Abstract
Mount Etna produces frequent eruptions from its summit craters and from fissures on its flanks. The flank fissures trend approximately radially to the summit, and are mainly concentrated in three rift zones that are located on the NE, S and W flanks. Many flank eruptions result from lateral magma transfer from the central conduit into fractures intersecting the flanks, although some eruptions are fed through newly formed conduits that are not directly linked to the central conduit. We analyzed the structural features of eruptions from 1900 to the present, one of the most active periods in the documented eruptive history of Etna, which comprised 35 summit and 33 flank events. Except for a small eruption on the W flank in 1974, all of the flank eruptions in this interval occurred on or near the NE and S rifts. Eruptions in the NE sector were generally shorter, but their fissure systems developed more rapidly and were longer than those in the S sector. In contrast, summit eruptions had longer mean durations, but generally lower effusion rates (excluding paroxysmal events characterized by very high effusion rates that lasted only a few hours). This database was examined considering the main parameters (frequency and strike) of the eruptive fissures that were active over the last ~2 ka. The distribution in time and space of summit and flank eruptions appears to be closely linked to the dynamics of the unstable E to S flank sector of Etna, which is undergoing periodic displacements induced by subvolcanic magma accumulation and gravitational pull. In this framework, magma accumulation below Etna exerts pressure against the unbuttressed E and S flanks, which have moved away from the rest of the volcano. This has caused an extension to the detachment zones, and has facilitated magma transfer from the central conduit into the flanks.
Highlights
Mount Etna (Italy) is one of the most active volcanoes on Earth
A few flank eruptions have been triggered by magmatic intrusions that are not fed through the central conduit, as shown by any lack of continuity between the flank eruptions and the summit craters of the volcano
In the present study, we have investigated the structural elements of eruptions since 1900 at Etna, with the integration of the database with the main parameters of older eruptive fissures
Summary
Mount Etna (Italy) is one of the most active volcanoes on Earth. it is nearly continuous, the summit activity does not pose a significant threat to human life and property. The volcanic activity occurs along radial fissures that form flank eruptions from three main "rift zones" [Rittmann 1973, Corazzato and Tibaldi 2006]: the NE Rift, the S Rift and the W Rift (Figure 1) In these cases, magma moves upwards through the central conduit, and at shallow levels (a few hundreds of meters, up to 1-3 km) it propagates laterally, penetrating, in most cases, into the rift zones (Figure 3a). A few flank eruptions have been triggered by magmatic intrusions that are not fed through the central conduit, as shown by any lack of continuity between the flank eruptions and the summit craters of the volcano (in terms of seismicity, surface deformation, and petro-chemical data) These eruptions are possibly directly fed by the reservoir beneath the volcano, and they are here named as "eccentric" or "peripheral" eruptions [Rittman 1973, Acocella and Neri 2003] (Figure 3b). The erupted volumes can somehow be correlated to this velocity, which suggests that the largest eruptions were produced by rapid propagation of the eruptive fissures
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