Eruption dynamics and tephra dispersal from the 24 November 2006 paroxysm at South-East Crater, Mt Etna, Italy

Abstract

Between 30 August and 15 December 2006,Mt Etna, Italy, underwent both effusive and explosive activity which took place fromthe South-East Crater, one of its summit craters. Several paroxysmal episodes followed in succession, separated by a fewdays of minor activity and characterised by dissimilar explosive style and intensity. Here, we report one of the most studied and powerful episodes, which started early in the morning on 24 November 2006 and lasted about 13 h. Excellent weather conditions enabled reconstructing in detail the onset and evolution of the eruptive phenomena both by live-camera recordings and direct observations. The explosive activity consisted of powerful Strombolian activity alternating with short periods of lava fountains. A weak volcanic plume rose up to ~2 km above the volcanic vent, followed by tephra fallout which covered the SE and S flanks of Etna. Campaigns allowed collecting about 40 tephra samples and mapping the fallout deposit. The clockwise shifting of the volcanic plume during the eruption caused the different timing of the fallout on the ground, thus widening the dispersal area. Voronoi's method was used to evaluate: i) the total grain-size distribution, indicating that the fallout deposit peaked at 1 ϕ, and, for the first time at Etna, ii) the total componentry distribution, finding thatmost of the particles were lithics, with a low proportion of juvenile vs. lithics (34:65). The total erupted mass was estimated ~1.9 × 108 kg, corresponding to a mass eruption rate of ~5 × 103 kg s−1. Physical parameters and textural features of the erupted products suggest that the 24 November 2006 explosive event may be classified as small-sized in the recent history of Etna, and that the eruptive dynamicwasmainly governed by magma/gas decoupling, which produced relatively fine-grained fallout deposits containing unusual elongated sideromelane ash particles.