A volcanologist's review of atmospheric hazards of volcanic activity: Fuego and Mount St. Helens

Rose, William I.; Wunderman, Richard; Hoffman, Mary F.; Gale, Lisa

doi:10.1016/0377-0273(83)90065-3

Cited by 48 publications

(10 citation statements)

References 28 publications

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“…The coarser grainsize of the Fuego and Ruapehu tephra fall deposits thus appear to be a fundamental characteristic of subplinian eruptions as opposed to more powerful Plinian eruptions. The Fuego initial GSD population is unimodal at both 1ϕ and 0.5ϕ intervals (Rose et al 1983, their Fig. 3), and is also unimodal without incorporation of the pyroclastic flow deposit data (Fig.…”

Section: Deposit Densitymentioning

confidence: 99%

Nature and significance of small volume fall deposits at composite volcanoes: Insights from the October 14, 1974 Fuego eruption, Guatemala

et al. 2007

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The first of four successive pulses of the 1974 explosive eruption of Fuego volcano, Guatemala, produced a small volume (∼0.02 km3 DRE) basaltic sub-plinian tephra fall and flow deposit. Samples collected within 48 h after deposition over much of the dispersal area (7–80 km from the volcano) have been size analyzed down to 8 φ (4 µm). Tephra along the dispersal axis were all well-sorted (σ φ = 0.25–1.00), and sorting increased whereas thickness and median grain size decreased systematically downwind. Skewness varied from slightly positive near the vent to slightly negative in distal regions and is consistent with decoupling between coarse ejecta falling off the rising eruption column and fine ash falling off the windblown volcanic cloud advecting at the final level of rise. Less dense, vesicular coarse particles form a log normal sub-population when separated from the smaller (Mdφ < 3φ or < 0.125 mm), denser shard and crystal sub-population. A unimodal, relatively coarse (Mdφ = 0.58φ or 0.7 mm σ φ = 1.2) initial grain size population is estimated for the whole (fall and flow) deposit. Only a small part of the fine-grained, thin 1974 Fuego tephra deposit has survived erosion to the present day. The initial October 14 pulse, with an estimated column height of 15 km above sea level, was a primary cause of a detectable perturbation in the northern hemisphere stratospheric aerosol layer in late 1974 to early 1975. Such small, sulfur-rich, explosive eruptions may substantially contribute to the overall stratospheric sulfur budget, yet leave only transient deposits, which have little chance of survival even in the recent geologic record. The fraction of finest particles (Mdφ = 4–8φ or 4–63 µm) in the Fuego tephra makes up a separate but minor size mode in the size distribution of samples around the margin of the deposit. A previously undocumented bimodal–unimodal–bimodal change in grain size distribution across the dispersal axis at 20 km downwind from the vent is best accounted for as the result of fallout dispersal of ash from a higher subplinian column and a lower “co-pf” cloud resulting from pyroclastic flows. In addition, there is a degree of asymmetry in the documented grain-size fallout pattern which is attributed to vertically veering wind direction and changing windspeeds, especially across the tropopause. The distribution of fine particles (<8 µm diameter) in the tephra deposit is asymmetrical, mainly along the N edge, with a small enrichment along the S edge. This pattern has hazard significance

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Section: Deposit Densitymentioning

confidence: 99%

Nature and significance of small volume fall deposits at composite volcanoes: Insights from the October 14, 1974 Fuego eruption, Guatemala

et al. 2007

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“… b Rose et al [1983, Table 4, p. 143]. In addition to an average of 64 wt % glass, the ash contains, in decreasing proportions, plagioclase feldspar, opx, amphibole, magnetite, ilmenite, and cpx. …”

Section: Samplesmentioning

confidence: 99%

Scattering matrices of volcanic ash particles of Mount St. Helens, Redoubt, and Mount Spurr Volcanoes

et al. 2004

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[1] We present measurements of the whole scattering matrix as a function of the scattering angle at a wavelength of 632.8 nm in the scattering angle range 3°-174°of randomly oriented particles taken from seven samples of volcanic ashes corresponding to four different volcanic eruptions: the 18 May 1980 Mount St. Helens eruption, the [1989][1990] Redoubt eruption, and the 18 August and 17 September 1992 Mount Spurr eruptions. The samples were collected at different distances from the vent. The samples studied contain large mass fractions of fine particles and were chosen to represent ash that could remain in the atmosphere for at least hours or days. They include fine ashfall samples that fell at a variety of distances from the volcano and pyroclastic flows that retained their fine fractions. Together, they represent a range of ashes likely to remain in the atmosphere in volcanic clouds following eruptions from convergent plate boundary volcanoes, Earth's most important group of explosive sources of ash. All measured scattering matrix elements are confined to rather limited domains when plotted as functions of the scattering angle following the general trends presented by irregular mineral particles. This similarity in the scattering behavior justifies the construction of an average scattering matrix for volcanic ash particles as a function of the scattering angle. To facilitate the use of the average scattering matrix for multiple-scattering calculations with polarization included, we present a synthetic scattering matrix based on the average scattering matrix for volcanic ashes and the assumption that the diffraction forward scattering peak is the same for randomly oriented nonspherical particles and projected-surface-area-equivalent spheres. This synthetic scattering matrix is normalized so that the average of its 1-1 element over all directions equals unity. It is available in the full range from 0°to 180°and can be used, for example, for interpretation of remote-sensing data after a volcanic eruption when the actual properties of the volcanic ash are not known. The measured results for the Mount St. Helens sample have been compared with results of Lorenz-Mie calculations for projected-surface-area-equivalent spheres with the refractive index of the Mount St. Helens particles. We find strong differences between measured and calculated values.

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“…However, other observations are not consistent with this hypothesis. Fresh large pumices collected near Mount St. Helens after the May 18 eruptions have total S content of <20 ppm [Rose et al, 1983]. Perhaps the rocks and pumice close to Mount St. Helens' cone represent magma from the top of the magma reservoir, magma already partially &gassed in SO2.…”

Section: Nearlymentioning

confidence: 99%

Sulfur dioxide content of Mount St. Helens' ash

Weschler¹

1984

J. Geophys. Res.

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A rapid heating (980°C)‐gas chromatographic‐mass spectrometric technique was developed to measure the SO2 produced from Mt. St. Helens' ash collected after the May 18, 1980, eruption. The average values of evolved SO2 for ash samples from Moses Lake, Missoula, and Helena are 215, 800, and 1250 ppm, respectively. The results suggest that the SO2 is associated primarily with new magmatic material. Experiments indicate that the SO2 is not due to sulfate species scavenged from the eruption plume or to sulfur gases adsorbed on the ash. Other possible sources include reduction of sulfate salts within the ash, bubbles of SO2 trapped within the ash, or sulfur blebs contained in the ash. Approximately as much SO2 or SO2 precursors are associated with the ash as Mount St. Helens injected into the stratosphere.

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A volcanologist's review of atmospheric hazards of volcanic activity: Fuego and Mount St. Helens

Cited by 48 publications

References 28 publications

Nature and significance of small volume fall deposits at composite volcanoes: Insights from the October 14, 1974 Fuego eruption, Guatemala

Nature and significance of small volume fall deposits at composite volcanoes: Insights from the October 14, 1974 Fuego eruption, Guatemala

Scattering matrices of volcanic ash particles of Mount St. Helens, Redoubt, and Mount Spurr Volcanoes

Sulfur dioxide content of Mount St. Helens' ash

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