Volcanoes of Oceania

The Pacific “Ring of Fire” is a horseshoe-shaped zone surrounding the Pacific Ocean where a concentration of volcanic and earthquake activity occurs (Figure 1).² Much of the volcanic activity is associated with subduction zones, which are convergent boundaries between tectonic plates. Subduction zones form when continental and oceanic crust collide. Thinner, denser oceanic crust is less buoyant than continental crust, so it sinks (subducts) beneath the continental crust. At depths of approximately 80km-160km, partial melting occurs to generate magma, which migrates upwards and may reach the Earth’s surface to produce volcanic landforms. Subduction zones generally produce volcanic arcs.

Figure 1.

The Pacific Ring of Fire² with Oceania Region Outlined.

In the Oceania region, the island arc countries of Papua New Guinea (PNG), the Solomon Islands, Vanuatu, Tonga, and New Zealand (Figure 1) are most at-risk from active volcanism.³ These countries contain active, explosive-type volcanoes that have produced major eruption crises in modern times. Recent examples are the 1951 eruption of Lamington volcano, PNG where pyroclastic flows swept down all sides of the volcano, killing an estimated 2,942 people; and the 1937 eruption of Rabaul volcano, PNG where 507 people were killed by pyroclastic surges and ashfall. Overall, since 1500ad, there have been ~9,300 volcanic fatalities recorded in Oceania due to volcanic activity (Table 1).^{Reference Brown, Jenkins, Sparks, Odbert and Auker4}

Table 1.

Volcanic Fatalities in Oceania since 1500AD, by Country³

Near-Vent Volcanic Hazards

Volcanoes are unique among natural hazards in that they can cause a wide range of hazardous phenomena. Close to volcanic vents, hazards can be highly dangerous and/or destructive to property and include pyroclastic flows and surges, ballistic projectiles, lava flows, lahars, thick ashfalls, debris avalanches, and gas and aerosol emissions.

A range of approaches is used to reduce volcanic risks to life safety. These include volcano monitoring and surveillance, land-use planning, warning systems, hazard maps, and public education campaigns. Following the 1937 eruption of Rabaul volcano, which was unmonitored at the time, a permanent observatory was established in 1940. It was destroyed during WWII and re-established in 1950. An unrest crisis during 1983-1985 was valuable in spurring preparedness efforts, particularly the development of a contingency plan that identified evacuation routes out of the area and safe refuges, as well as public education on the volcanic hazard.³ The value of these efforts became apparent in 1994/1995 when a powerful explosive eruption forced the temporary abandonment of Rabaul City: approximately 100,000 residents evacuated their homes, but only five lives were lost.³

While volcano monitoring and surveillance (and associated measures) have demonstrably saved lives, residual risks remain, particularly from small, sudden, unheralded eruptions which may be deadly at close range. Since 2000, 39 lives have been lost due to volcanic activity in Oceania (Table 2). This catalogue is dominated by the December 9, 2019 eruption at Whakaari volcano, New Zealand, with the death toll at 21 at the time of writing.⁵

Table 2.

Fatal Incidents in Oceania since 2000^{3,Reference Brown, Jenkins, Sparks, Odbert and Auker4}

^a This event is under active investigation. Likely fatal cause is a base surge. Number of fatalities is at time of writing.⁵

Far-Reaching Volcanic Hazards

Volcanic ashfall is generated by all explosive eruptions, dispersed by prevailing winds, and may be deposited on communities and farmland hundreds or even thousands of kilometers away.^{Reference Stewart, Wilson and Sword-Daniels6} The wide geographic reach of ashfalls, and sometimes also volcanic gases and aerosols, make them the volcanic hazard most likely to affect the greatest numbers of people.^{Reference Loughlin, Vye-Brown, Sparks, FitzGerald, Tarrant and Aitken7} Lahars (volcanic mudflows) can also affect areas further away (typically tens of kilometers) from volcanoes, as they travel down river systems.

Ashfalls are generally disruptive rather than damaging, but occasionally they can cause fatalities. Following the eruption of Manam volcano, PNG in late 2004, five people (two elderly people and three children) died from respiratory complications following ash inhalation (Table 2).^{Reference Brown, Jenkins, Sparks, Odbert and Auker4,8} A further four people died and one was injured by a lahar in the valley on the north side of the island.^{Reference Brown, Jenkins, Sparks, Odbert and Auker4} The following year, 14 people were injured and one killed by heavy ashfalls in Warisi village on the eastern side of Manam island, reportedly due to buildings collapsing under the weight of the debris,^{Reference Brown, Jenkins, Sparks, Odbert and Auker4,9} as well as burning down due to the hot debris.

More commonly, ashfalls can affect the habitability of downwind communities, including aspects such as contamination of drinking-water supplies, degradation of outdoor and indoor air quality, damage to buildings, crop damage, and food security. These aspects of environmental health can be important drivers of evacuation decisions, particularly if impacts are sustained. As shown in Table 3, since 2000, nearly 100,000 people across Oceania have been displaced by volcanic ashfall, with approximately two-thirds in PNG and one-third in Vanuatu.¹⁰ Forced migrations and protracted displacements bring insecurity, the potential for politicization of the population, and can be drivers of instability in the region. This applies to both the community that has to relocate as well as the host community. Internally-displaced persons (IDPs) place pressure on resources, job opportunities, food, health access, and civil and political rights.

Table 3.

Numbers of People Displaced by Volcanic Ashfall in Oceania, 2000-2020

In the following section, the recent 2017-2018 Ambae eruption, which caused the entire population of the island to be evacuated twice, is discussed.