New Zealand Journal of Geology and Geophysics abstracts
Holocene volcanic geology, volcanic hazard, and risk on Taveuni, Fiji
SHANE J. CRONIN
VINCENT E. NEALL
Institute of Natural Resources
Massey University
Private Bag 11 222
Palmerston North, New Zealand
email: s.j.cronin@massey.ac.nz
Abstract The Holocene volcanic geology of Taveuni has been
mapped in order to produce a volcanic hazard and risk assessment for the
island. Taveuni is the third-largest island of the Fiji group and home to 14
500 people. At least 2.7 km3 of olivine-alkali-basalt magma was
erupted from over 100 events throughout the Holocene. Vents are concentrated
along a northeast-striking rift zone that is parallel to other regional
structural trends. There is an overall trend of younging southward along the
rift. Holocene lavas and tephras are grouped within six newly defined eruptive
periods, established on a basis of radiocarbon dating. Within these periods, 14
tephra layers, useful as local marker horizons, are recognised. At least 58% of
Holocene eruptions produced lava flows, while almost all produced some tephra.
Individual eruption event volumes ranged between 0.001 and 0.20 km3
(dense rock equivalent). Many eruptions involved at least some phases of
phreatic and/or phreatomagmatic activity, although dominant hydrovolcanic
activity was limited to only a few events.
A volcanic hazard map is presented, based on the Holocene geology map and
statistical analyses of eruption recurrence. The highest levels of ground-based
and near-vent hazards are concentrated along the southern portion of the
island's rift axis, with the paths of initial lava flows predicted from present
topography. Tephra fall hazards are based on eruption parameters interpreted
from mapped Holocene tephra layers. Hawaiian explosive-style eruptions appear
to be a dominant eruptive process, with prevailing low-level (<3 km)
southeasterly winds dispersing most tephra to the northwestern quadrant.
Vulnerable elements (population centres, infrastructure, and economy) on
Taveuni have been considered in deriving a volcanic risk assessment for the
island. A number of infrastructural and subdivision developments are either
under way or planned for the island, driven by its highly fertile soils and
availability of freehold land. The area identified with the present greatest
volcanic risk, in south Taveuni, is also where rapid and ongoing population
growth is centred. The results from this study may be used within planning
strategies to minimise vulnerability of future developments on the island as
well as contributing to national and community-level emergency or contingency
plans.
Keywords Fiji; Taveuni; Holocene; basaltic volcanism;
geologic mapping; volcanic hazards; volcanic risk
New Zealand Journal of Geology & Geophysics, 2001, Vol 44: 417-437
0028-8306/01/4403-0417 $7.00/0 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (3731K); (scanned from paper original: notes about this process)
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