Stromboli eruption 2007: a new propagating fracture opening on the Sciara del Fuoco?
9 March: At around 15:30, the summit activity ceases and a new effusive vents opens on the Sciara at about 500 m elevation, feeding a vicous lava flow (see previous photo page).
During the following hour, a strange phenomenon is observed about 8-10 times: streaks of rolling clouds of white vapour and brown dust clouds appear on the Sciara along a straight line beneath the new vent. These clouds move steadily downslope for hundreds of meters. Each is more intense than the preceding one and propagates further downslope, almost reaching the shore. Lacking a video camera, we've put together several still pictures taken at 0.2 second distance during several such episodes. Is this mark a new fracture cutting across the Sciara del Fuoco caused by the instrusion of new lava or a movement of a large block of the Sciara itself?
This phenomenon lasted for about 1 hour only, but became more and more vigorous. Towards the end of this period, we also observed another, inquieting thing: brown clouds of dust were whirled up by something happening on the Sciara in the sector hidden behing the crest of the Sciara at our side and next to the other lava flow. Was this a parallel fracture opening up here as well, thus cutting a huge slice into the Sciara? We can only guess... Later on, rockfalls from the front of the new lava flow, as well as seemingly movements along what we believe might be a a new opening fracture turned loose material into small pyroclastic flows (see next photo page). After about 6:30pm, both pyroclastic flows and the appearance of these white and brown steam and dust clouds ceased.
Low-res gif animations from still pictures