Smithsonian Institution
Global Volcanism Network Bulletin v. 20, no. 4, April 1995

Rabaul (Papua New Guinea)  Tavurvur explosions stop on 16 April

New Britain, Papua New Guinea
4.27S, 152.20E; summit elev. 688 m
All times are local (= GMT + 10 hours)

Two strong explosions took place at the intra-caldera cone Tavurvur
on 30 March; after that, the repose intervals between explosions at
Tavurvur lengthened, lasting from several hours to more than 24
hours. Tavurvur discharged several noteworthy explosions on 13-15
April; explosions ceased on 16 April.
During the first half of April, explosions sent ash clouds 1-2 km
above the crater, but they were typically spasmodic and relatively
mild. Ash predominantly fell to the SE (mainly over Talwatt and
occasionally at Kokopo, with smaller amounts in Rabaul on a few
days). Accompanying the normally gray ash emissions were weak
roaring sounds heard late on the 3rd, low rumbling sounds on the
9th, and lightning seen in and around the billowing ash column on
the 11th.
At 1206 on 13 April an impressive explosion occurred. It began with
fast-rising, spear-headed jets of dark ash, which fed a billowing
ash cloud that rose to about 2 km above the crater. Some ballistic
blocks landed in the bay immediately W and NW of Tavurvur. On 14
April, moderate-to-strong explosions started at about 0920, with
the most intense activity occurring between 1030 and 1040.
Resulting eruption clouds were dark gray and quite dense; fallout
was heavy at Tavurvur and immediately downwind (SE). In and around
the eruption column, lightning was noted. The activity declined
slowly through the day and stopped at about 2320.
Strong explosions resumed at about 1320 on 15 April. During a
roughly 1 hour period, several large eruption clouds rose to about
2 km. These ash clouds remained intact as they drifted to the SE.
Prolonged moderate ash emission also took place from early to
mid-afternoon. During the early hours of 16 April, mild explosive
activity took place; it stopped at about 0600. From that time
onward activity chiefly consisted of weak white vapor emissions.
Following a period of heavy rainfall on the 24th, however, these
emissions again became more voluminous, but by the next day they
returned to a very low level.
Seismicity in the first half of April, until the 16th, partly
consisted of low-frequency earthquakes associated with Tavurvur's
explosions. Explosion sizes appeared to correspond to earthquake
amplitudes. Six high-frequency earthquakes also occurred (compared
to 5 in March and 4 in February). These earthquakes all had
epicenters outside the caldera--five to the N-NE and one to the SW.
During April, electronically measured tilt in the interior of the
caldera at Matupit Island continued to show a trend of very slow
deflation. Other ground deformation measurements failed to show
significant trends.
An aerial inspection, on 8 April, revealed that Tavurvur's surface
was covered with fresh black ash. Numerous gray blocks had also
landed, mainly on the S flank and inside the old crater. The
fumarole previously emitting blue-vapor (located about 1/3 of the
way down the 1994 lava flow) was inactive. One white-vapor fumarole
was noted where the lava had advanced over the crater rim. The
crater displayed variably colored sublimate deposits and small
erosional gullies. A step-like structural form was seen on the
crater's E side, and a smooth, bowl shape was seen on its W side.
Inside the crater there were neither visible vents nor a lava
Vulcan continued weak white vapor emissions, coming mainly from the
crater of the 1994 cone. Fumaroles at the base of the 1994 crater
had been mostly buried by mud leaving only one on the W side of the
crater. The upper one of the two pit craters on the N flank of the
1994 cone had caved in. Temperature of hot springs along the N
shore were consistent with previous months' readings at ~100 deg C.
The State of Emergency in Rabaul was lifted on 10 April, making way
for the Gazelle Restoration Authority to promote the rehabilitation
New eruptions began in Rabaul Caldera on 19 September 1994
(Bulletin v. 19, nos. 8 and 9), ending a repose period of ~51
years. Following the pattern of the last two eruptive episodes
(1878 and 1937-43), there were almost simultaneous outbursts on
opposite sides of the caldera as the intra-caldera cones Tavurvur
and Vulcan began erupting at 0605 and 0717, respectively. The
eruption at Vulcan was the more powerful but ended on 2 October.
The eruption at Tavurvur, peaking during the first five days of
activity, thereafter displayed either slow decline or episodic
return to explosive activity (Bulletin v. 19, nos. 8-12, and v. 20,
nos. 1-3).
Information Contact: David Lolok and Ben Talai, Rabaul Volcano
Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.