic site effects due to thick volcanic weathered formations. This programme emphasizes the fundamental role in such tropical volcanic islands, of a good knowledge of the weathered formations, for the assessment of most natural hazards. This initial hazard mapping represented the first step to achieve specific regulatory Risk Prevention Plans for an efficient land use risk mitigation and reduction policy in Mayotte. (C) 2010 Elsevier B.V. All rights reserved.