Lightning-induced volcanic spherules

Genareau, Kimberly; Wardman, John; Wilson, Thomas; McNutt, Stephen R.; Izbekov, Pavel

doi:10.1130/g36255.1

Cited by 39 publications

(43 citation statements)

References 26 publications

(28 reference statements)

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“…Overall, LIVS represent a small percentage (<1%) of the ash grains for both eruptions studied here, consistent with previous observations (Genareau et al, 2015). Additionally, LIVS formed in the eruption column or plume can travel great distances before being deposited or can be fused to unaltered ash particles during transport.…”

Section: Discussionsupporting

confidence: 91%

“…Analyses of ashfall samples from the 4 April 2009 event at Redoubt permits direct comparison with a previous study (Genareau et al, 2015) that measured LIVS from ashfall deposited following the 23 March 2009 explosion (event 5). Seismic durations and maximum column heights of events 5 and 19 were comparable: 20 min and 16.4 km versus 31 min and 15.2 km, respectively (Schneider & Hoblitt, 2013;Wallace et al, 2013).…”

Section: Discussionmentioning

confidence: 97%

“…However, the ash plume from event 19 traveled in a southeast direction, whereas the majority of other events dispersed ash to the north of the volcano (Wallace et al, 2013). Individual LIVS ranging in size from 20 to 80 μm in diameter, in addition to spherule aggregates, were observed in fall deposits from event 5 (Genareau et al, 2015). In the deposit of event 19 examined here, individual LIVS are more numerous and smaller than those observed in the event 5 deposits, and no spherule aggregates were observed.…”

Section: Discussionmentioning

confidence: 98%

“…We focus here on samples from the 4 April 2009 eruption of Mount Redoubt (event 19 of the explosive series) and the 2016 eruption of Pavlof, because Each curve is an average of five separate measurements using ash dispersed in doubly deionized water and (b, c) postexperimental pseudo ash samples, showing existence of grains >50 μm. Ash samples were sieved to remove larger grains (>100 μm) prior to mounting, as previous observations of LIVS in ashfall samples indicate they are <100 μm (Genareau et al, 2015). The rhyolite sample in (b) is similar to the trachybasalt sample in (c), and all four pseudo ash samples showed comparable changes in the grain sizes.…”

Section: Natural Ash Samplesmentioning

confidence: 99%

“…Lightning-induced volcanic spherules (LIVS) were first documented in ashfall deposits from the 2009 eruption of Mount Redoubt (Alaska, USA) and the 2010 eruption of Eyjafjallajökull (Iceland; Genareau et al, 2015). LIVS represent an important record of electrical activity within volcanic columns and plumes (Harper et al, 2015;Lane et al, 1995;Miura et al, 2002;Smith et al, 2018;Van Eaton et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Lightning Effects on the Grain Size Distribution of Volcanic Ash

Genareau

Wallace

Gharghabi

et al. 2019

Geophysical Research Letters

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Natural volcanic ashfall samples were examined, and high‐current (~100 kA) electrical impulse experiments were conducted to reveal the changes in grain size that can occur during lightning discharge. Experiments on pseudo ash samples manufactured from volcanic deposits of both rhyolitic and basaltic composition show that aggregates of very fine grained ash particles (<32 μm) melt and degas to form vesiculated pumice fragments >100 μm in size. In some cases, bubbles <5 μm in diameter expand and detach from the outer surface of the pumice to form hollow spheres of glass, one type of lightning‐induced volcanic spherule, while other bubbles fragment. Volcanic ashfall from the 2009 Redoubt eruption and the 2016 Pavlof eruption contains both pumiceous grains and individual spherules. Results of this study reveal that volcanic lightning will alter the grain size distribution of ash through melting, vesiculation, and fragmentation of individual particles or ash aggregates.

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Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 98%

Section: Natural Ash Samplesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Lightning Effects on the Grain Size Distribution of Volcanic Ash

Genareau

Wallace

Gharghabi

et al. 2019

Geophysical Research Letters

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The effects of dynamics on the triboelectrification of volcanic ash

Harper

Dufek

2016

JGR Atmospheres

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Lightning is often observed during explosive volcanic eruptions, and the charging processes associated with these displays have been attributed to several mechanisms. In this work we delineate a set of experiments designed to quantify silicate-based triboelectric charging in the volcanic context. Using natural samples from three different volcanoes, we show that the rate of triboelectrification in a fluidized bed depends on the energy input into the granular system. Experiments are conducted employing nonintrusive electrostatic sensors, ensuring that all charge exchange arises solely from particle-particle collisions. At higher fluidization energies, particles undergo more frequent and energetic collisions, facilitating the transfer of charge. This finding implies that triboelectric charging could help promote charging in regions of the eruptive system that contain numerous particle-particle collisions such as the conduit and gas thrust regions. Our experiments also suggest that surface charge density is capped, at least in part, by atmospheric conditions, specifically the breakdown characteristics of the gas.

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Size limits for rounding of volcanic ash particles heated by lightning

et al. 2017

Self Cite

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Volcanic ash particles can be remelted by the high temperatures induced in volcanic lightning discharges. The molten particles can round under surface tension then quench to produce glass spheres. Melting and rounding timescales for volcanic materials are strongly dependent on heating duration and peak temperature and are shorter for small particles than for large particles. Therefore, the size distribution of glass spheres recovered from ash deposits potentially record the short duration, high‐temperature conditions of volcanic lightning discharges, which are hard to measure directly. We use a 1‐D numerical solution to the heat equation to determine the timescales of heating and cooling of volcanic particles during and after rapid heating and compare these with the capillary timescale for rounding an angular particle. We define dimensionless parameters—capillary, Fourier, Stark, Biot, and Peclet numbers—to characterize the competition between heat transfer within the particle, heat transfer at the particle rim, and capillary motion, for particles of different sizes. We apply this framework to the lightning case and constrain a maximum size for ash particles susceptible to surface tension‐driven rounding, as a function of lightning temperature and duration, and ash properties. The size limit agrees well with maximum sizes of glass spheres found in volcanic ash that has been subjected to lightning or experimental discharges, demonstrating that the approach that we develop can be used to obtain a first‐order estimate of lightning conditions in volcanic plumes.

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Lightning-induced volcanic spherules

Cited by 39 publications

References 26 publications

Lightning Effects on the Grain Size Distribution of Volcanic Ash

Lightning Effects on the Grain Size Distribution of Volcanic Ash

The effects of dynamics on the triboelectrification of volcanic ash

Size limits for rounding of volcanic ash particles heated by lightning

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