Sketch
map of the upper W flank and the summit area of Etna, showing the
approximate directions of lava flows coming from the Bocca Nuvoa as
of 25 October, 1900 h. The extent of lava flows emplaced on 22 and
25 October is preliminary. The approximate locations of the eruptive
fissure and of the SE vents within the Bocca Nuova are also shown.
WARNING:
Access to the summit craters is EXTREMELY
DANGEROUS. Activity in the Bocca Nuova and the Voragine
is very intense, and bombs are falling over all of the summit
area. Access to the craters themselves is absolutely impossible.
Besides this, weather conditions are often unstable, even during
the summer; summit visitors may be surprised by snowstorms (as
occurred on 24 July 1999) or thunderstorms: one man was killed
by lightning at about 2000 m elevation near Piano Provenzana
on 30 August. Any person who enters the area beyond the Torre
del Filosofo mountain hut (2900 m elevation) or the hut of the
guides on the northern flank (Baita delle guide, 3000 m elevation)
goes at his/her own risk and is not covered by any insurance
in case a rescue operation (e.g., with helicopters) is necessary.
|
28
October 1999 update.
On the afternoon of 27 October, a lava flow fed by vigorous activity
at the Bocca Nuova since about noon cut the Forestale road on the
W flank at about 1750 m elevation and burned a section of a beautiful
pine forest. This is the longest flow produced so far by the ongoing
summit activity of Etna, and one of the longest flows ever produced
by an Etnean summit eruption.
27
October 1999 update.
During the past six days (that is, since the 21 October update), eruptive
activity from the Bocca Nuova has continued at fluctuating, though
generally very high levels, and vigorous Strombolian activity and
overflow of lava onto the W flank are occurring as this update is
written (1100 h local time=GMT+2). The following provides a summary
of the activity between 21 and 26 October; photos and updated maps
will be added in the forthcoming days.
After several days of near continuous activity with periods of strong
fountaining, powerful Strombolian explosions and milder explosive
activity, accompanied by surges of lava overflowing onto the W flank
of the volcano, a period of relative quiet ensued on 20 October, permitting
a group of volcanologists from the UK to reach the rim of the Bocca
Nuova. At this time, Strombolian activity occurred from at least three
vents - one in the NW part of the crater, another one in the W and
a third one in the SE. All had sizeable pyroclastic cones around them.
A small volume of lava traveled through the overflow channel on the
W rim of the crater, but active lava did apparently not extend much
downslope.
Early the next morning, sometime around 0300 h, an episode of vigorous
lava fountaining began, and new lava spilled through the overflow
channel; furthermore a broad lava flow spilled over the WSW crater
rim over a width of about 100 m, and covered an area to the south
of the previously formed lava flow-field, including about 100 m of
the dirt road that until 17 October connected the N and S ascent routes
on Etna; then the flow ran down the upper WSW flank of the volcano.
Although the available information is very sketchy, this activity
appears to have lasted until about 0500 that morning. Bad weather
precluded visual observation of the volcano throughout the rest of
that day, but on the morning of 22 October, the perfectly clear viewing
conditions had returned.
Sometime around 0700 on 22 October, Giuseppe Scarpinati (Italian correspondent
of the French Association Volcanologique Européenne "L.A.V.E."),
from his home in Acireale on the SE flank of Etna, observed mild Strombolian
activity (one explosion every 15-20 seconds) at the Bocca Nuova and
vigorous lava spattering at the effusive vents that lie on the ESE
base of the Southeast Crater cone; lava emission from these vents
had apparently increased compared to the previous days. For the next
few hours, the activity at the Bocca Nuova gradually increased, and
by 1130, another episode of high lava fountaining and lava overflow
was in full course. From Catania huge jets of incandescent material
to several hundred meters above the crater rim were plainly visible,
and a dense, ash-poor column of yellowish gas rose at least 4 km above
the summit. Marco Fulle (Astronomical Observartory of Trieste, Italy)
