Smithsonian Institution
Global Volcanism Network Bulletin v. 19, no. 12, December 1994

Rabaul (Papua New Guinea)  Explosive activity at Tavurvur declines
       and finally stops

New Britain, Papua New Guinea (4.27S, 152.20E)
All times are local (= GMT + 10 hours)

"The 1994 eruption of the Rabaul volcanoes (see Bulletin v. 19,
nos. 8-11) stopped in December. Explosive activity at Tavurvur
varied in strength during the month and stopped completely on 23
December. Vulcan remained quiet, with the last explosive activity
on 2 October. Vulcan exhibited only very weak fumarolic activity
during December from both the 1937 and 1994 craters. A landslide
took place on the NW inner wall of its 1994 crater some time
between 2 and 5 December, leaving a near-vertical face.

"Following the decline in explosive activity during November, there
was very little activity at Tavurvur on 1-2 December. A new phase
of explosive activity began at about 2300 on 3 December; this
peaked in intensity on the 5th and then declined slowly until 19
December. The decline was evident in the ash content of the clouds
and their height (up to 2 km altitude at the peak of activity) but
not in the explosion intervals (1-40 minutes). Ash emissions
usually lasted about a minute. The ash clouds were blown mainly NNW
over Rabaul Town, where there was light-moderate ashfall, and
occasionally to the SE. A series of explosions would sometimes
create a discontinuous ash plume. There were no audible sounds
associated with the explosions. During an aerial inspection on 9
December, a small lava mound was seen on the floor of the crater
and incandescence was seen in cracks between the rocks.

"At night on 19 and 20 December, weak roaring and rumbling sounds
were heard; incandescent projections were noted on 20 December. At
0137 on 21 December there was a large explosion that was heard and
felt over a wide area. For the next two days, there were many of
these explosions as well as some long (up to 6 hours) periods of
quiescence. The ash content of the explosion clouds was higher than
during the first two-thirds of the month and the ash emissions
lasted up to 3 minutes. Due to changes in the prevailing wind
direction, a 20-km-long horizontal plume spreading both NW and SE
was generated at a height of 1-2 km. On 23 December, there were
only a few short periods of weaker explosive activity. The last
explosion noted occurred at 1500. From then until the end of the
month, the only visible activity was emission of white vapour,
low-moderate in volume, from the crater. The vapour rose several
hundreds of meters above sea level, rarely to a kilometer.

"Seismicity in December consisted mainly of explosive and
low-frequency earthquakes associated with the activity at Tavurvur
-- the level of seismic activity followed the visual activity.
Between 13 and 19 December, a new type of event came to dominate
the records. These events were of longer duration and lower
amplitude than the low- frequency events that had been recorded
since the start of the eruption. More normal events returned with
the explosive activity on 20 December and continued until the 26th.
Seismic activity was very low from then until the end of the month.
There were again very few high-frequency earthquakes: 30 in
December, compared to 37 in November and 58 in October. Ground
deformation from electronic tiltmeters and dry-tilt measurements
showed a further reduction in the rate of deflation."

Information Contacts: Same as for Manam.