The exceptional activity and growth of the Southeast Crater, Mount Etna (Italy), between 1996 and 2001

Abstract

Between 1971 and, the Southeast Crater was the most productive of the four summit craters of Mount Etna, with activity that can be compared, on a global scale, to the opening phases of the Pu'u 'Ō'ō-Kūpaianaha eruption of Kīlauea volcano, Hawai'i. The period of highest eruptive rate was between 1996 and 2001, when near-continuous activity occurred in five phases. These were characterized by a wide range of eruptive styles and intensities from quiet, non-explosive lava emission to brief, violent lava-fountaining episodes. Much of the cone growth occurred during these fountaining episodes, totaling 105 events. Many showed complex dynamics such as different eruptive styles at multiple vents, and resulted in the growth of minor edifices on the flanks of the Southeast Crater cone. Small pyroclastic flows were produced during some of the eruptive episodes, when oblique tephra jets showered the steep flanks of the cone with hot bombs and scoriae. Fluctuations in the eruptive style and eruption rates were controlled by a complex interplay between changes in the conduit geometry (including the growth of a shallow magma reservoir under the Southeast Crater), magma supply rates, and flank instability. During this period, volume calculations were made with the aid of GIS and image analysis of video footage obtained by a monitoring telecamera. Between 1996 and 2001, the bulk volume of the cone increased by~36×10 6 m 3 , giving a total (1971-2001) volume of~72×10 6 m 3 . At the same time, the cone gained~105 m in height, reaching an elevation of about 3,300 m. The total DRE volume of the 1996-2001 products was~90×10 6 m 3 . This mostly comprised lava flows (72×10 6 m 3 ) erupted at the summit and onto the flanks of the cone. These values indicate that the productivity of the Southeast Crater increased fourfold during 1996-2001 with respect to the previous 25 years, coinciding with a general increase in the eruptive output rates and eruption intensity at Etna. This phase of intense summit activity has been followed, since the summer of 2001, by a period of increased structural instability of the volcano, marked by a series of important flank eruptions.

A year of lava fountaining at Etna: Volumes from SEVIRI

“…This compares with intensities of between 15 and 205 m 3 s À1 estimated for Etna's 1996 to 2001 fountaining events [Behncke et al, 2006] and 183 m 3 s À1 for fountains associated with Etna's 1989 eruption [Bertagnini et al, 1990]. On a global scale, we can also compare our Etna values with rates of between 9 and 308 m 3 s À1 estimated for 13 fountaining events at Pu'u 'O'o (Kilauea) during 1983-1984[Wolfe et al, 1987, and of up to 340 m 3 s…”

The contribution of synchrotron X-ray computed microtomography to understanding volcanic processes

“…The first one concerns samples of basaltic (SiO 2 = 45-52 wt%) composition and erupted from persistently degassing volcanoes characterized by mild to moderate explosive activity. This category includes ( Barberi et al, 1993;Robin et al, 1993;Bertagnini et al, 2003;Behncke et al, 2006;Gurioli et al, 2008 and references therein for information about these volcanoes and their eruptive activity). The second category refers to pumice clasts of trachytic (SiO 2 = $ 58-69 wt%, Na 2 O 2 + K 2 O = >$ 7 wt%) composition that were collected from deposits left by explosive activity that occurred at Campi Flegrei, an active caldera situated west of the urban centre of Naples, Italy.…”

Topographic Maps of Mount Etna’s Summit Craters, updated to December 2015

“…Etna: (1) the Voragine (VOR), or Chasm, earlier called Central Crater (CC), is the oldest, and has been observed at least since 1858 (Behncke, Neri, & Sturiale, 2004;Lyell, 1858); (2) the NE-Crater (NEC) is a cinder cone that built up from 1911 (McGetchin et al, 1974); (3) the Bocca Nuova (BN) started as a pit crater next to VOR in 1968, and collapsed in 1970 to form a large depression, now joined to VOR (Calvari et al, 1995;Chester, Duncan, Guest, & Kilburn, 1985;Giammanco, Sims, & Neri, 2007;Slatcher et al, 2015), and (4) the SE-Crater (SEC), which formed during the 1971 eruption (Behncke et al, 2006;Calvari, Coltelli, Muller, Pompilio, & Scribano, 1994;Guest, 1973), and has been the most active summit crater over recent decades (Behncke et al, 2006;Bonaccorso & Calvari, 2013;Calvari et al, 2011). Finally, the New SE-Crater (NSEC) (the fifth and youngest summit crater) has formed at the eastern base of the SEC, starting from a little pit crater that opened in late 2007 (Acocella et al, 2016;Behncke et al, 2016;Del Negro et al, 2013).…”

“…Etna is among the world's most active volcanoes ( Figure 1), with almost continuous eruptive activity from the four summit craters Falsaperla & Neri, 2015). Its uppermost region is therefore continuously changing Bisson, Spinetti, Neri, & Bonforte, 2016;Giammanco et al, 2016;McGetchin, Settle, & Chouet, 1974;Murray, 1976Murray, , 1980aNeri et al, 2008;Slatcher, James, Calvari, Ganci, & Browning, 2015), with new vents appearing suddenly and becoming wider and deeper (Calvari, Muller, & Scribano, 1995;Murray, 1980b), and cinder cones building up rapidly owing to powerful explosive activity (Behncke, Neri, Pecora, & Zanon, 2006Calvari & Pinkerton, 2004;McGetchin et al, 1974). This means that the available maps of the summit zone soon become dated in accurately representing its morphology.…”