The geology of the volcanic islands in the South Pacific generally consists of lava flows, pyroclastics, breccias and conglomerates, all weathered to varying degrees according to the age of the individual island concerned. Geomorphology is often dominated by volcanic mountains forming a central highland area, such as on Rarotonga in the Cook Islands, Viti Levu in Fiji, Ambrym in Vanuatu and Tahiti in French Polynesia. Orientation of the major drainage networks tends to be in a radial fashion outward from the central highlands. If the volcanoes are aligned in a chain, then the volcanic peaks form an elongated mountainous spine to the island. Examples include Savai’i in Samoa, Kadavu in Fiji, Santa Isabel in Solomon Islands and Pentecost in Vanuatu. On such islands, the orientation of the major river networks is controlled by the linear arrangement of the volcanic mountains. Within individual catchments, drainage patterns are typically dendritic because of the lack of geological or structural controls other than the volcanoes. Drainage densities are high. Centripetal drainage patterns are seen where a river drains a breached volcanic caldera, such as the Tavua and Lovoni rivers on the islands of Viti Levu and Ovalau in Fiji, respectively.
KeywordsTropical Cyclone Storm Surge Solomon Island Hydrometric Station Bankfull Discharge
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