Effusive Activity at Mount Etna Volcano (Italy) During the 20th Century: A Contribution to Volcanic Hazard Assessment

Mount Etna is an open conduit volcano, characterised by persistent activity, consisting
of degassing and explosive phenomena at summit craters, frequent flank eruptions, and
more rarely, eccentric eruptions. All eruption typologies can give rise to lava flows, which
represent the greatest hazard by the volcano to the inhabited areas. Historical documents and
scientific papers related to the 20th century effusive activity have been examined in detail, and
volcanological parameters have been compiled in a database. The cumulative curve of emitted
lava volume highlights the presence of two main eruptive periods: (a) the 1900–1971 interval,
characterised by a moderate slope of the curve, amounting to 436 · 106 m3 of lava with
average effusion rate of 0.2 m3/s and (b) the 1971–1999 period, in which a significant increase
in eruption frequency is associated with a large issued lava volume (767 · 106 m3) and a higher
effusion rate (0.8 m3/s). The collected data have been plotted to highlight different eruptive
behaviour as a function of eruptive periods and summit vs. flank eruptions. The latter have
been further subdivided into two categories: eruptions characterised by high effusion rates and
short duration, and eruptions dominated by low effusion rate, long duration and larger
volume of erupted lava. Circular zones around the summit area have been drawn for summit
eruptions based on the maximum lava flow length; flank eruptions have been considered by
taking into account the eruptive fracture elevation and combining them with lava flow lengths
of 4 and 6 km. This work highlights that the greatest lava flow hazard at Etna is on the south
and east sectors of the volcano. This should be properly considered in future land-use planning
by local authorities.

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