Almost daily I look at the news on Earth Alert and more often than not there is that yellow or orange triangle indicating ash warnings in Bougainville Island, …remind me of the name…? Well, I probably will not forget its name again; it was worth my while to make myself familiar with BAGANA volcano, so I’ll pass on to you what I have learnt.
in researching for a volcano post, have I felt so utterly sad at heart as when I read about the recent (20th century) history of Bougainville Island. The sufferings of her native people at the hands of foreigners from throughout the world are unspeakable, unbearable and intolerable! So far it is not clear whether the thousands of lives lost during their civil war 1989-1999 (-2001) have not been in vain. I hope with all my heart that recent developments may, at least, prepare a walkable path in direction of a dignified and peaceful existence for the Natives of Bougainville.
Bougainville Island* belongs geographically to the Solomon Islands group; politically it is now the Autonomous Region Bougainville, of Papua New Guinea (I’ll use PNG for short). Seventeen post-Miocene strato volcanoes have been identified on this island. From NW to SE, these are the Tore, Balbi and Numa Numa in the Emperor (Mountain) Range; and Billy Mitchell, Bagana, Reini, and Bakanovi volcanoes – as well as the Takuan and Toroka groups of volcanoes constructed within the nested calderas of Loloru volcano – in the Crown Prince (Mountain) Range. Many of these have been active in the Holocene, some in historical times (like Billy Mitchell, Bagana’s direct neighbor, in 1580 with a VEI 6).
*Louis-Antoine, Comte de Bougainville (1729-1811), was a French admiral and explorer. In his circumnavigation 1766-69 he sailed through what is now known as the Solomon Islands which, due to the hostility of the people there, he avoided – but didn’t fail to name Bougainville Island for himself in passing by.
The Solomon Islands group is a complex collage of crustal units or terrains which have formed and accreted within an intra-oceanic environment since Cretaceous times. Bougainville Island is the NW part of the Solomon island arc. Two main stages of subduction and volcanic arc activity characterize the development of Bougainville Island. “The first stage started in the Eocene, about 45 million years ago, when the Pacific Plate was subducted beneath the Australian Plate along the line of the Kilinailau Trench. The second began about 10 million years ago when the Australian Plate was subducted beneath the Pacific Plate along the line of the New Britain-Bougainville-Makira Trench. The first event marked the birth of Bougainville and Buka as a pile of volcanic rocks on the ocean floor.
The Kilinailau Trench ceased to be active about 10 million years ago when the steady north-westward motion of the Pacific Plate brought the thick oceanic crust of the Ontong Java Plateau into the Kilinailau Trench. The thick crust caused a problem because thick crust is not readily subducted. One could say it was a severe case of indigestion, or of biting off more than one could chew. The shortening of the crust could no longer be accommodated at the Kilinailau Trench and so a new trench formed, this time on the south-western side of the islands, allowing the Australian plate to be subducted beneath the Pacific Plate. This second stage of subduction yielded the more recent volcanic rocks on Bougainville Island, and has culminated in the development of Balbi, Bagana and Loloru volcanoes.” (citation from “Bougainville before the conflict” )
A Benioff zone dips steeply NE beneath Bougainville Island; its dip increases downward to nearly vertical beneath the volcanoes, and the maximum depth of earthquake foci here is > 500 km. Bougainville Island and its volcanic chain are built up of lavas and pyroclastic deposits mostly of andesitic composition, although some dacitic rocks are present as well. Modal and chemical analyses show that these rocks belong to the calc-alkaline suite characteristic of orogenic regions.
Bagana is one of Melanesia’s youngest and most active volcanoes. It was discovered in 1842 when in eruption and historical records describe frequent eruptions since that time. The volcano lacks instrumental monitoring and sits far from population centers.
Most of its 22 recorded eruptions have been explosive (VEI=2-3), with some pyroclastic flows, and about half of them have produced lava flows. Some explosive eruptions produced nuee ardentes and voluminous ash clouds; several people were killed by the “great explosion” in December 1883 or January 1884. Major eruptions occurred in 1950, 1952, and 1966. Long-term extrusion and accumulation of viscous andesitic lavas have built up this massive cone to 1750 m a.s.l. erupting throughout much of the 20th century, and presently almost continuously since 1972. There is also a near permanent steam emission with volcanic gases, frequently with ash plumes of low to medium hight.
Bagana is classified as a lava cone, i.e. mainly built up by lumps of tough lava without layers of tephra in between them. Calculations taking in account its very viscous blocky lava and the very slow flow speed (1-3 m/d) arrive at a possible age of no more than 300 years. Its young thick lava flows form dramatic flow features like prominent levees that descend the whole of the cone and terminate in very well-preserved tongue-shaped lobes with fronts up to 150m thick, hugging the foot of the volcano on all sides. “Existing classifications do not provide a name for this kind of activity; in a recent review of volcanism in PNG the term ‘baganian’ was coined to draw attention to Bagana’s unusual style of activity compared to that of other volcanoes in PNG.” The summit crater usually contains an active lava dome that is repeatedly destroyed during explosive activity.
