Pago is the historically active cone growing in the Witori caldera on the northern coast of central New Britain. The immediate area is intensely volcanically active with the remains of at least two calderas, Witori and Buru and ten additional volcanoes. Pago, the active vent in the Witori caldera is very young, perhaps only 350 years.
We wrote about multiple volcanoes in this region over the years. I did a post on the Rabaul caldera system in 2019. Granyia covered Ulawun and Bamus in 2017. I reviewed activity on Langila in 2019. Finally, Granyia reviewed Ritter Island off the west coast of New Britain Island in 2015. Any of these posts would be a great place to start for a review of New Britain and regional tectonics.
The island of New Britain is intensely volcanic with multiple active volcanoes and remains of multiple caldera systems. Volcano Discovery lists at least 27 identified volcanic systems on the main island and offshore to the NW. Activity appears to be migrating toward the NW off the NW coastline over time. Recent and currently active volcanoes include Langila at the far western end of the island, Pago (Witori) near the northern coast in the center of the island, and Tavurvur (Rabul) at the far NE tip.
The political division of this part of New Britain is called West New Britain, and includes most of the western part of the island and the volcanic islands off the N. It is just a bit larger than 20,000 km2 with a population of just over 260,000. The District Capital is Kimbe and the local government area nearest Witori is called Hoskins Rural. There are at least 7 local tribes in West New Britain speaking over 25 languages.
Primary economy in this part of New Britain is driven by large palm oil plantations in the Kimbe region. There is some logging in the interior, and the most prominent road snakes along the northern coastline dotted with local villages. The closest airport to Witori is the Hoskins Airfield. It serves Kimbe and is located 16 km NNE of Pago. It was closed for a time due to ashfall from the 2002 – 2003 eruption sequence. Climate is generally tropical, very wet, with a tropical rainforest.
I have not yet found any known webcams looking at Pago. The closest manned volcano observatory listed by WOVO is Rabaul. Regional volcanic ash advisories are issued by the Darwin Volcanic Ash Advisory Centre. The Kimbe Volcano Observatory may have run out of money, as it was quiet during 2012 activity at Pago.
Region
The northern coast of New Britain east of the Willaumez Peninsula is known as Cape Hoskins. The area has at least ten extinct Quaternary volcanoes and an active one, Pago. The extinct volcanoes are mostly stratovolcanoes, layered with lava flows, domes, pyroclastic flows, lahars, tephras and alluvial sediments. Volcanic products are typically andesites to basaltic andesites, though basalts, dacites and rhyolites are also present. Much of the area is covered by meters of tephras, generally rhyolitic pumice.
There are least three calderas in Cape Hoskins, the active Witori caldera now occupied with the Pago vent, Busui and Buru. Four of the other 8 volcanoes are relatively well preserved, with steep-sided cones.
The Oto volcanic group includes 5 stratovolcanoes and a caldera that dates early to late Pleistocene. The oldest volcanoes, Ko and Husa date 900 – 800 ka. The younger Oto, Mululus and Mateleloch volcanoes date 190 – 70 ka. Busui is listed as a caldera, though so heavily eroded that it does not show prominently on a Google Earth satellite view. It may be the depressed central area between the three newer volcanoes. This complex lies to the NW of Witori, with the caldera likely defining the depression encircled by the newer stratovolcanoes.
Lolo is a small, nearly symmetrical andesitic stratovolcano N of Witori on the N coast of New Britain near Cape Hoskins. It overlaps the older Kapberg volcano to the W. Lava flows are prominent, and it is topped with a 250 m crater.
Buru is described as a partly preserved cinder cone topping out some 250 m above the surroundings. It is located SW of Pago and SE of Oto. There is a swampy depression N of it called the Buru Caldera but no obvious cinder cone and only a partial circular depression appears in Google map and satellite view. Buru may be younger than Witori, as both structures appear to coincide in time, neither one obviously younger nor older than the other. As an aside, erosion and repopulation of the terrain by the rain forest works really, really well in this part of the world to obscure volcanic structures and past activity.
Volcano
The Witori caldera measures 5.5 x 7.5 km. The historically active Pago cone was built over the last 350 years within the caldera. The flanks of Witori are gently sloping pyroclastic and airfall dacites. Pago has covered much of the caldera floor with at least 10 dacitic lava flows extruded after the caldera forming eruptions. The youngest of these was erupted during the 2002 – 2003 eruption sequence. Most of these show up nicely on satellite view of the caldera floor. The Buru caldera cuts the SW flank of Witori. Pago has grown to the same height as the caldera rim, about 250 m high. It is 300 m in diameter.
