Bull Volcanol (2006) 69: 149–173 DOI 10.1007/s00445-006-0061-x RESEARCH ARTICLE Boris Behncke . Marco Neri Emilio Pecora . Vittorio Zanon The exceptional activity and growth of the Southeast Crater, Mount Etna (Italy), between 1996 and 2001 Received: 22 April 2005 / Accepted: 10 February 2006 / Published online: 27 April 2006 # Springer-Verlag 2006 Abstract Between 1971 and 2001, 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, total- ing 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. Keywords Mount Etna . Lava fountaining . Microplinian . Remote video monitoring . Volume calculations . Cone growth Introduction Although basaltic volcanic eruptions are typically asso- ciated with the effusion of lava flows, they can show significant variations in eruptive styles and volume fluxes and are capable of producing significant amounts of tephra to construct sizeable pyroclastic edifices. The classic example is Kīlauea on Hawai‘i, which is famous for its episodic lava fountaining (e.g., Wolfe et al. 1988) and is currently under-going one of the most long-lived historical effusive eruptions (Heliker and Mattox 2003). Another basaltic volcano which displays similar types of activity is Mount Etna (Italy), where most eruptions produce voluminous lava flows (Chester et al. 1985). However, explosive activity including lava fountaining is also common (Allard et al. 2005; Branca and Del Carlo 2004, 2005). In contrast to Kīlauea, this latter type of activity is generally limited, at Etna, to summit eruptions, and can be considerably more violent. Conditions for direct observa- tion and quantitative analysis are less favorable at Etna than at Kīlauea, because its summit area is remote and often veiled in clouds. In addition, the activity can be hazardous for observers at close range. Nonetheless such observation and analysis is crucial not only for a better understanding of the dynamics of the volcano, but also because explosive Editorial responsibility A. Harris B. Behncke (*) . M. Neri . E. Pecora . V. Zanon Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania, Piazza Roma, 2-95123 Catania, Italy e-mail: behncke@ct.ingv.it Tel.: +39-095-7165860 Fax: +39-095-501658 e-mail: neri@ct.ingv.it Tel.: +39-095-7165858 Fax: +39-095-501658