Geologic Background:
One of Melanesia's youngest and most active
volcanoes. Bagana sits along Bougainville's axial
highlands. Reports are rare but typical activity includes
long-term lava dffusion and slow dome growth, coupled
with moderate explosive activity ending with dome
destruction. Bagana is a massive symmetrical lava cone
largely constructed by an accumulation of viscous
andesitic lava flows. The entire lava cone could have
been constructed in about 300 years at its present rate
of lava production. Eruptive activity at Bagana is
characterized by non-explosive effusion of viscous lava
that maintains a small lava dome in the summit crater,
although explosive activity occasionally producing
pyroclastic flows also occurs. Lava flows form dramatic,
freshly preserved tongue-shaped lobes up to 50-m-thick
with prominent levees that descend the volcano's flanks
on all sides.
Historic Activity:
- At least 15 eruptions from 1865 to 1970.
Recent Activity:
- Beginning in 1975, a lava dome had been growing in
Bagan's summit crater and lava has flowed sluggishly down
the N and NW flanks. A period of vigorous summit crater
lava dome growth, accompanied by strong seismicity and
increased ash emission started in Oct. 1984 and continued
until Mar. 1985. From Feb. 1986 to Sept. 1987 there was
extrusion of a thick viscous lava flow on the north
flank. In late Sept. the dome became unstable and was
destroyed as hot avalanches of dome material flow down
the slopes. A new flow from the dome down the east flank
formed in Feb. 1988 and is 1.5 kilometers long and
continues to slowly advance as of July 1988. Increased
lava production in Septerber began feeding a new lobe of
the flow from the dome which was continuing in Nov. 1988.
On Jan 22, 1989 a collapse of the crater wall resulted in
drainage of lava from the crater. From Nov. 1989 to Aug.
1990 flow spilled over crater rim as thick block
flow.
- Political unrest prevented any reports from Aug. 1990
to Jan. 1992. During that period the eruption continued
with extrusion of sluggish lava into the summit crater
and onto the volcano's flanks.
- Following the Aug. 16, 1995 earthquake (Ms 7.8) 140
km to the northwest, Bagana was visited. Strong vapor
emissions were resulting in a 15-20 km long plume and a
lava flow which has been active for a number of years was
still active. There was no indication of recent explosive
activity.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 3, No. 5 to V. 14,
No. 12)
- Global Volcanism Network (V. 15, No. 1 to V. 20, No.
8).
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