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Report on Rabaul (Papua New Guinea) — June 2007

Bulletin of the Global Volcanism Network, vol. 32, no. 6 (June 2007)
Managing Editor: Richard Wunderman.

Rabaul (Papua New Guinea) Six explosions occurred June-July 2007; ashfall and sulfurous odors

Please cite this report as:

Global Volcanism Program, 2007. Report on Rabaul (Papua New Guinea). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 32:6. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200706-252140.

Volcano Profile |  Complete Bulletin


Rabaul

Papua New Guinea

4.271°S, 152.203°E; summit elev. 688 m

All times are local (unless otherwise noted)


During April and May 2007 (BGVN 32:05) and through mid-June 2007, the Rabaul Volcanological Observatory (RVO) reported that low-level activity continued at Tavurvur. Between the afternoon of 19 June and the morning of 20 June, four explosions occurred (at 1745 and 1928 hours on 19 June, and at 0319 and 0933 on 20 June) producing shockwaves that rattled windows of houses in Rabaul Town and surrounding areas. The explosions also showered the flanks with lava fragments.

Ash clouds from the 19 and 20 June explosions rose about 2 km before being blown to the NW, resulting in moderate ashfall in Rabaul and downwind areas such as Ratavul, Volavolo, and Nonga villages (each on the SE shore of Talili Bay about 10 km NW from the Tavurvur summit). Weak-to-moderate glow was visible at night, and occasional weak-to-loud roaring noises, probably due to steam production, continued to be heard during the above 1-day period. RVO attributed the June-July 2007 eruptions to result from residual unquenched magma remaining from the eruption of October 2006 (figure 47).

Figure (see Caption) Figure 47. Eruption of the Tavurvur cone, seen from across the harbor formed by Rabaul caldera. The photo was taken at 0900 on 7 October 2006. Courtesy of Reinhard Lorenz.

Summaries of geophysical activity at Rabaul for June-July 2007 are shown in tables 6 and 7. After the four big explosions on 19 and 20 June, Tavurvur emitted variable volumes of white vapor containing very little ash content for the next two days. These emissions were accompanied by blue vapor clouds that rose less than 1 km before drifting N-NW. Very fine ashfall occurred downwind, including in Rabaul Town where mild smell of hydrogen sulphide (H2S)gas was evident. Occasional weak roaring noises were heard accompanying the vapor emissions, and weak-to-moderate glow was visible at night. Thick white vapor was emitted from the crater on the morning following rain on the night of 21 June 2007.

Table 6. Summary of seismic activity at Rabaul during June-July 2007. Courtesy of RVO.

Date High-frequency earthquakes: date (number) Low-frequency earthquakes: date (number) Explosion earthquakes: date (number) Comments on level of seismicity
04-15 Jun 2007 None -- -- Low
16-20 Jun 2007 8 June (1), 18 June (3), 19 June (1) (all originated NE of Rabaul caldera) 19 June (26) 19 June (2), 20 June (2) Low to moderate
20-21 Jun 2007 21 June (1) (originated NE of Rabaul) 43 total 21 June (1) (weak) Low to moderate
22-25 Jun 2007 Eight total. 102 total. Five originated NE of caldera, two from S (~2.5 km S of Raluana), one from NW (~2 km S of Watom Island). -- Low to moderate
26-29 Jun 2007 -- Range of 27-44 per day (slightly higher than normal background) -- Low to moderate
02-14 Jul 2007 None 3-6 July (range of 9-11/day), 7-10 July (range of 2-6/day), 10-14 July (1-7/day) 5 July (1) Low
14-17 Jul 2007 None Five on 14 July, 0 on 15 July, 55 on 16 July 17 July (1) Slight increase to moderate
18-21 Jul 2007 -- Eleven total -- Decrease to low

Table 7. Summary of Rabaul ground deformation, June-July 2007. Courtesy of RVO.

Date Global positioning system (GPS) Water tube tilt monitoring Comments
04 Jun-08 Jun 2007 slight uplift slight uplift insignificant!
08 Jun-18 Jun 2007 slight inflation slight inflation pressure build-up
20 Jun-22 Jun 2007 no apparent deformation no apparent deformation --
22 Jun-26 Jun 2007 slight uplift slight uplift --
26 Jun-28 Jun 2007 stable stable --
28 Jun-29 Jun 2007 slight subsidence slight subsidence --
03 Jul-06 Jul 2007 low-level deformation low-level deformation --
06 Jul 2007 minor inflation minor inflation --
07 Jul-08 Jul 2007 stable stable --
09 Jul-10 Jul 2007 further inflation further inflation precursor to ash release on 10-11 July
11 Jul 2007 subsidence subsidence --
14 Jul-16 Jul 2007 minor inflation minor inflation horizontal movement twice that of vertical movement
18 Jul-22 Jul 2007 inflation trend inflation trend northward movement

By 22 June activity had returned to a low level, with emissions consisting of moderate to dense white and blue vapor rising to about 1 km. An odor of H2S gas was evident in Rabaul Town on 22 and 25 June (along with rain that stung the eyes on 25 June). Occasional weak roaring noises continued to be heard accompanying the vapor emissions, and weak to moderate red glow was visible at night.

