250010-254801
(was 0500-0504)
Rabaul Volcanological Observatory (RV0)
P.O. Box 386
Rabaul
Papua New Guinea

Note: RVO is a Branch of the Geological Survey of Papua New Guinea (PNG), which itself is a Division of the Department of Mining and Petroleum.

Scientific staff:

Herman Patia - Volcanology
David Lolok - Volcanology
Ima Itikarai - Seismology

Total staff : 25 established positions and 5 part-time observers (new departmental structure, August 1995).

The Rabaul Volcano Observatory (RVO), established after the 1937 eruption at Rabaul, is responsible for monitoring the activity of the 14 active and 23 dormant volcanoes spread along three volcanic arcs throughout Papua New Guinea (see map). More than 150 eruptions have been recorded in the last 200 years.

The main observatory is at Rabaul. There are also " outstation " observatories at 4 of the most active volcanoes (i.e. Ulawun, Langila, Manam, Karkar), and at Esa'Ala. Due to social unrest, monitoring of Bagana and Lamington was discontinued in the early 1990's.

RABAUL

The 1994-95 eruption considerably disrupted the monitoring network at Rabaul. The rapidity of onset of the eruption and its impact, compounded by a climate of drastic budget contraction and personnel losses, prompted a revision of the monitoring strategy. The emphasis in this revision is toward :

1) real-time monitoring methods;

2) rationalisation of techniques;

standardisation of equipment with modular and wherever possible off-the-shelf components;

limiting human intervention in the chain of data collection, computer logging and treatment for analysis;

simultaneous assessment of the various parameters with the USGS-designed BOB data display system.

The first step in that direction was made within 3 weeks into the eruption, thanks to the considerable technological assistance received from a USGS team of the Volcano Disaster Assistance Program. Further upgrading will be made possible in the coming years through a generous Australian (AusAid) aid program, with the technical assistance of AGSO.

Currently, the monitoring of Rabaul Caldera is essentially based on seismic and ground deformation methods. Temperature of fumaroles and hot springs are also being monitored at intervals. Geochemical monitoring has been limited to basic analyses of hot spring waters collected at irregular intervals. Microgravity measurements that were carried out since 1973 were unfortunately interrupted a few months prior to the 1994 eruption, due to instability of our aged Lacoste and Romberg gravimeter. Over the last three decades, other investigations or temporary monitoring were carried out by visiting scientists, which included : differential magnetic field measurements; ²²²Rn and Hg⁰ anomalies and emission level; a multi-disciplinary investigation of the gas phases, hydrochemical, and microbiological processes in Greet Harbour; several seismic refraction surveys; several bathymetric and side scan sonar surveys of the Bay ; two heat flow surveys ; localised on-land geoelectric surveys.

Seismology

The seismic network in operation prior to the September 1994 eruption was essentially as described in earlier editions of this directory, and relied on manual measurements on Develocorder and Helicorder records. Although a bit slow, the recording systems and data analysis procedures were well suited for volcano-tectonic earthquakes, but they proved totally inadequate to monitor the 1994 eruption. In addition, 10 of the 14 stations were destroyed by volcanic products, vandalised or otherwise disabled in the first week of the eruption. Within a month, however, 8 new stations and digital data-acquisition systems had been deployed by the VDAP team.

The current seismic network is composed of 11 stations linked to RVO by UHF or VHF radio telemetry, with USGS-made modulators and demodulators. 10 stations are located around Rabaul, including one at RVO, and use Mark Products seismometers (8 vertical L4 and 2 three-component L22). The other station is located 25 km E of the caldera and has an electronically simulated Wood-Anderson horizontal seismometer, recorded on Helicorders at RVO at three different gain steps, for magnitude determination. In addition, a 2-component horizontal " Omori " mechanical seismograph is still in use at RVO, as a strong motion instrument. The signals from all the Rabaul stations are recorded on the IASPEI PC-QUAKE data acquisition system. All vertical seimometers are also recorded on Helicorders, equipped with in-house designed enhancers, and are also monitored using RSAM and SSAM. P and S arrivals are picked interactively, using XPLAY and epicenters are determined with Hypo-71. The velocity model currently in use was shown to be deficient, and plans are being drawn to determine a new model.

Ground deformation

All real time ground deformation monitoring (from electronic tiltmeters and tide gauges) had progressively been lost over the few years prior to the 1994 eruption, by lack of appropriate funding and technical expertise. From the onset of the eruption, ash density in the caldera prevented EDM monitoring. During the first week the only accessible ground deformation data were from two water tube tiltmeters on the outer rim of the caldera. Dry tilt measurements on Matupit Island resumed on the 5^th day of the eruption, Sea shore survey around the whole bay within 8 days into the eruption, and geodetic levelling to Matupit Island within 2 weeks. By the 4^th week two electronic tiltmeters were deployed by the USGs'VDAP team, and a few dry tilt stations could be re-occupied. Currently, ground deformation are monitored by the following techniques and instruments .

