Size Distributions and Mineralogy of Ash Particles in the Stratosphere from Eruptions of Mount St. Helens

Farlow, N. H.; Oberbeck, V. R.; Snetsinger, K. G.; Ferry, G. V.; Polkowski, G.; Hayes, Dennis M.

doi:10.1126/science.211.4484.832

Cited by 65 publications

(46 citation statements)

References 7 publications

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“…A further challenge for volcanic ash detection is that usually volcanic eruptions also emit substantial amounts of sulfur dioxide, which forms sulfate aerosol or leads to a liquid sulfate coating on ash particles typically on a timescale of a few days after the eruption (Farlow et al, 1981). Infrared limb measurements are highly sensitive to atmospheric particles and can be severely affected by enhanced stratospheric sulfate aerosol as happened after the Mt.…”

Section: Sulfate Aerosol Simulationsmentioning

confidence: 99%

“…For this reason we restricted the simulations to particle size distributions with median radii up to 5 µm. In situ measurements of small volcanic ash particles in the middle troposphere and UTLS found particle concentrations ranging from 7 × 10 −4 to 40 cm −3 (Mossop, 1964;Farlow et al, 1981;Schumann et al, 2011). This most likely range is highlighted in Table 4.…”

Section: Volcanic Ash Simulationsmentioning

confidence: 99%

“…The extinction coefficients, particle size distribution median radii and the corresponding particle concentrations used for the simulations are given in Table 5. The most likely range of sulfate aerosol particle sizes and concentrations covering undisturbed and volcanically enhanced conditions is underlined according to in situ (Mossop, 1964;Farlow et al, 1981;Deshler et al, 1992Deshler et al, , 1993 and remote sensing measurements (Stothers, 2001;Bauman et al, 2003). Table 5.…”

Section: Sulfate Aerosol Simulationsmentioning

confidence: 99%

“…Tian et al, 2010), volcanic ash (e.g. Farlow et al, 1981) and sulfate aerosol clouds (e.g. Deshler et al, 1992Deshler et al, , 1993.…”

Section: Simulation Setupmentioning

confidence: 99%

“…The median radii (µ) of the corresponding particle size distributions are given in Table 2 together with the scattering radii (r sca ) that are weighted by the Mie scattering efficiency (Q sca ) and the effective radii (r eff ) that solely depend on the particle size distribution. Because volcanic ash size distributions have widths ranging from 1.1 to 2.2 (Farlow et al, 1981;Pueschel et al, 1994) we chose a constant width of 1.6, which is in the middle. Figure 2 shows that with increasing particle size the increase of the extinction coefficient from 825 to 950 cm −1 becomes smaller and disappears for a scattering radius of 4.9 µm.…”

Section: From Optical Properties To Infrared Limb Spectramentioning

confidence: 99%

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Volcanic ash detection with infrared limb sounding: MIPAS observations and radiative transfer simulations

Grießbach¹,

Hoffmann²,

Spang³

et al. 2014

Atmos. Meas. Tech.

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Abstract. Small volcanic ash particles have long residence times in the troposphere and the stratosphere so that they have significant impact on the Earth's radiative budget and consequently affect climate. For global long-term observations of volcanic aerosol, infrared limb measurements provide excellent coverage, sensitivity to thin aerosol layers, and altitude information. The optical properties of volcanic ash and ice particles, derived from micro-physical properties, have opposing spectral gradients between 700 and 960 cm −1 for small particle sizes. Radiative transfer simulations that account for single scattering showed that the opposing spectral gradients directly transfer to infrared limb spectra. Indeed, we found the characteristic spectral signature, expected for volcanic ash, in measurements of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) after the eruption of the Chilean volcano Puyehue-Cordón Caulle in June 2011. From these measurements we derived an ash detection threshold function. The empirical ash detection threshold was confirmed in an extensive simulations study covering a wide range of atmospheric conditions, particle sizes and particle concentrations for ice, volcanic ash and sulfate aerosol. From the simulations we derived the upper detectable effective radius of 3.5 µm and the detectable extinction coefficient range of 5 × 10 −3 to 1 × 10 −1 km −1 . We also showed that this method is only sensitive to volcanic ash particles, but not to volcanic sulfate aerosol. This volcanic ash detection method for infrared limb measurements is a fast and reliable method and provides complementary information to existing satellite aerosol products.

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Section: Sulfate Aerosol Simulationsmentioning

confidence: 99%

Section: Volcanic Ash Simulationsmentioning

confidence: 99%

Section: Sulfate Aerosol Simulationsmentioning

confidence: 99%

“…Tian et al, 2010), volcanic ash (e.g. Farlow et al, 1981) and sulfate aerosol clouds (e.g. Deshler et al, 1992Deshler et al, , 1993.…”

Section: Simulation Setupmentioning

confidence: 99%

Section: From Optical Properties To Infrared Limb Spectramentioning

confidence: 99%

See 3 more Smart Citations

Volcanic ash detection with infrared limb sounding: MIPAS observations and radiative transfer simulations

Grießbach¹,

Hoffmann²,

Spang³

et al. 2014

Atmos. Meas. Tech.