Most of the eruptions from Witori lay tephras down that have evidence of abundant water in the vent area at the time of the eruption. Today, there is no lake in the caldera, though one may have existed prior to older caldera-forming eruptions. Multiple caldera-forming eruptions created a caldera complex. Water-magma contact may have triggered the following phreatomagmatic eruption. More recent eruptions tend to be drier, which may indicate the growth of the post-caldera cone within the caldera.
Pyroclastic flows from the major caldera-forming eruptions from Witori are generally distributed in every direction from the vent. The largest of these, W-K2, from the largest eruption, extended more than 40 km from the volcano to Kimbe. Tephra ash falls tend to spread based on prevailing winds at the time of the eruptions. Each tephra layer has multiple airfall units with thicknesses less than a meter near the source.
Witori – Pago is quite the active system. The Smithsonian GVP lists 7 eruptions since 1911, with 4 of them 2002 – 2012. The volcano was mostly quiet during the 19th Century following a VEI 4 in 1800. In the 800 years between 1050 – 1800, there are at least 5 eruptions as large as VEI 4. Since 800 AD, the activity decreased in magnitude and increased in frequency, with some eruptions forming central cones like Pago that were destroyed by subsequent eruptions.
The VOGRIPA database lists the 1800 eruption as a VEI 4, ejecting 0.1 km3 of material. A previous VEI 4.3 in 1550 ejected about the same amount of material. The most recent caldera-forming eruption took place in 844 AD, a VEI 6.3 that ejected 20 km3. Before that a VEI 5.8 710 AD ejected 6 km3. A previous VEI 5.8 310 AD ejected another 6 km3. The largest eruption took place 1370 BC, a VEI 6.5 that ejected up to 30 km3. It was preceded in 4000 BC by a VEI 6 that ejected 10 km3. All major eruptions 4000 BC – 844 AD are thought to have been caldera-forming eruptions. The major tephra layers cover extensive areas in New Britain due to large volumes and prevailing easterly winds. The largest eruption covered an extensive area with tephra falls and pyroclastic flows. These buried obsidian and other artifacts, indicate the area was repeatedly occupied. Human habitation in the region has been traced back at least 40,000 years. The major tephra events formed new coastal plains favorable for human occupation.
Eruptions
There was a VEI 3 from Pago in 1911 that dusted the region surrounding the volcano with volcanic ash that persisted for at least 22 years. This was followed by a small eruption in 1920 and a VEI 2 in 1933. Fire Mountains of the Islands discusses Pago on pp 320 – 326. It has an alternate description of the 1911 eruption, listing it as active 1911 – 1933. Large, caldera-constrained lava flows were produced during the early part of this eruption, particularly 1914 – 1918. The volcano was quiet for the next 70 years, waking up in Aug 2002 producing another VEI 3. There were some reports of mild summit and flank fumarole activity in 1990.
The Aug 2002 announced itself with ejection of a rapidly rising plume passing 9 km as reported by passing airliners. The plume generally traveled NW. The first and most vigorous explosion took place early in the morning followed by a second blast a few hours later. Explosions continued for the rest of the day. 3 days later, 6 – 8,000 people had been evacuated from local villages. Ashfall was not particularly thick at a few mm, and lava was being extruded from vents within the crater, forming cones around them. The plume quickly returned to a relatively low plume with low ash content.
The eruption continued through until mid-Sept. There were intermittent explosions with low ash content that produced low level plumes. Five vents on the NW flank of Pago were active and releasing short dacitic lava flows into the crater. The vents were generally aligned toward the NW along a local fault. In a lot of ways, the 1911 and 2002 eruptive sequences were similar – explosive beginnings followed by extended effusive dacitic lava flows.
The US and Japan worked with the Rabaul Volcano Observatory to install long planned but never acquired monitoring equipment on Pago and set up a volcano observatory in Kimbe. It was returning data by mid-October. It will take a few months before sufficient data is returned to develop any sort of hazard map and plan. Eventually, there were 13,000 of the 15,000 within the effected area downwind either directly impacted or evacuated.
