Cyclic formation of debris avalanches at Mount St Augustine volcano

Begét, James E.; Kienle, J.

doi:10.1038/356701a0

Cited by 130 publications

(82 citation statements)

References 19 publications

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“…Instability of BZ, MSH and SHV could be intimately associated with the high magma viscosity and strength that results in much disturbance of a volcanic edifice during magma ascent, intrusion or extrusion, and thus frequently triggers large-scale sector collapses (Belousov et al 1999;Voight 2000). At the same time BZ, MSH and perhaps even SHV were apparently less unstable than Augustine, Egmont, Bandai, Shiveluch, and Harimkotan volcanoes, which throughout their histories generated numerous debris avalanches that were provoked by minor intrusions of viscous magmas, but produced no confirmed directed blasts (Beget and Kienle 1992;Palmer et al 1991;Yamamoto and Suto 1996;Belousov et al 1999;Belousov and Belousova 1996). However, a blast deposit was reported for Augustine by Siebert et al (1995), and a phreatic blast occurred at Bandai-san (Sekiya and Kikuchi 1889;Glicken and Nakamura 1988).…”

Section: Volcanic Edifices and Summary Of Past Eruptive Activitiesmentioning

confidence: 99%

Directed blasts and blast-generated pyroclastic density currents: a comparison of the Bezymianny 1956, Mount St Helens 1980, and Soufrière Hills, Montserrat 1997 eruptions and deposits

2007

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We compare eruptive dynamics, effects and deposits of the Bezymianny 1956 (BZ), Mount St Helens 1980 (MSH), and Soufrière Hills volcano, Montserrat 1997 (SHV) eruptions, the key events of which included powerful directed blasts. Each blast subsequently generated a high-energy stratified pyroclastic density current (PDC) with a high speed at onset. The blasts were triggered by rapid unloading of an extruding or intruding shallow magma body (lava dome and/or cryptodome) of andesitic or dacitic composition. The unloading was caused by sector failures of the volcanic edifices, with respective volumes for BZ, MSH, and SHV c. 0.5, 2.5, and 0.05 km 3 . The blasts devastated approximately elliptical areas, axial directions of which coincided with the directions of sector failures. We separate the transient directed blast phenomenon into three main parts, the burst phase, the collapse phase, and the PDC phase. In the burst phase the pressurized mixture is driven by initial kinetic energy and expands rapidly into the atmosphere, with much of the expansion having an initially lateral component. The erupted material fails to mix with sufficient air to form a buoyant column, but in the collapse phase, falls beyond the source as an inclined fountain, and thereafter generates a PDC moving parallel to the ground surface. It is possible for the burst phase to comprise an overpressured jet, which requires injection of momentum from an orifice; however some exploding sources may have different geometry and a jet is not necessarily formed. A major unresolved question is whether the preponderance of strong damage observed in the volcanic blasts should be attributed to shock waves within an overpressured jet, or alternatively to dynamic pressures and shocks within the energetic collapse and PDC phases. Internal shock structures related to unsteady flow and compressibility effects can occur in each phase. We withhold judgment about published shock models as a primary explanation for the damage sustained at MSH until modern 3D numerical modeling is accomplished, but argue that much of the damage observed in directed blasts can be reasonably interpreted to have been caused by high dynamic pressures and clast impact loading by an inclined collapsing fountain and stratified PDC. This view is reinforced by recent modeling cited for SHV. In distal and peripheral regions, solids concentration, maximum particle size, current speed, and dynamic pressure are diminished, resulting in lesser damage and enhanced influence by local topography on the PDC. Despite the different scales of the blasts (devastated areas were respectively 500, 600, and >10 km 2 for BZ, MSH, and SHV), and some complexity involving retrogressive slide blocks and clusters of explosions, their pyroclastic deposits demonstrate strong similarity. Juvenile material composes >50% of the deposits, implying for the blasts a dominantly magmatic mechanism although hydrothermal explosions also occurred. The character of the magma fragmented by explosions (highly viscous, phen...

