The 1951 eruption of Mount Lamington, Papua New Guinea: Devastating directed blast triggered by small-scale edifice failure

doi:10.1016/j.jvolgeores.2020.106947

Journal of Volcanology and Geothermal Research

Volume 401, 1 September 2020, 106947

https://doi.org/10.1016/j.jvolgeores.2020.106947 Get rights and content

Highlights

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We present results of field reinvestigation of pyroclastic deposits of the 1951 catastrophic eruption of Mount Lamington volcano, Papua New Guinea.
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Six-days-long pre-climactic activity was associated with intrusion of small cryptodome /dome.
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As a result of edifice destabilization a small-volume debris avalanche with volume ~ 0.03 km³ was produced. The edifice collapse triggered explosive fragmentation of the dome and climactic explosion.
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The eruptive cloud initially rose vertically but subsequently collapsed and formed PDC which flowed radially.
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The 1951 blast of Mt.Lamington is similar to blasts of volcanoes Bezymianny (1956), St.Helens (1980), and Montserrat (1997).

Abstract

The catastrophic explosion of Mount Lamington volcano, Papua New Guinea on January 21, 1951 produced a devastating pyroclastic density current (PDC) that knocked down dense tropical rainforest over an area of 230 km² and killed approximately 3000 people. We present results of a field reinvestigation of the 1951 PDC deposit combined with an analysis of the available photographs and eyewitness accounts of the eruption first published in the fundamental work of G. A. M. Taylor (1958).

We have concluded that the six-days-long pre-climactic activity before the 1951 eruption (which included felt local seismicity, frequent ash-laden explosions of vulcanian type, bulging of the volcano slope accompanied with landslides) was associated with shallow-level intrusion of a highly viscous magma body (cryptodome/dome) of andesitic composition with a volume of approximately 0.01 km³. This intrusion destabilized Mount Lamington's prehistoric intra-crater lava dome.

On January 21 the destabilized dome gravitationally collapsed and produced a relatively small-volume debris avalanche, the deposit of which was not recognized during Taylor's original investigation. The debris avalanche had a volume of approximately 0.02–0.04 km³, travelled a distance (L) of 8.5 km and had the ratio of vertical drop (H) to runout (L) of 0.14. The edifice collapse decompressed the intruding cryptodome and triggered its explosive fragmentation.

Photographs of the climactic explosion show that the eruptive cloud initially rose vertically but subsequently collapsed upon the terrain around the vent, and formed a PDC which flowed radially outward. The enhanced northward propagation of the PDC to a maximum distance of 13 km reveals that the northern breach in the ancient crater's high walls influenced the distribution of the deposit. In the studied NE-N-NW sector of the devastated area, in the zone proximal to the volcano, the PDC emplaced a normally graded layer of coarse ash and lapilli mixed in the base with picked-up soil and plant fragments. The layer gradually becomes thinner and finer-grained with distance from the volcano. The PDC deposit has a volume of approximately 0.025 km³ and consists of approximately 80% juvenile rock fragments derived from the explosively fragmented cryptodome. The remaining 20% consists of accidental clasts derived from the old volcanic edifice. The juvenile material is crystal-rich andesite with a unimodal vesicularity distribution (4 to 36%). The reconstructed eruption sequence, the PDC tree blowdown pattern and characteristics of the PDC deposit are similar to those of catastrophic laterally-directed blasts of volcanoes Bezymianny in 1956, Mount St.Helens in 1980, and Soufriere Hills, Montserrat in 1997. In contrast to the cases of these “classic” lateral blasts, the blast cloud of Lamington was initially vertically-directed before collapsing to produce a PDC. We speculate that the climactic explosion of Mount Lamington was initially vertical because the rupture surface of the triggering sector collapse intersected the apex of the intruding cryptodome (it exposed a subhorizontal surface of the cryptodome apex), while at Bezymianny, Mount St.Helens, and Soufriere Hills the rupture intersected the main body of the cryptodome/dome, and exposed their steeply inclined surfaces.

Introduction

The “directed blast” type of volcanic explosions was first described by G. Gorshkov (1963) who studied the 1956 eruption of Bezymianny volcano in Kamchatka, Russia (Gorshkov, 1959; Belousov, 1996). This blast, which involved approximately 0.15 km³ of magma, toppled and singed vegetation over an elliptically-shaped area of 500 km², with the volcano at one of the ellipse foci. A remarkably similar explosive event at Mount St. Helens In 1980 was described as “lateral blast” (Hoblitt et al., 1981). Comparison of these two eruptions with a much smaller blast at Soufriere Hills volcano on Montserrat in the Lesser Antilles in 1997 allowed Belousov et al., 2007 to summarize the main features of this peculiar type of volcanic eruption. Directed/lateral blasts occur under certain conditions during shallow intrusions (cryptodomes) and/or extrusions (domes) of viscous magma. A characteristic feature of a directed blast is the inclined ejection of a gas-pyroclastic mixture that initially is denser than air and thus not buoyant. Consequently, the ejected mixture gravitationally collapses and generates a highly inflated, mobile, and destructive pyroclastic density current (PDC). The inclined character of the initial ejection produces a radially asymmetric but bilaterally symmetric PDC or blast PDC (after Belousov et al., 2007). Lateral blasts at Bezymianny, Mount St. Helens and Soufriere Hills, Montserrat were all triggered by voluminous landslides (sector collapses) from the volcanoes' flanks (Belousov et al., 2007). These landslides unloaded the intruding /extruding magma body that led to its explosive fragmentation with inclined (“lateral” or “directed”) ejection of the resulted gas-pyroclastic mixture oriented in the direction of the triggering landslide. These three well-documented eruptions were described in multiple research papers and thus can be called “classic” blasts. Two other notable eruptions of the 20th century that can be tentatively (because of the lack of some critical observational data about their eruption courses and deposits) classified as directed blasts are the May 8, 1902 eruption of Mount Pelée on Martinique (Lacroix, 1904) and the January 21, 1951 eruption of Mount Lamington in Papua New Guinea (Taylor, 1958).

