Rabaul (Papua New Guinea)  Major eruption sends plume to 18 km and
      covers Rabaul town with ash

Rabaul
New Britain, Papua New Guinea (4.27xS, 152.20xE)
All times are local (= GMT + 10 hours)

Vulcan and Tavurvur, two vents on opposite sides of Rabaul Caldera (figures 1 and 2), erupted on the morning
of 19 September and sent ash as high as 18 km above sea level.  This
caldera forms a sheltered harbor whose N end is occupied by Rabaul,
New Britain's largest city.  The report of August seismicity was sent
from the Rabaul Volcano Observatory (RVO) on 9 September.  Satellite
interpretations are courtesy of the U.S.  National Oceanic and
Atmospheric Administration (NOAA), with Total Ozone Mapping
Spectrometer (TOMS) data from the NASA Goddard Space Flight Center.
Although communication with Rabaul was cut off for many days, RVO
reports were received for 23 and 27 September.  Information based on
reports from local and international news services is noted, and may
not be accurate.

August seismicity.  The total number of detected events for August
was 448, compared to 220 in both June and July (see Bulletin v. 19,
no. 7).  The month was quiet until 25-28 August when 227
earthquakes were detected, with more than half of them on the 26th.
Unusually for Rabaul, these earthquakes tended to be discrete
events not occurring in swarms.  Only 34 of the August events were
located, 25 of them during 25-28 August.  Most located earthquakes
were along the ring fault near Tavurvur, or offshore to the S and
SW; 17 hypocenters had location errors of <1 km.  The largest
event, on 26 August, was ML 2.6, but none of the earthquakes were
felt.  On 28 August, the caldera network recorded what appeared to
be a low-frequency earthquake.  Signals with a dominant frequency
of ~1 Hz recorded on some of the inner network stations were very
complicated with no clear phase arrivals or onsets.  These signals
probably originated close to the Matupit Island seismometer.  No
seismicity was recorded after 29 August.

Seismic precursors, 18-19 September.  RVO reported that at 0300 on
18 September, a M 5.1 earthquake occurred beneath the harbor.  An
aftershock sequence from this event merged into an intensifying
swarm of high-frequency (A-type) earthquakes.  Peak intensity of
this swarm occurred around 2400 that night with ~2 felt
events/minute, but then tapered off slightly toward morning.  By
0600 on 19 September the eruption had begun.  Thus, only 27 hours
of unusual seismicity preceded the eruption.  Inspection of the
seismograms since the onset of the eruption revealed several
long-period events in the 12 hours prior to the M 5.1 earthquake.

Initial eruptive activity, 19 September.  Tavurvur began erupting
around 0600 on 19 September, followed by an explosion from Vulcan
~1-1.5 hours later.  RVO volcanologist Patrice de Saint Ours was
quoted in press reports that day as stating that the pattern of
eruptions was very similar to 1937, and that the vents were no
longer visible from the observatory because of the ash cloud,
estimated by ground observers to be >3 km high.  Most press reports
described thick mushroom-shaped pulses of ash rising from the
vents, hot ash falling near the vents, and loud explosion noises.
Aerial video footage showed vigorous, thick, light-brown ash
columns, and the surface of the harbor covered with ash and
floating pumice.  Other press reports on 19 September stated that
Rabaul town was covered with 20-25 cm of ash, and that
thunderstorms mixed rain with the ash, forming a heavy mud that
damaged buildings and vegetation.  The press reports also described
columns of gray ash rising thousands of meters into the air, ejecta
as large as trucks, and "black muddy rain."  Ash fell across New
Britain and New Ireland (figure 1, inset).

A pilot report received at Port Moresby at 1034 placed the top of
the volcanic ash cloud between 15 and 18 km altitude.  A later
pilot report noted the presence of drifting ash ~185 km SW of
Rabaul well above 6 km altitude.  GMS satellite imagery as late as
2132 on 19 September revealed an obvious plume fanning out to the
S through WNW.  The W part of the plume was tracking W and WNW at
~110 km/hour, and had moved across central Papua New Guinea; plume
height was estimated to be 21-30 km, well into the stratosphere.
The S part of the plume, at an altitude of 12-18 km, had begun to
move SE at ~55 km/hour around an upper tropospheric ridge.  A
satellite infrared image taken a few hours earlier, at 1800 on the
19th (figure 3), showed similar plume morphology.  Initial
estimates of plume height during the first two days of activity
were between 18 and 30 km.  Space Shuttle astronauts who observed
and photographed the plume (figure 4) estimated its height as at
least 18 km based on altitudes of storm clouds in the area.

