Instabilities in the summit region of Mount Etna during the 1999 eruption

Abstract

During the 1999 eruption of Mount Etna, Sicily, the summit of the volcano changed dramatically. Lavas erupted from a fissure on the southern flank of SE Cone formed a large compound flow field that buried a substantial part of the northern wall of Valle del Bove and the ground between there and SE Cone. Hot mass flow deposits formed on the eastern and western flanks of the Chasm following a period of intense Strombolian activity. At the same time, a new vent opened on the southern flank of SE Cone and there was a major rockfall from its summit. Seven weeks later, part of the outer western rim of Bocca Nuova crater collapsed during another period of intense Strombolian activity, and lava emerged at a high effusion rate through the breached crater wall. Following a subsequent collapse of the Bocca Nuova crater rim, a hot avalanche flowed a few hundred metres on top of the previous lava flow field. Similar deposits have been described on other volcanoes, but their importance in the evolution of the summit of Etna has not previously been recognised.