## 2 The Volcanic Activity on Mt. Etna Leading to the Paroxysmal Episodes of 2012  
Mtt. Etna (Italy) is a persistent active volcano and one of the most active in the world, [24; 25]. In the last century, Mt. Etna erupted every 1.5 years on average [8], offering considerable opportunities for experimental geochemical monitoring of the volcanic activity [1; 2; 6; 7; 8; 9; 10]. Mt. Etna's activity has spanned from degassing [26] to lava effusion and explosive activity that has passed from pure strombolian explosions to powerful lava fountains [27; 28; 29; 30; 31; 32]. Over time, Mt. Etna's eruptions have been occurred either in the summit craters or by lateral fissures (flank eruptions), according to three rift zones--S Rift, NE Rift, and W Rift--with the most significant flank eruptions occurring due to the opening of eruptive fissures in the S and NE Rift areas [32; 33].  
In particular, the NE Rift system located on the northeastern flank of the volcano (Figure 1a,c) includes several north-northeast-striking eruptive fissures that have frequently erupted (e.g., in 1911, 1923, 1947, and 2002 [27; 34]). After 2002, a low-temperature fumarole area located at the top of the NE Rift formed (BTL fumaroles, Figure 1c), showing persistent hydrothermal activity. Many authors have already described the thermal anoma  
Figure 1: (a) Digital elevation model of Mt. Etna volcano showing the locations of the sites mentioned in the text and the main volcano—tectonic landforms (e.g., caldera border, craters, fracture lines). NEC, VOR, BN, and NSEC stand for North-East Crater, Voragine, Bocca Nuova, and New South-East Crater (modified from [23]); (b) Google Earth image of the southern Mediterranean region, with an indication of the Mt. Etna volcano (red area with a yellow contour); (c) Google Earth image of the monitored area, corresponding to the box outlined in the red frame in figure (a).  
lies, which are dispersed around the active fractures of Mt. Etna [18; 26; 35; 36; 37]. However, the time variations of these mild thermal anomalies have been little considered in recent studies on volcanic activity [7; 21], possibly because the relative low heat fluxes cannot be observed due to the discontinuous surveys and the low resolution of the sensors. In 2018, [PERSON] et al. [21], focusing on the monthly averages of steam-heated flux, showed that the intensity of the hydrothermal circulation in the upper segment of Mt. Etna's NE Rift, from 2009 to 2012, did not depend only on the atmospheric conditions but mainly on the eruptive activity occurring at that time at the New SE summit crater (NSEC) [27; 38]. The NSEC, which in 2010 was a degassing pit that opened on the E flank of the SE summit crater, started growing in early 2011 by feeding a number of lava fountain episodes and paroxysms [4; 8; 21; 27; 29; 30; 38]. In this paper, we deepen the discussion carried out by [PERSON] et al. [21] by detailing the results from the short-term variations (hours, days) recorded in the upper segment of Mt. Etna's NE Rift, applying the method already proposed and tested in other studies [22; 39; 40]. The considered variable is a set of temperature data collected on a linear array of a few temperature probes. In particular, we show the vertical shifts of the steam condensation level and the hourly variations of the diffuse heat flux between September 2009 and 2012. Then, we focus on the subset of data recorded after January 2012 to discuss the hourly variations of the steam condensation level and the steam-heated soil flux (hereafter SH\({}_{\text{Flux}}\)) during the last period of intense paroxysms and the following rest period.