Monitoring the December 2015 summit eruptions of Mt. Etna (Italy): Implications on eruptive dynamics

A lengthy period of eruptive activity fromthe summit craters ofMt. Etna started in January 2011. It culminated in
early December 2015 with a spectacular sequence of intense eruptive events involving all four summit craters
(Voragine, Bocca Nuova,NewSoutheast Crater, and Northeast Crater). The activity consisted of high eruption columns,
Strombolian explosions, lava flows andwidespread ash falls that repeatedly interferedwith air traffic. The
most powerful episode occurred on 3 December 2015 from the Voragine. After three further potent episodes
fromthe Voragine, activity shifted to the NewSoutheast Crater on 6 December 2015, where Strombolian activity
and lava flow emission lasted for two days and were fed by the most primitive magma of the study period. Activity
once more shifted to the Northeast Crater, where ash emission and weak Strombolian activity took place
for several days. Sporadic ash emissions from all craters continued until 18 December, when all activity ceased.
Although resembling the summit eruptions of 1998–1999, which also involved all four summit craters, thismultifaceted
eruptive sequence occurred in an exceptionally short time window of less than three days, unprecedented
in the recent activity of Mt. Etna. It also produced important morphostructural changes of the summit
area with the coalescence of Voragine and Bocca Nuova in a single large crater, the “Central Crater”, reproducing
themorphological setting of the summit cone before the formation of Bocca Nuova in 1968. The December 2015
volcanic crisis was followed closely by the staff of the Etna Observatory to monitor the on-going activity and forecast
its evolution, in accordance with protocols agreed with the Italian Civil Protection Department.