The Dakataua Caldera is located at the northern tip of the Willaumez (Talasea) Peninsula jutting out from central New Britain, Papua New Guinea (PNG). We covered multiple volcanoes in New Britain in past posts, the most recent of which was Witori. There are also posts on the Rabaul Caldera and activity at Langila in 2019, Ulawun & Bamus in 2017, Ritter Island just off the W coast in 2015. These would be a good place to start with review of the island of New Britain and local tectonics.
The Willaumez (Talasea) Peninsula is located on the north coast of central New Britain. The peninsula extends N around 50 km and averages 10 km wide. There is a small settlement at Talasea with aircraft service. Part of the area is cultivated, growing coconuts and cocoa. Most of it is covered with thick rain forest. There are a number of scattered native villages, mainly near the coast. Climate is hot and humid with average rainfall nearly 450 cm per year, most of which falls in the rainy season Dec – Feb. Travel is difficult, limiting past geologic investigations.
The peninsula is sparsely populated, with at least 6,000 people. The largest town is Talasea, midway up the east coast of the peninsula. Some 3,700 live within 30 km of the caldera; 114,000 within 100 km. There is little infrastructure on the peninsula. New Britain was captured by the Japanese in 1942. It was retaken by the US in Mar 1944 in the Battle of Talasea and is now part of Papua New Guinea.
Lake Dakataua is crocodile infested. It has a surface area around 48 km2, essentially two lobes connected by a shallow strait. Maximum depth is 120 m. It is alkaline, likely formed by rainwater filling the caldera. There is no life below 80 m due to lack of oxygen. The lake is stratified, with increasing acidity and CO2 the deeper into it you go. There are two thermoclines at 22 m and 40 – 45 m. Temperature decreases as you go deeper in the lake.
The lake supports a variety of aquatic plant life, a couple sponge species, multiple invertebrate and bird species. While the lake has significant life, particularly in the shallows, it does not have any fish. There is a folk legend that the lake has a monster called the migo (or masala). A 1993 Japanese film crew captured the wake of something on the lake they claimed to be the migo. It was likely a saltwater croc.
There have been multiple waves of human habitation on the peninsula over the last 71 ka. Analysis of artifacts like pottery shards and obsidian tools yielded that date. It is the obsidian that is important, as it is obsidian (erupted rhyolites), valued for tool making, that keeps drawing inhabitants back into the region following massive volcanic eruptions (mostly from Witori). The thicker the tephra / pyroclastics from the eruption, the longer the repopulation process took. There are extensive obsidian flows near Talasea in the middle of the Willaumez Peninsula and at Mopir to the SW of Witori.
Region
The peninsula is almost entirely volcanic, with 11 largely andesitic volcanoes, a caldera, a number of rhyolitic deposits, and numerous small cinder cones. The nonvolcanic part of the peninsula is generally raised coral reefs. From N to S, the major systems include Datataua, Bola, Lotomgan Group, Garua, Bangum, and Garbuna at the base of the peninsula. This is a lot of volcanic activity to pack into a 50 km long spit of land.
Bola (Wangore) is a symmetrical stratovolcano just to the S of Dakataua caldera. It tops out at 1,155 m. The andesitic cone is forested, with a 400 m wide crater at the summit. There are three explosion craters on its NE flank. The most recent lava flow came from the summit crater and flowed to the W. The summit is pristine with weak fumaroles. The most recent eruption may have been only a few hundred years ago.
The Lotomgan Group is a small group of pyroclastic cones just to the S of Bola. They top out at 555 m and were formed via andesitic and rhyolitic eruptions. There have been no eruptions over the last 10 ka.
The Garua (Talasea) Harbour volcanic field is a group of relatively recent lava domes and pyroclastic cones. They ring the harbor on the W and form Garua Island to the E. Much of the field is rhyolitic. There are active hot springs on the shores of Garau Harbour, with the best ones on the N and S. These include large boiling pools, fumaroles and small geysers on the N shore, and boiling pools, fumaroles and mudpots near the S shore of the bay. These top out at 565 m. There is a single rhyolite lava flow E of the village of Voganakai that appears to have come from the Gulu ash cone. It covers at least 60 km2. The larger rhyolitic flows have flat tops except near the cinder cones or the flow fronts.
