Distal deposition of tephra from the Eyjafjallajökull 2010 summit eruption

Stevenson, J.A, Loughlin, S.C., Rae, C., Thordarson, T., Milodowski, A.E, Gilbert, J.S., Harangi, S., Lukacs, R., Hojgaard, B., Arting, U., Pyne-O'Donnell, S., MacLeod, A., Whitney, B. and Cassidy, M. (2012) Distal deposition of tephra from the Eyjafjallajökull 2010 summit eruption. Journal of Geophysical Research, 117, B00C10. (doi:10.1029/2011JB008904).

Abstract

The 2010 Eyjafjallajökull lasted 39 days and had 4 different phases, of which the first and third (14-18 April and 5-6 May) were most intense. Most of this period was dominated by winds with a northerly component that carried tephra towards Europe, where it was deposited in a number of locations and was sampled by rain gauges or buckets, surface swabs, sticky-tape samples and air filtering. In the UK, tephra was collected from each of the Phases 1-3 with a combined range of latitudes spanning the length of the country. The modal grainsize of tephra in the rain gauge samples was 25 µm, but the largest grains were 100 µm in diameter and highly-vesicular. The mass loading was equivalent to 8-218 shards cm², which is comparable to tephra layers from much larger past eruptions. Falling tephra was collected on sticky tape in the English Midlands on 19, 20 and 21st April (Phase 2), and was dominated by aggregate clasts (mean diameter 85 µm, component grains <10 µm). SEM-EDS spectra for aggregate grains contained an extra peak for sulphur, when compared to control samples from the volcano, indicating that they were cemented by sulphur-rich minerals e.g. gypsum. Air quality monitoring stations did not record fluctuations in hourly PM10 concentrations outside the normal range of variability during the eruption, but there was a small increase in 24-hour running mean concentration from 21-24 April (Phase 2). Deposition of tephra from Phase 2 in the UK indicates that transport of tephra from Iceland is possible even for small eruption plumes given suitable wind conditions. The presence of relatively coarse grains adds uncertainty to concentration estimates from air quality sensors, which are most sensitive to grainsizes <10 µm. Elsewhere, tephra was collected from roofs and vehicles in the Faroe Islands (mean grainsize 40 µm, but 100 µm common), from rainwater in Bergen in Norway (23-91 µm) and in air filters in Budapest, Hungary (2-6 µm). A map is presented summarising these and other recently-published examples of distal tephra deposition from the Eyjafjallajökull eruption. It demonstrates that most tephra deposited on mainland Europe was produced in the highly-explosive Phase 1 and was carried there in 2--3 days.

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