The 2011–2012 summit activity of Mount Etna: Birth, growth and products of the new SE crater ☆ Boris Behncke, Stefano Branca ⁎, Rosa Anna Corsaro, Emanuela De Beni, Lucia Miraglia, Cristina Proietti Istituto Nazionale di Geofisica e Vulcanologia-Osservatorio Etneo, Piazza Roma 2, Catania, Italy abstract article info Article history: Received 17 July 2013 Accepted 13 November 2013 Available online 28 November 2013 Keywords: Etna Summit eruptions Scoria cone growth Lava and tephra volume Collapsing foam model Between January 2011 and April 2012, the Southeast Crater (SEC) on Mount Etna was the site of 25 episodes of lava fountaining, which led to the construction of a new pyroclastic cone on the eastern flank of the SEC. During these episodes lava overflows reached 4.3 km in length with an area of 3.19 km 2 and a volume of 28 × 10 6 m 3 . The new cone, informally called New Southeast Crater (NSEC), grew over a pre-existing subsidence depression (pit crater), which had been formed in 2007–2009. The evolution of the NSEC cone was documented from its start by repeated GPS surveys carried out both from a distance and on the cone itself, and by the acquisition of comparison photographs. These surveys reveal that after the cessation of the lava fountains in April 2012, the highest point of the NSEC stood 190 m above the pre-cone surface, while the cone volume was about 19 × 10 6 m 3 , representing 38% of the total (bulk) volume of the volcanic products including pyroclastic fallout erupted in 2011–2012, which is 50 × 10 6 m 3 (about 33 × 10 6 m 3 dense-rock equivalent). Growth of the new cone took place exclusively during the paroxysmal phases of the lava fountaining episodes, which were nearly always rather brief (on the average 2 h). Overall, the paroxysmal phases of all 25 episodes represent 51 h of lava fountaining activity — the time needed to build the cone. This is the fastest documented growth of a newborn volcanic cone both in terms of volume and height. Mean effusion rates during the lava fountaining episodes on 20 August 2011 (E11), as well as 12 and 24 April 2012 (E24 and E25) exceeded 500 m 3 /s (with maximum rates of 980 m 3 /s during E11) and thus they are among the highest effusion rates ever recorded at Etna. The composition of the erupted products varies in time, reflecting different rates of magma supply into the shallow feeding system, but without notable effects on the eruptive phenomenology. This implies that the dynamics leading to the epi- sodic lava fountaining was largely, though not entirely, controlled by the repeated formation and collapse of a foam layer in the uppermost portion of the magmatic reservoir of the NSEC. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The formation of pyroclastic cones can occur in different volcanic settings, such as in volcanic fields or at the summit or on the flanks of stratovolcanoes. Many of those newly constructed volcanic cones are typically related to mild to moderately strong explosive activity, ranging in magnitude from Strombolian to violent Strombolian and lava fountaining. The most common type of landform resulting from this type of activity is monogenetic scoria (or cinder) cones (Macdonald, 1972). Parícutin (Mexico), a large monogenetic scoria cone, is the most famous example of this type (Foshag and Gonzalez, 1956; Luhr and Simkin, 1993); another well documented case is the growth of the “Laghetto” cone on the south flank of Mount Etna (Italy) in 2001 (Calvari and Pinkerton, 2004; Fornaciai et al., 2010) and two large coa- lescent scoria cones formed during the 2002–03 Etna eruption (Andronico et al., 2005; Fornaciai et al., 2010). Conversely, long periods of repeated explosive activity form large polygenetic cones. The growth of this type of polygenetic volcanic landform has been observed right from its birth in some recent cases such as Cerro Negro in Nicaragua (McKnight and Williams, 1997). The growth of the Pu'u ‘Ō’ō cone at Kīlauea volcano (Hawai'i) is particularly well documented (Heliker and Mattox, 2003; Heliker et al., 2003). On Etna volcano the explosive activity at its summit vents has led to the growth of large scoria cones during the XX century (Fig. 1). In particular, in May 1911 a 100 m wide pit crater was formed by collapse at the northeast base of the sum- mit cone at 3100 m a.s.l. (Ponte, 1920). In the following years this new chasm, named Northeast Crater (NEC), soon became the site of intense explosive activity, which, especially between 1955 and 1981, led to the growth of a polygenetic scoria cone. Between 1977 and 1981, the NEC cone grew to become the highest point of Etna, at 3350 m a.s.l. (Tanguy and Patanè, 1984; Chester et al., 1985), though later collapse of its crater rims reduced its height to 3329 m (Neri et al., 2008). In the same way, the youngest and presently most active of Etna's summit Journal of Volcanology and Geothermal Research 270 (2014) 10–21 ☆ This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works License, which permits non- commercial use, distribution, and reproduction in any medium, provided the original au- thor and source are credited. ⁎ Corresponding author. Tel.: +39 095 7165800. E-mail address: stefano.branca@ct.ingv.it (S. Branca). 0377-0273/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jvolgeores.2013.11.012 Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores