Sketch
map of the summit craters of Etna, based on fieldwork made between
7 September and 1 October by Behncke and others.
WARNING:
Access to the summit craters is EXTREMELY
DANGEROUS. Activity in the Bocca Nuova and the Voragine
is very intense, and bombs are falling to quite some distance
beyond the crater rims. 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.
|
18
October 1999 update.
The following information is very preliminary and needs to be confirmed,
but its main lines are
essentially accurate. Bad weather is preventing visual observations
of the activity at the summit craters for most of the time since the
early afternoon of 17 October.
During the past five days, eruptive activity has continued with numerous
episodes of vigorous lava fountaining at both the Voragine and the
Bocca Nuova. On the evening of Saturday 16 October Etna greeted the
population of eastern Sicily with the spectacular display of lava
fountains jetting from the Bocca Nuova. This was followed, after a
few hours of an apparent decline in the activity, by renewed strong
explosive activity on the next morning (17 October). Marco Fulle (Trieste
Astronomical Observatory) watched the activity of the Bocca Nuova
at that time from the dirt road circling around the western side of
the summit cone complex and reported that continuous lava jetting
to several hundred meters above the crater rim occurred from several
vents within that crater, and bombs were dropped onto the outer flanks
of the main summit cone, covering about half the distance between
the western crater rim and the dirt road. Bombs also fell to the SE,
to as far as the saddle between the main summit cone and the Southeast
Crater cone. Fulle lost visibility by about 1400 h (local time=GMT+2)
due todeteriorating weather conditions, but it appears that thereafter
something exceptional happened: lava began to overflow onto the W
flank of the main summit cone.
Informations about the exact site of this overflow and the direction
of the lava flow are conflicting as of 18 October, early afternoon:
while some news reports said that the overflow occurred at the Voragine
and was directed towards NW, other sources place the overflow at the
W rim of the Bocca Nuova, or even report that a new fracture has opened
on the W side of the main summit cone, and that lava is directed westwards.
At 1500 h, Marco Fulle telephonically reported from Rifugio Sapienza
that local mountain guides visited the western side of the summit
area this morning and observed that the western rim of the Bocca Nuova
had collapsed, and that lava was moving in a broad river down the
W side of the main summit cone, interrupting the dirt road and spilled
down the W flank of the mountain, towards the forests of Bronte. The
guides furthermore reported that the flow came down a good part of
the steep W slope of Etna, but there were no informations available
about the extent of the lava. Fulle himself attempted to reach the
area this morning but was only able to see very intense lava fountaining
at the Bocca Nuova before clouds covered the scene; Fulle did not
dare go further due to the high levels of activity and the poor visibility.
From what little can be understood at this time it is clear that Etna
is repeating in much detail the events of 1964: in that year, a major
summit eruption completely filled the former Central Crater, built
a large pyroclastic cone on top of the crater fill, and lava overflowed
the crater rim towards NE, NNW, W, SW, S and SE. That eruption also
included lava emission from a fissure on the E side of the main summit
cone. At the height of the eruption, the SSW rim of the Central Crater
collapsed, allowing lava to spill down on that side. The events of
this year, with the long-lasting effusive activity near the Southeast
Crater cone, and the intense activity in the Voragine and Bocca Nuova,
are similar in many respects, but they are notably more intense. The
collapse of the W rim of the Bocca Nuova is but the latest of these
events; if the activity continues at a similar scale, then lava will
travel a few kilometers down on the W flank of Etna.
15
October 1999 update.
Vigorous eruptive activity has continued at the Bocca Nuova since
the 12 October summit visit, while the Northeast Crater and the Voragine
may have calmed down somewhat. Near continuous ejections of incandescent
bombs occur from the Bocca Nuova to a height of several hundred meters
above the crater rim. It is assumed that the crater is rapidly filling.
Just as this update
is posted, at about 1850 h (local time=GMT+2) on 15 October, vigorous
lava fountaining has resumed at the Voragine (or the Northeast Crater?
- difficult to recognize from Catania. At the Palazzo delle Scienze,
in the center of the city, a distinct, dull rumbling noise is audible.
The activity may be the initiation of a new paroxysmal eruptive episode;
more detail will be made available in the next few days.
13
October 1999 update: very intense summit activity, and summit visit
on 12 October.
During the past few days, eruptive activity in the summit craters
of Etna has continued at very high levels, mainly at the Bocca
Nuova and the Northeast Crater. Sometime around 11 October,
explosive activity also resumed in the Voragine which had remained
relatively inactive for several weeks.
During the weekend of 9-10 October, numerous persons observed vigorous
incandescent ejections from the Bocca Nuova and the Northeast Crater;
bombs were frequently thrown far beyond the rims of these craters
and rolled down the slopes of their cones. Dark ash-laden plumes commonly
rose every few minutes from the Northeast Crater to a height of several
hundred meters, due to the almost total absence of wind. The activity
reached a climax on 11 October when bombs were ejected from the Bocca
Nuova to a distance of several hundred meters, and some bursts rose
more than 300 m above the lip of the crater. On the morning of 12
October, Sandro Privitera (Dipartimento di Scienze Geologiche, University
of Catania) observed that activity was also occurring from the Voragine;
reports in local newspapers indicate that this activity had already
occurred on the previous day.
On the afternoon of 12 October, Boris Behncke (Dipartimento di Scienze
Geologiche, University of Catania) and Angelo Amara (University of
Catania) reached the W flank of the main summit cone, at a distance
of about 250 m from the W rim of the Bocca Nuova. Activity within
that crater was extremely vigorous (although local mountain guides
reported that it had been more intense the day before), and virtually
continuous, with ejections of dense jets of bombs to hundreds of meters
above the crater rim. About 99 per cent of the bombs fell back into
the crater, as the ejections were mainly vertically directed, but
occasional larger bursts sent bombs beyond the NW and SW crater rims.
Eruptive activity occurred from at least 4 locations within the crater,
of which one in the W part of the crater was the most active. This
vent may lie in the place where a circular subsidence depression had
been observed on 1 October, about 80 m SW of the NW vent which had
been the source of the major eruptive episode on 20 September. This
latter vent erupted less frequently during the 12 October visit, and
produced no activity for about 30 minutes before it reopened violently
at 1830 h (local time=GMT+2). At this moment there occurred the first
in a series of powerful detonations which ejected abundant lithics
along with incandescent bombs, and a tephra-laden plume rose rapidly
to about 500 m above the crater rim. Lithics were showered over the
NW flank of the main summit cone while bombs fell only to about 50
m below the crater rim. The explosions from this vent initiated about
30 minutes of much more intense activity when broad bursts of countless
bombs occurred almost simultaneously from the presumed W vent, the
NW vent and still another vent adjacent to the W vent to the S; jets
of bombs rose at intervals of less than 1 second. There were some
rare ejections of bombs from the area of the SE vents which had been
the source of most activity during summit visits by Behncke and others
on 1 and 6 October. Much of this activity was accompanied by a surprisingly
low noise level, but the explosions at the NW vent produced loud detonations
and air concussions.
The Northeast Crater emitted dark ash almost continuously; each emission
was announced by a dull rumbling sound followed within a few seconds
by the appearance of a dense ash plume at the crater rim. After nightfall
it was seen that only about 10 per cent of the emissions were accompanied
by ejections of incandescent bombs; however, these were quite powerful
and sent bombs over a wide sector of the Northeast Crater cone. Other
emissions appeared to eject mainly lithics: while no incandescent
pyroclastics were seen to rise over the crater lip, the sound of many
large rocks falling onto the crater rim was well audible.
Activity in the Voragine was at relatively low levels. While staying
near the front of the 22 July 1998 lava flow on the dirt road which
connects the northern and southern ascension routes to the summit,
several loud explosions were heard coming from that crater, but no
incandescent ejecta rose above the crater rim, indicating that the
activity was quite deep-seated.