Eruptive activity, 20-23 September.  Video of the eruption, taken
from a helicopter about 1.5 days after its start, showed massive,
gray-to-black ash columns billowing vigorously from Vulcan and
Tavurvur.  The maximum height of the cloud was reported by the
press to be ~20 km, with blocks as big as cars falling into the
harbor.  Black ash appeared to be falling over a wide area and
scenes from Rabaul town showed buildings and vegetation blanketed
by ash.

Night winds on 19 September, which were generally blowing NNE-NE
(taking the ash over New Ireland), changed direction at dawn on the
20th and started blowing N-NNW, and as the afternoon progressed the
winds became more westerly.  By 1532 on 20 September the plume had
narrowed compared to previous GMS satellite images and the core was
moving WSW at ~55 km/hour at an altitude of ~12 km.  As night fell
on 20 September the cloud had reached the main island of Papua New
Guinea between Lae and Milne Bay; residents in the town of Lae, 600
km away, reported ashfall.

On 21 September, witnesses said huge mushroom clouds of dense,
black smoke and debris continued to rise high above Tavurvur and
Vulcan.  Much of the falling ash combined with rain, turning to a
heavy mud mixture that demolished some houses and destroyed coconut
plantations.  The airport was buried under debris, many roads were
blocked, and the harbor was covered with debris and floating
pumice.

The plume was still moving WSW at 1832 on 21 September at ~7.5 km
altitude, and was visible for up to 90 km SW of the origin.  Soon
after this time the plume was no longer clearly visible on GMS
imagery, indicating that strong explosive activity, which had
ejected ash high into the atmosphere almost continuously since
about 0600 on 19 September, had declined.  Some residents returned
to Rabaul town during a brief respite from the falling ash.
However, by the morning of 22 September Vulcan was ejecting massive
amounts of whitish ash and Tavurvur was emitting dark blackish-gray
ash.  GMS satellite imagery for 1230 on 22 September revealed a new
mid-high level plume that was ~40 km long and moving WSW.  The
plume was estimated to be at ~7.5 km altitude, and could still be
seen at 1530 on GMS infrared images.

A report from RVO for the period from 1500 on 22 September through
0900 the next day indicated that volcanic and seismic activity
remained relatively stable.  Steady emissions continued from
Tavurvur with a dark gray ash-and-vapor cloud rising ~2 km and
blowing NE over Rabaul town.  Low rumbling sounds accompanied the
stronger emissions.  At night, incandescent ejecta could be seen
falling on the NW flank, but incandescence was rarely visible in
the eruptive column due to its high ash content.  Intermittent
pulses of stronger activity from Vulcan produced jets of a
vapor-rich ash at intervals of 5-15 minutes.  Collapse of the
column generated pyroclastic surges that traveled 2-5 km from the
vent, mostly to the NE.  Generally there was a low volume of ash in
the eruption cloud.  The column height was about 1.5 km.  At night
witnesses saw incandescent ejecta accumulate around the vent at the
beginning of each pulse.

An aerial inspection by volcanologists at 1620-1640 on 22 September
revealed little morphological change at Tavurvur, with the active
vent located on the W side of the 1937 crater.  At Vulcan, the only
active vent was near sea level on the breached NE-flank crater.
Eruptions were Surtseyan, highly explosive, and vapor-rich with low
ash content.  No great deformation was noted since the start of the
eruption.  Overall, volcano-seismic activity showed a steady small
decline during 20-22 September.  During the inspection, visibility
over Rabaul was generally very good, but there were occasional ash
falls.

