The continuing story of Etna's New Southeast Crater (2012-2014): Evolution and volume calculations based on field surveys and aerophotogrammetry

During the years 2013-2014, the New Southeast Crater (NSEC) at the summit of Mount Etna produced frequent episodes of lava fountaining (paroxysms), and its cone continued to grow at unprecedented rates. Many of the episodes were of rather brief duration and violently explosive, producing mostly pyroclastic material and minor volumes of lava. Other episodes, especially those since mid-December 2013, were characterized by violent Strombolian activity without producing sustained lava fountains and significant amounts of tephra, but emitting more voluminous lava flows. One episode of intense Strombolian and effusive activity that was possibly fed from the NSEC conduit occurred from vents located approximately 1 km north of the crater, on the east flank of the Northeast Crater, in July-August 2014. The evolution of the NSEC cone between 2012 and 2014 was documented by repeated GPS surveys carried out both from a distance and on the cone itself, by the acquisition of comparison photographs, and by two aerophotogrammetric surveys. From these surveys the highest point of the NSEC results to have grown from 190 m (May 2012) to ̴215 m (October 2014) above the pre-cone surface reaching an elevation of 3290 m, and its volume more than doubled to ̴ 50.0 ± 6.5 × 106 m3, representing the 40% of the total (bulk) volume of the volcanic products including pyroclastic fallout erupted in 2011-2014, which is 147.2 × 106 m3 (101.3 × 106 m3 dense-rock equivalent). The whole of the 2011-2014 NSEC activity marks an unusually high frequency of rather explosive, tephra-rich eruptive episodes compared to Etna's activity in past decades and centuries, although the average magma production rate in this interval is close to the supposed long-term output rate of the volcano. The latest eruptive episodes show a tendency of the NSEC coalescing with the old Southeast Crater cone, which therefore represents a miniature example of a growing compound volcano at the summit of Etna.