Geologic Background:
The 10-km-wide Manam island, located 16 km NNE
of Bogia on the north coast of New Guinea, is the
emergent summit of one of the most active volcanoes in
the Bismarck Arc during historical time. Its composite
cone contains two summit craters (Main and South
Craters). Four large radial valleys extend from the
unvegetated summit of the conical 1807-m-high
stratovolcano to its lower flanks. These "avalanche
valleys," regularly spaced 90 degrees apart, channel lava
flows and pyroclastic avalanches that have sometimes
reached the coast. Five satellitic centers are located
near the island's shoreline. Two summit craters are
present; both are active, although most historical
eruptions have originated from the southern crater,
concentrating eruptive products during the past century
into the SE avalanche valley.
Historic Activity:
- The first recorded eruption was in 1616. At least 40
eruptions have occurred from 1616 to 1982.
- More recently, a period of activity began in December
1956 that lasted through January 1966.
- Lava flows and a nuee ardente from the South Crater
occurred in June and December 1974.
Recent Activity:
- Activity resumed in early February 1983. From April
to Sept. 1985, moderate to strong explosions and
ashfalls. Sept. 1985 to May 1986 weak activity and minor
ash emissions. May 1986 to Feb. 1987, weak to strong
explosions and ashfalls. March to July 1987 strong to
violent strombolian eruptions. The eruption on June 30,
1987 resulted in pyroclastic flows with an estimated
volume of 5-10 million cubic meters.
- From July to Dec. 1987 low level strombolian activity
continued. January- February 1988 only vapor emission,
glow, and rumbling. During May 1988 small tephra clouds
were reported. Mild activity continued during July.
August 1988 thru March 1990 were marked by weak vapor
emission and glow.
- Increased activity in late March through April 1991
with more explosions. Quiet during May and June but
renewed activity in July 1991. Low (and declining) levels
of activity from September to December 1991. Continued
low level activity with projection of incandescent lava
fragments above crater rim thru February 1992. Strongest
activity since 1987 occurred during March 1992. The
intensity of the eruption declined in late March and
early April but on April 8, 1992 activity began to
increase at both the Southern Crater and Main Crater. On
April 11, 1992 major activity occurred at the Southern
Crater for about 2 hour during which strong explosions
projected incandescent lava fragments to about 1 km above
the rim. Scoria flows were directed into both the SE and
SW valleys and a lava flow occurred in the SW valley.
Activity at the Southern Crater then decreased and ended
by April 13 when activity shifted to Main Crater. On
April 13, the frist reports of a lava flow from Main
Crater were received. Lava was flowing into the NE Valley
for the first time since 1960. The source of the flow was
a breach in the flank of an efecta cone that infilled a
large portion of the previously deep, funnel-shaped Main
Crater. With the advent of lava effusion from Main Crater
only mild explosve active from the crater occurred.
Activity continued at both craters during May and June.
On June 7th after series of loud explosions most activity
stopped. Minor steaming and occasional glow at night
continued through July.
- On August 10, 1992 activity began to increase again,
culminating on August 31 with a major eruptions which
produced a column to 5 km above the crater, a lava flow
and a pyroclastic flow which reached the coast. Activity
continues through September into October when increased
activity begins to occur again. The eruptive column
reached 10-km and lava flows and pyroclastic flows
occurred which destroyed 18 buildings. Strong explosive
active during early November resulted in pyroclastic
flows down NE and NW valleys (first time down NW valley
since 1958). Activity declined in December to
moderate-to- thick vapour with light ash content.
- Low level activity continued at both craters through
April 1993. Activity began to increase in mid-May and
continued through June, with a moderate eruption occuring
on July 14, 1993. The eruption produced ashfall,
pyroclastic flows, and lava flows. Activity was low for
the remainder of July. Occasional explosions produced
ash-laden clouds on August 6-7, 1993. A short but strong
eruption occurred from the Southern Crater on Oct. 3-6.
Pyroclastic flows were emplaced in the southeast valley,
together with a short-lived lava flor that stopped at 150
m elevation (from 1,750 m) giving it a length of Å4 km.
Moderate eruptive activity has continued to the end of
the year.
- A brief eruption occurred from Southern Crater on
Jan. 5, 1994. An increase in activity started on Jan. 3.
The peak of the eruption occurred during the night of
Jan. 5-6, with strong incandescent projections to Å1 km,
and ash much higher. Lava effusion into SE Valley was
voluminous, and the foot of the flow almost reached the
coast, Å5 km from the summit crater. The volume of ash
emission, and the seismicity, decreased from Jan 6-8.
Weak white vapor emission from February to July.
Eruptions from July 5 to 7 produced explosions and ash
clouds. Following intermittent periods of minor eruptiove
activity during the previous months, activity began to
increase in Sept. Activity peaked during the period Oct.
14 to 18 during which an eruptive column reached 6 to 10
km above the vent and a lava flow poured out at a very
high rate through a breach on the east side of South
Crater. Explosive activity continued from South Crater
until Dec. 14, 1994.
- Activity in 1995 consisted of weak vapor
emissions.
- Generally low level activity in early 1996. Ejection
of incandescent lava fragments on April 12 from South
Crater. Low level activity continued thru August.
Increased eruptive activity during mid-September resulted
in very light ashfall over villages on the NW side of the
island. A series of large eruptions took place during
October and November, and culminated with a paroxysmal
phase on Dec. 3. The Dec 3 eruption accounted for 13
deaths in a coastal village.
- 1997 began with low level of activity in January but
larger eruptions occurred in February. Again low level
activity in March. Increased emissions from South Crater
occurred on April 3-5 and from Main Crater during last
week of April and off and on during May. Mild activity
from Main Crater during June and during July mild to
moderate activity occurred from South Crater. Low level
activity at both craters during August and Sept. Mild
eruption from South Crater on Oct. 26. Low level activity
through end of year.
- Low level activity through late September 1998, then
strong eruptions in October and November resulting in
pyroclastic flows and lava flows.
- Mild activity throughout 1999.
- Mild activity in early 2000. Activity increased in
June. Continued mild activity for remainder of year
- Mild activity in early 2001. Small eruption on June
4.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 2, No. 4 to V. 14,
No. 12)
- Global Volcanism Network (V. 15, No. 1 to V. 26, No.
6).
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