The initial giant umbrella cloud of the May 18th, 1980, explosive eruption of Mount St. Helens

Sparks, R. S. J.; Moore, James G.; Rice, C. J.

doi:10.1016/0377-0273(86)90026-0

Cited by 145 publications

(92 citation statements)

References 11 publications

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“…Kieffer and Sturtevant (1988) assumed 10 kg m −3 for flow density at MSH for a boundary layer 14 m thick at ∼9 km from source, but in contrast for a region 15-18 km from source at MSH, Bursik et al (1998) calculated a bulk current density of 1.5 kg m −3 , only 36% greater than atmospheric density at a similar altitude (1.1 kg m −3 ). The latter value is consistent with the buoyant lift-off that occurred about 5 min after blast initiation, generating a giant plume that carried about 30% by mass of the PDC (Sparks et al 1986). The lift-off was enabled by progressive loss from the PDC of particles by sedimentation, and by airentrainment and heating, thus reducing current density to less than atmospheric density.…”

Section: Directed Blast Effectssupporting

confidence: 78%

“…Zones of devastation produced by the blasts and associated PDCs coincide approximately with the regions covered by their deposits, excluding the fallout from the thermal plume rising above the blast-affected area (Sparks et al 1986;Sisson 1995). For BZ and MSH they have similar areas, 500 and 600 km 2 , respectively (Gorshkov 1959;Lipman and Mullineaux 1981); the total area of the SHV blast zone, excluding an unknown part in the sea, has been estimated as ∼10 km 2 .…”

Section: Directed Blast Effectsmentioning

confidence: 80%

“…The deposit is veneered at all locations by an uppermost layer D of fines and accretionary lapilli (layer A3 of Fisher 1990; blast ashfall of Sisson 1995; Unit 3 of Ritchie et al 2002), which is an ash fallout deposit of the finest particles from the high-rising thermal plume associated with the blast PDC (Sparks et al 1986;Mayberry et al 2002). This layer is dispersed over a wider region than that affected directly by the PDC and represents about 30% of the mass carried by the PDC (Sparks et al 1986).…”

Section: Interfluve Faciesmentioning

confidence: 99%

“…This layer is dispersed over a wider region than that affected directly by the PDC and represents about 30% of the mass carried by the PDC (Sparks et al 1986). …”

Section: Interfluve Faciesmentioning

confidence: 99%

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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: Directed Blast Effectssupporting

confidence: 78%

Section: Directed Blast Effectsmentioning

confidence: 80%

Section: Interfluve Faciesmentioning

confidence: 99%

“…This layer is dispersed over a wider region than that affected directly by the PDC and represents about 30% of the mass carried by the PDC (Sparks et al 1986). …”

Section: Interfluve Faciesmentioning

confidence: 99%

See 2 more Smart Citations

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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“…These satellites are the backbone of the global missile early warning system and make observations of the Earth in the shortwave IR regions, with 10-s revisit rate (Pack et al 2000). DoD scientists have documented the detection of volcanic eruptions in this imagery and have reported evidence for a characteristic spike in radiance coincident with the initiation of explosive eruptions (Moore and Rice 1984;Sparks et al 1986;Pack et al 2000). The attenuation of IR radiation by intervening cloud and water vapor places documented limitations on the detection of all eruptions.…”

Section: Fig 9 Cloud (A) Liquid Water Path and (B) Effective Radiusmentioning

confidence: 99%

Aviation Applications for Satellite-Based Observations of Cloud Properties, Convection Initiation, In-Flight Icing, Turbulence, and Volcanic Ash

Mecikalski¹,

Feltz²,

Murray³

et al. 2007

Bulletin of the American Meteorological Society

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Modeling ash fall distribution from a Yellowstone supereruption

Mastin

Eaton

Lowenstern

2014

Geochem Geophys Geosyst

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We used the volcanic ash transport and dispersion model Ash3d to estimate the distribution of ashfall that would result from a modern-day Plinian supereruption at Yellowstone volcano. The simulations required modifying Ash3d to consider growth of a continent-scale umbrella cloud and its interaction with ambient wind fields. We simulated eruptions lasting 3 days, 1 week, and 1 month, each producing 330 km 3 of volcanic ash, dense-rock equivalent (DRE). Results demonstrate that radial expansion of the umbrella cloud is capable of driving ash upwind (westward) and crosswind (N-S) in excess of 1500 km, producing more-or-less radially symmetric isopachs that are only secondarily modified by ambient wind. Deposit thicknesses are decimeters to meters in the northern Rocky Mountains, centimeters to decimeters in the northern Midwest, and millimeters to centimeters on the East, West, and Gulf Coasts. Umbrella cloud growth may explain the extremely widespread dispersal of the 640 ka and 2.1 Ma Yellowstone tephra deposits in the eastern Pacific, northeastern California, southern California, and South Texas.

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The initial giant umbrella cloud of the May 18th, 1980, explosive eruption of Mount St. Helens

Cited by 145 publications

References 11 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

Aviation Applications for Satellite-Based Observations of Cloud Properties, Convection Initiation, In-Flight Icing, Turbulence, and Volcanic Ash

Modeling ash fall distribution from a Yellowstone supereruption

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