witnessed the activity from a distance of a few hundred meters, and
reported that the activity apparently occurred from a N-S fissure
at least 100 m long in the W part of the Bocca Nuova, ejecting a continuous
sheet of very fluid lava. A spectacular torrent of lava ran down the
W flank of the main summit cone at a speed of about 50 m per minute,
carrying huge incandescent blocks more than 10 m across with it. It
seems that this flow covered older lava in the central part of the
new lava flow-field, and it extended about half way down the W flank
of Etna, much less far than the first large surge of lava on 17-19
October. An overflow may have also occurred on the NNW side of the
Bocca Nuova, following a similar path as the lava flow emplaced on
4 September 1999 on the W side of the Voragine.
After climaxing between 1200 and 1230, the activity and the volume
of overflowing lava gradually deminished, but sporadic violent explosions
threw large bombs hundreds of meters beyond the crater rims in all
directions; some bombs fell onto the SE side of the Southeast Crater
cone, close to the area of lava effusion. As a precaution, all tourists
had been evacuated by the local mountain guides from the summit area
and brought down to the Rifugio Sapienza, and the cable car on the
S flank of Etna was temporarily stopped. By 1600 h, the activity was
limited to a few sporadic expulsions of ash and very rare but powerful
explosions which ejected large bombs over the entire main summit cone
and as far as the Southeast Crater cone; the last one of these occurred
at about 1630. After 1700 the crater remained perfectly quiet.
When Boris Behncke and Giuseppe Scarpinati reached the summit area
on that same day, they witnessed the last strong explosion and a few
weak ash emissions thereafter; no activity was observed until 2130.
Between 2000 and 2100 Behncke and Scarpinati visited the area of effusive
activity at the ESE base of the Southeast Crater cone where spattering
had ceased several hours earlier, but lava emission from at least
3 vents continued, and incandescent gas was emitted forcefully from
two large hornitos that had grown during the activity earlier that
day. Flowing lava was seen to a distance of about 500 m from the active
vents, both to the NE and E.
Near continuous but rather passive ash emission on the morning of
23 October heralded another episode of high lava fountaining and lava
overflow onto the W flank which began at about 1000 h. This activity
culminated at about 1045 but was somewhat less intense than the eruptive
episode of the previous day; jets of incandescent lava were seen rising
up to about 200 m from vents in the W part of the Bocca Nuova. The
lava flows emplaced on the W flank during this episode were probably
shorter than those produced earlier during the week. There were also
unconfirmed reports of activity within the Voragine during this eruptive
episode.
Relatively mild Strombolian activity persisted through the evening
of 24 October, and minor volumes of lava flowed through the main overflow
channel onto the W flank of the main summit cone without extending
significantly further. On the evening of 24 October, the activity
became more vigorous and offered a spectacular display to a group
of mountain guides who ascended tje volcano from N. During the night
loud explosions occurred at intervals of several minutes, some of
these explosions caused aerial shock waves that rattled windows and
doors as far away as Giardini-Naxos and Taormina (24 and 28 km to
the NE, respectively).
On the morning of 25 October, ash was emitted sporadically from the
Bocca Nuova as Boris Behncke and a group of the Student's Volcano
Monitoring Project (Heidberg near Hamburg, Germany) drove towards
the volcano from Giardini-Naxos. Powerful explosions which dropped
many large bombs to a distance of several hundred meters from the
Bocca Nuova were seen while approaching the summit area from Piano
Provenzana, and when arriving at Punta Lucia (about 2.5 km NNW of
the Bocca Nuova) at about 1130, continuous fountaining was in progress
at the crater. Broad jets of lava generally rose 100-200 m above the
crater rim, but occasional jets soared to 500 m height, and bombs
fell abundantly, mostly in the direction of the Voragine and the N
side of the Bocca Nuova. Lava was flowing over the W rim of the crater
and descended the W flank of Etna. A large pyroclastic cone stood
near the vent that produced most of the fountaining (in the NW part
of the Bocca Nuova); the summit of this cone was standing about 30
m above the NW crater rim. Marco Fulle and Roberto Carniel (Stromboli
On-line) observed the activity from the SW side of the Bocca Nuova
and reported that the activity occurred from a number of vents aligned
along a N-S trending fissure in the W part of the Bocca Nuova, and
that the main focus of activity shifted from the S end of the fissure
to its N end between 1145 and 1300.
