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Growth of complex volcanic ash aggregates in the Tierra Blanca Joven eruption of Ilopango Caldera, El Salvador

Hoult, Henry; Brown, Richard J.; Van Eaton, Alexa R.; Hernandez, Walter; Dobson, Katherine J.; Woodward, Bryan


Henry Hoult

Alexa R. Van Eaton

Walter Hernandez

Katherine J. Dobson

Bryan Woodward


Aggregation processes control both the residence time and dispersal of volcanic ash during eruptions yet remain incompletely understood. The products of aggregation vary from simple ash clusters to large, complexly layered accretionary lapilli. Here we detail the micro-stratigraphy of a single population of accretionary lapilli that grew during the ∼431 CE Tierra Blanca Joven eruption from Ilopango Caldera, El Salvador. The accretionary lapilli were sampled 10 km from the caldera source within a sequence of ash-rich pyroclastic density current deposits and intercalated fall material, known as unit D, which is traceable >40 km from Ilopango. Scanning electron microscopy and image analysis reveal common facies that form distinct layers within the accretionary lapilli. Each facies is distinguished by quantitative and qualitative variations in particle size distribution, porosity, and particle fabric. We infer that these textures resulted from aggregation conditions that differed in terms of liquid water availability, particle concentration and grain size distributions. In our proposed model, a characteristic sequence of facies accreted from core to rim in the accretionary lapilli during passage through ash clouds generated by vent-derived plumes and pyroclastic density currents. The accretionary lapilli are mostly composed of smaller aggregates (ash clusters, ash pellets) and grew predominantly by accretion of already-formed aggregates, rather than by grain-by-grain accretion of individual particles. This finding is consistent with observations of rapid aggregate growth in volcanic plumes, suggesting a common evolutionary pathway for accretionary lapilli formation across diverse eruptions.


Hoult, H., Brown, R. J., Van Eaton, A. R., Hernandez, W., Dobson, K. J., & Woodward, B. (2022). Growth of complex volcanic ash aggregates in the Tierra Blanca Joven eruption of Ilopango Caldera, El Salvador. Journal of Volcanology and Geothermal Research, 431, Article 107670.

Journal Article Type Article
Acceptance Date Sep 2, 2022
Online Publication Date Sep 8, 2022
Publication Date 2022-11
Deposit Date Oct 13, 2022
Publicly Available Date Sep 9, 2023
Journal Journal of Volcanology and Geothermal Research
Print ISSN 0377-0273
Electronic ISSN 1872-6097
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 431
Article Number 107670


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