Bangum is a 988 m moderately eroded stratovolcano just to the N of neighboring Garbuna volcanoes. While there is some dispute about an active thermal area on the volcano, the consensus appears to be no such area. There is no recorded eruption over the last 10 ka. The volcano is described as a Pleistocene stratovolcano.
Garbuna volcano is part of a volcanic group including three volcanic peaks – Krummel, Garbuna and Welker. It is a basaltic to dacitic stratovolcano that erupted in Oct 2005 after 1,800 years of inactivity. The three cones are aligned along a 7 km N-S line at the base of the Willaumez Peninsula. Garbuna is at the center of the group and has a large vegetation free area that may be the largest hydrothermal field in PNG. There is a prominent lava dome and blocky lava flow in the thermal area. Krummel volcano on the S end of the string has a summit crater breached to the NW. The highest peak in the group is Welcker volcano, which has erupted blocky lava flows that reached the E coast of the peninsula.
The Garbuna eruption 1,800 years ago was dominantly explosive, took place between a pair of massive eruptions from Witori, and produced pyroclastic flow and airfall deposits. There was not an andesitic phreatomagmatic phase for this eruption. There was a second period of eruptive activity from Garbuna Mar – Oct 2008 that produced ash, steam, and a dome. The Mar 2008 eruption was classed as a VEI 1, while the Jul eruption was classed as a VEI 2. Garbuna has an extensive solfatara field with numerous vents, boiling pools and mud pots. These have built mounds of sulfur as high as 2 m around some vents.
Volcano
The Dakataua caldera located at the northern tip of the Willaumez Peninsula of New Britain. It is a double ring caldera with the largest measuring 10.5 x 13.5 km in diameter. The inner ring measures just over 6 km. The volume of the collapse is around 75 km3. There are two fault-bounded blocks in the caldera that appear to be remnants of the ancestral volcano. Post-eruption Mount Makalia is an andesitic volcano in the center of the caldera. The volcano erupts mainly andesites and basaltic andesites, though there have been dacites found.
There is a major submarine debris field NE of the volcano that may be due to flank collapse prior to the caldera formation eruption. Its volume is also unknown. The most recent caldera-forming eruption may have been as recent as 1,150 years ago. This was followed by at least 5 sub-Plinian or Vulcanian eruptions.
The freshwater lake measures 12 km in diameter with a surface only 50 m above sea level. There is a N-S trending line of post-caldera cones, explosion craters that forms the inner caldera rim and a large peninsula that nearly bisects the horseshoe shaped caldera lake. This peninsula has Mount Makalia, a stratovolcano that is the largest post-caldera cone in the center of the caldera.
Mount Makalia is a shield volcano with at least 11 overlapping explosion craters on the SW flank. Two of them have small lakes. It has mostly erupted andesite lavas, with some basaltic andesite and dacite lavas. The most recent eruption toward the end of the 19th Century created a lava flow which flowed through a breach in the eastern side of the summit crater. The flow split into two lobes on the way down the flank and failed to reach the lake. The lava flow sourced from a fissure in the summit crater and built three small cinder cones within the crater. This flow is clearly visible on satellite photos. There are thermal areas in the crater and at the foot of the volcano.
The ancestral volcano is estimated at 2,500 – 3,000 m tall. This estimate is based on the exterior slopes of the caldera and comparison of its sea-level diameter with neighboring New Britain volcanoes. The original volcano was a composite cone mainly built of basaltic andesites, though there is some basalt and dacite present. Ash deposits are generally extensively weathered and do not appear as outcrops except around parts of the ring fracture. There are a number of locales around the coastline with unsorted and loose material, likely mudflows / lahars or pyroclastic flows from the original cone.
Post-caldera activity is located on the small peninsula into the caldera. There was an andesite erupted from the outer ring fracture that flowed into the caldera. This lava is similar to those of Mount Makalia. There is an island in the lake constructed of ash deposits from post-caldera activity. Outside the caldera to the E, there are a cluster of explosion craters, the largest of which is 2 km in diameter. These craters did not produce any lavas, though the ash deposits are also similar to Makalia and are also thought to be post-collapse activity.
There are a pair of named blocks – Benda and Doko – which are bounded on all sides by near-vertical scarps. These appear to be part of the ancestral mountain and are similar in composition to the ring wall. Identical rock is found near sea level outside the caldera. These are generally andesites and dacites, chemically distinct from post-caldera activity.
