Geologic Background:
The symmetrical basaltic-to-andesitic Ulawun
stratovolcano is the highest volcano of the Bismarck arc,
and one of Papua New Guinea's most frequently active.
Ulawun volcano, also known as the North Son, rises above
the north coast of New Britain opposite Bamus volcano,
the South Son. The upper 1,000 m of the 2,334-m-high
volcano is unvegetated. A prominent E-W-trending
escarpment on the south may be the result of large-scale
slumping. Satellitic cones occupy the NW and eastern
flanks. A steep-walled valley cuts the NW side of Ulawun
volcano, and a flank lava-flow complex lies to the south
of this valley.
Historic Activity:
- Historical eruptions date back to the beginning of
the 18th century. Twenty-three eruptions (including 1700,
1898, 1915, 1941, 1960, 1963, 1967, 1970, 1973, 1978, and
1980) since 1700.
- Twentieth-century eruptions were mildly explosive
until 1967, but after 1970 several larger eruptions
produced lava flows and basaltic pyroclastic flows,
greatly modifying the summit crater.
Recent Activity:
- Increased seismicity and vapor emission began in
January 1983. Increased seismicity continued through
March 1984 with mild explosive activity in November and
December 1983. A mild strombolian eruption began on Sept.
4 and ended on Sept. 11, 1984.
- Mild eruptive activity also occurred in Dec. 1984 and
Jan. 1985 which built lava dome and small cinder cone in
crater. Brief spectacular strombolian eruption with small
lava flows began on Nov. 17 and ended on Nov. 22,
1985.
- A mild eruption began on Jan. 1, 1989 and continued
till Jan. 10, with dark grey ash clouds rising as much a
2 km above the summit. Intermittent ash emission resumed
from March 5 to April 28, 1989. Intermittent gray to
brown emissions were reported July 15-24, 1989, and
occasional ash emission occurred throughout the remainder
of the year.
- Seismic activity changed subtly at the end of
December 1992. Beginning on Jan. 12, 1993 and continuing
through the end of the month, Ulawun emitted dark ash
clouds and showed night glow in the crater.
- Beginning in late March seismicity began to increase
and by April 19, 1994 dark gray emissions were observed.
Fine ashfalls were reported on the NW side on April 28
and a steady weak red glow was seen on April 30.
Increased activity continued thru June and then decreased
in July.
- Low-level activity continued thru June 1996. Activity
consisted of small to moderate volumes of white vapor
emissions and low-level seismic activity.
- Strong explosions in mid-October 1999. Then vapor
emissions through end of year.
- Low-level activity in early 2000. An eruption started
on Sept 29 with an ash cloud reaching a height of about
11 km. Several nearby towns were evacuated. A moderate
eruption occurred from Sept 28 to Oct 2 with eruptive
plume reaching 10-12 km.
- In 2001, a moderate eruption occurred from April 25
to 30 with eruptive plume reaching nearly 14 km.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 3, No. 5 to V. 14,
No. 12)
- Global Volcanism Network (V. 15, No. 1 to V. 26, No.
6).
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