Electrical charging of ash in Icelandic volcanic plumes

TL;DR

This study investigates the electrical charging mechanisms of volcanic ash in Icelandic eruptions through laboratory measurements of particle size, triboelectrification, and radioactivity, providing insights into volcanic lightning and plume electrification.

Contribution

It presents new laboratory data on ash particle properties and charging processes from recent Icelandic eruptions, enhancing understanding of volcanic plume electrification mechanisms.

Findings

Particle size distribution influences ash charging efficiency.

Radioactivity in ash may contribute to self-charging.

Laboratory measurements support existing charging hypotheses.

Abstract

The existence of volcanic lightning and alteration of the atmospheric potential gradient in the vicinity of near-vent volcanic plumes provides strong evidence for the charging of volcanic ash. More subtle electrical effects are also visible in balloon soundings of distal volcanic plumes. Near the vent, some proposed charging mechanisms are fractoemission, triboelectrification, and the so-called "dirty thunderstorm" mechanism, which is where ash and convective clouds interact electrically to enhance charging. Distant from the vent, a self-charging mechanism, probably triboelectrification, has been suggested to explain the sustained low levels of charge observed on a distal plume. Recent research by Houghton et al. (2013) linked the self-charging of volcanic ash to the properties of the particle size distribution, observing that a highly polydisperse ash distribution would charge more effectively than a monodisperse one. Natural radioactivity in some volcanic ash could also contribute to self-charging of volcanic plumes. Here we present laboratory measurements of particle size distributions, triboelectrification and radioactivity in ash samples from the Gr\'{i}msv\"{o}tn and Eyjafjallaj\"{o}kull volcanic eruptions in 2011 and 2010 respectively, and discuss the implications of our findings.