Impacts of category 5 tropical cyclone Fantala (April 2016) on Farquhar Atoll, Seychelles Islands, Indian Ocean

• Published in: Geomorphology (Amsterdam, Netherlands) Vol. 298; pp. 41 - 62
• Main Authors: Duvat, Virginie K.E., Volto, Natacha, Salmon, Camille
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2017; Elsevier
• Subjects: Atoll reef islands; Environment and Society; Environmental Sciences; Geography; Global Changes; Humanities and Social Sciences; Satellite image analysis; Sediment transport pathways; Seychelles Islands; Shoreline changes; Tropical cyclone impacts; Tropical cyclone impacts; Shoreline changes; Sediment transport pathways; Seychelles Islands; Satellite image analysis; Atoll reef islands
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/j.geomorph.2017.09.022

This paper provides new insights on the impacts of a category 5 tropical cyclone on Indian Ocean atoll reef islands. Using multi-date aerial imagery and field observations, the contribution of tropical cyclone Fantala to shoreline and island change, and to sediment production and transport, was assessed on Farquhar Atoll, Seychelles Islands. Results show that the two largest islands (>3km2) only suffered limited land loss (−1.19 to −8.35%) while small islets lost 13.17 to 28.45% of their initial land area. Islands and islets exhibited contrasting responses depending on their location, topography and vegetation type. Depending on islands, the retreat of the vegetation line occurred either along all shorelines, or along ocean shoreline only. The structure (wooded vs. grassy) and origin (native vs. introduced) of the vegetation played a major role in island response. Five days after the cyclone, beach width and beach area were multiplied by 1.5 to 10, depending on the setting, and were interpreted as resulting from both sediment reworking and the supply of large amounts of fresh sediments by the reef outer slopes to the island system. Fourth months after the cyclone, extended sheets of loose sediments were still present on the reef flat and in inter-islet channels and shallow lagoon waters, indicating continuing sediment transfer to islands. •This is the first study of a tropical cyclone's impacts on an Indian Ocean atoll.•Category 5 tropical cyclones can be constructive for atoll reef islands.•Assessing intertidal cyclone-driven features is key to fully apprehend impacts.•Using convolution filters helps detecting shoreline position and sediment deposits.•The vegetation type played a major role in island response.