Tavurvur remained quiet during 26-28 June 2007. Variable amounts of white fume were produced, the quantity of steam present reflecting atmospheric conditions (such as temperature and humidity). Moderately strong night-time glow was still present, but Tavurvur made no sound. A slight smell of H2S lingered downwind. An M 6.7 earthquake that occurred at 1252 on 28 June was located beneath the Solomon Sea, but it was not related to volcanic activity. Tavurvur remained quiet during 2-4 July 2007, releasing variable amounts of white vapor.

A big explosion occurred at 0511 on 5 July, producing a shock wave that rattled houses in Rabaul Town and surrounding villages. A thick gray ash cloud rose ~ 2 km above the summit before being blown N to NW. Fine ashfall occurred in Rabaul and areas downwind. A weak glow was visible at night and occasional weak to loud roaring noises were occasionally heard. A slight smell of sulphur lingered downwind. A thermal image taken from RVO indicated that the volcano was relatively cool. A weak glow was visible around the crater rim on 7 July.

Tavurvur released pale gray ash clouds from about 1400 on 10 July to 11 July 2007. The ash clouds rose less than 500 m above the summit and were blown to the N and NW of the volcano. Fine ashfall occurred at Rabaul and villages downwind between 10 and 11 July. From 12 until 14 July, the emission returned to white, thin-to-thick vapor accompanied by blue vapor that continued to drift to the N and NW. Downwind there was still a weak smell of sulphur in the emission. Occasional low roaring noise was heard and a weak to moderate glow was visible above the crater rim.

During 14-16 July, Tavurvur was only releasing variable amounts of white vapor accompanied by blue vapor. Occasional low roaring noise was heard during the above period and a weak to moderate red glow was visible above the crater rim.

A large single explosion occurred at Tavurvur at 0648 on 17 July 2007. The explosion was accompanied by a loud booming noise and a thick brown ash cloud that showered the flanks with lava fragments. The ash cloud rose about 1.5 km above the summit before curving NW of the volcano over Rabaul and Malaguna village. Fine-to-moderate ashfall occurred in Rabaul and Malaguna and areas downwind.

Low activity at Tavurvur continued during 18-22 July 2007. After the explosion on 17 July, Tavurvur continued to release variable amounts of white vapor accompanied by blue vapor that was blown N to NW of the volcano. Some of the white vapor emissions contained a small amount of ash. Smell of sulphur occurred on the downwind side of the vapor plume on 19 July. Occasional low roaring noise continued to be heard during the above period and a weak to moderate red glow was visible above the crater rim.

MODVOLC Thermal Alerts. MODIS satellite thermal anomalies measured between 16 November 2006 and 23 July 2007 are shown in table 8; no thermal anomalies were measured between 17 November 2006 and 12 February 2007.

Table 8. MODIS thermal anomaly data for 2007 for Rabaul. Courtesy of Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System.

Date (UTC) Time (UTC) Number of Pixels Satellite
13 Feb 2007 1225 2 Terra
08 Mar 2007 1230 1 Aqua
08 Mar 2007 1530 2 Terra
15 Mar 2007 1235 1 Terra
22 Mar 2007 1240 1 Terra
24 Mar 2007 1525 2 Aqua
05 Jun 2007 1220 1 Terra
05 Jun 2007 1520 1 Aqua
12 Jun 2007 1230 1 Terra
14 Jun 2007 1515 1 Aqua
23 Jun 2007 1510 1 Aqua
16 Jul 2007 1515 1 Aqua
23 Jul 2007 1225 1 Terra

Geologic Background. The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor utilized by what was the island's largest city prior to a major eruption in 1994. The outer flanks of the 688-m-high asymmetrical pyroclastic shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the east, where its floor is flooded by Blanche Bay and was formed about 1400 years ago. An earlier caldera-forming eruption about 7100 years ago is now considered to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the northern and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and western caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.

Information Contacts: Steve Saunders and Herman Patia, Rabaul Volcanological Observatory (RVO), Department of Mining, Private Mail Bag, Port Moresby Post Office, National Capitol District, Papua New Guinea (URL: http://www.pngndc.gov.pg/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Reinhard Lorenz.