The catastrophic explosion of Mount Lamington produced a pyroclastic density current (PDC) that knocked down dense tropical forest over an area of 230 km² and killed approximately 3000 people. The PDC impact—its tree blowdown pattern, estimated temperature (200 °C), and propagation velocity (27–94 m/s) (Taylor, 1958)—are similar to those of the classic blast PDCs (Belousov et al., 2007).

We present results of our field reinvestigation of the 1951 deposits combined with the analysis of the available photographs and eyewitness accounts of the eruption first published in the fundamental work of G.A.M. Taylor (1958). At the time of Taylor's study, the relationships between sector collapses, debris avalanche deposits, and lateral blasts were completely unknown. Our main goals were to study the deposits, to reconstruct the eruptive sequence of the 1951 eruption, and to access the similarity/dissimilarity to the classic lateral blasts. This comparison allows us to better understand the mechanisms of blast-generating eruptions. We also present new data constraining ages and origin of deposits that pre-date the 1951 eruption in order to place this eruption in context of the volcano's eruption history.

Section snippets

Sampling

Our mapping and sampling of the 1951 erupted products was conducted in two field campaigns: in 1982 by R. Hoblitt (Hoblitt, 1982) and in 2010 by A.Belousov, M.Belousova, and H. Patia correspondingly in 11 and 60 locations shown on Fig. 1b. For grain size, component analyses, and density/vesicularity measurements, 113 samples (1–3 kg each, depending on the grain size of the sampled deposit) were collected (23 in 1982 and 90 in 2010).

Sampling of volcaniclastic deposits that pre-date the 1951

Regional tectonics and geology

Mount Lamington is located in the eastern part of the island of New Guinea on the Papuan Peninsula (Fig. 1a). This region has one of the most complex tectonic regimes on Earth (Fig. 2). Here the Australian Plate moving towards north-northeast obliquely collides with the Pacific Plate that moves towards west-southwest at 110 mm/year with a convergent component of 70 mm/year across the New Guinea region (Tregoning and Gorbatov, 2004). The collision led to fragmentation of the plate edges into

Pre-climactic activity

No instrumental monitoring of the volcano existed before the eruption. The available observational data on the pre-climactic activity (pp. 12–14 from Taylor (1983), 2nd edition of Taylor (1958)) and our interpretations of the volcanic phenomena are summarized in Table 2.

The first signs of the unrest were occasional slight earth tremors that residents of the settlements nearest to the volcano started to feel since the beginning of January 1951. With time these tremors became stronger and more

Deposits of the 1951 blast PDC

As noted by Taylor (pp.63–64 from Taylor, 1983), the deposit of January 21, 1951 climactic eruption consisted of a relatively thin, extensive component that covered the entire devastated area (the deposit of “ash hurricane”) (Fig. 8) and relatively thick “ponderous ash flow nuee ardentes” that filled some river valleys (Fig. 9).

In the course of our field work at Mount Lamington conducted in 1982 (Hoblitt, 1982) and then in 2010 we found that in distal areas, where the blast PDC deposit (the

Discussion

Preclimactic activity before the January 21, 1951 explosion of Mount Lamington in many aspects resembles the preclimactic activity observed before blasts of Bezymianny in 1956, and Mount St. Helens in 1980 (Table 5). In the Bezymianny and Mount St. Helens examples, the preclimactic activity was associated with the slow ascent/ intrusion of highly viscous magma into shallow levels beneath as well as inside the edifices of the volcanoes. Thus it is plausible to conclude that at Mount Lamington

Conclusions

The reconstructed mechanism of the 1951 eruption of Mount Lamington (cryptodome intrusion + edifice failure + blast with generation of the devastating PDC) as well as the effects and characteristics of the blast PDC deposit are similar to those of “classic” directed blasts at Bezymianny, Mount St. Helens, and Soufriere Hills on Montserrat.

We attribute the salient differences (more symmetric area of devastation and less pronounced layering of the blast deposit) to the fact that the Lamington

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research would not be possible without remarkable field assistance of volcanologist Herman Patia (Rabaul Volcano Observatory, PNG), who untimely passed away in 2012. Funding for field trip to Lamington in 2010 (for A.B., M.B. and H.P.) and analytic works was provided by Earth Observatory of Singapore (Nanyang Technological University) and for R.H in 1982 by USGS. Wally Johnson helped us to search data about the 1951 eruption in various archives in Australia. The National Library of

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¹: Passed away.

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The 1951 eruption of Mount Lamington, Papua New Guinea: Devastating directed blast triggered by small-scale edifice failure

Highlights

Abstract

Introduction

Section snippets

Sampling

Regional tectonics and geology

Pre-climactic activity

Deposits of the 1951 blast PDC

Discussion

Conclusions

Declaration of competing interest

Acknowledgements

J. Volcanol. Geotherm. Res.

J. Volcanol. Geotherm. Res.

Tectonophysics

J. Volcanol. Geotherm. Res.

J. Volcanol. Geotherm. Res.

J. Volcanol. Geotherm. Res.

Tectonophysics

Lithos

J. Volcanol. Geotherm. Res.

Preliminary note on volcanic eruptions in the Goropu Mountains, southeastern Papua, during the period December, 1943, to August, 1944

J. Geol.

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Annual Rev. Earth Planet. Sci.

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