Low-frequency catastrophic coastal disaster events around Tonga: Survey of coastal boulder distribution on Tongatapu Island and analysis using stochastic modelling of tropical cyclones

摘要

A field survey of the coastal boulder distribution on Tongatapu Islandwas performed to obtain evidence of the old coastal disaster. Thedevelopment potential of the tropical cyclone around this area wasestimated using the stochastic tropical cyclone model. Thirty-eightboulder datasets, including boulder information not reported in previousstudies were collected. Information concerning historical tropicalcyclone data is very limited for the assessment of the low-frequencydisaster event. A stochastic model was applied to generate a 25,000-yearsimulation of the tropical cyclone. If the Haiyan-like tropical cycloneattacks the Tongatapu Island, most boulders would be transported byhigh waves. According to the result of the frequency analysis of thisstudy, this is not an entirely unlikely situation. The strong tropicalcyclone often transverses to the Southeast around the Tongatapu Island.These characteristics are in rough agreement with the fact that theboulder distribution aggregates to the northwest coast of the Tongatapu.