LAVA LAVA LAVA
Bagana’s flanks are covered with andesitic thick, steep-sided blocky lava flows. The flows typically descend mid-slope within the confines of tall lava blocky lava, but emerge from the levees on the lower flanks to form sub-circular flow fields. The lava flows are of a massive to moderately vesicular andesite. As can be seen in the sketch, left, lava flows go down in every direction from the crater.
Chemically analysed lavas from Bagana can be assigned to one of three age groups (pre-1943, 1943-53, or 1959-75). They appear to represent distinct batches of magma that were successively erupted from Bagana, possibly from a high-level reservoir that was periodically emptied and refilled.
The andesites are regarded as fractionates of mantle-derived mafic magmas. Most of the crystal fractionation probably took place during ascent from the mantle source region, and before entry into the reservoir beneath the volcano. An average chemical composition of the analysed Bagana Andesites is similar to those of the mean for more than 800 analysed volcanic rocks from P.N.G. (and is therefore proposed as a reference andesite composition for further studies).
Image right: Closer view of the block-lava flow down Bagana’s SW flank taken in April/May 2004. The initially confined lava flow followed the leveed path and then began to escape at several places. The fresh block lava’s darker color stands in mild contrast to sparsely vegetated, older levee banks, which have a speckled appearance. (© Ima Itikarai, RVO)
MONITORING BAGANA IN THE 20TH CENTURY…
During the last 200 years, Bougainville has been under German, Australian, Japanese jurisdiction and Papua New Guinea today.
1884-1914 was the period of German occupation of New Guinea, which, if nothing else, was a good thing regarding volcanology. Though their being there was for preying upon land and people in the first place, it seems that every governor, captain, missionary, even business people, took down some, often quite detailed, reports of natural events like volcano eruptions and tsunamis; German naturalists and scientists also produced a wealth of research results. To mention here the geologist Karl Sapper, who after his visit to German New Guinea became an established figure in international volcanology, particularly after publication of his landmark “Vulkankunde” (“Volcanology”) in 1927.
Through the troubled times from the beginning of WW 1 to the end of WW 2, when Bougainville changed hands frequently and really belonged nowhere, only occasional inspections and military observations brought news from Bagana (after the Pacific War, the Australians even run a POW prison at the foot of Mt. Bagana).
Image right: Bougainville. 1944. Aerial photograph of three Douglas SBD Dauntless Dive Bomber aircraft passing the active volcano of Mount Bagana on bombing operation against Kavieng. (Naval Historical Collection; Australian War Memorial)
Scientists were either called in by the local governments when Bagana seemed to become threatening to communities nearby, or sometimes visited out of volcanological interest.
I read one of those reports and… OMG, since when do scientists know about the nature of pyroclastic flows? Surely Mt. Pelee has taught everyone a lesson in 1902? And here’s Mr. Best, who “spent six days camped about three miles from the base of the crater on the western side. The camp site was located about one mile outside a clearly defined blast zone which extended westwards from the base of the mountain for about two miles”… but if that wasn’t dangerous enough… read for yourself:
I know, or have read, that Bagana’s pyroclastic flows tend to be short and usually expire halfway up flanks, but “tends” and “usually” spells to me “certain death” if the volcano doesn’t keep within the trend…
According to residents, Bagana’s activity had not been as high in the first half of the 20th century as it is now. The Rabaul Volcano Observatory (RVO), established 1940 (after the 1937 eruption at Rabaul), received reports from its “outstation” observers in Bougainville quite regularly from sometime in the 1950s (until 1989, when civil unrest commenced; any existing equipment was destroyed and reporting ceased at that time).
The discovery of the enormous gold- and silver-bearing porphyry-copper deposit at Panguna lead to the eventual commissioning in 1972 of the huge Panguna Mine (measures on Google Earth 2.5 km in diameter), and to an ongoing interest in the condition of Bagana volcano from the extraction company. A seismometer operated by Port Moresby Geophysical Observatory (PMGO) was established near the mine, which to some extent could also be used to monitor activity at nearby Bagana volcano. The mine was closed down in 1989.
GVP (Global Volcanism Program) Bulletins began in 1978, when there was still an observation post ~10 km S of Bagana, the observer communicating to the RVO. Reading through the following 11 years’ reports, it becomes clear that Bagana is displaying a continuous behavior of the fluctuating activity of a young dome-building volcano. Characteristic are periods of increased seismicity followed by new lava extrusions in strombolian fashion, including some more explosive events and pyroclastic flows interspersed with a few months of less activity.
– Sept 1987: Activity of the lava flow on the N flank of Bagana has probably ended, 12 years after its commencement.