At about 1945, Behncke and Amara visited the area of effusive activity
on the ESE base of the Southeast Crater cone where lava is still issuing
quietly, more than 8 months after the beginning of effusive activity
in that area. A vigorous lava flow about 2 m wide was fed by a vent
lying in a slightly elevated zone made up of slabs of older lava,
while a smaller flow (about 0.5 m wide) issued from a vent about 5
m further to the N. The larger of the two flows first moved to the
NE and then turned E; incandescence could be seen to a few hundred
meters downslope, but it is not known whether that represented the
maximum extension of active lava. The effusion rate was estimated
at about 1 cubic meter per second; if this value is applied to the
past month, then about 2.5 million cubic meters have to be added to
the more than 40 million cubic meters of lava emitted between 4 February
and early September.
Strong ash emission from the Northeast Crater was visible on the morning
of 13 October and is continuing in a pulsating manner as of the early
afternoon of this day.
7
October 1999 update: reactivation of the Bocca Nuova on 5 October,
and summit visit on 6 October.
Just as the previous update was
posted on this site, on the afternoon of 5 October, vigorous eruptive
activity resumed at the Bocca Nuova after about two weeks of
relative calm. A few hours later, after nightfall, Giuseppe Scarpinati
(Italian correspondent of the French Association Volcanologique Européenne,
LAVE) telephonically reported that strong explosions from the Bocca
Nuova were visible with the naked eye from his home in Acireale (about
18 km from the summit of Etna) every more or less 10 minutes. Huge
incandescent bombs were ejected as far as half way down the southern
flank of the main summit cone, and each explosion was accompanied
by a loud detonation whose sound arrived about 30 seconds after the
visible ejection of the bombs. Furthermore, Scarpinati noted a continuous
but fluctuating glow at the Northeast Crater and a slight increase
in the effusive activity at the ESE base of the Southeast Crater
cone.
The day after (6 October), Boris Behncke (Dipartimento di Scienze
Geologiche, University of Catania) and two students of Physical Geography
at the University of Trier (Germany) visited the summit area of Etna,
making the ascent from the northern side (Piano Provenzana). While
staying at Piano Provenzana (about 6.5 km NNE of the summit), at about
1040 h (local time=GMT+2), a very loud detonation at the summit was
heard, followed within a few moments by the ascent of a huge "smoke
ring" at least 100 m in diameter. During the next 10 minutes
or so, a series of loud rumblings and several loud explosions occurred,
probably all at the Bocca Nuova, which, according to the local mountain
guides, had displayed similar activity during the previous night and
the early morning. Ash emissions frequently occurred from the Northeast
Crater and less frequently from the Bocca Nuova.
Behncke and his companions arrived at the northeastern base of the
Northeast Crater at about 1215 h, and made observations of the eruptive
activity for about three hours. During this period, powerful explosions
occurred at the Bocca Nuova at intervals of more or less 10 minutes,
and minor activity occurred between the explosions. Each explosion
initiated with the uprise of large bombs (some of which were several
meters across), followed immediately by a loud detonation and the
appearance of a bluish-white gas plume. Many bombs were ejected far
beyond the crater rim and fell up to 150 m to the S, and SW of the
crater rim, and as far N as the base of the Northeast Crater cone.
The source of this activity was evidently in the southern part of
the crater, probably at the SE eruptive center which was buried under
lava on 20-21 September and had been quiet since then. Ash emissions
occurred less frequently from the northern part of the crater, it
is likely that the source was at the NW vents which had also been
silent after 21 September. Due to this activity it was impossible
to climb to the crater rim or to the Voragine.
The Northeast Crater produced near continuous Strombolian activity,
with jets of lava rising a few tens of meters above the crater rim,
and some stronger explosions sent bombs up to 150 m high above the
rim. While most lava jets were vertical, and the bombs fell back into
the crater, bombs ejected by the larger explosions were scattered
over the upper flanks of the Northeast Crater cone and some fell even
into the adjacent Voragine. The noise level was generally low, but
from an area located just below the NW flank of the cone it could
be heard that the activity occurred at quite some depth within the
active central pit of the crater. Brownish-gray ash plumes were frequently
generated, and some of the Strombolian bursts were densely charged
with small bombs. This activity marks the return to the classical
"persistent" activity for which the Northeast Crater had
become famous in the 1950's to 1970's; similar activity had most recently
occurred at this crater in 1996.
It is not
without pride that I announce the posting of five unique photographs
of the 4 September 1999 Voragine eruption on this web site. To get
an impression of the magnitude of that event, go
to this page.

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