Pyroclastic flows from the 1991 eruption of Unzen volcano, Japan

Yamamoto, Takahiro; Takarada, Shinji; Suto, Shigeru

doi:10.1007/bf00301514

Cited by 146 publications

(99 citation statements)

References 30 publications

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“…In this analysis, horizontal distance is used, therefore, the speed along the mountain slope may be as much as 10% larger. These values are almost the same as that for pyroclastic flows measured by visual observations (e.g., Fukui et al, 1991;Yamamoto et al, 1993).…”

Section: Source Location and Amplitude Variation Of Infrasonic And Sesupporting

confidence: 86%

Quantitative Analysis of Pyroclastic Flows Using Infrasonic and Seismic Data at Unzen Volcano, Japan.

Yamasato

1997

J,Phys,Earth

108

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The process of the collapse of the dacitic lava dome and the development of pyroclastic flows at Unzen volcano, Japan, were studied using infrasonic, seismic and video records. Characteristic infrasonic and seismic signals were recorded corresponding to the collapse of lava blocks from the dome, the drop of blocks on the slope and the migration of pyroclastic flow on the mountain slope. Small infrasonic and seismic waves are excited when the lava dome starts to collapse. When the lava blocks fall onto the mountain slope and are fragmented, larger waves are excited. This suggests that the seismic waves are generated by the collision of pyroclastics on the mountain slope and that the infrasonic waves are excited by small fractures of the dome and the fragmentation of pyroclastics. Some of the infrasonic signals show an obvious Doppler effect, indicating that the pyroclastic flows emit infrasonic signals during their propagation. The location of dome collapse and the path of pyroclastic flows can be identified and traced by a network of low-frequency microphones. The migrating source of infrasonic signals and probably seismic signals is inferred to be located near the front of pyroclastic flows by comparison with video images. This suggests that the fragmentation of pyroclastics occurs mainly near the front of pyroclastic flows. The speed of pyroclastic flows is estimated as 10-30 m/s from the infrasonic records. The excitation of infrasonic and seismic signals is affected by the topography of the mountain slope. The infrasonic energy is almost the same order as the seismic energy but the ratio of infrasonic to seismic energies increases for larger and more mobile pyroclastic flows. This means that the development of pyroclastic flows is controlled not only by the volume of lava and gravitational force, but also by the explosivity related to the pore gases in the lava.

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Section: Source Location and Amplitude Variation Of Infrasonic And Sesupporting

confidence: 86%

Quantitative Analysis of Pyroclastic Flows Using Infrasonic and Seismic Data at Unzen Volcano, Japan.

Yamasato

1997

J,Phys,Earth

108

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“…The relationship between both the average carapace generation rate and the talus adjusted rate, and the extrusion rate is linear. This relationship is corroborated by various observations that rockfall activity, to a first order, varies with extrusion rate (Calder et al, 2005) and that at a larger scale pyroclastic flow is also extrusion rate dependant (Yamamoto et al, 1993;Uhira et al, 1994).…”

Section: 15: Average Carapace Generated and Talus Readjustedsupporting

confidence: 67%

Modelling the lava dome extruded at Soufrière Hills Volcano, Montserrat, August 2005–May 2006

Hale

Calder²,

Loughlin

et al. 2009

Journal of Volcanology and Geothermal Research

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During many lava dome-forming eruptions, persistent rockfalls and the concurrent development of a substantial talus apron around the foot of the dome are important aspects of the observed activity. An improved understanding of internal dome structure, including the shape and internal boundaries of the talus apron, is critical for determining when a lava dome is poised for a major collapse and how this collapse might ensue. We consider a period of lava dome growth at the Soufriere Hills dome growth using measured dome volumes and extrusion rates to drive the model and generate the evolving configuration of the dome core and carapace/talus domains. The evolution of the model is compared with the observed rockfall seismicity using event counts and seismic energy parameters, which are used here as a measure of rockfall intensity and hence a first-order proxy for volumes. The range of model-derived volume increments of talus aggraded to the talus slope per recorded rockfall event, approximately 3,000 -13,000 m 3 per rockfall, is high with respect to estimates based on observed events. From this, it is inferred that some of the volumetric growth of the talus apron (perhaps up to 60 -70%) might have occurred in the form of aseismic deformation of the talus, forced by an internal, laterally spreading core. Talus apron growth by this mechanism has not previously been identified, and this suggests that the core, hosting hot gas-rich lava, could have a greater lateral extent than previously considered.3