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Section: Volcanic Edifices and Summary Of Past Eruptive Activitiesmentioning

confidence: 99%

Directed blasts and blast-generated pyroclastic density currents: a comparison of the Bezymianny 1956, Mount St Helens 1980, and Soufrière Hills, Montserrat 1997 eruptions and deposits

2007

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“…The Mount St. Helens avalanche deposit displays a hummocky landscape and distinctive features that enabled old debrisavalanche deposits to be recognised in volcanic regions worldwide (Ui 1983;Siebert 1984). Thus, it was discovered that large-scale slope failures were common events in the history of many volcanoes, and that some volcanoes experience multiple failures (Inokuchi 1988;Beget and Kienle 1992;Komorowski et al 1993;Siebert et al 1995;Belousov and Belousova 1996;Belousova 1994.…”

Section: Introductionmentioning

confidence: 99%

Multiple edifice failures, debris avalanches and associated eruptions in the Holocene history of Shiveluch volcano, Kamchatka, Russia

Belousov

Belousova

Voight

1999

Bulletin of Volcanology

168

114

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Investigation of well-exposed volcaniclastic deposits of Shiveluch volcano indicates that large-scale failures have occurred at least eight times in its history: approximately 10,000, 5700, 3700, 2600, 1600, 1000, 600 14 C BP and 1964 AD. The volcano was stable during the Late Pleistocene, when a large cone was formed (Old Shiveluch), and became unstable in the Holocene when repetitive collapses of a portion of the edifice (Young Shiveluch) generated debris avalanches. The transition in stability was connected with a change in composition of the erupting magma (increased SiO 2 from ca. 55-56% to 60-62%) that resulted in an abrupt increase of viscosity and the production of lava domes. Each failure was triggered by a disturbance of the volcanic edifice related to the ascent of a new batch of viscous magma. The failures occurred before magma intruded into the upper part of the edifice, suggesting that the trigger mechanism was indirectly associated with magma and involved shaking by a moderate to large volcanic earthquake and/or enhancement of edifice pore pressure due to pressurised juvenile gas. The failures typically included: (a) a retrogressive landslide involving backward rotation of slide blocks; (b) fragmentation of the leading blocks and their transformation into a debris avalanche, while the trailing slide blocks decelerate and soon come to rest; and (c) longdistance runout of the avalanche as a transient wave of debris with yield strength that glides on a thin weak layer of mixed facies developed at the avalanche base. All the failures of Young Shiveluch were immediately followed by explosive eruptions that developed along a similar pattern. The slope failure was the first event, followed by a plinian eruption accompanied by partial fountain collapse and the emplacement of pumice flows. In several cases the slope failure depressurised the hydrothermal system to cause phreatic explosions that preceded the magmatic eruption. The collapse-induced plinian eruptions were moderate-sized and ordinary events in the history of the volcano. No evidence for directed blasts was found associated with any of the slope failures.

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“…The pre-2006 eruption elevation was 1,260 m (4,134 ft) ASL and the exact change to summit elevation has yet to be determined. Repeated sector collapses during the late Holocene have produced debris avalanches into Cook Inlet (Begét and Kienle, 1992). Historical eruptions include significant activity in 1883, 1885, 1963-64, 1976, 1986, and 2005- …”

Section: Steam Plumes Rockfalls Installation Of Multigas Stationmentioning

confidence: 99%

2015 Volcanic activity in Alaska—Summary of events and response of the Alaska Volcano Observatory

Dixon¹,

Cameron²,

Iezzi³

et al. 2017

Scientific Investigations Report

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For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit https://www.usgs.gov or call 1-888-ASK-USGS.For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov.Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.Suggested citation: Dixon, J.P., Cameron, C.E., Iezzi, A.M., and Wallace, Kristi, 2017Kristi, , 2015 Volcanic activity in Alaska-Summary of events and response of the Alaska Volcano Observatory: U.S. Geological Survey Scientific Investigations Report 2017-5104, 61 p., https://doi.org/10.3133/sir20175104. DatumAltitude and elevation as used in this report, refers to distance above sea level, unless otherwise noted.Locations in latitude and longitude are presented in degrees and minutes rounded to the nearest minute referenced to the WGS 1984 datum. Supplemental InformationSpecific conductance is given in microsiemens per centimeter at 25 degrees Celsius (µS/cm at 25 °C).Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L) or micrograms per liter (µg/L).

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Cyclic formation of debris avalanches at Mount St Augustine volcano

Cited by 130 publications

References 19 publications

Directed blasts and blast-generated pyroclastic density currents: a comparison of the Bezymianny 1956, Mount St Helens 1980, and Soufrière Hills, Montserrat 1997 eruptions and deposits

Directed blasts and blast-generated pyroclastic density currents: a comparison of the Bezymianny 1956, Mount St Helens 1980, and Soufrière Hills, Montserrat 1997 eruptions and deposits

Multiple edifice failures, debris avalanches and associated eruptions in the Holocene history of Shiveluch volcano, Kamchatka, Russia

2015 Volcanic activity in Alaska—Summary of events and response of the Alaska Volcano Observatory

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