There are a couple competing theories about Dakataua’s pair of concentric ring fractures. The first is a relatively straightforward climactic eruption, caldera collapse around a ring fracture. Magma resurgence did not build a central dome. Rather, it and subsequent withdrawal created the internal ring and blocks between the two rings, a process not unlike what formed the internal caldera ring in Suswa. A second theory has the internal ring and blocks caused by the way the caldera fragmented and collapsed during the eruption.
Eruptions
The most recent eruption from Makalia took place 1880 – 1890. This information was collected from villagers in 1963 at the northern end of the Willaumez Peninsula. It produced three cinder cones and a lava flow. The publication Fire Mountains of the Islands lists Makalaia – Dakataua as an example of a what they call a ‘sleeper’ volcano, capable of producing eruptions larger than when each was last active in the 19th Century.
The most recent caldera forming eruption is described as the “Dk” event was a VEI 5-6 that took place around 1,388 years ago (635 – 670 AD). This was part of a significant volcanic pulse in New Britain with Rabaul and Witori also producing significant eruptions very near that time. There as many as 8 caldera systems located along an arc parallel zone some 380 km long. Over the last 20 ka, the average major VEI 5+ eruption took place once every 1,000 years, with 74% of them (14 of 19) from Witori and Rabaul.
The Dk event erupted some 10 km3 of bulk tephras. It was difficult to date as its tephras did not travel a large distance to the S, though eruption dating has settled in the 1,400 – 1,370 years before present range. The Dakataua eruption produced a Plinian plume and ignimbrite tephras. It also had abundant water in the vent area at the time of the eruption.
A 1970 estimate of the volume of the caldera collapse was 75 km3. A bathymetry survey around the northern tip of the peninsula shows irregular features, blocks 1 – 2 km in diameter. Thickness of the debris is 10 – 30 m at 300 m under the surface. Some of the large blocks may indicate sector collapse prior to caldera formation. The area covered by the debris is around 30 km2. Estimated tsunami runup caused by the debris avalanche is around 3.5 m.
Four of the Dakataua tephra-forming eruptions were phreatomagmatic, including the Dk event. There is a pyroclastic flow on top of the tephras which suggest that the eruption may have destroyed a cone or cones. Major eruptions from Dakataua before 3,300 years ago are difficult to determine because recent tephra layers from other volcanoes (mostly Witori) mask the flanks of the volcano.
Tectonics
As Dakatuau is some 73 km NW of Witori, a distance where regional tectonic differences between the two volcanoes are negligible at best, I am repeating the tectonic narrative from our Witori post below.
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 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 requires 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 south of 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
Dakataua is another example of volcanic activity in New Britain. While not recently or vigorously as active as neighboring Witori or Rabaul at the far eastern end of the island, the system supports a post-caldera stratovolcano, numerous maars, and an active hydrothermal system. The caldera-forming eruption was sufficiently complex that it formed a double-ringed caldera, with the interior ring possibly forming after the main eruption. There is also a debris field in the ocean to the NW of the caldera that appears to have come from the system. While it is undated, it may have taken place before the caldera-forming eruption. The system appears to have an active magma source, so future activity should be expected.
One of the other observations about this system is that much of the descriptive information on it is up to half a century old. This a system woefully in need of a full geologic workup and monitoring if for no other reason than to see it in light of current knowledge. This shortage of geologic workup of the region also manifests itself in a lack of available photos and videos of the volcanoes of the Willaumez.
Additional information
Dakataua – Oregon State University, Sept 2010
Fire Mountains of the Islands, RW Johnson, ANU E Press, online version, 2013
Obsidian sources at Talasea, West New Britain, Papua New Guinea, J Sprecht, 1981
Lapita all over: Land-use on the Willaumez peninsula, Papua New Guinea, Specht & Torrence, Jan 2007
The volcanoes and caldera of Talasea, New Britain: Geology and petrology, Lowder & Carmichael, 1970
Volcano collapse and tsunami generation in the Bismarck volcanic arc, Papua New Guinea, Silver, et al, Jun 2009
Archaeological studies of the middle and late Holocene, Papua New Guinea, Specht, et al, Jan 2007
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volcanohotspot.wordpress.com 
Wakeup call this morning in ANC 0843 L. M 4.6, some 58 km N, 25 km deep. Initial shock, spun up quickly, and then rolled for a while afterwards. No damage. Cheers –
https://earthquake.alaska.edu/event/023qqz70l
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