Effusive activity and vapor emissions continued through the end of Feb 2003. Lava effusion stopped by May. By Oct 2003, Pago was mostly quiet, with generally low seismicity, and the vents continuing to release thin, white vapor. This period of quiet continued until Feb 2004, when a pair of explosions were reported early Feb 24. Based on seismic data, these were determined to be weather-related thunderstorm events. Degassing continued through Feb 2006. Activity picked up a bit Aug 2007 with lava fragments ejected from one of the upper vents in Aug. There was a corresponding increase in white vapor emissions.
The volcano was mostly quiet until May – July 2012, when the Darwin VAAC issued five volcano plume advisories, the first three over 12 km above the crater on May 3, and the other two on July 10. Three of these went above 12 km. Given the plume heights, one would expect an extended eruptive sequence. I have found nothing suggesting this went any farther than the two blasts, as there was no MODIS thermal imagery afterwards like we saw in the early stages of the 2002 effusive eruptive sequence documenting the lava flows. Note that the Kimbe Volcano Observatory is referred to as an outstation observatory, with access to a seismograph. The observers manning it need to be trained, and in HF contact with the Rabaul Volcano Observatory to report what they are seeing. Sadly, various posts are no longer filled with local observers. It appears that Kimbe is one of these.
Tectonics
Volcanic activity on New Britain is driven by subduction of the Solomon Sea Plate / Woodlark Plate beneath the South Bismarck Plate along the New Britain Trench S of New Britain. The overall tectonic feature of the region is the collision of the Indo-Australian Plate with the Pacific Plate. This has fragmented northern portions of the Indo-Australian Plate into multiple smaller plates / platelets / micro-plates.
While the motion of the Australian Plate is generally NE, the motion of the Pacific Plate is generally NW at 13 cm/yr. Resolving this motion created a pair of strike-slip fault zones, the Ramu – Markham bisecting the northern fifth of the island of New Guinea and the San Cristobal Trench just south of Bougainville and the Solomon Islands. Motion is distributed in a zone of tension between at least four smaller plates / platelets / micro-plates. From NW to SE these are the North Bismarck Plate, South Bismarck Plate, Solomon Sea Plate and the Woodlark Plate. Some depictions combine Solomon Sea and Woodlark Plate into a single entity. The South Bismarck Sea microplate is rotating clockwise about 9° / Ma due to the combined motion of the collision. The North Bismarck Sea microplate is rotating the opposite direction, but more slowly, opening a spreading center between the two microplates on the sea floor.
The island of New Britain is located at the SE corner of the South Bismarck Plate that includes the northern fifth of the island of New Guinea north of the Ramu – Markham Fault Zone. The New Britain Trench is a narrow 50 – 75 km wide trough that generally parallels the western two-thirds of New Britain offshore to the SE. It bends through a 60 – 70° angle southward at the northern part of New Britain.
Subduction of the Solomon Sea Plate drives both the intense volcanic activity in New Britain and a significant earthquake field. Deep earthquakes have been measured below 500 km along the subducting plate.
Conclusions
Expect the Witori – Pago system to remain active, as the tectonics of the region will continue to produce ample supplies of eruptible magmas as long as the major Indo-Australian – Pacific Plate collision continues. Most concerning is the apparent lack of current monitoring, perhaps due to budgetary issues, so future eruptions may first be known by either satellite or aviation notifications or local calls for help. Local notification may end up being physical ashfall, earthquakes and sounds from an ongoing eruption. Given the past explosive nature of this system popping off with little warning, apparent lack of monitoring is worrisome.
Additional information
Volcano Discovery – Pago volcano
Papua New Guinea: Pago eruption information release 6, 12 Aug 2002, Relief Web
Plant succession on Pago and Witori volcanoes, New Britain, K Paijmans, Pacific Science, 1973
Pago volcano, Papua New Guinea, Volcano Photos, geographic.org
Present-day crustal motion in Papua New Guinea, Tregoning, et al, Oct 2000
New Britain Trench, Papua New Guinea: an extensional element in a regional sinstral strike-slip system, ID Lindley, Dec 2006
Tectonics of the New Guinea region, Baldwin, et al, Annual Review of Earth and Planetary Sciences, Mar 2012
Analysis of volcanic activity patterns using MODIS thermal alerts, Rothery, et al, Bulletin of Vulcanology, July 2005
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Another temporary volcanic island in the Tonga Islands. This one is Home Reef, which built a temporary island a couple weeks ago. Discolored water is visible in Google Maps. Home Reef built at least five ephemeral islands since 1852. It is located some NNE of Hunga Tonga. Cheers –
https://www.sciencealert.com/a-new-island-has-arisen-in-the-pacific-following-underwater-eruption
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