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Abstract Over the last decades, remote observation tools and models have been developed to improve the forecasting of ash‐rich volcanic plumes. One challenge in these forecasts is knowing the properties at the vent, including the mass eruption rate and grain size distribution (GSD). Volcanic lightning is a common feature of explosive eruptions with high mass eruption rates of fine particles. The GSD is expected to play a major role in generating lightning in the gas thrust region via triboelectrification. Here, we experimentally investigate the electrical discharges of volcanic ash as a function of varying GSD. We employ two natural materials, a phonolitic pumice and a tholeiitic basalt (TB), and one synthetic material (soda‐lime glass beads [GB]). For each of the three materials, coarse and fine grain size fractions with known GSDs are mixed, and the particle mixture is subjected to rapid decompression. The experiments are observed using a high‐speed camera to track particle‐gas dispersion dynamics during the experiments. A Faraday cage is used to count the number and measure the magnitude of electrical discharge events. Although quite different in chemical composition, TB and GB show similar vent dynamics and lightning properties. The phonolitic pumice displays significantly different ejection dynamics and a significant reduction in lightning generation. We conclude that particle‐gas coupling during an eruption, which in turn depends on the GSD and bulk density, plays a major role in defining the generation of lightning. The presence of fines, a broad GSD, and dense particles all promote lightning.
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gas-tight shock tube apparatus for laboratory volcanic lightning under varying atmospheric conditions
Explosive volcanic eruptions generate electrical discharges, a phenomenon termed volcanic lightning (VL). VL is increasingly well-investigated and monitored for modern eruptions, however volcanism has been active since Earth’s origin. Thus, investigating VL under different atmospheric conditions is relevant for studies of early atmospheric chemistry and potential prebiotic reactions. We developed an experimental setup to investigate VL in varying atmospheres. We present the first experiments of laboratory discharges in particle-laden jets in varying atmospheric conditions. The new experimental setup is a mobile fragmentation bomb erupting into a gas-tight particle collector tank. This setup enables the testing of different atmospheric conditions, changes in the carrier gas of the jet, changes in the pressure within the tank, monitoring of the jet behaviour, and sampling of the atmosphere together with the decompressed solid materials. We find that the number and magnitude of near-vent electrical discharge events are similar in CO2-CO and air atmospheres.
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- Award ID(s):
- 2042173
- PAR ID:
- 10538591
- Publisher / Repository:
- Presses Universitaires de Strasbourg
- Date Published:
- Journal Name:
- Volcanica
- Volume:
- 6
- Issue:
- 2
- ISSN:
- 2610-3540
- Page Range / eLocation ID:
- 437 to 445
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.30909/vol.06.02.437445