– Febr. 1988: The lava dome in the summit crater had a flat top but its sides were very steep, particularly noticeable on its SW flank where the dome stood ~30-40 m above [the SW rim] of the summit crater. The lava flow was being fed from the top of the dome and it appeared that the direction of flow could change quite easily.
– Jan 1989: Avalanche breaches summit; lava drains from crater
– Nov. 1989: Aerial reconnaissance on the 10th and 11th revealed that the summit, fully occupied by blocky lava, was overflowing on several sides. A main lava flow, active since 1987, extended to the foot of the volcano on the E flank (13:02). Lava also progressed slowly into the channel of the N lava flow (inactive since 1987), into the upper part of the prominent [1966-75] lava channel on the S flank, and spread over the upper NW flank. Very frequent rockfalls or avalanches occurred on all sides below the summit, producing short-lived red glow at night.
– Jan. 1990: “Seismic monitoring… ceased on the 24th, due to the loss of telemetry as the result of the current civil disturbance…” “In the current period of social unrest on Bougainville Island, no instrumental data is being recorded, and the only information on Bagana’s activity is from visual observations from a site 15 km SSW of the volcano.”
When observations resumed on 3 April, Bagana was in a fairly high level of activity.
– A significant change occurred on the night of 14 January 1991, when part of the summit lava dome collapsed onto the SE flank of the volcano, and initiated a new lava channel between the 1966-75 and 1987-90 lava flows. Apparently, the blocky lava flow is slowly advancing in the saddle between Bagana and the nearby Pleistocene Reini Volcano.
The last report of that century reaches GVP in 1995: Bagana, sitting ~140 km NW of the 16 August M 7.8 earthquake’s epicenter, makes people uneasy. The report described a change in activity, specifically the “black thick clouds coming out of the volcano” and stated that “lava had fallen along the SW coastline.”
Eight years have gone by while both the volcano and the people around it did their business but neither took much note of the other. Great unrest and civil war shook Bougainville Island, her people fighting for and against independence from PNG, for and against protecting their country from severe environmental damage, for and against the possibility of improving economy by exploiting their land – a Gordian knot which to cut is near impossible for a small country. At the same time Bagana very probably did its best to draw attention but the noise of its rumblings was drowned by the war (if you’d like to read more about the civil war in Bougainville please google “Bougainville conflict”).
…AND IN THE 21ST CENTURY
Bulletins on GVP resume Jan. 2003
Since the last ear-and-eye reports, progress in satellite technology has taken great strides – remote sensing is the key word. From 2000 on, MODVOLC thermal alerts inform us that Bagana is still going on, fluctuating like it has done for over 30 years. Satellite photographs show dome-building and -collapsing, new lava flows and ash plumes.
A nationwide seismic network consisting of 10 stations was established in 2013 (funded by the EC), but only one of them was installed on Bougainville, at the NE tip of the island.
One of the latest additions to remote monitoring is the Near Real Time Volcanic HotSpot Detection System MIROVA by the Universities of Turin and Florence (Italy). Click here to see Bagana’s current Radiative Power recording. This is the latest one before posting:
Researching for this post about a part of the world I have never visited in my life nor heard much of its history, I read a lot of articles and blog entries. One I would like to recommend is this enlightening and touching piece by Mark Scott: Bougainville: Island of Scars.
In another blog post, by Gideon Davika on Bougainville’s unique house styles I found this picture of new houses as they are built now on the island. Traditional styles and materials, combined with the latest carpentry techniques that young Bougainvilleans attain from attending vocational schools or technical colleges, bring out the most lovely buildings I can imagine for living in a warm sea climate like that of Bougainville:
Disclaimer: I am not a scientist, all information in this (and any of my other posts) is gleaned from the www and/or from books I have read, so hopefully from people who do get things right! If you find something not quite right, or if you can add some more facts, please leave a comment.
Enjoy! – GRANYIA
SOURCES & FURTHER READING
– GVP, Bagana
– Andesites of Bagana volcano, Papua New Guinea: chemical… (1978, PDF)
– Geological–tectonic framework of Solomon Islands, SW Paciﬁc:… (1998, PDF)
– Bougainville Civil War (Wikipedia)
– Panguna mine (Wikipedia)
– Investigation of Eruptive Activity at Mt. Bagana… (1952, PDF)
– Post miocene volcanoes on Bougainville Island, … (1968, paywalled)
– Volcanic activity in Papua New Guinea before 1944… (1986, PDF) – an annotated bibliography
of reported observations
– An Investigation of Tremor at Bagana Volcano… (1971, PDF)
– Australian War Memorial
– Bougainville before the conflict (2005, PDF) – highly recommended! –
– Geological maps of Bougainville
– Bougainville: Island of Scars – a very informative and touching article in the New Zealand Geographic
– bougainville24.com (lovely Blog by many writers on daily life plus pictures)