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Citation Information

Type Journal Article - Journal of Volcanology and Geothermal Research
Title Nabukelevu volcano (Mt. Washington), Kadavu--a source of hitherto unknown volcanic hazard in Fiji
Volume 131
Issue 3-4
Publication (Day/Month/Year) 2004
Page numbers 371-396
URL https://www.sciencedirect.com/science/article/abs/pii/S0377027303004141
Nabukelevu volcano (805 m) is a small (ca. 3.4 km3) hornblende/biotite–andesite dome–breccia complex. It is the youngest in a Plio–Pleistocene series of volcanoes related to a presently inactive subduction zone in southern Fiji. We present new evidence of up to four Holocene eruption episodes from this volcano, with onshore evidence of the latest activity post-1686±40 years BP, and offshore evidence of tephra falls between 2250±70 and 780±50 years BP. Scoriaceous pyroclastic flow deposits of one eruptive episode contain pottery fragments, presumably entrained from habitation areas during emplacement. Like many composite edifices in moist climates, Nabukelevu is prone to failure, the propensity in this case exacerbated by up to three edifice-cutting fault zones. The fault-induced weak and saturated zones have been the focus of repeated edifice failure through late Holocene debris avalanches of between 10–100 million m3. Many of these avalanches entered the sea, and these or additional submarine failures of the lower island flanks have led to emplacement of at least one major late Holocene submarine mass-flow deposit with distinctive mineralogy in the Suva Basin to the north. Two of the debris avalanches dated at post-2350±140 and post-1750±60 years BP apparently inundated local habitation areas, and the deposits incorporate pottery and human remains. A widespread local legend describing catastrophic events on Nabukelevu corresponds in content with geologic findings to provide additional evidence of a late Holocene eruptive and debris avalanche disaster on Kadavu during the latter part of the last ca. 2000 years of human occupation, possibly as recent as between AD 1630 and 1680. The present hazardscape of the Nabukelevu area includes common landslides induced by frequent earthquake swarms and cyclones. Larger edifice failures, possibly related to volcanism or fault movement, have the potential to create local tsunami, which under favourable conditions could reach areas near Fiji’s capital, Suva, 110 km to the north.

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