The eruptive activity continued to increase gradually between 1200
and 1300, and culminated in the spectacular collapse of a large portion
of the WNW rim of the Bocca Nuova. This collapse produced a series
of avalanches from which dense, brownish dust plumes rose, rapidly
reducing visibility of the Bocca Nuova to a minimum. Large rocks were
seen flying down the slope, creating the impression that a new vent
had opened there, but later no evidence of such a vent was found,
instead a deep notch was formed through which a large torrent of lava
ran downslope at a velocity of several tens of meters per minute,
carrying boulders up to 20 m in diameter with it. These boulders appeared
to be derived in part from the collapsed crater rim and in part from
the rapidly disintegrating pyroclastic cone near the erupting main
vent.
At the same time of the collapse a portion of the crater rim to the
south of the collapse area was pushed upwards from behind by the rising
lava within the crater, forming a conspicuous pinnacle 10-20 m higher
than the crater rim nearby. Carniel and Fulle observed that this block
while being uplifted was also rotated outwards by more than 45°.
Minor collapse occurred repeatedly for about 30 minutes while vigorous
lava fountaining continued from the erupting vents, mainly the northernmost
one. Lava flowing through the newly formed breach was repeatedly covered
with debris from the collapse events but continued to flow without
any modification. Fallout from the fountain was most intense on the
N side of the Bocca Nuova where the rapidly accumulating mass of fluid
bombs gradually transformed into a rootless lava flow that advanced
along the flow emplaced on 22 October in the same area, but evidently
extended further downslope.
At about 1330, bombs reached ever greater distances from the Bocca
Nuova, with some impacts as far as the place where a small wooden
shack is placed by the guides of Piano Provenzana during the summer
(at about 3000 m), and observations at close range became impossible.
However, from the SW side of the main summit cone, Carniel and Fulle
were able to follow the course of the activity until the paroxysmal
episode ended by about 1630. This was followed by a series of powerful
but isolated explosions which threw bombs hundreds of meters beyond
the Bocca Nuova rim.
The eruptive episode of 25 October thus lasted a total of 6 hours,
much longer than the episodes of 22 and 23 October, and it was followed
by milder persistent activity which continued for at least 5 hours
afterwards. By 1900, the main vent in the Bocca Nuova produced frequent
Strombolian bursts, and lava flow through the new breach in the crater
rim continued at a reduced rate.
Observations made at nightfall (precisely, between 1730 and 1930)
by Behncke and the German group from Bronte on the W flank revealed
that a major new lava flow with at least 7 active branches had descended
the W flank of Etna, and the farthest flow front had extended as far
as the previous longest flow emplaced on 17-18 October, to about 1900
m elevation. By about 1810 the front of the longest branch began to
eat through a small patch of forest a few hundred meters above the
Forestale road. It was entirely consumed during the following 45 minutes.
However, the flow front was still some 9.5 km away from the town of
Bronte, and the flow appeared to be slowing.
The new lava flow came down slightly to the N of the flows produced
during the preceding week, and the longest branch extended almost
5 km from the Bocca Nuova, thus being one of the longest flows ever
produced by a summit eruption.
On the morning of 26 October, the activity consisted mostly of isolated
ash-rich explosions which apparently came from the southernmost vent
on the fissure in the W part of the Bocca Nuova. Towards the evening
the activity became more continuous and instead of single, violent
explosions there was mild Strombolian activity. Fulle and Carniel
observed the activity from the SW side of the main summit cone and
reported that up to 7 vents aligned along the fissure were active,
most vigorously at the N and S ends of the fissure. Explosions also
occurred from two vents in the SE part of the Bocca Nuova where little
activity had been observed (whenever possible) during the last week.
Today (27 October), vigorous Strombolian activity continued as of
the late forenoon. Jets of lava were rising tens of meters above two
main vents in the W part of the Bocca Nuova. A new large pyroclastic
cone has grown around the northernmost vent, and lava continues to
overflow on the W side of the crater, with active flow fronts extending
to about 2500 m elevation.
The current
activity of Etna is among the most spectacular seen in many decades,
even though it is not of the magnitude of a large flank eruption.
The most striking feature of this activity is its long duration -
the summit craters are vigorously active since mid-July, and since
5 October, the Bocca Nuova has been erupting near continously. Even
though being similar in some respects, the current activity is more
intense and more varied than that of 1964 when lava was emitted from
the main summit cone onto the W flank for the last time.
To
learn more about the 1964 eruption, visit
this page.

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