Geologic Background:
Aoba (or Ambae) is the largest basaltic shield
volcano in the New Hebrides arc, with the base about
3,000 m below sea level, the summit about 1,500 m above
sea level, and a volume of about 2,500 cu. km. This
rainforest-covered island lies in front of the
d'Entrecasteaux collision zone, between the north and
south Aoba Basins along an approx. N50°E fracture
transverse to the arc. Two concentric summit calderas,
the largest 5 km in diameter, enclose the central crater
containing the 2-km-diameter Lake Voui (Vui). Numerous
secondary craters and cones lie along the N50°E
frature, out to the extremities of the island, where
previous magma-seawater interactions have produced
several maars. Lake Voui and the Manaro Ngoro summit
explosion craters and cones formed about 420 years ago.
The Ndui Ndui lava flows issued from the N50°E
fissure about 300 years ago and reached the NW coast.
Aoba is considered the potentially most dangerous volcano
of the Vanuatu archipelago because of the wide
distribution of very young deposits related to strong
explosive eruptions.
Historic Activity:
- The central crater of Lake Vui was active around 1590
and the most recent lava flows occurred around 1670.
- Around 1870, mud flows destroyed a village on the
lower slopes of the volcano.
- An eruption possibly occurred in 1914 with ashfalls
(?) and lahars.
Recent Activity:
- Three anomalous "boiling" areas with large bubbles
and burned vegetation were observed in July 1991.
- Unusual seismic activity was felt during Dec. 1-7,
1994, but no evidence of change in crater or
fumaroles.
- On March 2, 1995, Lake Voui began steaming all over,
bubbling up in the center, and there were black sediment
ejections. A gas plume rising 2-3 km above the lake began
the next day and strong continuous tremor occurred
between March 4-6, with lower levels of tremor continuing
through March 13. On March 17, a warning of possible
evacuation was issued.
Data Sources:
- Global Volcanism Network (V. 16, No. 7 to V. 26, No.
1).
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