Fragmentation of debris avalanche material during flowage — Evidence from the Pungarehu Formation, Mount Egmont, New Zealand

Ui, Tadao; Kawachi, Shigeo; Neall, Vincent E.

doi:10.1016/0377-0273(86)90016-8

Cited by 65 publications

(25 citation statements)

References 5 publications

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“…This best-fit model-based particle diameter was greater than the median size of small-volume samples, and was perhaps also larger than field values even if much larger sample sizes were considered, although we must also recognize that fragmentation occurred during the flowage process (cf. Ui et al 1986). In part this result may reflect the very small range of sizes considered in the original Pouliquen analysis, and also the need to extrapolate the size calibration procedure lo very poorly sorted materials.…”

Section: Discussion Of Model Resultsmentioning

confidence: 99%

“…Some volcanoes, such as Mount St Augustine (Alaska), Shiveluch (Kamchatka, Russia) and Egmont (New Zealand) have collapsed repeatedly (Beget & Kienle 1992;Belousov et al 1999;Ui et al 1986;Palmer et al, 1991). Work by Boudon et al (1999) and Deplus et al (1999) has shown that volcanoes in the Carribbean arc also have been prone to sector collapse in the past.…”

Section: Comparisons and Contrastsmentioning

confidence: 99%

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The 26 December (Boxing Day) 1997 sector collapse and debris avalanche at Soufrière Hills Volcano, Montserrat

Voight

Komorowski²,

Norton

et al. 2002

Memoirs

102

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Abstract:The southern sector of Soufriere Hills Volcano failed on 26 December 1997 (Boxing Day), after a year of disturbance culminating in a devastating eruptive episode. Sector collapse produced a c. 50 x l0 6 m 3 volcanic debris avalanche, and depressurized the interior of the lava dome, which exploded to generate a violent pyroclaslic density current. The south-directed growth of a lava lobe and build-up of lava-block talus, since early November 1997. brought the hydrothermally weakened sector to a condition of marginal stability. Limit-equilibrium stability analyses and finite-difference stress-deformation analyses, constrained by geomechanical testing of edifice and debris avalanche materials, suggest that the sector collapse was triggered by a pulse of co-seismic exogenous lava shear-lobe emplacement. Slip-surface localization was influenced by strain-weakening.The source region fragmented into avalanche megablocks, and further disruption generated a chaotic avalanche mixture that included variably indurated and coloured hydrothermally altered material, and much talus. The avalanche consisted of several flow pulses that reflected complexities of source disruption and channel topography. In the proximal zone, within 1.5 km from source, many megablocks preserve pre-collapse stratigraphy. At major bends the avalanche separated into channelled and overspill flows. In the distal region, >2.5 km from source, stacked sets of the main lithologies occur with a hummocky surface and abrupt flowage snouts, beyond which sparse hummocks occur in a thinly spread deposit. Textures suggest emplacement by laminar mass transport of partly saturated debris riding on a frictionally sheared base. Three-dimensional numerical simulations of emplacement governed by a Coulomb-type (Pouliquen) basal friction law imply low values of friction (< 15 o ), consistent with geotechnical test data and the localized presence of pore-water pressures. The best-fit model suggests an emplacement time <3 minutes and a typical maximum velocity of about 40 ms -1 , which are consistent with field estimates.Following over a year of disturbance, the southern flank of Soufriere Hills Volcano failed on 26 December (Boxing Day) 1997, generating the most devastating episode of the entire eruption . The complex series of events resembles, on a smaller scale, the debris avalanche and directed blast that occurred at Mount St Helens in 1980 (Lipman & Mullineaux 1981. At Soufriere Hills, an andesilic lava dome had grown over the unstable, hydrothermally weakened southern sector of the edifice. When this sector collapsed on Boxing Day, the interior of the lava dome was exposed and depressurized, and it exploded to generate a powerful pyroclastic density current that ravaged the southwestern flank and entered the sea. This paper focuses on the mechanics of the sector collapse and on the emplacement dynamics, characteristics and properties of the deposit of the resulting debris avalanche (Fig. I). It is based primarily on fieldwork conducted at various times i...

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Section: Discussion Of Model Resultsmentioning

confidence: 99%

Section: Comparisons and Contrastsmentioning

confidence: 99%

The 26 December (Boxing Day) 1997 sector collapse and debris avalanche at Soufrière Hills Volcano, Montserrat

Voight

Komorowski²,

Norton

et al. 2002

Memoirs

102

View full text Add to dashboard Cite

show abstract

“…All these characters are those of the blocks and matrix facies of a volcanic debris -avalanche (Ui et al 1986). …”

Section: On-land Investigationsmentioning

confidence: 99%

“…Ignimbrite deposits typically present a fiat surface. In contrast, debris-avalanche deposits are characterized by a typical hummocky surface (Ui et al 1986). …”

Section: Hummocky Morphologymentioning

confidence: 99%

Emplacement of a Debris Avalanche during the 1883 eruption of Krakatau (Sunda Straits, Indonesia)

et al. 1992

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“…The most spectacular of these three deposits is the Pungarehu Formation with an estimated minimum volume of 7.5 km 3 . This deposit was mapped between 10 and 27 km from the present summit and covers an area of between 200 and 250 km 2 (Neall 1979; Ui et al 1986). In this study, two previously unrecognised debris-avalanche deposits have been identified on the eastern flanks of Egmont Volcano beneath a thick mantle of tephric and andic soil material, as well as laharic deposits that have mostly subdued their topographic expression.…”

Section: Introductionmentioning

confidence: 99%

Stratigraphy, age, and correlation of voluminous debris‐avalanche events from an ancestral Egmont Volcano: Implications for coastal plain construction and regional hazard assessment

Alloway

McComb²,

Neall

et al. 2005

Journal of the Royal Society of New Zealand

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Fragmentation of debris avalanche material during flowage — Evidence from the Pungarehu Formation, Mount Egmont, New Zealand

Cited by 65 publications

References 5 publications

The 26 December (Boxing Day) 1997 sector collapse and debris avalanche at Soufrière Hills Volcano, Montserrat

The 26 December (Boxing Day) 1997 sector collapse and debris avalanche at Soufrière Hills Volcano, Montserrat

Emplacement of a Debris Avalanche during the 1883 eruption of Krakatau (Sunda Straits, Indonesia)

Stratigraphy, age, and correlation of voluminous debris‐avalanche events from an ancestral Egmont Volcano: Implications for coastal plain construction and regional hazard assessment

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