Four 2-component Akashi water-tube tiltmeters are operated in underground vaults; two can be read daily, one weekly, the last one at irregular intervals due to inaccessibility following the eruption. Four Applied Geomechanics 701 platform electronic tiltmeters are in operation, at sites concurrently monitored by dry tilt stations. Their signal, transmitted via UHF radio telemetry, is logged in the USGS P-C driven, Low Data Rate acquisition system and displayed on BOB. 16 of the 26 former dry tilt stations have been buried by products of the eruption and subsequent mudflows; 8 stations may still be recoverable. Effort is being made to have the stations central to the caldera read monthly and the outer ones quarterly.

The network of levelling lines has also been severely affected by the eruption : benchmarks in sections up to 7 km long are now buried under pyroclastic products meters thick, or destroyed by road-clearing and in the attempts of protecting the town from mudflows. A large effort is now required for the recovery and for re-equipping of the network. Comparisons with pre-eruption data will be difficult.

The four automatic pressure-transducer tide gauges set-up in the late 1980' s on pylons near Tavurvur and Vulcan and outside the caldera, developed chronic, long term instability, and were eventually disused in 1993. Currently, 2 float tide gauges remain in operation, side by side at Rabaul wharf (one analog Stevens instrument, operated by RVO, and one punched-tape Fisher and Porter instrument operated by the University of Hawaii for tsunami and El Ni????atch). Unfortunately, their role as " level datum " is compromised by their location in the northern end of the bay, without proper reference far enough outside the caldera. Their elevation was affected by the post-eruption subsidence of the caldera.

One of the most rewarding techniques has been sea shore surveying, a crude method developed in-house, where the level of solid marks around the Bay is measured with respect to sea level and reduced by reference to a tide gauge record. From an original network of 34 stations around the caldera only 6 marks were non-recoverable after the eruption, providing therefore, in spite of its low resolution ( ± 2 cm), the best coverage of the vertical ground deformation. The network counts now 35 stations within the caldera and 11 stations outside. Readings are taken several times per month.

Due to lack of funding for replacement of reflectors, the original EDM were discontinued in early 1994. Since then, shortage of staff has become a problem. Should this situation improve, re-occupation of the network for comparison with pre-eruption data will be difficult for some of the reflector sites have of course been destroyed, and the former " base line " was affected by wider-than-expected deformation.

It is hoped that real-time GPS monitoring will be introduced shortly. Depending on its results we might be able to phase out some other monitoring techniques from the routine surveying effort. As planned, the GPS network will consist of one Ashtek base station at RVO and rover stations positioned at strategic sites for continuous monitoring. One rover station would be used to survey at intervals the former EDM and levelling benchmarks and a number of reference stations outside the area potentially affected by ground deformation.

Thermometry and Geochemistry

The temperature of a number of fumaroles and hot springs were monitored at fortnightly intervals. Following the eruption new sites are progressively being selected on Vulcan and Tavurvur to resume this monitoring. Water samples from some hot springs will continue to be collected at intervals for basic geochemical monitoring. The COSPEC donated to RVO at the time of the eruption will be a useful additional tool for the monitoring of both Rabaul and outstation volcanoes. At the time of writing, it is also hoped that a simple geochemical program will be devised to monitor the emission levels and ratios of selected gas components.

OUTSTATION OBSERVATORIES

Langila and Manam, which are more or less continuously active, and Ulawun and Karkar, which have had a number of discrete eruptions during the past few decades, are under continuous surveillance from a local observation post. The volcanoes in the Esa'Ala area, although much less active, are also under continuous surveillance.

The basic surveillance consists of one (or two, in the case of Langila) seismic stations on the flanks of these volcanoes, with local recording on smoked paper or by ink pen. Minimal but useful ground deformation data is also obtained at Manam from daily readings of a pair of Akashi water-tube tiltmeters in a vault beneath the observatory. Preliminary results of this monitoring and visual observations at all stations, but Karkar, are reported daily to RVO via HF radio by Observatory staff or part-time observers. Three of these stations (Manam, Karkar and Ulawun) also have telephone (and fax) links with RVO.

A new and potentially permanent monitoring network was added at Pago volcano in 2002, with several seismic stations, leveling lines, and visual observations. The base for this monitoring is in Kimbe, West New Britain.

Additional ground deformation data are obtained when appropriate or affordable, by re-occupying levelling lines (on the floor of the caldera at Karkar and on the lower flanks of Manam), dry tilt stations (6 on Karkar, 4 on Ulawun and Manam) and EDM lines (on Karkar, Manam and Ulawun).

Occasional inspections of these and other volcanoes (e.g. Kadovar, Bam, Long, Umboi, Ritter, Makalia, Pago, Hargy, Bamus, Lolobau, Lamington, Balbi, Billy Mitchell, Bagana, Loloru) are also an opportunity for temperature readings at fumaroles or hot springs.

OTHER ACTIVITIES

In addition to volcano monitoring, the functions of the Rabaul Volcano Observatory include : geologic reconnaissance and tephrastratigraphic studies, volcanic hazard assessments, assistance in the preparation and revision of volcano emergency plans, and studies of the patterns of activity of the monitored volcanoes with a view to the detection of eruption precursors and provision of warnings.