Abstract
Determining the volume of the various types of products of a highly frequent active volcano can be very difficult, especially if most of them are deposited on a growing volcanic cone. The New South-East Crater (NSEC) of Mt Etna, Italy, may be considered one of the best case studies because of tens of paroxysmal episodes which it produced in the last few years. On 25-26 October 2013, a lava fountain at the NSEC produced magma jets up to 500 m high, a maximum ~8 km high column, a multilobate lava flow field 1.3 to 1.5 km long, and almost 30 m of growth in height of the NSEC cone. Mapping of explosive and effusive deposits allowed us to calculate the total volume of erupted products, including lava flows, proximal and distal tephra fallout, and the amount of coarse pyroclastics on the cone. The estimation of the latter products was also confirmed subtracting digital elevation models (DEMs) obtained at different stages of the NSEC growth. Results show that the volume of tephra fallout away from the cone was only <5 % of the total erupted magma, while the total volume of pyroclasts (distal plus proximal fallout) is about a third of the lava volume. Our analysis suggests that, at least for the studied event, three fourth of the involved magma was already partially degassed and thus emitted as lava flows. Hence, the main distinctive character of lava fountains at Etna, i.e. formation of eruption column and propagation of tephra-laden volcanic plumes to tens of km away from the volcano, would not contribute significantly to the final budget of erupted magma of the 25-26 October 2013 eruption. We finally propose that the same magma dynamics probably occur also during most of the common lava fountain episodes.
Highlights
Lava fountaining at the New South-East Crater (NSEC) passed into violent Strombolian activity, often producing powerful explosions caused by the bursting of huge lava blisters, which sent sprays of meter-sized incandescent bombs up to several hundred meters high; most of these bombs were observed to fall onto the northern base of the NSEC cone
In spite of various research on single paroxysmal episodes in recent years, to date only this study quantifies, on the base of field data, the dense rock equivalent (DRE) magma volumes erupted as proximal tephra, distal tephra, and lava flows
The estimation of the total mass and the relative percentages of lava and tephra may address the evaluation of the eruption dynamics during paroxysmal episodes at Etna, and gain insights into the wide spectrum of eruption intensity (MER) and style observed in the last years at the summit craters
Summary
The simultaneous occurrence of intense explosive and effusive activity—often in brief, paroxysmal eruptive episodes—has been observed at a number of basaltic volcanoes, such as Pacaya (Rose et al, 2013) and Fuego in Guatemala (Lyons et al, 2010), Klyuchevskoy in Kamchatka (Zharinov and Demyanchuk, 2016), Manam in Papua New-Guinea (Tupper et al, 2007), Pavlof in Alaska (Waythomas et al, 2014), Llaima in Chile (Romero et al, 2013), and Mt Etna in Italy (Behncke et al, 2006; Calvari et al, 2018). The New South-East Crater (NSEC) of Etna (Figure 1) is a young and still growing volcanic cone, which formed by accumulation of lava and proximal pyroclastics (Figure 2a; Behncke et al, 2014). These products were mostly emplaced around a primordial pit-shaped vent located on the eastern flank of the South-East Crater (SEC; Andronico et al, 2013, 2014a,b), one of the summit craters of Etna, between 2011 and 2013, when 48 paroxysmal episodes or “paroxysms” took place (Corsaro et al, 2017; Giuffrida and Viccaro, 2017). Retrieved aerosol particle size dispersal to far as Lampedusa, more than 350 km downwind (Sellitto et al, 2016)
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