Instrumental Volcano Surveillance and Community Awareness in the Lead-Up to the 1994 Eruptions at Rabaul, Papua New Guinea

Abstract

Instrumental volcano surveillance and community awareness played key roles in preparing for the outbreak of the 1994 VEI 4 volcanic eruptions at Rabaul (pop. 17,000). The eruptions were preceded by 23 years of fluctuating unrest involving swarms of caldera earthquakes (max M L 5.2) and co-seismic uplift of parts of the floor of Rabaul Caldera. Eruption contingency planning was formally driven by government authorities and involved all sections of the community. Community awareness of the volcanic threat was enhanced by the dissemination of relevant information by the Public Information Unit of the East New Britain Provincial Government and reached a peak in the mid-1980s at the time of a large increase in the strength and frequency of earthquake activity (between August 1983 and. However, the intensity of the unrest declined after July 1985 and another 9 years elapsed before a new and dramatically stronger phase of unrest took place. The strong and sustained earthquake activity on 18 September 1994, together with marked co-seismic uplift that took place that night, was the final episode of volcanic unrest prior to the outbreak of eruptions on the morning of 19 September 1994. Memories and stories of the seismic prelude to the previous eruptions, in 1937, are reported to have been a major influence on community response to the seismicity on 18 September 1994. The evacuation of all areas within the caldera proceeded efficiently from late afternoon of 18 September until the early hours of 19 September. These areas were almost deserted when the eruptions started at two vents, Tavurvur and Vulcan, on opposite sides of the caldera at 0606 and 0717 LT respectively on the morning of 19 September 1994. Ten deaths in the first six weeks of eruptive activity were volcano-related. Damage inflicted by the eruptions was severe. About 70% of Rabaul Town was destroyed by tephra fall from Tavurvur, and several villages were obliterated by pyroclastic flows and heavy tephra fall from Vulcan. The 23 years of precursory activity and the events around the start of the 1994 eruptions delivered a number of important lessons in the fields of volcano surveillance, communications and disaster management. Perhaps the most important lessons of all are that co-existence with active and potentially active volcanoes requires (i) open and effective lines of communication between volcano scientists, government officials, town authorities and the general public, facilitated by designated public information officers, and (ii) the establishment and frequent exercising of eruption contingency plans.

Anticipating future Volcanic Explosivity Index (VEI) 7 eruptions and their chilling impacts

“…Large magmatic-hydrothermal systems buffer incoming magma intrusions, and then show unrest in repeated episodes before they finally erupt again. Petrologic evidence for repeated intrusions before the VEI 7 Minoan eruption of Santorini (Druitt et al, 2012), be- Table 3. fore smaller recent eruptions at Rabaul (Bouvet de Maisonneuve et al, 2015), and instrumentally monitored unrest at Rabaul and Campi Flegrei (Acocella et al, 2015;McKee et al, 2017) reflect such buffering.…”

“…Experience from unrest and smaller eruptions at Rabaul (1979Rabaul ( -1994McKee et al, 2017), Campi Flegrei (1500s and ca. 1950Acocella et al, 2015;Chiodini et al, 2016;Kilburn et al, 2017), and Pinatubo (1990Newhall and Punongbayan, 1996a, and papers therein) also showed that despite prolonged early unrest, the final runup to eruption was just hours to days.…”

The 1994–2001 eruptive period at Rabaul, Papua New Guinea: Petrological and geochemical evidence for basalt injections into a shallow dacite magma reservoir, and significant SO2 flux

“…The eruptions can be divided into two phases: Phase 1 -September 1994 to April 1995; Phase 2 -late November 1995 onward. Detailed accounts and analysis of Phase 1 and parts of Phase 2 have been documented in GVN (1994), Blong and McKee (1995), Bouvet de Maisonneuve et al (2015), McKee et al ( , 2017, and McKee (unpublished data). Eruptions at both sites produced identical dacites but the compositions of Tavurvur eruptives extended to mafic andesites.…”

“…Tavurvur and the other near Vulcan, at about 3 am on 18 September 1994 (GVN, 1994;McKee et al, 2017). The following 27 hours included a period of sustained strong caldera seismicity and massive ground deformation.…”

“…The two ~M5 earthquakes recorded 27 hours prior to the eruption (GVN, 1994;McKee et al, 2017) occurred at shallow depth (1-2 km) near Tavurvur and Vulcan and probably reflect rupture that initiated magma ascent from the caldera-extensive reservoir possibly triggered by mafic magma recharge. Simple models for magma chambers located beneath shallow volcanic piles indicate that the overpressure needed to induce wall-rock rupture is of the order of 1-10…”