On the morning of 27 September, RVO reported that Vulcan was no
longer erupting, but an ash plume from Tavurvur was still present,
and there was an ashy haze over Rabaul town.  Seismicity had
decreased to about the detection limit using the Real-time Seismic
Amplitude Measurement (RSAM) averaging method.  The observatory
reported ~40 mm of fine powdery ash at their location, and ~50 cm
of ash at the airport, with the ash-fall layer thickening rapidly
towards Matupit Island.  The press initially reported up to a meter
of ash in Rabaul town, but later estimates were consistently around
75 cm for most areas.  No accurate mapping of the ashfall has been
completed.  Press reports on 25 September estimated that 25% of the
buildings in the greater Rabaul area had been completely destroyed,
and that another 50% had significant structural damage.
Preliminary damage assessments reported on 27 September by the
United Nations Dept.  of Humanitarian Affairs (DHA) indicated that
40% of the buildings in the area had been seriously damaged.

Satellite-based SO2 data.  The Meteor-3 satellite overflew the
eruption plume from Rabaul at 1538 on 19 September.  Preliminary
results from the TOMS instrument showed SO2 column amounts no
higher than background and a slight column ozone increase in the
region that was most likely due to the presence of SO2.  Another
pass at 1520 on 20 September showed an SO2 plume of ~45,000 km2,
with an SO2 mass estimated at a maximum of 80 kilotons (kt) +- 50%.
At 1503 the next day, preliminary results showed that the estimated
size of the SO2 plume was 50,000 km2, with an SO2 mass estimated at
70 kt +- 50%.  The SO2 detected on 21 September had probably been
produced since the overflight on the previous day because the small
tropospheric plume noted at that time would have either dispersed
or been chemically converted within 24 hours.  Preliminary data
from the overflight at 1430 on 23 September showed an estimated
size of at least 40,000 km2 for the SO2 plume, with an estimated SO2
mass of 35 kt +- 50%.  By 1410 on 24 September, SO2 column amounts
were no higher than background levels in the vicinity of the
volcano.

Evacuations and official response.  On the night of 18-19
September, during the period of strong continuous seismicity, an
estimated 30,000 people evacuated from Rabaul town and surrounding
villages.  Apparently, most of the people left before the eruptions
began, but evacuations by road and sea to the towns of Kokopo (20
km SE) and Kerevat (~25 km SW), continued on 19 September.  The
airport closed just as Tavurvur began erupting.  Evacuees went to
missions and townships along the Gazelle Peninsula, where they were
housed in camps, schools, church halls, and hospitals.  Authorities
were preparing to provide food and shelter for up to 70,000 people.

Ships rescued thousands of villagers off beaches near Rabaul town
on 20 September.  Press reports indicated that although Rabaul town
was totally evacuated, there were small villages in the surrounding
hills where people were trapped and taking shelter in schools and
churches.  As of 21 September, 45,000 people had been displaced, of
whom 25,000 were located in Kokopo and the remainder at Kerevat and
nearby mission and government stations.  By 23 September, the U.N.
DHA reported that a total of 53,000 people had been displaced.  The
only reported casualties were one boy killed when he was hit by a
truck during the evacuation, and one man struck by lightning.

Following the declaration of a state of emergency in Rabaul, the
Prime Minister of Papua New Guinea made a helicopter inspection on
the afternoon of 19 September.  Notices to Airmen (NOTAMs) issued
from the Port Moresby Flight Information Region on 19-20 September
advised pilots to exercise caution and informed them that the
airspace within a 110 km radius of the Rabaul airport was closed to
all air traffic unless authorized by emergency management
officials.  A NOTAM on the 22nd advised aircraft to avoid an
abnormally colored cloud, especially yellow-brown or grayish
layers.  It further stated that the ash particles could contaminate
engine oil and cause engine deterioration within hours.  The duty
manager of Air Niugini (national airline of Papua New Guinea) said
all flights to and from New Britain and New Ireland provinces had
been suspended.  Relief flights were using an abandoned airstrip at
Tokua (~20 km SE of Rabaul), which had received no ashfall.

Looting in Rabaul town was reported during both the evacuation and
on 21 September, when military forces were brought in to help local
police.  News reports frequently mentioned looting by residents who
had not evacuated or by non-residents going into the evacuated
area.  By the evening of 21 September, the army had sealed off all
outlying roads and only allowed entry by authorized personnel.

