Stromboli eruption update: 8 April 2003
The effusive eruption from a vent along the Sciara del Fuoco is still going on as on 8
April 2003. Effusion of lava takes place from 4 vents at 590 m a.s.l.,with effusion rate
decreasing since early March. Thermal mapping of the lava flow field and of the craters
interior revealed on early April a talus of debris artially obstructing the summit craters
bottom. Frequent inner collapses and lithic ash emission increased the possibility of
sudden gas
explosions, which eventually happened on 3rd April 2003. Lithic angular blocks
up to 50 cm wide have been expulsed from crater 3 (the SW crater), falling
mainly on the north flank of the cone up to 300 m distance.
On 5 April, at 9:12 am local time, scientists from INGV-CT were doing a
helicopter flight for the daily surveys with a portable thermal camera. We
surveyed the active lava flow field expanding on the upper sector of the Sciara
del Fuoco, above a flat zone at the base of the 28 December 2002 eruptive
fissure. Three vents along this surface were feeding small lava flows, and the
summit craters of the volcano were producing a very diluted gas cloud. A few
minutes after the start of the survey, the gas plume coming out from the
craters and moved west by the strong wind was suddenly crossed by a reddish ash
emission, that we interpreted as further collapses within the craters. However,
the red ash was soon substituted by juvenile, darker material coming out from
crater 1 (the NE crater). This formed a hot jet with cauliflower shape rapidly
growing above the crater. Two-three seconds later, also crater 3 produced a hot
jet of juvenile material. The eruptive process then evolved very rapidly, with
jets from craters 1 and 3 joining together. A very powerful explosion took
place, which pushed the helicopter away from the crater, suddenly increasing
its velocity of 30 knots/hour. A mushroom-shaped dark cloud rised from the
craters, expanding vertically up to an elevation of about 2 km a.s.l., 1 km
above the volcano’s summit. The eruptive cloud was surrounded at its base by a
dark-grey cloud similar to a base-surge, while it was still expanding
vertically and assuming the mushroom shape. Bombs, ash and blocks fell on the
NE flank of the volcano above 400 m elevation, causing burning of the
vegetation. Most of the ejecta were brought by the wind westward, falling on
Ginostra and damaging two houses. No people have been injured by the event.
Continuing the helicopter survey after the paroxysm, we could observe that the
lava flow field on the upper Sciara del Fuoco was completely covered by a brown
carpet of debris ejected from crater 1 during the initial phase of the event. A
very thick steam cloud was rising from this site, suggesting vaporisation of
wet material above the still active lava flows. In the meanwhile, several
alternating black and reddish pulses were taking place, mainly from crater 3.
Several fingers of light-brown debris were expanding from the NW flank of
crater 1 along the middle part of the Sciara del Fuoco. The upper part of the
volcano above 700 m elevation was completely covered by a continuous carpet of
pyroclastic products. Il Pizzo Sopra La Fossa, a hill standing above the summit
craters, showed on the north flank a number of new fractures concave towards
north and extending between the summit of the volcano and the south base of
crater 1. The presence of these fractures makes it possible that new landslides
can occur on the summit of the volcano. Within a few minutes from the start of
the paroxysm, the upper Sciara del Fuoco showed active flows emerging from the
carpet of debris covering the lava flow field. The explosive event caused
abundant emission of the so-called “golden pumice” mixed with little brown
scoria. The golden pumice comprised little crystals and was very vesiculated.
Often surrounded lithic blocks of crystalline, angular material with light grey
groundmass and centimetre-sized crystals of pyroxene.
A helicopter survey carried out on 8 April showed four active vents pouring out
lava on the upper Sciara del Fuoco at 590 m a.s.l.. Two of the flows were
expanding along the middle Sciara del Fuoco, causing detachment of blocks from
the flow front and little rock falls reaching the sea. Within the summit
craters a thick carpet of debris has accumulated following the paroxysm of 5
April. This has reduced the craters depth of about 50 m thickness, causing
partial obstruction(from: webpage www.ct.ingv.it).
Address:
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95123 Catania (Italy)