View full text Add to dashboard Cite

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Impact of the lateral blast on the spatial pattern and grain size characteristics of the 18 May 1980 Mount St. Helens fallout deposit

et al. 2015

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The 18 May 1980 eruption of Mount St. Helens started with a lateral blast that fed a pyroclastic surge, which then uplifted to form a co‐blast plume. Thirty minutes later, Plinian activity started at the vent and fluctuated in intensity for ~9 h. The resulting fallout deposit, documented to > 600 km from vent, presents some striking features: (1) displacement of the overall deposit to the north of the vent, (2) a secondary thickness and mass maximum at ~300 km from vent, (3) a total grain size distribution dominated by fine ash (62 wt % of the deposit < 63 µm), and (4) individual grain size distributions that vary dramatically in the crosswind direction from strongly bimodal in the south to skewed unimodal in the north. Results from a new deconvolution of the individual grain size distributions show that they are a combination of a coarse subpopulation that decreases in size with distance from vent and a constant fine subpopulation with a mean of ∼15 µm. Relative proportions of each subpopulation vary asymmetrically in the crosswind directions, with the fine subpopulation preponderant toward the north and the coarse one dominating the south of the deposit, both reach their absolute maxima in mass on the deposit axis. Componentry analyses of selected samples show that blast‐derived material is greatly enriched toward the north of the deposit. These results indicate that the co‐blast plume dispersed fine‐grained material over great distances and dominated the fine subpopulation. Comparison with reanalysis data of atmospheric wind fields and satellite images of the spreading ash cloud suggests contrasting ash transport and depositional processes for the (early) co‐blast plume and the (later) vent‐derived Plinian plumes. The co‐blast plume is displaced to the north; it had a high overshoot height, and eastward dispersion via strong winds low in the stratosphere (~10–15 km). The Plinian plumes were lower and dispersed most of the material to the southeast as the direction of high‐velocity winds shifted just before the late climactic Plinian eruptive phase. Fine ash (fine subpopulation) was deposited continuously throughout the deposit, with an increase of sedimentation rate ~300 km from the vent where there is a secondary maximum in the deposit mass and thickness. Fine ash probably settled by a combination of enhanced sedimentation mechanisms, including not only aggregation but also gravitational convective instabilities of cloud base, hydrometeor formation and destruction, and entrainment of small particles by larger ones. Finally, we show that half of the deposit (by mass) in the medial area was deposited by the co‐blast plume, and that a significant proportion of the Mount St. Helens fallout deposit is nonjuvenile, which has implications for the magmatic budget of this eruption.

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Far‐travelled ash in past and future eruptions: combining tephrochronology with volcanic studies

Cashman

Rust

2019

J Quaternary Science

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Studies of recent eruptions have improved our understanding of volcanic ash transport and deposition, but have also raised important questions about the behaviour of far-travelled (distal) volcanic ash. In particular, it is difficult to reconcile estimates of distal ash mass and transport distance determined from eyewitness accounts, mapped deposits, satellite-based observations and cryptotephra records. Here we address this problem using data from well-characterized eruptions that, collectively, include all four data types. Data from recent eruptions allow us to relate eyewitness accounts to mapped deposits on the ground and satellite-based observations of ash in the air; observations from an historical eruption link eyewitness accounts to cryptotephra deposits. Together these examples show that (i) 10-20% of the erupted mass is typically deposited outside the mapped limits; (ii) estimates of the ash mass transported in volcanic clouds cannot account for all of this unmapped ash; and (iii) ash fall observed at distances beyond mapped deposits can have measurable impacts, and can form cryptotephra deposits with high (>~1000 cm −3 ) shard counts. We conclude that cryptotephra data can be incorporated into volcanological studies of ash transport and deposition and provide important insight into both the behaviour and impacts of far-travelled volcanic ash particles.

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Size Distributions and Mineralogy of Ash Particles in the Stratosphere from Eruptions of Mount St. Helens

Cited by 65 publications

References 7 publications

Volcanic ash detection with infrared limb sounding: MIPAS observations and radiative transfer simulations

Volcanic ash detection with infrared limb sounding: MIPAS observations and radiative transfer simulations

Impact of the lateral blast on the spatial pattern and grain size characteristics of the 18 May 1980 Mount St. Helens fallout deposit

Far‐travelled ash in past and future eruptions: combining tephrochronology with volcanic studies

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