Mt. Etna - November 16, 2006 paroxysm

The activity at the South East Crater (SEC, 3340 m a.s.l.) was recently characterized by lava flow emission together with explosive paroxysms, the most violent of which occurred on November 16, 2006 accompanied by collapses of the eastern sector of SEC.

Before the November 16 paroxysm, several rock-failures with blocks of some cubic meters in volume occurred at the eastern flank of the SEC cone (information by Etna Alpine Guides), and on November 15, a new north-south oriented fracture, 10 m long and 0.3 m wide, emitting steam, was noticed at the southern base of the SEC cone at 3050 m. In the early morning of November 16, at around 500 UT, the eastern sector of the SEC edifice started to be affected by ground fracturing and the rock sliding increased its intensity, along with a sharp growth of the volcanic tremor amplitude (See also INGV reports at At 615 UT, the eruptive activity began near the summit of the SEC cone, with a strongly increased strombolian activity and the onset of phreato-magmatic explosions, associated to lava flow emission directed eastward into the Valle del Bove. After few hours, at 1400 UT, the entire eastern flank of the SEC cone had collapsed, leaving a horse-shoe shaped niche, at the base (3050 m a.s.l.) of which a gully (~250 m long and ~15 m deep) developed.Lava flows, originated from a vent located about 50 m below the SEC summit (~3300 m), advanced within this gully and flowed further for about 2 km downslope into the Valle del Bove.

Suddenly, at 1425 UT a few meters high puff of brown ash laden steam took place at the base of the niche  (~3050 m a.s.l.), immediately joined by another one just 20 m upslope. Few seconds later, the puffs evolved into ~200 m high brownish plumes immediately followed by a 300-400 m high black eruptive curtain, laden with juvenile and lithic clasts, produced by several explosions, along an east-west oriented fracture. From the RAI movie (filmed by Giovanni Tomarchio) at least 50 distinct explosions can be recognized in about 1 minute. The curtain was sustained for a short time (a little more than 1 minute), and then collapsed giving rise to a gravity driven pyroclastic flow, which went downslope along the flank of the SEC cone and into the upper sector of the Valle del Bove. The flow advanced fast, channelled in the above-mentioned gully with relatively low (no more than 50 m high) dark brown billows, accompanied by clouds of white steam which rose up to more than 500 m high. Most of its deposit settled in the gully and was later covered by lava flows in the following hours, whereas the elutriated fine-grained fraction extended for ~1.4 km downslope and covered an area of ~2 km2 with an average thickness of ~2 cm. After this paroxysm, the explosive activity continued at the SEC with a decreasing intensity. In the following first couple of hours, material containing large amounts of buried snow repeatedly fell into the vent from the steep niche slopes, and produced minor steam explosions due to the sudden vaporization of the snow. Lava was emitted from a segment of the eruptive fracture in the niche at 3050 m, and flowed into the Valle del Bove, with a continued activity until about 500 UT of November 17.

This circumstance, along with the limited extension of the pyroclastic flow, fortunately avoided eventual dramatic consequences. However,  this paroxysm, though short and limited to the summit area of the volcano, is significant in unfolding some crucial phenomena that might be looked at as potentially hazardous.