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“…PDCs may form from lava dome collapses, such as at Unzen (Yamamoto et al 1993;Fujii & Nakada 1999), and Merapi (Voight et al 2000;Bourdier & Abdurachman 2001); from column collapses, such as at Mount Vesuvius, Italy (Bullard 1962;Lirer et al 1973); or from directed blasts as at Mount St Helens, Washington, USA (Kieffer 1981;Moore & Sisson 1981); and the Boxing Day event at SHV Voight et al 2002). This work largely deals with PDCs generated by lava-dome collapse, but also includes two events that are, to some degree, transitional and include an explosive component.…”

Section: Previous Workmentioning

confidence: 99%

“…Ash-cloud surges can have a significant lateral component of motion, and have been known to detach and move independently from their parent flows (Fisher 1995). For example, decoupled pyroclastic surges were responsible for fatalities at Mt Pelée, Martinique in 1902 (Fisher & Heiken 1982); Unzen, Japan on 3 June 1991 (Yamamoto et al 1993); at Soufrière Hills Volcano (SHV), Montserrat on 25 June 1997 (Loughlin et al 2002a, b); and at Merapi Volcano, Indonesia on 18-19 December 1930, 22 November 1994and October -November 2010(Bourdier & Abdurachman 2001Smithsonian Institution 2011;Jenkins et al 2013). Several of these events, and their resultant deposits, have been well described and their dynamics analysed in detail retrospectively.…”

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confidence: 99%

Chapter 10 The effect of topography on ash-cloud surge generation and propagation

Ogburn

Calder

Cole

et al. 2014

Memoirs

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Abstract:The relationship between valley morphology and ash-cloud surge development for 12 pyroclastic density currents (PDCs) at Soufrière Hills Volcano (SHV), Montserrat is investigated. Channel slope, sinuosity and cross-sectional area were measured from highresolution digital elevation models (DEMs) using geographical information system (GIS) software; and were compared to geometric parameters of the deposits. The data illustrate three surge-generation regimes: a proximal area of rapid expansion; a medial deflation zone; and a steadier distal surge 'fringe'. The extent to which these regimes develop varies with flow volume. For larger flows, within the proximal and medial regimes, a strong inverse correlation exists between surge detachment and valley cross-sectional area. Surge detachment is also correlated with observed and modelled flow velocities. Areas of topography-induced increases in velocity are interpreted to result in more pervasive fragmentation and fluidization, and thus enhanced surge generation. Distally, surge deposits appear as fringes with decaying extents, indicative of more passive expansion and decreasing velocity. The results indicate that surge mobility and detachment are a complex product of flow mass flux and topography, and that future efforts to model dense-dilute coupled flows will need to account for and integrate several mechanisms acting on different parts of the flow.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.The development and subsequent decoupling of dilute, turbulent ash-cloud surges from dense basal pyroclastic flows is poorly understood, unpredictable and often results in deadly consequences. Ash-cloud surges can have a significant lateral component of motion, and have been known to detach and move independently from their parent flows (Fisher 1995). For example, decoupled pyroclastic surges were responsible for fatalities

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Pyroclastic flows from the 1991 eruption of Unzen volcano, Japan

Cited by 146 publications

References 30 publications

Quantitative Analysis of Pyroclastic Flows Using Infrasonic and Seismic Data at Unzen Volcano, Japan.

Quantitative Analysis of Pyroclastic Flows Using Infrasonic and Seismic Data at Unzen Volcano, Japan.

Modelling the lava dome extruded at Soufrière Hills Volcano, Montserrat, August 2005–May 2006

Chapter 10 The effect of topography on ash-cloud surge generation and propagation

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