Electrical properties of volcanic ash samples from Eyjafjallaj\"okull and Gr\'imsv\"otn

TL;DR

This study investigates the electrical charging properties of volcanic ash from Eyjafjallajökull and Grímsvötn, revealing differences in charge polarity and particle size distribution that influence volcanic lightning phenomena.

Contribution

It provides new insights into the relationship between particle size distribution and electrical charge in volcanic ash from two Icelandic eruptions.

Findings

Eyjafjallajökull ash charges slightly positively

Grímsvötn ash charges substantially negatively

Charge polarity correlates with particle size distribution

Abstract

Volcanic ash is known to charge electrically, producing some of the most spectacular displays of lightning in nature. Here we investigate the electrical characteristics of ash from two different Icelandic volcanoes - Eyjafjallaj\"okull in 2010 and Gr\'imsv\"otn in 2011. Laboratory tests investigated the charge transferred to a conducting plate due to fall of volcanic ash through an insulating cylinder. Ash from the Eyjafjallaj\"okull eruption was found to charge slightly positively, whilst Gr\'imsv\"otn ash was substantially negatively charged. Measurement of the volumetric ratio of particle diameters showed the Eyjafjallaj\"okull ash to have a bimodal distribution, and the Gr\'imsv\"otn ash a monomodal distribution. Previous experiments with single-material particle systems show that smaller particles charge negatively and larger ones positively. Since charge is carried by individual particles, the charging is likely to be dominated by the number size distribution, therefore the large negative charge of the Gr\'imsv\"otn ash is likely to be related to a large number of small particles within the number size distribution of the ash.