At the request of the Papua New Guinea government, the USGS Volcano
Disaster Assistance Program sent three volcanologists to Rabaul on
28 September.  They took telemetered seismic stations with a
PC-based data acquisition and analysis system, several telemetered
tiltmeters, and other deformation-monitoring instrumentation.  This
equipment was requested because RVO was unable to locate
earthquakes with only three seismic stations remaining in
operation.  The other stations were incapacitated by tsunamis,
vandalism, or heavy ashfall.

Historical activity.  The last of two Holocene caldera-forming
eruptions at Rabaul took place only ~1,400 years ago.  Several
large historical eruptions have formed cones within the caldera.
The first known historical eruption at Rabaul was in September 1767
from an unidentified cone.  In May 1791 Tavurvur emitted columns of
black smoke.  Native accounts describe activity from Sulfur Creek
between 1845 and 1850 that may have caused fatalities from falling
pumice blocks.  A submarine eruption in February 1878 formed Vulcan
Island and produced large amounts of pumice; Tavurvur also began
erupting at about the same time and continued for approximately
three weeks.  The largest historical Rabaul eruption, 29 May-2 June
1937, caused >500 fatalities, buried Rabaul town in >=5 cm of
andesitic ash and pumice, and generated a tsunami that threw ships
onshore.  During this eruption, Tavurvur was active for <1 day, but
activity at Vulcan built the cone from sea level to a height of 243
m.  Phreatic eruptions occurred at Tavurvur in February and March
1940, and intermittent explosive eruptions from June 1941 to March
or April 1942 left a small crater on the floor of the larger 1937
crater.  Another eruption during November-December 1943 built a new
small crater at Tavurvur.  Seismicity and deformation were very
high from September 1983 through July 1985 (Mori and others, 1989),
but resulted in no eruptive activity.

References: Almond, R.A., and McKee, C.O., 1982, Location of
volcano-tectonic earthquakes within the Rabaul Caldera: Geological
Survey of Papua New Guinea report 82/19.

McKee, C.O., Johnson, R.W., Lowenstein, P.L., Riley, S.J., Blong,
R.J., de Saint Ours, P., and Talai, B., 1985, Rabaul caldera, Papua
New Guinea: volcanic hazards, surveillance, and eruption
contingency planning:  Journal of Volcanology and Geothermal
Research, v. 23, p.  195-237.

Mori, J., McKee, C., Itikarai, I., Lowenstein, P., de Saint Ours,
P., and Talai, B., 1989, Earthquakes of the Rabaul
Seismo-Deformational Crisis September 1983 to July 1985: Seismicity
on a caldera ring fault:  IAVCEI Proceedings in Volcanology 1, J.H.
Latter (ed.), Volcanic Hazards: Assessment and Monitoring, p.
429-462.

Information Contacts: C. McKee, R. Stewart, and I. Itikarai, Rabaul
Volcano Observatory, P.O. Box 386, Rabaul, Papua New Guinea; Jim
Lynch, NOAA/NESDIS Synoptic Analysis Branch, Room 401, 5200 Auth
Road, Camp Springs, MD 20746 USA; George Stephens, NOAA/NESDIS,
Room 510, 5200 Auth Road, Camp Springs, MD 20746 USA; Ian Sprod,
Code 921, NASA Goddard Space Flight Center, Greenbelt, MD 20771 USA
(Email: ian@skye.gsfc.nasa.gov); Cindy Evans, Space Shuttle Earth
Observations Office, Mail Code C102, Lockheed Engineering &
Sciences, P.O. Box 58561, Houston, TX 77258 USA (Email:
evans@sn.dnet.nasa.gov); Graeme Wheller, Volcanex International Pty
Ltd, 521 Tinderbox Bay, TAS 7052 Australia (Email:
g.wheller@geol.utas.edu.au); Kevin Vang, School of Earth Sciences,
Macquarie University, Sydney, NSW 2019 Australia (Email:
kevin.vang@mq.edu.au); International Civil Aviation Organization,
Air Navigation Bureau, 1000 Sherbrooke Street West, Suite 400,
Montreal, Quebec H3A 2R2 Canada; U.N. Department of Humanitarian
Affairs, Palais des Nations, CH-1211 Geneva 10, Switzerland;
Associated Press; United Press International; Reuters; Papua New
Guinea Post-Courier.